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Publication Number: FHWA-HRT-13-028
Date: October 2013

 

Guidelines for Sampling, Assessing, and Restoring Defective Grout in Prestressed Concrete Bridge Post-Tensioning Ducts

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Location

Incorrect Values

Corrected Values

Table 32 on page 90

CD3         0.08 < Cl0.20b

CD3         0.2 < Cl ≤ 0.50b

Table 33 on page 91

CD3         0.02 < Cl ≤ 0.50

CD3         0.2 < Cl ≤ 0.50

 

FOREWORD

Post-tensioned (PT) tendons have been widely utilized in concrete bridges in the United States. The advantages of PT bridges compared to bridges constructed using conventional reinforcement include greater span length, structural efficiency, reduced materials, and a more streamlined appearance. However, PT tendons can be susceptible to corrosion and ultimately failure if physical deficiencies (PDs) or chemical deficiencies (CDs) are present. Examples of PDs include separation, segregation, presence of soft material, and free water, while an example of a CD includes concentrations of chloride that exceed the allowable limit as specified by the American Association of State Highway and Transportation Officials and other specifications. The failure of a few tendons can compromise overall structural integrity.

Inspections of bridge PT tendons have revealed both PDs and CDs as well as strand tendon failures caused by corrosion have been reported. This study was performed to provide bridge owners with a practical protocol for inspecting, sampling, analyzing, evaluating, and responding to bridge grout concerns.

Jorge E. Pagán-Ortiz
Director, Office of Infrastructure
Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

 

TECHNICAL REPORT DOCUMENTATION PAGE
1. Report No.:
FHWA-HRT-13-028
2. Government Accession No. 3. Recipient’s Catalog No.
4. Title and Subtitle:
Guidelines for Sampling, Assessing, and Restoring Defective Grout in Prestressed Concrete Bridge Post-Tensioning Ducts
5. Report Date:
October 2013
6. Performing Organization Code
7. Author(s):
Teddy S. Theryo, William H. Hartt, and Piotr Paczkowski
8. Performing Organization Report No.

9. Performing Organization Name and Address:
Parsons Brinckerhoff, Inc.
2202 North West Shore Blvd. Suite 300
Tampa, FL 33607

William H. Hartt, PhD, PE, F-NACE
Consulting Engineer
20914 Morada Court
Boca Raton, FL 33433

10. Work Unit No.
11. Contract or Grant No.
12. Sponsoring Agency Name and Address:
Office of Infrastructure Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296
13. Type of Report and Period Covered:
Final Report
14. Sponsoring Agency Code
15. Supplementary Notes:
The Contracting Officer’s Technical Representatives (COTRs) were Y.P. Virmani and H. Ghasemi, HRDI-60. An expert task group comprised of members from industry, academia, State transportation departments, and the post- tensioning industry provided valuable technical input and guidance. This study was part of the Long-Term Bridge Performance Program.

16. Abstract:

A significant proportion of the U.S. bridge inventory is based on bonded post-tensioned (PT) concrete construction. An important aspect of maintaining corrosion protection of these PT systems is assuring that tendon ducts are properly grouted with an acceptable material. Grout is a cementitious material typically used to provide corrosion protection to the strands used in PT concrete bridges. However, inspections have revealed fractured strands and, in some cases, failed tendons as a consequence of corrosion, even with the newer prepackaged, preapproved thixotropic grouts. Studies to-date have attributed this corrosion to physical or chemical grout deficiencies (or both), the former consisting of air voids, free water, and unhardened, segregated, or separated grout and the latter of chloride concentration in excess of what is specified by the American Association of State Highway and Transportation Officials and other specifications. Based on collected information and data analysis, State transportation departments can evaluate if grout deficiencies are present in the tendons of their PT bridges and determine the significance of any deficiencies. Durability concerns associated with PT tendons were raised as early as 1999 when tendon failures were seen in some PT bridges as a result of strand corrosion due to the collection of bleed water in grout voids at tendon profile locations like anchorages and crest areas. While the development of prepackaged thixotropic grout was thought to provide a solution to the bleed water problem, corrosion-caused tendon failures on relatively new PT bridges have occurred, and forensic studies have revealed separation and segregation of grout materials as well as the presence of soft material, free water, and high chloride and sulfate content. (1–3) Consequently, it has become important to examine the overall quality of materials and construction for some in-place grouts in existing PT bridges. The purpose of this study is to provide State transportation departments with guidance regarding tendon inspection, grout sampling, data analysis, and interpretation.

17. Key Words:
Post-tensioned tendons, Bridges, Corrosion, Grout, Chlorides, Grout defects, Inspection, Sampling
18. Distribution Statement:
No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161.
19. Security Classif. (of this report):
Unclassified
20. Security Classif. (of this page):
Unclassified
21. No of Pages:
130
22. Price
Form DOT F 1700.7 (8-72) Reproduction of completed pages authorized

 

 

 

SI* (MODERN METRIC CONVERSION FACTORS)
APPROXIMATE CONVERSIONS TO SI UNITS
Symbol When You Know Multiply By To Find Symbol
LENGTH
in inches 25.4 millimeters mm
ft feet 0.305 meters m
yd yards 0.914 meters m
ml miles 1.61 kilometers km
AREA
in2 square inches 635.2 square millimeters mm2
ft2 square feet 0.093 square meters m2
yd2 square yard 0.836 square meters m2
ac2 acres 0.405 hectares ha
mi2 square miles 2.59 square kilometers km2
VOLUME
fl oz fluid ounces 29.57 millimeters mL
gal gallons 3.785 liters L
ft3 cubic feet 0.028 cubic meters m3
yd cubic yards 0.765 cubic meters m3
Note: volumes greater than 1000 L shall be shown in m3
MASS
oz ounces 28.35 grams g
lb pounds 0.454 kilograms kg
T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t")
TEMPERATURE (exact degrees)
°F Fahrenheit 5 (F-32)/9 Celsius °C
ILLUMINATION
fc foot-candles 10.76 lux lx
fl foot-Lamberts 3.426 candela/m2 cd/m2
FORCE and PRESSURE or STRESS
lbf poundforce 4.45 newtons N
lbf/in2 poundforce per square inch 6.89 kilopascals kPa
APPROXIMATE CONVERSIONS FROM SI UNITS
Symbol When You Know Multiply By To Find Symbol
LENGTH
mm millimeters 0.039 inches in
m meters 3.28 feet ft
m meters 1.09 yards yd
km kilometers 0.621 miles mi
AREA
mm2 square millimeters 0.0016 square inches in2
m2 square meters 10.764 square feet ft2
m2 square meters 1.195 square yards yd2
ha hectares 2.47 acres ac
km2 square kilometers 0.386 square miles mi2
VOLUME
mL millimeters 0.034 fluid ounces fl oz
L liters 0.264 gallons gal
m3 cubic meters 35.314 cubic feet ft3
m3 cubic meters 1.307 cubic yards yd3
MASS
g grams 0.035 ounces oz
kg kilograms 2.202 pounds lb
Mg (or "t") megagrams 1.103 short tons (2000 lb) T
TEMPERATURE (exact degrees)
°C Celsius 1.8C+32 Fahrenheit °F
ILLUMINATION
lx luxx 0.0929 foot-candels fc
cd/m2 candela/m2 0.2919 foot-Lamberts fl
FORCE and PRESSURE or STRESS
N newtons 0.225 poundforce lbf
kPa kilopascals 0.145 poundforce per square inch lbf/in2
*SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. (Revised March 2003)

Table of Contents

CHAPTER 1. BACKGROUND

CHAPTER 2. OBJECTIVES OF INSPECTION

CHAPTER 3. PT SYSTEMS
BACKGROUND
PT TENDON TYPES
PT BRIDGE TYPES
Cast-in-Place (CIP) PT Box Girder Bridges on False Works
CIP PT Concrete Slab and T-Girder Bridges
CIP Segmental Balanced Cantilever Bridge
Precast Spliced I-Girder Bridge
Precast Spliced U-Girder Bridge
Precast Segmental Balanced Cantilever Bridge
Precast Segmental Span-by-Span Bridge
Concrete Cable-Supported Bridge
Special PT Concrete Substructures

CHAPTER 4. GROUT DEFICIENCIES
BACKGROUND
Cl Threshold
Previous Investigations
Deficiencies

CHAPTER 5. MINIMUM NUMBER OF TEST SAMPLES
GENERAL
INSPECTION OPTIONS
INSPECTING Cl CONTENT (OPTION 1)
Project with Complete Grouting Records
Project with Incomplete or No Grouting Records.
INSPECTING ALL GROUT DEFICIENCIES (OPTION 2)
Probability of Defect Indicator
Consequence of Failure Indicator
Risk Level
Acceptable Fraction of Tendons with Undetected Deficient Grout
Minimum Number of Inspected Tendons
Sampling Procedure Summary
EXAMPLES
Typical Balanced Cantilever Bridge
Typical Spliced Girder Bridge
Typical Span-by-Span Segmental Bridge
Typical PT Bridge with Draped Tendons

CHAPTER 6. GROUT SAMPLING AND TEST METHODS
GENERAL CONSIDERATIONS
Sample Size
Analyses
Tools, Equipment, and Instrumentation
Reporting

CHAPTER 7. STRATEGIC SAMPLING LOCATIONS
BACKGROUND
BALANCED CANTILEVER BRIDGE
Continuity Tendon (Internal Tendon in the Bottom Flange)
Cantilever Tendon (Internal)
PRECAST SEGMENTAL SPAN-BY-SPAN BRIDGE
CIP PT BRIDGE
SPLICED GIRDER BRIDGE

CHAPTER 8. RESTORATION METHODS
GENERAL
TEMPORARY RESTORATION
External Tendon
Internal Tendon
PERMANENT RESTORATION
External Tendon
Internal Tendon
Grout Cap
RESTORATION MATERIAL

CHAPTER 9. INTERPRETATION OF RESULTS AND COURSES OF ACTION
BACKGROUND
Evaluation Approach and Interpretation
Examples
Reinspections, Non-Destructive Testing (NDT), and Monitoring

APPENDIX A. TYPICAL BALANCED CANTILEVER BRIDGE PLANS

APPENDIX B. TYPICAL SPLICED GIRDER BRIDGE PLANS

REFERENCES

LIST OF FIGURES

Figure 1. Illustration. Basic PT anchorage system
Figure 2. Photo. Old generation of PT anchorage system
Figure 3. Photo. New generation of PT anchorage system
Figure 4. Illustration. Internal tendon
Figure 5. Illustration. External tendon
Figure 6. Photo. External tendons at deviator
Figure 7. Photo. CIP concrete box girder bridge on false works
Figure 8. Illustration. CIP bridge typical tendon layout
Figure 9. Photo. Blister at the top flange
Figure 10. Illustration. Transverse internal tendon in the diaphragm
Figure 11. Photo. CIP PT concrete slab bridge
Figure 12. Illustration. PT slab bridge typical tendon layout
Figure 13. Photo. CIP segmental balanced cantilever bridge
Figure 14. Photo. CIP balanced cantilever bridge during construction using form traveler
Figure 15. Photo. Typical bottom flange blister
Figure 16. Illustration. Typical vertical tendon in the web
Figure 17. Illustration. Typical vertical tendon in the diaphragm
Figure 18. Photo. Precast spliced girder bridge
Figure 19. Photo. Precast spliced girder bridge during erection
Figure 20. Photo. Precast spliced U-girder bridge during erection
Figure 21. Photo. Precast U-girder supported on temporary false work
Figure 22. Photo. Precast segmental balanced cantilever bridge erection using a segment lifter
Figure 23. Photo. Precast segmental span-by-span erection using an overhead gantry
Figure 24. Illustration. Typical precast segmental span-by-span external PT tendon layout
Figure 25. Photo. Precast segmental cable stayed bridge
Figure 26. Illustration. Cross section of precast segmental columns
Figure 27. Photo. PT straddle bent during construction
Figure 28. Photo. Failed tendon cross section
Figure 29. Photo. Longitudinal section of a tendon section with types 1–3 grout identified
Figure 30. Photo. Opened tendon end showing predominantly type 3 grout and strand corrosion products
Figure 31. Photo. Opened tendon end showing types 3 and 1 grout and strand corrosion products
Figure 32. Photo. Opened tendon end revealing type 4 grout (bottom half), type 1 grout (center region), and strand corrosion products (upper region)
Figure 33. Photo. Opened anchorage on the Carbon Plant Road bridge over IH-37
Figure 34. Equation. Reaction of the ferrous ion with water and sulfate ion to yield ferrous hydroxide and sulfuric acid
Figure 35. Flowchart. Inspection options
Figure 36. Flowchart. Grout inspection processes
Figure 37. Graph. Risk matrix
Figure 38. Equation. Overall probability of defect indicator
Figure 39. Equation. Overall consequence of failure indicator
Figure 40. Equation. Risk
Figure 41. Equation. Probability mass function for hypergeometric distribution
Figure 42. Graph. Example of PMF for hypergeometric distribution
Figure 43. Equation. CDF
Figure 44. Graph. Example of CDF for a hypergeometric distribution
Figure 45. Graph. Minimum number of tendons required to detect at least one tendon with deficient grout assuming 5 percent of the samples are defective
Figure 46. Graph. Minimum number of tendons required to detect at least one tendon with deficient grout assuming 10 percent of the samples are defective
Figure 47. Graph. Minimum number of tendons required to detect at least one tendon with deficient grout assuming 20 percent of the samples are defective
Figure 48. Graph. Minimum number of tendons required to detect at least one tendon with deficient grout assuming 30 percent of the samples are defective
Figure 49. Graph. Balanced cantilever bridge—tendon risk categories
Figure 50. Graph. Spliced girder bridge—tendon risk categories
Figure 51. Graph. Span-by-span segmental bridge—tendon risk categories
Figure 52. Graph. PT bridge—tendon risk categories
Figure 53. Photo. Dial gauge used to determine the depth of a grout air void
Figure 54. Photo. Grout sample acquisition at an opened internal tendon end cap by light chipping
Figure 55. Photo. Concrete excavation to expose an internal tendon
Figure 56. Photo. Internal tendon access at an intermediate location by drilling
Figure 57. Photo. Access hole in an internal tendon at an intermediate location revealing strand and grout
Figure 58. Photo. View of a duct interior revealing a channel air void
Figure 59. Illustration. Bridge representation used to identify grout sampling locations
Figure 60. Illustration. Chart used to record the location and information for individual grout samples
Figure 61. Illustration. Chart used to record and present analysis results for individual grout samples
Figure 62. Photo. Removing a permanent grout cap
Figure 63. Photo. Exposed anchor head after grout sampling
Figure 64. Photo. Locating internal tendons in the web wall using GPR
Figure 65. Photo. Partial removal of a grout cap
Figure 66. Illustration. Typical cantilever tendon inspection point locations
Figure 67. Illustration. Typical continuity tendon inspection point locations
Figure 68. Illustration. Typical span-by-span bridge external tendon inspection point locations
Figure 69. Illustration. CIP PT bridge inspection point locations
Figure 70. Illustration. Spliced bulb-tee girder bridge inspection point locations
Figure 71. Photo. Spliced bulb-tee girder bridge CIP joint detail
Figure 72. Illustration. Spliced U-girder bridge inspection locations
Figure 73. Photo. Temporary restoration of an external tendon
Figure 74. Photo. Permanent restoration of an external tendon using heat shrink sleeve
Figure 75. Illustration. Permanent restoration of an internal tendon duct
Figure 76. Photo. Completed restoration of a partially cut grout cap prior to coating
Figure 77. Photo. Applying elastomeric coating over a grout cap
Figure 78. Photo. Completed permanent restoration of a grout cap
Figure 79. Flowchart. Inspection, sampling, evaluation, and actions for levels 1 and 2 inspections for option 1
Figure 80. Flowchart. Inspection, sampling, evaluation, and actions for levels 1 and 2 inspections for option 2
Figure 81. Illustration. Segment layout—part 1
Figure 82. Illustration. Segment layout—part 2
Figure 83. Illustration. Bulkhead details
Figure 84. Illustration. Longitudinal PT layout—part 1
Figure 85. Illustration. Longitudinal PT layout—part 2
Figure 86. Illustration. Longitudinal PT layout—part 3
Figure 87. Illustration. Longitudinal PT layout—part 4
Figure 88. Illustration. Longitudinal PT layout—part 5
Figure 89. Illustration. Longitudinal PT layout—part 6
Figure 90. Illustration. Longitudinal PT layout—part 7
Figure 91. Illustration. Longitudinal PT layout—part 8
Figure 92. Illustration. Plan and elevation—main channel unit
Figure 93. Illustration. Bridge section
Figure 94. Illustration. Pier cap PT details
Figure 95. Illustration. Tendon profile—main channel unit
Figure 96. Illustration. Modified Florida bulb-T78 beam end segment
Figure 97. Illustration. Modified Florida bulb-T78 beam haunch segment
Figure 98. Illustration. Modified Florida bulb-T78 beam drop-in segment
Figure 99. Illustration. Modified Florida bulb-T78 beam end block detail
Figure 100. Illustration. Typical sections—haunch segment

LIST OF TABLES

Table 1. Bridge condition—probability of defect indicator
Table 2. Construction and inspection records—probability of defect indicator
Table 3. Visual evaluation—probability of defect indicators
Table 4. Tendon geometry and length—probability of defect indicators
Table 5. Weight factors for probability of defect indicator
Table 6. Consequence of failure indicator versus cost of repair or tendon replacement
Table 7. Consequence of failure indicator versus element/tendon redundancy
Table 8. Consequence of failure indicator versus bridge importance
Table 9. Weight factors for consequence of failure indicator
Table 10. Acceptable fractions of undetected tendons with deficient grout
Table 11. Minimum number of tendons required to detect at least one tendon with deficient grout (75 percent confidence)
Table 12. Minimum number of tendons required to detect at least one tendon with deficient grout (95 percent confidence)
Table 13. Balanced cantilever bridge—probability of defect indicator
Table 14. Balanced cantilever bridge—consequence of failure indicator
Table 15. Balanced cantilever bridge—minimum recommended number of tendons for inspection
Table 16. List of continuity tendons
Table 17. List of external draped tendons
Table 18. List of selected transverse tendons
Table 19. List of cantilever tendons
Table 20. Spliced girder bridge—probability of defect indicator
Table 21. Spliced girder bridge—consequence of failure indicator
Table 22. Spliced girder bridge—minimum recommended number of tendons for inspection
Table 23. List of longitudinal draped tendons
Table 24. List of diaphragm tendons
Table 25. List of pier cap tendons
Table 26. Span-by-span segmental bridge—probability of defect indicator
Table 27. Span-by-span segmental bridge—consequence of failure indicator
Table 28. Span-by-span segmental bridge—minimum recommended number of tendons for inspection
Table 29. PT bridge—probability of defect indicator
Table 30. PT bridge—consequence of failure indicator
Table 31. PT bridge—minimum recommended number of tendons for inspection
Table 32. CD classifications as determined by grout Cl levels from an option 1 inspection and resultant recommended actions
Table 33. CD and PD classifications as determined by grout Cl levels and in-place grout structure by an option 2 inspection and resultant recommended actions

 

CHAPTER 1. BACKGROUND

The purpose of this report is to provide guidance for grout sampling, testing, analysis, and interpretation of test results. The following topics are presented and discussed: (1) post-tensioned (PT) bridge types, (2) types of grout deficiencies, (3) statistical approach to grout sampling, (4) grout sampling protocol and test methods, (5) locations for sampling, and (6) interpretation of results and determination of courses of action. Consideration is given to the possibility that extraction of a statistically significant number of samples from PT structures may pose a significant challenge for State transportation departments because of the possibility that invasive inspection and sample acquisition methods might compromise long-term bridge durability and structural integrity.

Durability issues for PT tendons in the United States came to the forefront in 1999 when bridge engineers became aware of failures that resulted from grout voids, associated bleed water, and tendon strand corrosion at higher elevations, such as at anchorages and crest areas. To date, 10 States have reported tendon problems that stem from grout deficiencies or excessive chlorides (Cl). (See references 1–4.) Most grouts used for PT bridge construction prior to 2001 consisted of a mixture of cement, water, and added admixtures and were typically mixed at the project site.

To improve grout performance as a corrosion protection method for tendons, the Post-Tensioning Institute (PTI) and some State transportation departments revised their grout specifications between 2001 and 2002. This resulted in the formulation of prepackaged, preapproved thixotropic grouts to eliminate bleed water and thus improve the level of protection provided to PT tendons. Prepackaged grout is a proprietary product that has been widely used in PT bridges since 2001.

While the development of prepackaged thixotropic grouts was thought to provide a solution to the bleed water problem, corrosion-caused tendon failures on relatively new PT bridges have continued to occur. Limited forensic studies involving these newer grouts have revealed the presence of grout segregation, soft grout, bleed water, and high Cl and sulfate contents. However, not all prepackaged grouts exhibited the above deficiencies. Consequently, it is important to investigative these newer grouts to examine the overall quality of in-place grouts in existing PT bridges. This report is intended as a guide for State transportation departments in this regard.

 

CHAPTER 2. OBJECTIVES OF INSPECTIONS

The overall objective of this study was to develop a general guide for State transportation departments for sampling grouts from external and internal tendons in existing PT bridges. To accomplish this, protocols for sampling grouts with both physical deficiencies (PDs) and chemical deficiencies (CDs) were developed. This report provides a rational approach to extract statistically significant numbers of grout samples for proper interpretation of the corrosion susceptibility to the enclosed strands. At the same time, the sampling approach is such that there is minimal negative impact on the future durability considering both grout sampling location and number.

Specific issues addressed in this report include the following:

 

CHAPTER 3. PT SYSTEMS

BACKGROUND

Anchorage systems in PT bridges are a proprietary system. Systems created by VSL International, Dywidag-Systems International, Freyssinet International, BBR VT International Ltd. (BBR), and Schwager Davis Inc. can be found in PT bridges in the United States. PT anchorage systems differ in shape, size, and material depending on use. In general, a basic PT anchorage system is comprised of a bearing plate, trumpet, wedge plate (anchor head), grout cap, and grout ports (see figure 1). Prior to drilling a hole through the grout port for internal trumpet inspection, it is necessary to determine the PT system used since each system has different grout port orientation and geometry to access the trumpet interior. The simplest way to identify the PT system and its detail is to locate the PT shop drawings for the project, if available.

Figure 1. Illustration. Basic PT anchorage system. This illustration shows a basic post-tensioned (PT) anchorage system consisting of a bearing plate, grout cap, grout port, wedge plate/anchor head, trumpet, coupler, and corrugated duct

©VSL International
Figure 1. Illustration. Basic PT anchorage system.

In 2003, the Florida Department of Transportation (FDOT) required an additional vertical grout port/vent located above the trumpet to facilitate post-grouting inspection and permanent grout cap in its PT specifications. The differences between the older and newer generations of PT anchorages systems are shown in figure 2 and figure 3. Many other State transportation departments have adopted PT anchorages with requirements similar to the FDOT requirements. For the new anchorages, the inspection access into the trumpet interior is much simpler through the vertical grout port.

Figure 2. Photo. Old generation of PT anchorage system. This photo shows an old generation post-tensioned (PT) anchorage system with only the horizontal grout port identified
©Dywidag-Systems International
Figure 2. Photo. Old generation of PT anchorage system.

Figure 3. Photo. New generation of PT anchorage system. This photo shows a sectioned new generation post-tensioned (PT) anchorage system with the vertical grout port, horizontal grout port, and grout cap
©Dywidag-Systems International
Figure 3. Photo. New generation of PT anchorage system.

 

PT TENDON TYPES

In general, PT bridges built in the United States consist of grouted internal tendons, grouted external tendons, or a combination of the two. A small number of bridges may also have greased unbonded tendons. This report only focuses on cement grouted tendons, which may be internal or external.

Internal tendons are located inside the structural concrete section, are housed in corrugated metal ducts or corrugated plastic ducts, and are bonded to the structural concrete by means of cementitious grout (see figure 4). The plastic corrugated ducts are made from high-density polyethylene (HDPE) or polypropylene material. The high-strength steel tendon can be strands, wires, or bars.

Figure 4. Illustration. Internal tendon. This illustration shows a segmental bridge superstructure showing example placement of internal longitudinal and transverse tendons. To the right, there is an expanded view of the cross section of three tendons with corrugated plastic duct or corrugated metal duct, grout, and concrete identified
Source: Parsons Brinckerhoff
Figure 4. Illustration. Internal tendon.

 

External tendons are typically located outside the perimeter of a concrete section, are housed in HDPE smooth duct, and are filled with cementitious grout. External tendons are not bonded with the concrete structural section (see figure 5 and figure 6).

Figure 5. Illustration. External tendon. This illustration shows a segmental bridge superstructure showing example placement of external longitudinal and internal transverse tendons. To the right, there is an expanded view of the cross section of a tendon with smooth plastic duct, grout, and strands identified
Source: Parsons Brinckerhoff
Figure 5. Illustration. External tendon.

Figure 6. Photo. External tendons at deviator. This photo shows five external tendons at a deviator block within a segmental bridge superstructure
Source: Parsons Brinckerhoff
Figure 6. Photo. External tendons at deviator.

 

PT BRIDGE TYPES

PT bridges can be grouped into several categories based on the design and construction methods. Typical possible tendon types used for each bridge group are discussed in the following sections.

Cast-in-Place (CIP) PT Box Girder Bridges on False Works

CIP concrete box girder bridges built on false works consist of single- to multi-cell box girders, as shown in figure 7. Typically, these types of bridges have an internally draped tendon in the webs. In a continuous multispan structure, the PT anchors are anchored in the end diaphragms, and some tendons may be anchored in the intermediate diaphragms. For long-span bridges, additional internal tendons are also provided in the top and bottom flanges and anchored in blisters (see figure 8 and figure 9). The top deck could be either transversely PT or reinforced concrete using mild reinforcement.

PT tendon types include the following:

Figure 7. Photo. CIP concrete box girder bridge on false works. This photo shows a cast-in-place (CIP) concrete box girder bridge on false works that is under construction
Source: Parsons Brinckerhoff
Figure 7. Photo. CIP concrete box girder bridge on false works.

 

Figure 8. Illustration. CIP bridge typical tendon layout. This illustration shows tendon layout for a cast-in-place (CIP) bridge showing draped longitudinal internal tendons, top longitudinal internal tendons, bottom span internal tendons, and a blister

Figure 8. Illustration. CIP bridge typical tendon layout.

 

Figure 9. Photo. Blister at the top flange. This photo shows the end of a cast-in-place box girder on a bridge under construction. There is a blister at the top flange with two tendons
Source: Parsons Brinckerhoff
Figure 9. Photo. Blister at the top flange.

 

Figure 10. Illustration. Transverse internal tendon in the diaphragm. This illustration shows longitudinal bridge segments with draped, bottom, and top longitudinal internal tendons and a transverse section with two internal tendons in the diaphragm
Source: Parsons Brinckerhoff
Figure 10. Illustration. Transverse internal tendon in the diaphragm.

 

CIP PT Concrete Slab and T-Girder Bridges

CIP concrete slab bridges (see figure 11) are very popular for short-span bridges. The CIP PT slab and T-girder bridges are also constructed on false works. Typically, this type of structure has shallow draped longitudinal internal tendons in the deck (see figure 12). In most cases, transverse internal tendons in the deck are also provided. The superstructure may be a single-span or multispan continuous structure from abutment to abutment.

PT tendon types include the following:

Figure 11. Photo. CIP PT concrete slab bridge. This photo shows a completed cast-in-place (CIP) post-tensioned (PT) concrete slab bridge
Source: Parsons Brinckerhoff
Figure 11. Photo. CIP PT concrete slab bridge.

 

Figure 12. Illustration. PT slab bridge typical tendon layout. This illustration shows a typical internal tendon layout as well as the location of vent holes at elevated parts on tendons

Figure 12. Illustration. PT slab bridge typical tendon layout.

CIP Segmental Balanced Cantilever Bridge

CIP segmental box girder bridges (see figure 13) are popular for long-span bridges. They are constructed using the balanced cantilever method with a set of form travelers (see figure 14). The segment is cast against the previous PT segment, which is about 15 ft long. This type of structure utilizes internal cantilever tendons in the top flange over the webs in combination with continuity internal tendons in the bottom flange anchored at blisters (see figure 15). Additional externally draped tendons may also supplement the internal tendons. The top deck is typically transversely PT with tendons encased in flat ducts. For long span bridges, it is also common to use vertical PT bars in the webs of segments close to the pier segment.

PT tendon types include the following:

Figure 13. Photo. CIP segmental balanced cantilever bridge. This photo shows a completed cast-in-place (CIP) segmental balanced cantilever bridge over a body of water
Source: Parsons Brinckerhoff
Figure 13. Photo. CIP segmental balanced cantilever bridge.

Figure 14. Photo. CIP balanced cantilever bridge during constructing using form traveler. This photo shows a cast-in-place (CIP) balanced cantilever bridge using form traveler under construction over a body of water
Source: Parsons Brinckerhoff
Figure 14. Photo. CIP balanced cantilever bridge during constructing using form traveler.

Figure 15. Photo. Typical bottom flange blister. This photo shows the interior of a box beam segment with bottom flange blisters
Source: Parsons Brinckerhoff
Figure 15. Photo. Typical bottom flange blister.

Figure 16: Typical vertical tendon in the web. This illustration shows the positioning of vertical tendons in a diaphragm.
Source: Parsons Brinckerhoff
Figure 16. Illustration. Typical vertical tendon in the web.

Figure 17: Typical vertical tendon in the diaphragm. This illustration shows a web. There are two sets of two vertical internal tendons on the left and right in the diaphragm

Figure 17. Illustration. Typical vertical tendon in the diaphragm.

 

Precast Spliced I-Girder Bridge

Precast spliced girder bridges have been gaining popularity within the last decade for medium-span bridges (see figure 18 and figure 19). Several long pieces of pretensioned American Association of State Highway and Transportation Officials (AASHTO) I-girders or bulb-tee girders are PT using draped internal tendons in the web to form a continuous multispan girder from end to end. The joints between the girders are CIP concrete. The diaphragms are typically cast at the splice locations and are reinforced concrete or PT transversely. A temporary support is provided at the CIP joint locations to stabilize the structure until the girders are made continuous. The deck slab is CIP after the first PT stage is applied. The final PT is applied after the CIP deck slab reaches minimum concrete strength.

PT tendon types include the following:

Figure 18. Photo. Precast spliced girder bridge. This photo shows a nearly completed precast spliced girder bridge over a body of water
Source: Parsons Brinckerhoff
Figure 18. Photo. Precast spliced girder bridge.

Figure 19. Photo. Precast spliced girder bridge during erection. This photo shows a precast spliced girder bridge during erection over a body of water. Cranes are being used to attach parts of the bridge
Source: Parsons Brinckerhoff
Figure 19. Photo. Precast spliced girder bridge during erection.

Precast Spliced U-Girder Bridge

Similar to precast AASHTO I-girder bridges, precast spliced U-girder bridges have also been gaining popularity recently for medium-span bridges, especially horizontally curved bridges (see figure 20 and figure 21) Several long segments of pretensioned or PT U-girders are PT using draped internal tendons in the web to form a continuous multispan girder from end to end. The joints between the girders are CIP concrete. The diaphragms are typically cast at the splice locations and are reinforced concrete or PT transversely. A temporary support is provided at the CIP joint locations to stabilize the structure until the girders are made continuous. The CIP deck slab is placed after the first stage PT is applied and the rest of the PTs are stressed after the CIP deck is hardened.

PT tendon types include the following:

Figure 20. Photo. Precast spliced U-girder bridge during erection. This photo shows a precast spliced U-girder bridge during erection
Source: Summit Engineering Group
Figure 20. Photo. Precast spliced U-girder bridge during erection.

Figure 21. Photo. Precast U-girder supported on temporary false work. This photo shows a precast U-girder being supported on temporary false work during construction
Source: Summit Engineering Group
Figure 21. Photo. Precast U-girder supported on temporary false work.

 

Precast Segmental Balanced Cantilever Bridge

Precast segmental balanced cantilever bridges are erected using the balanced cantilever method either with an overhead gantry, a beam and winch, a segment transporter/lifter, or a ground-based crane (see figure 22). The segments are precast using match cast in short-line or long-line casting yard that is about 10 to 12 ft long. During segment erection, epoxy is applied at the match cast joints and stressed by internal cantilever tendons in the top flange.

PT tendon types include the following:

Figure 22. Photo. Precast segmental balanced cantilever bridge erection using a segment lifter. This photo shows a precast segmental balanced cantilever bridge being erected over a highway using a segment lifter
Source: Parsons Brinckerhoff
Figure 22. Photo. Precast segmental balanced cantilever bridge erection using a segment lifter.

 

Precast Segmental Span-by-Span Bridge

Precast span-by-span bridges consist of precast match cast segments that are 10 to 12 ft long and erected using an under-slung gantry or an overhead gantry as shown in figure 23. The entire span is temporarily supported by overhead or under-slung gantry stressed together using PT bars after epoxy is applied on the match cast joint. The CIP joints are cast between precast segments and the diaphragm segments. Permanent longitudinal external tendons are PT from both diaphragms to complete the span construction. The process is repeated at the next adjacent span.

PT tendon types include the following:

Figure 23. Photo. Precast segmental span-by-span erection using an overhead gantry
Source: Parsons Brinckerhoff
Figure 23. Photo. Precast segmental span-by-span erection using an overhead gantry.

Figure 24. Illustration. Typical precast segmental span-by-span external PT tendon layout. This illustration shows plan and elevation views of typical precast segmental span-by-span external post-tensioned (PT) tendon layout
Source: Parsons Brinckerhoff
Figure 24. Illustration. Typical precast segmental span-by-span external PT tendon layout.

 

Concrete Cable-Supported Bridge

There are three types of concrete cable-supported bridges in the United States as follows:

The superstructure of concrete cable-supported bridges can be precast box girder or CIP deck consisting of two edge girders and transverse floor beams.

The CIP cable-stayed bridge concrete deck construction typically utilizes a set form traveler and is constructed with a balanced cantilever construction method. The previously cast segments are supported by stay cables until the CIP deck reaches the mid-span. Next, a closure segment is placed between the two tips of cantilevers. The CIP deck is typically designed in the form of PT transverse floor beams supported on reinforced concrete edge girders where the stay cable anchorages are located. The pylons and pier columns can be CIP or precast elements with vertical PT.

The precast segmental cable-stayed bridge deck consists of precast box girders. The construction method of the precast deck is very similar to a precast segmental balanced cantilever bridge, except the previously erected segments are supported by stay cables. The segments are PT longitudinally with internal grouted tendons, external tendons, and internal transverse tendons, including diaphragm tendons. The pylons and pier columns can be CIP or precast elements with vertical PT.

An extradosed segmental bridge is a hybrid between a balanced cantilever bridge and a cable stayed bridge and has a very low tower height-to-span ratio. The superstructure of an extradosed bridge is very similar to CIP or precast segmental cable stayed bridges.

The pylon cross beams that support the superstructure of the three types of cable-stayed bridges are normally PT with internal tendons.

PT tendon types include the following:

Figure 25. Photo. Precast segmental cable stayed bridge. This photo shows a precast segmental cable stayed bridge over a body of water
Source: Parsons Brinckerhoff
Figure 25. Photo. Precast segmental cable stayed bridge.

Special PT Concrete Substructures

Aside from the previously listed superstructure bridge types, PT substructures such as PT segmental precast piers (see figure 26), pylon or CIP PT straddle bents (see figure 27), C-bents, pier caps, and pile caps are also common. Most of these structures utilize internal tendons except segmental precast piers—internal, external vertical PT, or combined.

PT tendon types include the following:

Figure 26. Illustration. Cross section of precast segmental columns. This illustration shows a cross section of precast segmental columns highlighting the typical layout of vertical tendons
Source: Parsons Brinckerhoff
Figure 26. Illustration. Cross section of precast segmental columns.

Figure 27. Photo. PT straddle bent during construction. This photo shows a post-tensioned (PT) straddle being bent during construction. PT end anchorages are identified at both ends of the PT straddle
Source: Parsons Brinckerhoff
Figure 27. Photo. PT straddle bent during construction.

 

CHAPTER 4. GROUT DEFICIENCIES

Background

The first line of corrosion protection of grouted PT tendon relies on adequate sealing of ducts from external sources of corrodants (i.e., water, air, Cl, and carbon dioxide), while the second line of corrosion protection relies on encasement and direct contact of strands with a cementitious grout for which a high pH (> 13) is maintained. Thus, if strands are inadequately grout coated, protection may still be feasible if the duct is adequately sealed and there are no internal sources of corrodants. Alternatively, even if the first protection (by duct) is lacking, the grout acts as a secondary protection to the PT tendon. A necessary but not sufficient condition for strand protection is that Cl, either as a background grout contaminant or from an external source, is maintained below a critical concentration.

PTI, the American Concrete Institute (ACI), and AASHTO all list 0.08 weight (wt) percent cement as an upper acid soluble Cl; limit for PT grout or prestressed concrete. (See references 5–8.) The applicable European standard lists this upper limit as 0.10 wt percent cement. (9) In sufficient concentration, Cl facilitates corrosion of conventional reinforcement and PT strand by  transitioning steel from a passive state for which corrosion rate is negligible to an active one where corrosion rate may be unacceptably high and reducing grout electrical resistivity, thus minimizing macrocell activity and a higher corrosion rate than would otherwise develop. The disclosure that grout may have Cl concentrations greater than the above limit (0.08 wt percent cement) and that approximately 100 PT bridge projects may have utilized this material has prompted immediate concerns regarding the long-term integrity of these bridges and a need for reactive strategies and actions. In the limited PT tendon grout sampling that has been performed to-date on a bridge that utilized this Clcontaminated grout, Clconcentrations as high as 5.27 wt percent grout were reported.(1) However, Clconcentration of this grout may have varied with production variables such that this contaminant was in an acceptable range for some lots but not others. The purpose of this section of this report is to define the deficiencies that are thought to have occurred with the contaminated grout and other PT grouts with emphasis placed on the consequences of Clconcentration possibly being in excess of the above specified limit of 0.08 wt percent cement.

1Approximately two-thirds of grout is typically composed of cementitious material.

Cl Threshold

The corrosion process in cementitious materials such as PT grout involves two phases: (1) a time to corrosion initiation, Ti, during which the steel is passive and (2) a period of corrosion propagation, Tp, to the point where repair, rehabilitation, or replacement becomes necessary. PT strands in grout that have a Cl; concentration below the threshold for active corrosion initiation are normally passive and exhibit a negligible corrosion rate. However, if Cl; is present above a limiting value, passivity is compromised, and active corrosion may occur at an unacceptable rate, provided oxygen and moisture are present. Oxygen and moisture are invariably present in grout pores of atmospherically exposed tendons, although water content may be minimal under extremely dry conditions, and oxygen concentration may be negligible if the grout is water saturated. From the standpoint of strand corrosion, a worst-case scenario arises in situations where the grout is subjected to repetitive wetting (presumably from periodic water infiltration from a source external to the duct) and drying. Such cycling may also be facilitated by temperature variations. Strand corrosion is particularly severe at an air-water interface. Both Ti and Tp are a function of a number of material and exposure variables, which are described in this chapter in conjunction with a discussion of the Clconcentration threshold.

The Clthreshold itself, CT (i.e., the concentration of this species required to initiate active corrosion) is understood to be greater than 0.08 wt percent cement for good quality, high alkalinity in-place grout, although a definitive concentration has not been defined. This is because CT is known to conform to a distribution rather than being a distinct value, and there are a number of variables of influence. For example, air voids greater in diameter than about 0.1 inches that intersect the reinforcement facilitate local premature corrosion initiation. (See references 10–17.) Such occurrences, either involving air voids or relatively large air pockets,  result from air entrapment because of inadequate duct venting, incomplete duct filling, strands pressing against the duct interior surface, strand congestion, subsidence, or poor consistency with segregation (or a combination of these). These occurrences have been reported within PT ducts irrespective of the advent during the past decade of thixotropic grouts. (See references 10 and 18 – 20.) Also, steel corrosion at air-grout interfaces, which can occur in conjunction with the previously listed causes, has been reported even with Clconcentrations below the prescribed upper limit of 0.08 wt percent.(21,22) However, the presence of Clshould enhance this attack because of steel depassivation or reduced grout resistivity (or both).

Other variables that have been reported to influence CT include mix proportions, cement type, tricalcium aluminate content, concentration of blended materials, water/cementitious materials ratio, temperature, relative humidity, and steel surface condition. However, it can be reasoned that CT depends on cement content alone irrespective of whether or not grout, mortar, or concrete is an issue since Clpredominantly resides in the cement phase.(23) As a result, CT is normally expressed on a cement wt percent basis. Also, it is the cementitious phase that is predominantly contiguous with conventional reinforcement or bonded PT strand. Thus, for conventional reinforcement, ACI reports CT as 0.2 wt percent cement for concrete, whereas Alonso et al. determined CT to be in the range of 0.39 to 1.16 wt percent cement (also for mortar).(24–26) Mean and standard deviations for CT in concrete have been reported as 0.896 and 0.260 wt percent cement, respectively.(27,28) While this seems high compared to the other CT values listed, the preceding values are not mean values but concentrations at which initial corrosion onset occurred. Thus, if two standard deviations are subtracted (0.260 × 2 = 0.520) from the listed mean (0.896) and if it is assumed that the data are normally distributed, then the result (0.376 wt percent cement) indicates that 2.5 percent of embedded steel should be active at this value. This concentration is in the same range as the other results. However, all the CT determinations listed previously are for conventional reinforcing steel embedded in sound cementitious material. Conversely, if steel is exposed in air and if free water is present, then CT is essentially 0 wt percent. Because the corrosion rate of active carbon steel in aqueous solutions and in cementitious materials is normally controlled by oxygen availability, variations in alloy composition or microstructure (or both) generally have little influence. Consequently, corrosion behavior of PT strand is expected to be generally similar to that for conventional reinforcement.

Previous Investigations

Previous forensic investigations of existing bridge tendons with prepackaged thixotropic grouts have reported the following four distinct grout textures/appearances:

Only type 4 has the requisite properties to render it a desired in-place grout. In some instances, all four grout types have been reported in the same general vicinity along tendons. Where multiple grout consistencies occurred, type 4 was typically found along the lower portion of ducts, while types 1 and 2 were found at the highest elevations, indicating that gravimetric forces played a role in the segregation. Regions where grout was segregated often exhibited an air void or pocket along the top of the duct interior. Figure 28 shows a cross section of a tendon subsequent to its failure 8 years after construction.2

2 Cl concentration of the grout from this bridge was below the specified 0.08 wt percent cement upper limit.

Figure 28. Photo. Failed tendon cross section. This photo shows a cross section through a failed external tendon showing strand corrosion products and wet plastic grout, segregated white grout, and sound gray grout. Void space is also identified

Figure 28. Photo. Failed tendon cross section.

In figure 28, the strands contact the duct inner surface at the upper-right portion of the tendon, and type 4 grout is apparent in the lower region. Type 3 grout, either outlined or delineated by a somewhat broad white line (labeled “C”), is also apparent at intermediate elevations, and soft, wet grout is seen near the top. As such, in this case, the segregated white grout tended to separate the gray grout from segregated soft, wet grout or air space, which is apparent near the top (labeled “A”). Thus, segregated white grout occurred either as a volume of material embedded in the grout or as an approximately 0.04-inch-thick layer at the top of the gray grout. The type 2 grout (not apparent in figure 28) has been identified as either unmixed or segregated silica fume. Because segregation involved gravimetric causes, the three undesired grout forms have been most pronounced at elevated horizontal locations, near the top of inclines, and at anchorages. Although not necessarily identifiable in figure 28, corrosion products are contiguous to the upper strands. Figure 29 shows a longitudinal overhead view of the strands and grout in figure 28 with the duct top half removed and all three segregated grout types identified. Section A shows type 1 segregated wet, soft grout, B shows type 2 black segregated grout, and C shows type 3 segregated chalky white grout.

Figure 29. Photo. Longitudinal section of a tendon section with types 1–3 grout identified. This photo shows a longitudinal section of an external tendon section showing type 1 segregated wet, soft grout, type 2 black segregated grout, and type 3 segregated chalky white grout

Figure 29. Photo. Longitudinal section of a tendon section with types 1–3 grout identified.

Figure 30 and figure 31 show opened tendon anchorages. In these cases, there was no grout contamination by Cl , and grout filling of the duct was complete. However, regions of varied grout quality and strand corrosion products are apparent. For example, the grout in figure 30 consists predominantly of type 3 grout with an interconnecting network of cracking. Corrosion products at some of the strand ends are also visible. Figure 31 illustrates much the same but with type 1 grout in the central region. Figure 32 is similar to figure 31 but with type 4 grout in the bottom region. Thus, poor grout quality for these ducts is pervasive.

Figure 33 shows an opened anchorage on the Carbon Plant Road bridge over IH-37 in Texas as reported by the Texas Department of Transportation (TxDOT).(1). Type 1 grout is seen in the upper region, while the lower portion consists of type 4 gray grout. Free water flowed from the anchorage upon opening, and corrosion of strands in the type 1 grout and air space was apparent.

Figure 30. Photo. Opened tendon end showing predominantly type 3 grout and strand corrosion products. This photo shows an opened external tendon end showing predominantly white chalky (type 3) grout and strand corrosion products
Source: Parsons Brinckerhoff
Figure 30. Photo. Opened tendon end showing predominantly type 3 grout and strand corrosion products.

Figure 31. Photo. Opened tendon end showing types 3 and 1 grout and strand corrosion products. This photo shows an opened external tendon end showing white chalky (type 3) and unhardened (type 1) grout on the bottom half and central region, respectively, and strand corrosion products at the top
Source: Parsons Brinckerhoff
Figure 31. Photo. Opened tendon end showing types 3 and 1 grout and strand corrosion products.

Figure 32. Photo. Opened tendon end revealing type 4 grout (bottom half), type 1 grout (center region), and strand corrosion products (upper region). This photo shows an opened tendon end revealing hardened gray grout (type 4; bottom half), unhardened grout (type 1; central region), and strand corrosion products (upper region)
Source: Parsons Brinckerhoff
Figure 32. Photo. Opened tendon end revealing type 4 grout (bottom half), type 1 grout (center region), and strand corrosion products (upper region).

Figure 33. Photo. Opened anchorage on the Carbon Plant Road bridge over IH-37. This photo shows an opened anchorage on the Carbon Plant Road bridge over IH-37 showing an air void near the top followed by a layer of type 4 grout and type 1 grout beneath

Figure 33. Photo. Opened anchorage on the Carbon Plant Road bridge over IH-37. (11)

Bertolini and Carsana reported forensic analysis results for a PT bridge for which a tendon failure was disclosed less than 2 years after construction.3(21) The cementitious grout was not identified by the manufacturer or as being thixotropic; however, a water/cement ratio of 0.32 was specified along with a commercial unidentified admixture specific for PT grouts. While most tendons examined were characterized as consisting of type 4 grout, some, including the anchorage area of the failed tendon, had a whitish unhardened plastic paste, which could be a combination of types 1 and 3. Such regions contained small hardened black spots, which could be type 2 grout. Heavy strand corrosion occurred in areas of the whitish grout.

3 The location of this bridge was not provided, but it is assumed to be in Italy.

The limited findings suggest the possibility that segregation and as many as four different textures/consistencies can result for in-place grouts with active strand corrosion occurring for segregated grout types 1–3(1,21,22) . These studies identified air voids/pockets as a major problem and indicated that upward water migration through the grout occurred during setting. The TxDOT study identified Cl, sulfide (S2−), sodium (Na+), and potassium (K+) in type 1 grout, and FDOT found higher levels of Cl; and calcium (Ca2+) in type 1 in comparison to the other types.(1,22)

Using an ex-situ leaching method, FDOT measured higher Cl concentrations at upper compared to lower elevations within a given duct cross section, suggesting that upward migration of this species occurred during grout setting. (22) The concentrations measured at elevated positions were relatively low (maximum ~0.04 wt percent), which was consistent with this grout not necessarily being from Cl contaminated batches. Also, any partitioning trend for sulfates (SO42−) between grout types was less distinct than for Cl and Ca2+; however, SO42− concentrations as high as 0.9 wt percent were found in the type 1 grout free water. Sulfates are invariably present in cement pore water, and several authors have associated this species with steel depassivation or passive current densities being an order of magnitude or more higher than for SO42− free simulated pore water solutions as well as passivity breakdown events. (See references 29–31 and 22.) Based on anodic polarization and immersion experiments in saturated calcium hydroxide solutions, Gouda reported the critical SO42− concentration for initiation of active steel corrosion as 0.2 percent.(30) One recommendation has been that the grout maximum cement S2− content be limited to 0.01 percent.(19) Schokker and Musselman reported advanced strand corrosion after relatively brief exposure periods in test assemblies that employed a standard commercial gypsum (hydrated calcium sulfate) grout and contiguous air space but no free water for the purpose of simulating a tendon failure in the Varina-Enon bridge in Virginia.(31) Bertolini and Carsana measured elevated SO42−, Na+, and K+ in the tendon grouts they examined and attributed strand corrosion and resultant fracture to the elevated pH range where the soluble hydrous iron oxide (HFeO2) corrosion product has been reported and low water resistivity was observed (1.64 ohm-ft). (21,31) Although thermodynamically feasible, such a role of HFeO2 has not been previously reported. It is projected that sulfates were responsible. The European standard lists an upper limit of 4.5 wt percent cement for sulfates and 0.01 wt percent cement for sulfides.(9)

In addition, sulfates may cause electrolyte acidification within occluded regions (crevices), such as the lines of contact between adjacent wires or strands where the solution becomes deaerated. The process is normally described in standard corrosion texts as involving Cl rather than SO42− , since the former is generally more pervasive; however, any hydrolysable ions, including sulfates, can have the same effect.(33) Thus, the reaction at issue is as follows:

Figure 34. Equation. Reaction of the ferrous ion with water and sulfate ion to yield ferrous hydroxide and sulfuric acid. Fe superscript 2+ plus 2 H subscript 2 O plus SO subscript 4 superscript 2 minus reacts to form Fe open parenthesis OH closed parenthesis subscript 2 plus H subscript 2 SO subscript 4
Figure 34. Equation. Reaction of the ferrous ion with water and sulfate ion to yield ferrous hydroxide and sulfuric acid.

Where sulfuric acid is a product. Because of the resultant drop in pH, corrosion rate in such circumstances is expected to be much greater than if the solution were near neutral or alkaline.

Deficiencies

Based on the findings discussed in this chapter, the following grout deficiencies are of concern:

The finding that corrosion-induced tendon failures have occurred relatively soon after construction compared to the intended service life, even in situations where Cl concentrations were relatively low and within the prescribed 0.08 wt percent cement limit, strongly indicates that segregation, subsidence, and incomplete duct filling are major issues.(1,21,22) Corrosion that occurs in such situations is likely to be enhanced by elevated Cl but will still initiate and propagate even if Cl concentrations are below the 0.08 wt percent limit.

 

 

CHAPTER 5. MINIMUM NUMBER OF TEST SAMPLES

GENERAL

The determination of the number of tendons to be inspected for grout sampling is an important part of this guideline. If not enough samples are collected, the inspection may not provide a good assessment of the actual condition in the bridge. However, if too many samples are removed, it may be too costly and, without proper restoration, may result in future durability issues. It is critical to select a reasonable number of tendons for each tendon type based on practical and logical considerations such as tendon redundancy, function, workmanship complexity, detailing, etc. For instance, the recommended number of samples for a relatively straight short horizontal tendon will be different than for a long-draped tendon or a cantilever tendon. This chapter provides guidance on the determination of a reasonable number of sampling locations for each type of tendon by utilizing a statistical risk-based approach to categorize and rank the elements of the PT system. The recommended numbers can be adjusted on a case-by-case basis.

As previously stated in chapter 4, there are two main sources of grout deficiencies as follows:

A single lot of grout typically varies in size from about 40,000 to 250,000 lb. Each lot consists of a series of batches about 1,100 lb each. It is expected that for the contaminated grout, the Cl content will be uniform within each batch, but the Cl content may differ slightly between batches in a single lot.(34,35) Depending on the size and length of a certain tendon, it is likely that the grout of each tendon originated from several batches.

Assuming that deficiencies stem from only grout material contamination, relatively few samples may be required for tendons grouted with the material from a single lot, provided the tendon grouting log information is available. In cases where tendons are grouted with multiple grout lots, a greater number of grout samples will be required in order to best assure that as many lots are included in the sampling as possible. However, the grout log information may not be available for every bridge. Therefore, the statistical grout sampling method is a reasonable approach as it is implemented in other fields in the industry by ASTM E141-10, “Standard Practice for Acceptance of Evidence Based on the Results of Probability Sampling.”(36)

Deficiencies caused by poor workmanship may require more samples because the variation in workmanship is likely to be more random in nature, and there may not be any correlation between different grouting locations. The two main sources of deficiencies can occur independently or concurrently at the same location. The combined effects of deficiencies and the uncertain nature of any poor workmanship complicate the formulation of the quantitative basis for an optimal and cost effective grout sampling/inspection program.

INSPECTION OPTIONS

In some cases, bridge owners may be concerned with the Cl contamination only. Therefore, the inspection guidelines provided in this chapter contain the following two options with two different inspection plans, as shown in figure 35:

In both options, the inspection is performed in two levels. Recognizing that invasive testing may create paths that allow corrodants access to strands and cause corrosion if the tendon is not properly restored/repaired, level 1 is intended to provide an initial indication of the grout condition in terms of preliminary screening tests, while level 2 provides a more comprehensive and higher confidence result. Bridge owners have the flexibility to select the inspection strategy and level of confidence and modify the inspection plans/procedures as appropriate for their bridge inventory and local conditions.

For owners who are only concerned with the grout Cl contamination, the sampling procedure for option 1 should be followed. Otherwise, the sampling procedure for option 2 is followed, as shown in figure 35.

Figure 35. Flowchart. Inspection options. This figure shows a flowchart for the inspection process for in-place tendon grouts. On the left, the first box is labeled “Grout sampling inspection.” Two arrows point from the box to the right. The top points to a box labeled  “Option 1: Testing for chloride concentration only.” That box points to a box labeled “Level 1,” which then points to another box labeled “Level 2.” The bottom arrow from the first box points to a box labeled “Option 2: Testing for all grout deficiencies.” That box points to a box labeled “Level 1 75 percent confidence,” which then points to another box labeled “Level 2 95 percent confidence.”
Figure 35 . Flowchart. Inspection options.

Option 2 adopts 75 and 95 percent confidence levels for levels 1 and 2, respectively. The 75 percent confidence approach requires fewer samples than the 95 percent confidence, but it should still provide reasonable findings.

INSPECTING Cl CONTENT (OPTION 1)

Option 1 assumes no grout PDs, voids, or strand corrosion. If grout PDs are found during sampling, it is recommended to perform an option 2 inspection.

Project with Complete Grouting Records

Level 1

Under this approach, either a minimum of three random samples is taken for each lot from the primary tendon types, or, alternatively, one sample is taken randomly from 50 percent of all batches (one sample per batch) depending on whichever of the two is larger (see chapter 7 for recommended locations of grout sampling). If the test results show that one or more samples has a Cl content higher than the threshold limit (0.08 wt percent cement), then a level 2 inspection is required. If all analysis results are below this limit, then no further sampling is required.

Level 2

Under this approach, a minimum of one random grout sample for each batch from the primary tendon types should be obtained (see chapter 9 for the interpretation of the test results for any further actions).

Project with Incomplete or No Grouting Records

Grout sampling for this type of project should follow the procedures based on statistical methods of sampling for all grout deficiencies (option 2).

INSPECTING ALL GROUT DEFICIENCIES (OPTION 2)

In general, the inspection process is performed in four steps (see figure 36). In the first step, an engineer should review the as-built plans, PT shop drawings, specifications, and construction records. Then, the engineer should conduct a walk-through visual inspection for the length of the bridge. The main objective of the walk-through inspection is to evaluate the overall condition of the structural system and identify possible defects and signs of deterioration. The visual inspection does not require any specialized equipment. The third step is to obtain grout samples and visually assess and document the grout condition and any signs of tendon defects. Depending on the type of structure/tendon, some specialized equipment/tools might be necessary. At this point, the possibility of causing a “weak spot” or distress in the element (e.g., tendon damage during drilling) and rendering it prone to corrosion in the future if not properly repaired becomes an important factor in selecting the number of tendons for sampling. Therefore, it is important to minimize the number of sampled tendons while still providing an acceptable level of accuracy in representation of the grout chemical composition and condition. Chapter 7 of this report discusses the strategy that should be used to identify and preselect test locations within a tendon that are most likely to have deficient grout.

Figure 36. Flowchart. Grout inspection processes. This flow chart lists the sequential inspection steps for pre-inspection activities, visual inspection and non-destructive testing (NDT), grout sampling inspection, and grout sample evaluation. Pre-inspection activities include review as-built plans, review construction records, review inspection documents, and review load rating. Visual inspection and NDT steps include walk through, duct sounding (external tendon), cracked concrete, signs of water leakage, corrosion protection system, and signs of corrosion. Grout sampling inspection steps include presence of voids, grout segregation, grout consistency, grout discoloration, presence of corrosion, borescope inspection, and grout sample collection. Grout sample evaluation steps include grout petrographic evaluation, corrodant concentration, and moisture content.

Figure 36 . Flowchart. Grout inspection processes.

Since there is no quantitative methodology for ranking and identifying deficient areas, the elements of the PT system should be categorized based on the qualitative opinion of experts. The risk-based inspection methodology was adopted, and tendons are prioritized in terms of the risk associated with the potential failure.(38) All tendons in the bridge are assigned to one of the following groups:

The risk is expressed as a product of a probability of defect indicator and a consequence of failure indicator, as shown in figure 37. The critical factors influencing risk are defined in terms of a series of tables with designated categories. Numerical values from 1 to 5 are assigned to each category, with 1 being the least probable or lowest consequence, 3 being intermediate, and 5 being most probable with very high catastrophic consequence.

Figure 37. Graph. Risk matrix. This figure shows a risk matrix where probability of a defect indicator is plotted on the y-axis ranging from 1 to 5, and consequence of failure indicator is plotted on the x-axis ranging from 1 to 5. For both axes, 1 indicates low and 5 indicates high. For low combinations of axes, risk is low and vice versa.

Figure 37. Graph. Risk matrix.

Probability of Defect Indicator

Bridge Condition/Service Performance

The overall condition and previous service performance history of a bridge is an important factor affecting the likelihood of an ongoing corrosion process. Existing serviceability issues such as visible cracks, discoloration of concrete, or poor overall workmanship (or a combination of these) should be considered in assigning this factor. Table 1 lists the probability of defect indicators for the bridge condition categories considered.

Table 1. Bridge condition—probability of defect indicator.
Bridge Condition Description Value
Poor Very high degradation probability 5
Moderate High degradation probability 4
Good Average degradation probability 3
Very Good Low degradation probability 2
Excellent Very low degradation probability 1

Construction Records

An important factor affecting the risk associated with the potential tendon failure is the availability of the construction records and previous inspection records. Recommended probability of defect indicators are listed in table 2.

Table 2. Construction and inspection records—probability of defect indicator.
Construction and Inspection Records Value
No construction and inspection records exist 5
Limited construction and inspection records exist 4
Some construction and inspection records exist 3
Comprehensive construction and inspection records exist 2
Very comprehensive construction and inspection records exist 1

Visual Condition Evaluation

The visual evaluation serves as an important first tool in selecting any problem areas and estimating the likelihood of more serious structural defects. The probability of defect indictors for the visual inspection categories are listed in table 3. The maximum value of the defect indicator should be selected from the list of assigned probability of defect indicators in this category.

Table 3. Visual evaluation—probability of defect indicators.
Visual Inspection Category Major Defect Moderate Defect Small Defect Very Small Defect No Defect
Signs of grout leakage 5 4 3 2 1
Workmanship 5 4 3 2 1
Cracked concrete 5 4 3 2 1
Duct condition (external PT) 5 4 3 2 1
Voids (external PT) 5 4 3 2 1
Signs of water leakage 5 4 3 2 1
Corrosion protection 5 4 3 2 1

Tendon Geometry and Length

It was observed from prior investigation experiences that it is unlikely to have defective grout in short straight tendons or tendons with small curvature changes. The likelihood of a defect is higher for multispan long tendons with large curvature changes and large distances between lowest and highest points, particularly tall vertical tendons. The probability of defect indicators for the tendon shape categories are listed in table 4.

Table 4. Tendon geometry and length—probability of defect indicators.
Tendon Geometry and Length Value
Long multispan tendons with large curvature changes/large distance between lowest and highest points; tall vertical tendons 5
Short single-span tendons with large curvature changes/large distance between lowest and highest points; short vertical tendons 4
Long tendons with small curvature changes 3
Long straight tendons or short tendons with small curvature changes 2
Short straight/horizontal tendons 1

Overall Probability of Defect Indicator

The overall probability of defect indicator, P, is determined as a weighted sum of the contributing factors as follows:

Figure 38. Equation. Overall probability of defect indicator. P equals the sum of P subscript i times W subscript i.

Figure 38. Equation. Overall probability of defect indicator.

Where:
Pi = Partial probability of defect indicator.
Wi = Appropriate weight factor, as shown in table 5.

Table 5. Weight factors for probability of defect indicator.
Probability of Defect Indicator Weight
Overall bridge condition 0.15
Construction and inspection records 0.15
Visual evaluations 0.30
Tendon geometry and length 0.40

Consequence of Failure Indicator

The consequence of failure indicator is intended to categorize the tendons  in terms of the effect that eventual failure due to corrosion resulting from an undetected defect will have on the structure.

Cost of Repair or Tendon Replacement

The relative cost of repair/replacement accounts for the funding that would be needed to restore the full functionality of the structure after the elements have become damaged or failed. Table 6 presents the consequence of failure indicators in this category.

Table 6. Consequence of failure indicator versus cost of repair or tendon replacement.
Rank Cost of Repair or Tendon Replacement
Very high 5
High 4
Moderate 3
Low 2
Very low 1

Element/Tendon Redundancy

Redundancy is generally defined as the extra capacity of a structural system to carry loads after partial damage or failure of its elements. For example, cantilever tendons have higher redundancy than bottom continuity tendons since a portion of the cantilever tendons is required to support the dead loads and erection equipment during free cantilever construction. After the cantilever tips from two adjacent piers are connected, the negative moments demand will be reduced. However, the extra tendons are typically left in place. Diaphragm tendons are also considered to have high redundancy due to the presence of a large amount of ordinary reinforcement. The consequence of failure indicators associated with the element/tendon redundancy are listed in table 7.

Table 7. Consequence of failure indicator versus element/tendon redundancy.
Element/Tendon Redundancy Value
Loss of some tendons will cause a catastrophic failure 5
Loss of some tendons will cause severe distress to the structure—repairable 4
Loss of some tendons will decrease the capacity of the structural system—possible need for posting, no structural distress 3
Sufficient safety reserve exists. Loss of a small number of tendons will slightly impact the capacity, but the system can remain in service without posting 2
Tendon does not contribute to the resistance of the structural system 1

Bridge Importance

The criticality of the bridge as an element of the transportation system is considered in this category. Major bridges carrying large volumes of traffic should be assigned to a high consequence category, while bridges in a rural area with low traffic volumes should be assigned a low number. Recommended consequence of failure indicators for this category are listed in table 8.

Table 8. Consequence of failure indicator versus bridge importance.
Bridge Importance Value
Critical bridges 5
Non-critical bridges 3
Less important bridges 1

Overall Consequence of Failure Indicator

The overall consequence of failure indicator, C, is determined as a weighted sum of the contributing factors as follows:

Figure 39. Equation. Overall consequences of failure indicator. C equals the sum of C subscript i times W subscript i

Figure 39. Equation. Overall consequence of failure indicator.

Where:
Ci = Partial probability of defect indicator.
Wi = Appropriate weight factor, as shown in table 9.

Table 9. Weight factors for consequence of failure indicator.
Consequence of Failure Indicator Weight
Cost for repair/tendon replacement 0.4
Element redundancy 0.4
Criticality of the bridge 0.2

Risk Level

Figure 37 is used to determine risk level and prioritize/categorize the tendons according to the relationship, as shown in figure 40.

Figure 40. Equation. Risk. Risk equals P times C.

Figure 40. Equation. Risk.

Where:
P = Overall probability of defect indicator.
C = Consequence of failure indicator.

Acceptable Fraction of Tendons with Undetected Deficient Grout

The recommended minimum number of sampled tendons depends on element risk and the possibility of creating distress for the structure throug intrusive inspection. The acceptable number of tendons with undetected deficient grout is lower for elements with high risk. Within a risk category, the acceptable number of tendons with undetected deficient grout decreases as the likelihood of structural distress associated with intrusive sampling increases. Table 10 presents recommendations regarding the acceptable number of tendons with undetected deficient grout to categories of element risk and inspection costs.

Table 10. Acceptable fractions of undetected tendons with deficient grout
Element Risk Structural Impact Caused by Sampling
High Medium Low
High 20 percent deficient 10 percent deficient 10 percent deficient
Medium 30 percent deficient 20 percent deficient 10 percent deficient
Low 30 percent deficient 30 percent deficient 20 percent deficient

Minimum Number of Inspected Tendons

To determine the minimum number of inspected tendons, tendons identified for testing are arranged in groups within which every tendon has approximately the same likelihood of having defective grout; each group is considered as a separate population. Depending on the total number of tendons in one group, N, as compared to the number of tendons in that group selected for inspection, n, selecting the sample n tendons from population N might significantly change the remainder of the population regardless of how many tendons with defective grout are in the sample. Therefore, it is assumed that the distribution of the number of tendons with defective grout in a random sample of n tendons is an approximately hypergeometric distribution with parameters m, k, and N, where m is the actual number of tendons with defective grout and k is the number of times when the selected tendon is with defective grout. The probability mass function (PMF) of this distribution is expressed as follows:

Figure 41. Equation. Probability mass function for hypergeometric distribution. P times open parenthesis X equals k closed parenthesis equals the product of open parenthesis binominal coefficient of m choose k closed parenthesis with the binominal coefficient of the difference between open parenthesis N and m choose difference between n and k closed parenthesis, divided by the binominal coefficient of open parenthesis N choose n closed parenthesis.

Figure 41. Equation. Probability mass function for hypergeometric distribution.

Where P(k) is the probability of observing k number of deficiencies when selecting without replacement n samples from the population of size N.(39) Figure 42 presents an example of PMF of the fraction of samples with defective grout calculated for N = 100, m = 25, n = 45, and k = 1…20. Each bar represents the probability that when 45 tendons are randomly inspected from a total population of 100 tendons, k tendons will have a defect. Since in this example 25 percent of tendons have defective grout, the expected and most probable number of successes (detection of tendon with defect) is 25 percent of 45, or 11 tendons.

Figure 42. Graph. Example of PMF for hypergeometric distribution. This bar graph shows an example of probability mass function (PMF) for hypergeometric distribution. PMF is on the y-axis, and the number of deficient grout samples is on the x-axis. The function peaks at a PMF of 0.182 and 11 deficient grout samples, and the curve is approximately bell shaped.

Figure 42. Graph. Example of PMF for hypergeometric distribution.

The cumulative distribution function (CDF) of the hypergeometric distribution is defined as follows:

Figure 43. Equation. CDF. CDF equals open parenthesis 1 minus P subscript d closed parenthesis equals P open parenthesis i is less than or equal to k closed parenthesis equals the sum from i equals 0 to k of the product of the binominal coefficient of open parenthesis m choose i closed parenthesis with binominal coefficient of the difference between open parenthesis N and m choose difference between n and i closed parenthesis, divided by the binominal coefficient of open parenthesis N choose n closed parenthesis.

Figure 43. Equation. CDF.

Figure 44 shows CDF for PMF for the example PMF presented in figure 42. Based on the properties of CDF, it can be determined that there is (1 – Pd) = 10 percent probability of discovering not more than eight defective tendons and a Pd = 90 percent chance of discovering eight or more defective tendons where Pd is defined as the probability of detecting more than i number of defective tendons in the population of N with m tendons being defective.

Figure 44. Graph. Example of CDF for a hypergeometric distribution. This bar graph shows an example of cumulative distribution function (CDF) for a hypergeometric distribution. CDF is on the y-axis, and number of deficient grout samples is on the x-axis. CDF becomes finite when the number of deficient grout samples equals 5, and CDF approaches 1 when the number of deficient grout samples equals 16.

Figure 44. Graph. Example of CDF for a hypergeometric distribution.

Calculations were performed to determine the minimum number of samples required to detect at least one tendon with defective grout, assuming different fractions of tendons with defective grout in the total population. For all considered cases, the probability of detection (confidence of detecting at least one) is set equal to 75 percent (level 1 inspection) and 95 percent (level 2 inspection). The results are presented in the table 11 and table 12. Based on the results in table 12, if 100 tendons are identified in one risk group and eight are initially tested with no defects, then there is a 95 percent probability that the fraction of tendons with defects in the selected population is less than 30 percent. By testing an additional five tendons, it can be assured that there is 95 percent probability that the fraction of tendons with defects in the selected population is less than 20 percent.

In some cases, it might be necessary to relax the assumptions by decreasing the probability of detecting at least one defective to minimize the number of tendons required to detect at least one tendon with defective grout. Figure 45 to figure 48 present the minimum required number of sampled tendons for confidence levels equal to 95, 85, and 75 percent assuming 5, 10, 20, and 30 percent of the tendons have defective grout. The figures are intended to assist in making informed decisions regarding the sample size to minimize the sampling effort.

Table 11. Minimum number of tendons required to detect at least one tendon with deficient grout (75% confidence).

Number of Identified Tendons Percent of Tendons with Deficient Grout
10 Percent 20 Percent 30 Percent
10 8 5 3
20 10 5 4
50 12 6 4
100 12 6 4
150 13 6 4
200 13 6 4
500 13 6 4
> 1,000 13 6 4

Table 12. Minimum number of tendons required to detect at least one tendon with deficient grout (95% confidence).

Number of Identified Tendons Percent of Tendons with Deficient Grout
10 Percent 20 Percent 30 Percent
10 10 7 6
20 15 10 6
50 22 12 7
100 25 13 8
150 26 13 8
200 26 13 8
500 27 13 8
> 1,000 28 13 8

Figure 45. Graph. Minimum number of tendons required to detect at least one tendon with deficient grout assuming 5 percent of the samples are defective. This graph shows the minimum number of tendons required to detect at least one tendon with deficient grout assuming 5 percent of the samples are defective. The required sample size is on the y-axis from zero to 60, and the total number of tendons is on the x-axis from zero to 1,000 for confidence levels of 75, 85, and 95 percent. The number of samples for a particular confidence increases rapidly with increasing tendon numbers at low tendon numbers but becomes independent of the number of tendons at high tendon numbers. A greater number of samples is required the higher the confidence level.

Figure 45. Graph. Minimum number of tendons required to detect at least one tendon with deficient grout assuming 5 percent of the samples are defective.

Figure 46. Graph. Minimum number of tendons required to detect at least one tendon with deficient grout assuming 10 percent of the samples are defective. This graph shows the minimum number of tendons required to detect at least one tendon with deficient grout assuming 10 percent of the samples are defective. Required sample size is on the y-axis from zero to 30, and total number of tendons is on the x-axis from zero to 1,000 for confidence levels of 75, 85, and 95 percent. Similar to figure 45, The number of samples for a particular confidence increases rapidly with increasing tendon numbers at low tendon numbers but becomes independent of the number of tendons at high tendon numbers. A greater number of samples is required the higher the confidence level. The trends are displaced to a lesser number of required samples than shown in figure 45.

Figure 46. Graph. Minimum number of tendons required to detect at least one tendon with deficient grout assuming 10 percent of the samples are defective.

Figure 47. Graph. Minimum number of tendons required to detect at least one tendon with deficient grout assuming 20 percent of the samples are defective. This graph shows the minimum number of tendons required to detect at least one tendon with deficient grout assuming 20 percent of the samples are defective. Required sample size is on the y-axis from zero to 15, and total number of tendons is on the x-axis from zero to 1,000 for confidence levels of 75, 85, and 95 percent. Similar to figure 46, The number of samples for a particular confidence increases rapidly with increasing tendon numbers at low tendon numbers but becomes independent of the number of tendons at high tendon numbers. A greater number of samples is required the higher the confidence level. The trends are displaced to a lesser number of required samples than shown in figure 46.

Figure 47. Graph. Minimum number of tendons required to detect at least one tendon with deficient grout assuming 20 percent of the samples are defective.

Figure 48. Graph. Minimum number of tendons required to detect at least one tendon with deficient grout assuming 30 percent of the samples are defective. This graph shows the minimum number of tendons required to detect at least one tendon with deficient grout assuming 30 percent of the samples are defective. Required sample size is on the y-axis from zero to 10, and total number of tendons is on the x-axis from zero to 1,000 for confidence levels of 75, 85, and 95 percent. Similar to figure 47, The number of samples for a particular confidence increases rapidly with increasing tendon numbers at low tendon numbers but becomes independent of the number of tendons at high tendon numbers. A greater number of samples is required the higher the confidence level. The trends are displaced to a lesser number of required samples than shown in figure 47

Figure 48 . Graph. Minimum number of tendons required to detect at least one tendon with deficient grout assuming 30 percent of the samples are defective.

Sampling Procedure Summary

The procedure to determine the recommended minimum number of sampled tendons to be tested consists of the following steps:

  1. Estimate the total number of tendons for each considered tendon type. Review the as-built plans, PT shop drawings, specifications, and construction records and identify all tendon types. Determine the number of tendons for each considered tendon type.
  2. Prioritize the tendons by assigning them to one of three risk categories (high, medium, or low).
  3. Determine the probability of defect indicator (see table 1 through table 5) for each considered tendon group.
  4. Determine the consequence of failure indicator (see table 6 through table 9) for each considered tendon group.
  5. Assign the group to one of the three risk categories as shown in figure 37.
  6. Based on the structural impact/distress caused by sampling tendons from each group, use table 10 to determine an acceptable fraction of tendons with undetected deficient grout.
  7. Determine the minimum number of sampled tendons. Use table 11 for level 1 inspection (75 percent confidence) and table 12 for level 2 inspection (95 percent confidence).

After the minimum number of sampled tendons to be tested is determined, it is necessary to locate the strategic inspection points for each tendon type (see chapter 7).

The selection of a random sample from the list of identified inspection locations involves the following steps:

  1. Assign a random number to each tendon.
  2. Sort each tendon according to the order it is numbered.
Note that a predetermined number (percentage) of tendons should be selected starting from the top or bottom of the list of tendon numbers.

EXAMPLES

Typical Balanced Cantilever Bridge

The procedure for option 2 inspection is presented in this section as an example using an existing precast segmental bridge. The plans for the considered bridge can be found in appendix A. The bridge consists of 10 spans with the total length of 2,256.33 ft. The following four distinct types of tendons are utilized in this bridge:

Overall, the bridge is in good condition and has excellent workmanship. It is assumed that construction records are not available or are incomplete. The sampling procedure used in this example is as follows:
  1. Estimate the number of the tendons for each tendon type.
    • Total number of cantilever tendons = 242.
    • Total number of continuity top and bottom tendons = 112.
    • Total number of draped tendons = 40.
    • Total number of transverse tendons = 694.
  2. Prioritize the tendons by assigning them to one of three risk categories.
  3. Determine the probability of defect indicator (see table 13).
  4. Table 13. Balanced cantilever bridge—probability of defect indicator.
    Category Weight(table 5) Tendon Type
    Transverse Cantilever Continuity External
    Bridge condition (table 1) 0.15 2 2 2 2
    Construction and inspection records (table 2 ) 0.15 5 5 5 5
    Visual inspection (table 3 ) 0.30 1 1 1 1
    Tendon shape and length (table 4 ) 0.40 1 2 2 4
    Probability of defect indicator 2 2 2 3

  5. Determine consequence of failure indicator (see table 14).

  6. Table 14. Balanced cantilever bridge—consequence of failure indicator
    Category Weight (table 9) Tendon Type
    Transverse Cantilever Continuity External
    Cost of repair or replacement (table 6 ) 0.40 3 5 4 2
    Element/tendon redundancy
    (table 7 )
    0.40 2 2 4 2
    Bridge importance (table 8 ) 0.20 5 5 5 5
    Consequence of failure indicator 3 4 4 3

  7. Assign tendon groups to appropriate risk categories (see figure 49).
  8. Figure 49. Graph. Balanced cantilever bridge—tendon risk categories. This graph shows a risk matrix for a cantilever bridge. Probability of a defect indicator is on the y-axis ranging from 1 to 5, and consequence of failure indicator is on the x-axis ranging from 1 to 5. For both axes, 1 represents low, and 5 represents high. For low combinations of the two numbers, risk is low and vice versa. Three bands of risk are indicated: low, medium, and high. A bridge with external draped tendons is indicated as having both a probability of defect indicator and consequence of failure indicator of 3. For transverse tendons, the probability of defect indicator is 2, and the consequence of failure indicator is 3. For cantilever and continuity tendons, the probability of defect indicator is 2, and the consequence of failure indicator is 4.

    Figure 49. Graph. Balanced cantilever bridge—tendon risk categories.

  9. For each identified group, select an acceptable fraction of tendons with undetected deficient grout and determine the minimum number of sampled tendons (see table 15).
  10. Table 15. Balanced cantilever bridge—minimum recommended number of tendons for inspection.
    Type of Tendon Total Number of Tendons Risk Structural Impact Caused by Inspection Acceptable Fraction Of Undetected Defective Minimum Number of Tendons for Inspection
    Level 1 Level 2
    Transverse tendon 694 Medium High 30 percent 4 8
    Cantilever tendon 242 Medium High 30 percent 4 8
    Continuity tendon 112 Medium Medium 20 percent 6 13
    External tendon 40 Medium Low 10 percent 12 22

  11. Randomly select the required number of tendons for each tendon type.

Table 16 through table 19 present the summary of all tendons. Each tendon is identified by its label. The first letter and number denotes the span number "S". The second letter denotes the tendon name as shown in the as-built plans. The last number helps identify the tendon in case there are two or more tendons with the same profile at one location. All of the data in tables are sorted with respect to the random number assigned to each tendon. Bold text indicates level 1 inspections, and bold italics indicates level 2 inspections.

Table 16. List of continuity tendons.
# Random Tendon ID # Random # Tendon ID # Random # Tendon ID # Random # Tendon ID
1 0.022 S7-C4-1 29 0.237 S1-C5-2 57 0.461 S1-C3-1 85 0.783 S8-C1-2
2 0.028 S5-T20-2 30 0.254 S4-T21-2 58 0.462 S2-C3-1 86 0.788 S4-C2-2
3 0.055 S7-C5-1 31 0.258 S4-T20-2 59 0.467 S4-C3-1 87 0.802 S2-C1-1
4 0.055 S7-T20-1 32 0.270 S8-C2-1 60 0.476 S2-T20-2 88 0.806 S5-C4-1
5 0.056 S9-T21-2 33 0.274 S10-C1-2 61 0.504 S3-C2-2 89 0.812 S2-C4-1
6 0.063 S9-C2-1 34 0.282 S2-C2-2 62 0.504 S1-T20-2 90 0.813 S1-C4-1
7 0.078 S5-T20-1 35 0.287 S9-C3-1 63 0.509 S8-C4-2 91 0.818 S6-C2-1
8 0.088 S3-C2-1 36 0.298 S9-C2-2 64 0.521 S7-T20-2 92 0.818 S3-T20-2
9 0.092 S6-C3-1 37 0.328 S7-C2-1 65 0.527 S5-C2-1 93 0.833 S3-C1-1
10 0.098 S5-C3-1 38 0.359 S6-C5-2 66 0.569 S4-C2-1 94 0.835 S3-C6-1
11 0.112 S2-C2-1 39 0.363 S10-C2-1 67 0.573 S1-C2-1 95 0.843 S1-C2-2
12 0.112 S6-C3-2 40 0.364 S6-T20-1 68 0.578 S7-C1-1 96 0.850 S3-C6-2
13 0.114 S5-C5-1 41 0.372 S7-C3-2 69 0.593 S7-C4-2 97 0.855 S6-C1-1
14 0.134 S5-C4-2 42 0.383 S6-T20-2 70 0.605 S1-C4-2 98 0.861 S5-C1-2
15 0.134 S8-C5-2 43 0.389 S7-C1-2 71 0.609 S3-C1-2 99 0.892 S8-C2-2
16 0.147 S7-C3-1 44 0.399 S6-C2-2 72 0.620 S2-C4-2 100 0.895 S10-C2-2
17 0.161 S8-T20-2 45 0.407 S8-C1-1 73 0.640 S1-C5-1 101 0.907 S4-T20-1
18 0.162 S7-C2-2 46 0.414 S5-C3-2 74 0.646 S2-C1-2 102 0.918 S3-T20-1
19 0.176 S4-C1-1 47 0.416 S1-T20-1 75 0.666 S9-C3-2 103 0.920 S4-C3-2
20 0.184 S4-C4-2 48 0.419 S2-T20-1 76 0.692 S8-C3-1 104 0.931 S10-T20-2
21 0.194 S8-C3-2 49 0.424 S1-C3-2 77 0.704 S5-C1-1 105 0.939 S3-C5-2
22 0.195 S3-C3-1 50 0.428 S9-T20-1 78 0.707 S7-C5-2 106 0.942 S1-C1-1
23 0.199 S9-C1-1 51 0.432 S3-C4-1 79 0.707 S5-C2-2 107 0.943 S3-C4-2
24 0.207 S10-C1-1 52 0.441 S6-C4-2 80 0.714 S3-C3-2 108 0.968 S1-C1-2
25 0.219 S9-C1-2 53 0.450 S8-C5-1 81 0.718 S2-C3-2 109 0.970 S8-C4-1
26 0.230 S10-T20-1 54 0.456 S6-C4-1 82 0.737 S4-T21-1 110 0.976 S6-C5-1
27 0.235 S4-C4-1 55 0.459 S4-C1-2 83 0.752 S9-T20-2 111 0.989 S9-T21-1
28 0.236 S6-C1-2 56 0.460 S5-C5-2 84 0.783 S8-T20-1 112 0.998 S3-C5-1

Table 17. List of external draped tendons.
# Random # Tendon ID # Random# Tendon ID
1 0.001 S10-E1-1 21 0.416 S9-E1-2
2 0.040 S7-E2-1 22 0.453 S4-E1-2
3 0.062 S4-E1-1 23 0.457 S4-E2-2
4 0.064 S10-E2-1 24 0.493 S3-E1-1
5 0.074 S7-E1-1 25 0.600 S4-E2-1
6 0.080 S10-E2-2 26 0.631 S5-E2-1
7 0.090 S9-E2-2 27 0.642 S3-E2-1
8 0.116 S9-E1-1 28 0.645 S8-E2-1
9 0.118 S3-E1-2 29 0.685 S1-E1-1
10 0.119 S8-E2-2 30 0.693 S8-E1-1
11 0.129 S7-E2-2 31 0.783 S1-E2-2
12 0.148 S2-E1-1 32 0.792 S5-E2-2
13 0.161 S3-E2-2 33 0.794 S2-E2-1
14 0.201 S1-E1-2 34 0.894 S10-E1-2
15 0.234 S2-E2-2 35 0.897 S7-E1-2
16 0.243 S5-E1-2 36 0.906 S5-E1-1
17 0.274 S2-E1-2 37 0.909 S9-E2-1
18 0.360 S6-E2-2 38 0.932 S1-E2-1
19 0.362 S6-E1-2 39 0.943 S8-E1-2
20 0.372 S6-E1-1 40 0.974 S6-E2-1

Table 18. List of selected transverse tendons.
# Random # Tendon ID
1 0.001 249
2 0.001 255
3 0.004 103
4 0.005 388
5 0.006 694
6 0.009 426
7 0.015 456
8 0.020 638

Table 19. List of cantilever tendons.
# Random # Tendon ID # Random # Tendon ID # Random # Tendon ID # Random # Tendon ID
1 0.016 P3-T11-2 62 0.285 P4-T1-2 123 0.503 P4-T2-2 184 0.741 P5-T3-1
2 0.016 P10-T2-1 63 0.288 P7-T10-1 124 0.504 P4-T2-1 185 0.744 P6-T1-1
3 0.020 P8-T5-2 64 0.291 P9-T3-1 125 0.504 P5-T9-2 186 0.746 P8-T14-2
4 0.022 P7-T9-1 65 0.304 P2-T3-2 126 0.509 P5-T3-2 187 0.759 P5-T7-1
5 0.027 P2-T10-1 66 0.306 P4-T8-2 127 0.511 P8-T10-1 188 0.760 P3-T1-1
6 0.032 P3-T7-1 67 0.307 P2-T8-2 128 0.522 P4-T5-2 189 0.762 P5-T6-2
7 0.038 P6-T2-1 68 0.309 P7-T5-1 129 0.525 P7-T7-2 190 0.763 P10-T4-2
8 0.038 P3-T4-2 69 0.309 P4-T10-1 130 0.528 P8-T10-2 191 0.782 P8-T4-1
9 0.046 P6-T4-2 70 0.309 P3-T8-2 131 0.529 P8-T13-1 192 0.782 P7-T6-2
10 0.049 P3-T5-2 71 0.322 P8-T2-1 132 0.531 P6-T14-2 193 0.789 P10-T2-2
11 0.050 P4-T10-2 72 0.328 P6-T5-1 133 0.533 P4-T16-2 194 0.798 P9-T9-1
12 0.053 P2-T8-1 73 0.343 P8-T7-1 134 0.536 P6-T9-2 195 0.807 P9-T4-1
13 0.055 P10-T1-1 74 0.350 P6-T4-1 135 0.538 P9-T6-2 196 0.808 P6-T8-1
14 0.058 P7-T4-2 75 0.351 P9-T1-1 136 0.540 P6-T13-1 197 0.810 P6-T9-1
15 0.058 P10-T5-1 76 0.353 P10-T6-2 137 0.548 P9-T1-2 198 0.815 P9-T7-2
16 0.059 P2-T5-1 77 0.359 P8-T9-1 138 0.549 P4-T11-2 199 0.836 P3-T10-2
17 0.061 P6-T13-2 78 0.369 P5-T11-2 139 0.552 P5-T10-2 200 0.838 P8-T9-2
18 0.070 P3-T14-1 79 0.377 P3-T10-1 140 0.560 P9-T12-1 201 0.838 P2-T7-2
19 0.074 P6-T8-2 80 0.377 P6-T11-2 141 0.568 P9-T14-1 202 0.844 P7-T13-1
20 0.084 P6-T7-1 81 0.380 P5-T1-1 142 0.568 P8-T3-2 203 0.847 P4-T4-1
21 0.085 P8-T12-2 82 0.380 P8-T14-1 143 0.569 P8-T7-2 204 0.853 P5-T7-2
22 0.089 P4-T7-1 83 0.381 P8-T5-1 144 0.572 P5-T10-1 205 0.858 P7-T13-2
23 0.097 P3-T1-2 84 0.381 P9-T16-2 145 0.578 P9-T5-2 206 0.860 P7-T10-2
24 0.100 P3-T6-1 85 0.389 P9-T8-2 146 0.581 P10-T7-2 207 0.862 P7-T4-1
25 0.104 P9-T5-1 86 0.396 P4-T9-2 147 0.582 P3-T14-2 208 0.865 P6-T5-2
26 0.105 P6-T1-2 87 0.398 P4-T4-2 148 0.586 P10-T3-2 209 0.872 P3-T2-2
27 0.107 P2-T1-2 88 0.398 P5-T4-1 149 0.590 P3-T15-1 210 0.876 P6-T14-1
28 0.109 P9-T12-2 89 0.399 P7-T11-1 150 0.608 P5-T1-2 211 0.878 P3-T15-2
29 0.112 P7-T8-1 90 0.399 P3-T5-1 151 0.609 P3-T9-2 212 0.886 P5-T13-2
30 0.120 P4-T7-2 91 0.400 P2-T5-2 152 0.618 P4-T6-1 213 0.888 P3-T12-2
31 0.134 P10-T4-1 92 0.403 P2-T9-2 153 0.626 P7-T12-2 214 0.889 P5-T11-1
32 0.136 P9-T7-1 93 0.404 P8-T3-1 154 0.627 P6-T7-2 215 0.891 P9-T15-2
33 0.138 P7-T8-2 94 0.405 P9-T15-1 155 0.629 P6-T12-1 216 0.892 P3-T4-1
34 0.146 P2-T6-1 95 0.405 P8-T8-1 156 0.630 P9-T11-2 217 0.894 P9-T10-1
35 0.153 P9-T16-1 96 0.410 P4-T13-1 157 0.630 P7-T2-2 218 0.895 P4-T6-2
36 0.159 P4-T8-1 97 0.412 P10-T1-2 158 0.630 P4-T14-2 219 0.907 P6-T3-1
37 0.162 P7-T9-2 98 0.413 P6-T3-2 159 0.633 P6-T12-2 220 0.925 P3-T13-2
38 0.163 P4-T9-1 99 0.415 P9-T6-1 160 0.633 P9-T13-1 221 0.933 P4-T11-1
39 0.165 P3-T13-1 100 0.416 P6-T6-1 161 0.636 P4-T12-1 222 0.937 P2-T7-1
40 0.165 P3-T16-1 101 0.418 P4-T16-2 162 0.640 P8-T6-1 223 0.940 P9-T13-2
41 0.165 P7-T14-1 102 0.420 P3-T2-1 163 0.644 P8-T11-1 224 0.940 P6-T6-2
42 0.169 P3-T16-2 103 0.435 P10-T6-1 164 0.652 P6-T10-2 225 0.952 P7-T14-2
43 0.182 P6-T10-1 104 0.435 P3-T11-1 165 0.654 P2-T10-2 226 0.962 P8-T1-2
44 0.185 P7-T3-2 105 0.437 P7-T1-1 166 0.659 P2-T1-1 227 0.964 P9-T3-2
45 0.186 P4-T15-2 106 0.441 P7-T2-1 167 0.660 P9-T10-2 228 0.965 P5-T5-2
46 0.189 P5-T4-2 107 0.446 P9-T2-1 168 0.664 P7-T12-1 229 0.967 P4-T3-1
47 0.194 P10-T8-2 108 0.447 P4-T3-2 169 0.668 P6-T2-2 230 0.968 P7-T5-2
48 0.207 P3-T3-2 109 0.449 P2-T2-1 170 0.669 P9-T9-2 231 0.969 P8-T4-2
49 0.210 P8-T8-2 110 0.452 P8-T1-1 171 0.669 P10-T8-1 232 0.971 P2-T2-2
50 0.221 P3-T8-1 111 0.466 P3-T3-1 172 0.671 P5-T12-1 233 0.971 P6-T11-1
51 0.228 P9-T11-1 112 0.471 P4-T5-1 173 0.671 P2-T6-2 234 0.974 P5-T5-1
52 0.234 P4-T13-2 113 0.472 P7-T7-1 174 0.677 P5-T2-2 235 0.975 P4-T15-2
53 0.250 P10-T5-2 114 0.479 P3-T7-2 175 0.699 P3-T12-1 236 0.976 P9-T14-2
54 0.252 P5-T9-1 115 0.480 P4-T1-1 176 0.708 P2-T3-1 237 0.979 P8-T13-2
55 0.254 P7-T3-1 116 0.482 P4-T14-2 177 0.713 P8-T12-1 238 0.979 P3-T9-1
56 0.256 P7-T11-2 117 0.487 P5-T12-2 178 0.720 P7-T1-2 239 0.982 P10-T3-1
57 0.258 P5-T6-1 118 0.488 P5-T13-1 179 0.726 P9-T2-2 240 0.984 P8-T2-2
58 0.261 P8-T6-2 119 0.489 P2-T9-1 180 0.727 P2-T4-1 241 0.990 P4-T12-2
59 0.262 P5-T2-1 120 0.493 P9-T4-2 181 0.728 P3-T6-2 242 0.992 P5-T8-2
60 0.265 P10-T7-1 121 0.495 P8-T11-2 182 0.729 P9-T8-1 235 0.975 P4-T15-2
61 0.277 P5-T8-1 122 0.500 P7-T6-1 183 0.737 P2-T4-2      

 

Typical Spliced Girder Bridge

In a second example, a typical existing spliced girder bridge was used with a 3-span configuration (main channel unit) as part of a 24-span bridge for a total length of 3,585 ft. The approaches were constructed with eight lines of Florida bulb-T78 precast prestressed concrete girders. The main channel unit is continuous over three spans that are 196.6 × 250 × 196.6 ft. It was constructed with eight lines of modified Florida bulb-T78 girders. Each girder line consists of two haunched pier segments, a main span drop-in segment, and two side span drop-in segments. Each segment is an individually precast pretensioned girder that supports its own weight and handling loads. All segments in one line of girder are continuously PT with four 15-internal draped tendons with 0.6-inch diameter from end to end. The haunch segment diaphragms are transversely PT with three tendons at each diaphragm. The plans can be viewed in appendix B.

The bridge is in good condition but has less than desirable workmanship based on visual inspection. The complete construction and inspection records are not available. The considered structure is a typical highway bridge carrying medium traffic volumes. It is assumed that the owner performed an option 2 inspection. The sampling procedure used in this example is as follows:

  1. Estimate the number of the tendons for each tendon type.
    • Total number of longitudinal draped tendons = 32.
    • Total number of pier cap transverse PT = 16.
    • Total number of diaphragm transverse PT = 6.
  2. Prioritize the tendons by assigning them to one of three risk categories.
  3. Determine the probability of defect indicator (see table 20).
  4. Table 20. Spliced girder bridge—probability of defect indicator.
    Category Weight (table 5) Tendon Type
    Longitudinal Draped Pier Cap Transverse Diaphragm Transverse
    Bridge condition (table 1) 0.15 3 3 3
    Construction and inspection records (table 2 ) 0.15 4 4 4
    Visual inspection (table 3 ) 0.30 1 1 1
    Tendon shape and length (table 4 ) 0.40 5 2 1
    Probability of defect indicator 3 2 2

  5. Determine the consequence of failure indicator (see table 21).
  6. Table 21. Spliced girder bridge—consequence of failure indicator.
    Category Weight(table 9) Tendon Type
    Longitudinal Draped Pier Cap Transverse Diaphragm Transverse
    Cost of repair or replacement (table 6) 0.40 5 4 3
    Element/tendon redundancy (table 7) 0.40 3 2 2
    Bridge importance (table 8) 0.20 3 3 3
    Consequence of failure indicator 4 3 3

  7. Assign tendon groups to appropriate risk categories (see figure 50).

  8. Figure 50. Graph. Spliced girder bridge—tendon risk categories. This graph shows a risk matrix for a spliced girder bridge. Probability of a defect indicator is on the y-axis ranging from 1 to 5, and consequence of failure indicator is on the x-axis ranging from 1 to 5. For both axes, 1 represents low, and 5 represents high. For low combinations of the two numbers, risk is  low and vice versa. Three bands of risk are indicated: low, medium, and high. Pier cap and diaphragm tendons are have a probability of defect indicator of 2 and consequence of failure indicator 3, while longitudinal draped tendons have a probability of defect indicator of 3 and consequence of failure indicator of 4.

    Figure 50. Graph. Spliced girder bridge—tendon risk categories.

  9. For each identified group, select an acceptable fraction of undetected deficient grout locations and determine the minimum number of sampled tendons (see table 22).
  10. Table 22. Spliced girder bridge—minimum recommended number of tendons for inspection.
    Type of Tendon Total Number of Tendons Risk Structural Impact Caused by Inspechion Acceptable Fraction Of Undetected Defective Minimum Number of Tendons for Inspection
    Level 1 Level 2
    Longitudinal draped 32 Medium High 30 percent 4 7
    Pier cap transverse 16 Medium High 30 percent 4 6
    Diaphragm transverse 6 Medium Medium 20 percent 5 6

  11. Randomly select the required number of tendons for each tendon type.

Table 23 through table 25 present the summary of all tendons. Each tendon is identified by its label. The first letters and number denote the girder number “G,” pier number “P,” and pier diaphragm number “DP.” The second letter denotes the tendon name “T” as shown in the as-built plans. All of the data are sorted with respect to the random number assigned to each tendon. The required number of tendons is selected from the top of the tendon list and is bold for the level 1 inspections and bold italic for the level 2 inspections.

Table 23. List of longitudinal draped tendons.
# Random # Tendon ID # Random # Tendon ID
1 0.494 G1-T4 17 0.954 G8-T2
2 0.876 G6-T2 18 0.843 G4-T2
3 0.387 G4-T1 19 0.883 G3-T4
4 0.725 G3-T3 20 0.817 G5-T2
5 0.396 G6-T1 21 0.283 G2-T3
6 0.931 G7-T4 22 0.930 G8-T1
7 0.809 G1-T1 23 0.196 G2-T1
8 0.582 G7-T1 24 0.071 G8-T3
9 0.409 G5-T1 25 0.866 G2-T2
10 0.487 G4-T4 26 0.269 G2-T4
11 0.847 G4-T3 27 0.287 G1-T2
12 0.587 G7-T3 28 0.284 G3-T1
13 0.966 G6-T3 29 0.467 G3-T2
14 0.913 G5-T4 30 0.126 G1-T3
15 0.540 G7-T2 31 0.095 G5-T3
16 0.459 G6-T4 32 0.226 G8-T4

Table 24. List of diaphragm tendons.
# Random # Tendon ID
1 0.068 DP11-T1
2 0.098 DP10-T2
3 0.414 DP10-T1
4 0.431 DP11-T2
5 0.699 DP10-T3
6 0.884 DP11-T3

 

Table 25. List of pier cap tendons.
# Random # Tendon ID
1 0.049 P10-T4
2 0.120 P10-T2
3 0.261 P12-T3
4 0.321 P11-T4
5 0.440 P11-T3
6 0.465 P9-T3
7 0.554 P11-T2
8 0.618 P9-T1
9 0.620 P11-T1
10 0.725 P12-T2
11 0.794 P9-T4
12 0.812 P12-T1
13 0.945 P10-T3
14 0.946 P10-T1
15 0.977 P9-T2
16 0.997 P12-T4

 

Typical Span-by-Span Segmental Bridge

In the third example, a typical eight-span precast segmental span-by-span bridge construction with a span configuration of 8 × 130 ft is examined. The superstructure consists of a single-cell box girder with 40-ft-wide top deck that is 8 ft deep. There are two types of PT tendons on this bridge as follows:

The bridge is in moderate condition and has bad workmanship based on visual inspection. Complete construction and inspection records are available. The bridge carries large volumes of heavy traffic. Option 2 was selected. The sampling procedure used in this example is as follows:
  1. Estimate the number of the tendons for each tendon type.
    • Total number of transverse tendons = 347.
    • Total number of external tendons = 48.
  2. Prioritize the tendons by assigning them to one of three risk categories.
  3. Determine the probability of defect indicator (see table 26).

  4. Table 26. Span-by-span segmental bridge—probability of defect indicator.
    Category Weight (table 5) Tendon Type
    Transverse External
    Bridge condition (table 1) 0.15 4 4
    Construction and inspection records (table 2) 0.15 1 1
    Visual inspection (table 3) 0.30 5 5
    Tendon shape and length (table 4) 0.40 1 4
    Probability of defect indicator 3 4

  5. Determine the consequence of failure indicator (see table 27).

  6. Table 27. Span-by-span segmental bridge—consequence of failure indicator.
    Category Weight (table 9 ) Tendon Type
    Transverse External
    Cost of repair or replacement (table 6) 0.40 2 3
    Element/tendon redundancy (table 7 ) 0.40 2 4
    Bridge importance (table 8) 0.20 5 5
    Consequence of failure indicator 3 4

  7. Assign tendon groups to appropriate risk categories (see figure 51).

  8. Figure 51. Graph. Span-by-span segmental bridge—tendon risk categories. This graph shows a risk matrix for a span-by-span segmental bridge. Probability of a defect indicator is on the y-axis ranging from 1 to 5, and consequence of failure indicator is on the x-axis ranging from 1 to 5. For both axes, 1 represents low, and 5 represents high. For low combinations of the two numbers, risk is low and vice versa. Three bands of risk are indicated: low, medium, and high. Transverse tendons are shown to have a probability of defect indicator of 3 and a consequence of failure indicator of 3, while external tendons have a probability of defect indicator of 4 and a consequence of failure indicator of 4.

    Figure 51. Graph. Span-by-span segmental bridge—tendon risk categories.

  9. For each identified group, select an acceptable fraction of undetected deficient grout locations and determine the minimum number of tendons to be sampled (see table 28).
  10. Table 28. Span-by-span segmental bridge—minimum recommended number of tendons for inspection.
    Type of Tendon Total Number of Tendons Risk Structural Impact Caused by Inspection Acceptable Fraction Defective Minimum Number of Tendons for Inspection
    Level 1 Level 2
    Transverse 347 Medium High 30 percent 4 8
    External 48 High Low 10 percent 12 22

  11. Randomly select the required number of tendons for each tendon type.

Typical PT Bridge with Draped Tendons

A five-span continuous bridge with a three-cell box girder superstructure was constructed on a 160-ft-long false-work per span. The bridge was PT with 4 19-strand draped internal tendons with 0.6-inch diameter per web from abutment to abutment. In addition, at each pier the box girder was also PT with top internal tendons and anchored at blisters located at the intersection of web and top deck. The top longitudinal tendons over the exterior web are 3 19-strand tendons with 0.6-inch diameter and 6 19-strand tendons with 0.6-inch diameter over the internal web. The top deck is transversely PT with four 0.6-inch internal tendons at 3-ft spacing. The diaphragm is transverse PT with six 31-strand tendons with 0.6-inch diameter. The diaphragm has ample redundancy due to the large amount of ordinary reinforcing bars. Each diaphragm also has 12 vertical internal PT bars with 13/8-inch diameter. The box girder is 7 ft deep. The bridge is in good condition and, it has no defects and average workmanship based on visual inspection. No construction and inspection records are available. The structure carries large traffic volumes. The procedure is as follows:

  1. Estimate the number of the tendons for each tendon type.
    • Total number of top transverse tendons = 267.
    • Total number of top longitudinal tendons = 72.
    • Total number of web longitudinal draped tendons = 16.
    • Total number of transverse diaphragm tendons = 36.
    • Total number of vertical diaphragm PT bars = 72.
  2. Prioritize the tendons by assigning them to one of three risk categories.
  3. Determine the probability of defect indicator (see table 29).
  4. Table 29. PT bridge—probability of defect indicator.
    Category   Tendon Type
    Weight (table 5) Transverse Top Longitudinal Transverse Diaphram PT Bars
    Bridge condition (table 1) 0.15 3 3 3 3 3
    Construction and inspection records (table 2) 0.15 5 5 5 5 5
    Visual inspection (table 3 ) 0.30 3 3 3 3 3
    Tendon shape and length (table 4) 0.40 1 1 5 3 1
    Probability of defect indicator 3 3 4 3 3

  5. Determine the consequence of failure indicator (see table 30).

  6. Table 30. PT bridge—consequence of failure indicator.
    Category   Tendon Type
    Weight (table 9) Transverse Top Longitudinal Transverse Diaphragm PT Bars
    Cost of repair or replacement (table 6) 0.40 2 2 4 1 1
    Element/tendon redundancy (table 7 ) 0.40 2 2 5 1 1
    Bridge importance (table 8) 0.20 3 3 3 3 3
    Consequence of failure indicator 2 2 4 1 1

  7. Assign tendon groups to appropriate risk categories (see figure 52).

  8. Figure 52. Graph. PT bridge—tendon risk categories. This graph shows a risk matrix for a post-tensioned (PT) bridge. Probability of a defect indicator is on the y-axis ranging from 
1 to 5, and consequence of failure indicator is on the x-axis ranging from 1 to 5. For both axes, 1 represents low, and 5 represents high. For low combinations of the two numbers, risk is low and vice versa. Three bands of risk are indicated: low, medium, and high. Transverse diaphragm tendons and post-tensioned bars have a probability of defect indicator of 3 and a consequence of failure indicator of 1 Transverse and top tendons have a probability of defect indicator of 3 and a consequence of failure indicator of 2. Longitudinal tendons have a probability of defect indicator of 4 and a consequence of failure indicator of 4.

    Figure 52. Graph. PT bridge—tendon risk categories.

  9. For each identified group, select an acceptable fraction of undetected deficient grout locations and determine the minimum number of tendons to be sampled (see table 31).

  10. Table 31. PT bridge—minimum recommended number of tendons for inspection.
    Type of Tendon Total Number of Tendons Risk Structural Impact Caused by Inspection Acceptable Fraction Defective Minimum Number of Tendons for Inspection
    Level 1 Level 2
    Transverse tendon 267 Medium High 30 percent 4 8
    Top tendon 72 Medium High 30 percent 4 8
    Longitudinal tendon 16 High High 20 percent 5 8
    Transverse diaphragm tendon 36 Low High 30 percent 4 7
    Vertical diaphragm PT bar 72 Low High 30 percent 4 8

  11. Randomly select the required number of tendons for each tendon type.

CHAPTER 6. GROUT SAMPLING AND TEST METHODS

GENERAL CONSIDERATIONS

Material (grout in the present case) characterization requires that both composition and structure (macro and micro) be determined. Composition is determined by wet chemistry and analytical techniques such as ion chromatography, X-ray florescence, and energy dispersive spectroscopy (EDS), while structure is determined by petrographic methodologies, electron microscopy, and X-ray diffraction.

As an initial step in the case of external tendons, the general appearance of the tendon should be documented. The duct should be inspected for any cracks or connections that could serve as conduits for corrosives from an external source. Access to grout and strands can be accomplished either by end cap removal or by sectioning away duct at an intermediate location along the tendon. In the latter case, duct wall thickness is determined from construction documents, and duct sectioning can be performed using either a plastic cutting wheel or a depth guard that limits grinding depth to that of the duct wall thickness. Caution should be used in duct sectioning so that strands are not impacted. It is important to recognize that these strands may press against the interior duct wall at some circumferential orientation. Upon exposing the grout, its visual appearance and presence of any strand corrosion (or lack thereof) should be documented. Direct access to strands may require removal of some grout cover, which is described later in this chapter. Alternatively, potential measurements can be made to assess the corrosion state of embedded strand. Figure 53 shows a dial depth gauge being used to measure the size of a grout air void at the top of a tendon at a location where access to the underlying grout was made on an external tendon.

Figure 53. Photo. Dial gauge used to determine the depth of a grout air void. This photo shows a hand holding a dial gauge used to measure duct thickness. It is placed above a location on a tendon where a small section of duct has been removed.
Source: Concorr Florida
Figure 53. Photo. Dial gauge used to determine the depth of a grout air void.

Internal tendons represent special challenges because intermediate locations along the length require concrete excavation, and there is greater potential that damage to the tendon may occur compared to external tendons. Similar to external tendons, the investigation should document the initial general appearance of internal tendon end caps. An appropriate number of these end caps (see chapter 5) should be opened, and their condition should be assessed. Figure 54 shows a grout sample being taken at an opened internal tendon end by chipping after the cap was removed. Note the plastic sheet beneath the anchorage to ensure no sample contamination. If the grout condition within these is good and grout Cl analysis results determine that concentration of this species is within acceptable limits, then no further sampling at intermediate locations should be required. However, if the grout appearance is problematic (i.e., undesirable grout types are encountered, see chapter 4), Cl contaminated, or otherwise defective, then consideration must be given to inspect and sample additional end caps, intermediate locations, or both. This access should be performed by standard concrete excavation methods but with due diligence being taken to ensure that reinforcement is not cut or otherwise compromised and the tendon itself is not damaged. Figure 55 shows concrete excavation to access an internal tendon subsequent to its being located using ground penetrating radar (GPR). Once the tendon is exposed, then inspection and analysis can be performed the same as for external tendons.

Figure 54. Photo. Grout sample acquisition at an opened internal tendon end cap by light chipping. This photo shows a worker removing a permanent grout cap from the end of an internal tendon at a blister using a large screwdriver and hammer.
Source: Parsons Brinckerhoff
Figure 54. Photo. Grout sample acquisition at an opened internal tendon end cap by light chipping.

Figure 55. Photo. Concrete excavation to expose an internal tendon. This photo shows a worker with a power chisel excavating concrete on a vertical surface in order to access an internal tendon.
Source: Concorr Florida
Figure 55. Photo. Concrete excavation to expose an internal tendon.

If a grout sample has been acquired from an end cap, then it is probably not necessary to acquire additional samples from the same tendon. However, it may be appropriate to determine the grout quality at intermediate locations, particularly the presence of any air pockets at high points. This can be done for internal tendons with minimal concrete and tendon disruption by drilling with a 1-inch-diameter bit, as shown in figure 56. There are noticeable changes in the drill noise and vibration when a tendon is contacted, which helps ensure that there is no strand damage. If an air pocket is disclosed, it can be inspected using a borescope.

Figure 56. Photo. Internal tendon access at an intermediate location by drilling. This photo shows a worker with a power drill excavating concrete on a vertical surface in order to access an internal tendon.
Source: Parsons Brinckerhoff
Figure 56. Photo. Internal tendon access at an intermediate location by drilling.

If it is necessary to acquire grout samples at intermediate locations on internal tendons, relatively small excavations can be used, as shown in figure 57. In the figure, an approximately 6-inch-diameter access was created to reveal the exposed strand and grout.

Figure 57. Photo. Access hole in an internal tendon at an intermediate location revealing strand and grout. This photo shows an access hole in an internal tendon at an intermediate location revealing strand, grout, and a plastic bag that was inserted to capture excavated grout.
Source: Parsons Brinckerhoff
Figure 57. Photo. Access hole in an internal tendon at an intermediate location revealing strand and grout.

Prior to opening a tendon end cap or duct at an intermediate location (external or internal), preparations should be made to capture a sample of any free water that might be present and otherwise lost. This involves placing an opened bag or sealable plastic container beneath the location(s) of anticipated runout.

Particular attention should be given to the following:

Figure 58. Photo. View of a duct interior revealing a channel air void. This photo shows a borescope view within a tendon. There is an air void at the top and grout on the bottom.
Source: Parsons Brinckerhoff
Figure 58. Photo. View of a duct interior revealing a channel air void.

The following should be collected and deposited in a clean freezer bag using a clean tool such as a flat blade screw driver, chisel, or chipping or a light duty power tool:

Samples should be collected as soon as practical after exposing the tendon interior since air exposure may alter composition and structure of the grout and of any corrosion products and free water that may be present. Individuals performing this work should wear clean plastic or rubber gloves to prevent contamination. In cases where the duct opening is at an intermediate position along a tendon and strands are found to have pressed against the duct interior surface, grout sample acquisition should be at the diametrical orientation where strands should have greatest cover. If corroding strands are present in void space, they should be examined using a borescope, either behind the anchor plate if access is at a tendon end or further along the tendon beyond the length where duct was removed at an intermediate location.

Sample Size

A minimum of 75 g of solid sample (this may consist of more than one piece) of each grout type should be obtained and designated by number/letter according to location. While powder can be used for chemical analyses, a solid sample is required for petrography. If soft, wet grout is found, then at least one sample should be placed in a bag and sealed in such a manner that as much air as possible is expelled and that enough pressure is exerted on the grout such that free water is separated. The grout itself should then be removed and placed in a separate bag, and the free water should be retained in the original bag for compositional analysis. Also, as noted in chapter 4, soluble ions have been reported to migrate upward through the grout as it hardens.(1,22) Consequently, concentration of these may be greater in the upper regions of the grout. This possibility should be taken into account when acquiring samples.

Analyses

The following techniques are available for compositional determinations:

Standard analysis methods to determine both acid and water soluble Cl are available. The former (acid soluble) represents the concentration that dissolves in nitric acid and is sometimes referred to as the “total” concentration of Cl considering that virtually all Cl is soluble. The latter (water soluble) is the Cl concentration that is dissolvable in water, which is invariably less than for acid soluble, reflecting the fact that some Cl is chemically bound by or absorbed on the cement calcium silicate hydrates. An upper limit of 0.08 wt percent cement acid soluble Cl has been defined for PT grout by multiple specifications and guides; however, several publications also list an upper limit for water soluble Cl as 0.06 wt percent cement. (See references 5–8.) It is recommended to determine the acid soluble Cl concentration since the possibility exists that Cl that is bound at one time may later become free and facilitate corrosion.

As a minimum, X-ray fluorescence and wet chemistry analysis should be performed. Components for which determinations should be made are Cl, SO42-, K+, and Na+, Cl, and SO42 are determinants of loss of passivity and onset of active corrosion, and K+ and Na+ are determinants of cement alkalinity. Any free water samples should be analyzed by ion chromatography. Estimating grout Cl concentrations on site in real time can be accomplished using the Germann Instruments (GI) Rapid Chloride Test (RCT) test kit for acid soluble Cl. The procedure requires a 5-g powdered sample and takes about 10–15 min to perform. A test kit for determining water soluble Cl concentration (GI RCT water) is also available; however, the test for acid soluble Cl is recommended.

Petrographic analysis should be performed in accordance with the applicable ASTM standard.(41) Researchers should also include an analysis and explanation of any grout color and consistency distinctions and lack of set. All analyses should be performed by the resident State transportation department or by a transportation department certified laboratory.

Additionally, an option is available to assess corrosion state and rate for strands embedded in grout. Corrosion state is determined by measuring potential. The methodology and data interpretation are described for conventional reinforcing steel in concrete in “Standard Practice for Calculation of Corrosion Rate and Related Information from Electrochemical Measurements.”(42) Corrosion rate is determined by measuring polarization resistance from which corrosion rate can be calculated.(43,44) Both techniques require a standard reference electrode, a high impedance voltmeter, access to grout in the vicinity where the strands of interest are embedded, and an electrical connection to one or more strands. In addition, polarization resistance measurements require an external (counter) electrode in contact with the grout and a means for imposing small potential changes on the strands via the counter electrode. Because surface area of the strands is likely not known, corrosion rate determinations are qualitative in nature. Lau et al. reported results using both measurement procedures on opened PT tendons.(22) The procedures should only be employed by people familiar with the technologies, equipment, and methods.

Tools, Equipment, and Instrumentation

The following lists contain needed information, equipment, and instrumentation for the respective categories.

Background information (as available) includes the following:

Equipment for concrete excavation and strand/grout access includes the following: Items for sample acquisition include the following: Items for tendon inspection include the following: Instrumentation for strand corrosion assessment includes the following:

Reporting

It is recommended that a common data collection and reporting format be employed by the transportation departments conducting grout sampling programs. Figure 59 shows a simplified bridge schematic where three horizontal PT tendons are in place on each side of the box segments. This allows for the identification and representation of grout sampling locations. Likewise, figure 60 provides a format for documenting individual grout samples, and figure 61 illustrates a tabular form for presenting data and analysis results.

Figure 59. Illustration. Bridge representation used to identify grout sampling locations. This illustration shows a bridge representation used to identify grout sampling locations. The plan view shows five spans in the northbound or eastbound directions and five additional spans in the southbound or westbound directions. The elevation view shows spans 1–5.

Figure 59. Illustration. Bridge representation used to identify grout sampling locations.

Figure 60. Illustration. Chart used to record the location and information for individual grout samples. This illustration shows a chart used to record the location and information for individual grout samples. Column headers include bridge designation, tendon designation, sample number, tendon type tendon/sample location (girder, span, and location on tendons), grout lot number, grout batch, grouting date, and notes.

Figure 60. Illustration. Chart used to record the location and information for individual grout samples.

 

Figure 61. Illustration. Chart used to record and present analysis results for individual grout samples. This illustration shows a chart used to record and present analysis results for individual grout samples. Column headers include bridge designation, tendon designation, sample number, grout type (1–4), grout analysis results (weight percent grout), free water analysis results (weight percent sample), and petrographic analysis summary. There is also a space to include a general description.

Figure 61. Illustration. Chart used to record and present analysis results for individual grout samples.

 

CHAPTER 7. STRATEGIC SAMPLING LOCATIONS

BACKGROUND

After the number of sampled tendons are determined based on the methodology presented in chapter 5, it is important to strategically locate the sampling areas in a certain type of tendon after the target tendons are selected. The target tendons should be randomly selected from the bridge being inspected. It is not always possible to remove grout samples from a cut window in the duct away from the anchorages of an internal tendon due to the strand configuration in the duct. If the tendon has a permanent grout cap over the anchor head, the simplest way to collect grout samples is from the cap internal area as shown in figure 62 and figure 63. Extracting grout samples from the grout cap should be used as the first option.

Figure 62. Photo. Removing a permanent grout cap. This photo shows a worker using a screwdriver and hammer to pry off the end cap on an internal tendon.
Source: Parsons Brinckerhoff
Figure 62. Photo. Removing a permanent grout cap.

Figure 63. Photo. Exposed anchored head after grout sampling. This photo shows the end cap grout from figure 63 after cap removal. The grout appears sound with no voids.
Source: Parsons Brinckerhoff
Figure 63 . Photo. Exposed anchor head after grout sampling.

Grout voids are typically formed by bleed water or trapped air during pumping of the grout. Bleed water tends to move upward in a tendon while transporting chemical compounds such as Cl, which is a similar trend with trapped air. However, trapped air can be anywhere along the tendon. Therefore, typical grout CDs and PDs can be found at the high elevation of the tendon.

This chapter provides a guideline on locating the strategic locations along each type of tendon, also known as the inspection point. In terms of internal tendons, prior to opening a hole in the tendon, the tendon should be located using GPR as shown in figure 64. It is not recommended to use as-built plans to locate internal tendons because tendon locations might change during construction.

For both options 1 and 2 inspections, at least one grout sample per tendon should be selected from the preselected tendons determined in chapter 5.

Figure 64. Photo. Locating internal tendons in the web wall using GPR. This photo shows a worker using ground penetrating radar (GPR) to locate an internal tendon within a web wall.
Source: Parsons Brinckerhoff
Figure 64. Photo. Locating internal tendons in the web wall using GPR.

BALANCED CANTILEVER BRIDGE

Continuity Tendon (Internal Tendon in the Bottom Flange)

If a permanent grout cap is accessible or exists, the cap should be removed from the blister (see figure 62 and figure 63). Alternatively, the cap can be partially removed using a core drill about 3–4 inches in diameter toward the upper location, as shown in figure 65. The cored section should be saved for later for grout cap repair. The grout sample should be removed as required in chapter 6 for further testing, and its physical condition should be inspected, including the exposed strands in the anchor head and the presence of voids. If the grout cap is not available/accessible or if a void is present in the grout cap, the trumpet interior should be inspected by drilling through a grout port over the trumpet area. This drilling has to be done with extreme care to avoid damage to any strand in the trumpet. If a void is present, a videoscope should be used to inspect the condition of the internal void area. For each continuity tendon selected randomly, both ends of the anchorage should be inspected as shown in figure 66 and figure 67. If severe corrosion is discovered, the entire grout cap and grout over the anchor head should be removed for further investigation.

 

Figure 65. Photo. Partial removal of a grout cap. This photo shows an end cap of an internal tendon after partial removal of the cap by coring. Sound, new exposed grout is seen where the end cap was cored.
Source: Parsons Brinckerhoff
Figure 65. Photo. Partial removal of a grout cap.

 

Figure 66. Illustration. Typical cantilever tendon inspection point locations. This illustration shows a bridge segment with a typical layout of cantilever tendons. Two inspection points 
(one on the top left and one on the top right) are identified at the anchorages. The direction of grouting is to the right, and the slope is to the left.
Source: Parsons Brinckerhoff
Figure 66. Illustration. Typical cantilever tendon inspection point locations.

 

Figure 67. Illustration. Typical continuity tendon inspection point locations. This illustration shows a bridge segment with a typical layout of continuity tendons. Two inspection points 
(one on the bottom left and one on the bottom right) are identified at the anchorages. The direction of grouting is to the right, and the slope is to the left. There is a closure segment in the middle of the bridge, and a blister close to the second inspection point on the bottom right.
Source: Parsons Brinckerhoff
Figure 67. Illustration. Typical continuity tendon inspection point locations.

After grout sampling and inspection are complete, the grout cap should be restored according to the procedure provided in chapter 8.

In some bridges, no permanent grout cap was installed, and the anchor heads are protected by concrete pour-back. As a result, grout samples cannot be obtained from the anchor head areas. It is recommended to remove grout samples from internal ducts at the end of the blister by chipping concrete over the duct. If grout cap inspection cannot be done, workers should drill through the trumpet and check the condition of the grout in the anchorage.

Cantilever Tendon (Internal)

The simplest way to access the cantilever tendon is from the top deck. Because maintenance of traffic is required, it is recommended to access this tendon at night. After the tendon is identified, a chipping gun should be used to remove concrete in the PT block-out a minimum 1 × 2 ft in plan view or larger if necessary. If permanent grout cap is present, a core drill should be used to remove about 3- to 4-inch-diameter specimen of grout cap front face toward an upper location. For a cantilever tendon, at least two inspection points are required, as shown in figure 66 and figure 67.

PRECAST SEGMENTAL SPAN-BY-SPAN BRIDGE

The majority of span-by-span segmental bridge construction consists of external tendons as shown in figure 68. The typical external tendon profile is designed as inclined tendon anchored at both diaphragms of a particular span and draped down at one or two deviators in the bottom flange. For each tendon, a minimum of three inspection points are recommended for grout sampling and investigation. The first point is at the grout cap at the diaphragm, the second point is at the top duct coupler adjacent to the diaphragm, and the third point is at the lower duct coupler close to a deviator.

Figure 68. Illustration. Typical span-by-span bridge external tendon inspection point locations. This illustration shows a span-by-span external tendon showing diaphragms in which the anchorages are embedded, tendon deviation saddles, and inspection points at the two end caps and also at a high point inboard of one of the anchorages.
Source: Parsons Brinckerhoff
Figure 68. Illustration. Typical span-by-span bridge external tendon inspection point locations.

CIP PT BRIDGE

The CIP box girder bridge typically has draped internal tendons in the webs (see figure 69). It is not always possible to access the end anchorages in the end diaphragms. However, it is feasible to probe the tendon from inside the box girder close to the anchorages. For a typical two-span continuous bridge, at least three inspection points should be selected—the first point adjacent to the anchorages, the second point at a high point, and the third point at the lowest point of the tendon. For multiple continuous span bridges with more than two spans, additional inspection points may be required.

Figure 69. Illustration. CIP PT bridge inspection point locations. This illustration shows two spans of a cast-in-place (CIP) post-tensioned (PT) bridge with three external tendons. Inspection points are identified at three high points and at one of the two low points on each of the three tendons.

Figure 69. Illustration. CIP PT bridge inspection point locations.

SPLICED GIRDER BRIDGE

A PT spliced girder bridge typically has three to four internal tendons from end to end of a multispan continuous unit as shown in figure 70, figure 71 for bulb-tee girders, and figure 72 for a U-girder bridge. Similar to a CIP PT bridge, it is almost impossible to access the anchorage area due to a lack of sufficient clearance at the bridge ends. For a three-span continuous bridge, it is recommended to have a minimum of three inspection points—the first adjacent to the anchorages, the second at the CIP closure joint near the pier, and the third at the highest area over the pier (see figure 70 and figure 72).

Figure 70. Illustration. Spliced bulb-tee girder bridge inspection point locations. This illustration shows several spans of a bridge and identifies tendon inspection locations as transition points from inclined to near horizontal runs. Also included is a section view of a spliced bulb-tee girder from the bridge showing conventional reinforcement and tendon positions.
Source: Parsons Brinckerhoff
Figure 70. Illustration. Spliced bulb-tee girder bridge inspection point locations.

 

Figure 71. Photo. Spliced bulb-tee girder bridge CIP joint detail. This photo shows spliced bulb-tee girder bridge cast-in-place (CIP) joint detail as supported by steel I-beams during construction prior to closure at the ends.
Source: Parsons Brinckerhoff
Figure 71 . Photo. Spliced bulb-tee girder bridge CIP joint detail.

Figure 72. Illustration. Spliced U-girder bridge inspection locations. This illustration shows a spliced U-girder bridge layout identifying inspection points at tendon ends and girder joints.
Source: Summit Engineering Group
Figure 72. Illustration. Spliced U-girder bridge inspection locations.

CHAPTER 8. RESTORATION METHODS

GENERAL

Restoration of the tendon damage as a result of inspection and grout sample collection is one of the most important activities in grout sampling. Improper repair/restoration will provide a future path for corrosive agents to the PT system and can compromise long-term durability. Two types of restorations can be performed after inspection and grout sample collection are completed: temporary restoration and permanent restoration.

Temporary restoration should be performed for the following reasons:

Temporary restoration should be able to protect the tendon systems from future corrosive agent intrusion for a maximum of 3 to 6 months before permanent restoration can be conducted. For bridges located in corrosive environments, permanent repair should be done as soon as possible. This requirement on how soon the permanent repair should be done can be adjusted by the local authority based on the conditions and requirements for each project.

An exposed open tendon should not be left for more than 4 h without proper temporary protection. Each day before leaving the project site, all areas of exposed tendons should receive a temporary protection prior to applying temporary restoration or permanent restoration. At minimum, waterproof tapes and plastic covers should be applied. If possible, permanent restoration of the corrosion protection should be performed on the same day as the inspection. The inspection team should provide a consistent and visible color marking at the inspection points based on the approved work plan (prior to the inspection) so that the client/owner of the bridge can keep track of what has been done for future maintenance activities. The industry repair standard practice should be adopted with owners’ approval, including the material ingredients, mixture proportions, mixing, placing, and curing method. The restoration material and methods should be included in the work plan and approved by the owners prior to onsite construction restoration.

TEMPORARY RESTORATION

External Tendon

The procedure for temporary restoration of external tendons is as follows:

Figure 73. Photo. Temporary restoration of an external tendon. This photo shows an external tendon for which the duct had been locally removed for inspection and then temporarily repaired using waterproof tape.
Source: Concorr Florida
Figure 73. Photo. Temporary restoration of an external tendon.

Internal Tendon

The procedure for temporary restoration of internal tendons is as follows:

  1. Properly clean any dust and soft material in the restoration area using a vacuum cleaner.
  2. Apply an approved hydraulic cement grout mortar over any exposed strands.
  3. For a metal duct, bend the duct back covering the mortar.
  4. Apply hydraulic cement mortar over the duct/magnesium ammonium phosphate concrete (MAPC) to the concrete surface.

PERMANENT RESTORATION

External Tendon

The procedure for permanent restoration of external tendons is as follows:

  1. Properly clean any dust and soft material in the restoration area by vacuum cleaner or dry air blower.
  2. Apply an approved hydraulic cement grout mortar over any exposed strands.
  3. Reattach the original two half pieces of PE ducts.
  4. Seal the cut lines with sealant.
  5. Wrap the restoration area with a minimum of 4 inches of heat shrink wrap at each end (see figure 74).

Figure 74. Photo. Permanent restoration of an external tendon using heat shrink sleeve. This photo shows an external tendon for which the duct had been locally removed for inspection and then permanently repaired using a heat shrink sleeve.
Source: Concorr Florida
Figure 74. Photo. Permanent restoration of an external tendon using heat shrink sleeve.

Internal Tendon

The procedure for permanent restoration of internal tendons is as follows:

  1. Properly clean any dust and soft material in the restoration area using a vacuum cleaner.
  2. Remove part of metal or plastic ducts.
  3. Apply an approved hydraulic cement grout mortar over any exposed strands.
  4. For plastic duct, cover the grout mortar with a piece of new plastic duct of the same dimensions with the opening. Weld the new plastic section with the existing duct around the cut perimeter and apply epoxy over the perimeter of the cut (see figure 75).
  5. Patch hydraulic cement mortar/MAPC over the restored duct to the concrete surface.
Note that it is not necessary to remove concrete all around the duct since this will cause more damage to the structure and will be more difficult to restore.

Figure 75. Illustration. Permanent restoration of an internal tendon duct. This three-part illustration shows permanent restoration of an internal tendon duct. First, an illustration shows an internal tendon where concrete has been excavated on all sides, and the duct has been cut away around the entire tendon circumference along an approximately 1-ft length revealing sound, hardened grout. This is followed by two schematic illustrations of an internal tendon for which an approximately 6- by 4-inch concrete excavation has taken place such that approximately 
one-half of the tendon circumference is exposed, and a rectangular section of duct has been cut away to reveal grout that can be sampled. A replacement section of duct is about to be positioned on the opened portion of the tendon as a repair. The second schematic shows the replacement duct section welded in place.

Figure 75 . Illustration. Permanent restoration of an internal tendon duct.

Grout Cap

The procedure for permanent restoration of grout caps is as follows:

  1. For an existing bridge with no grout cap or if the grout cap has been damaged during removal, install a new grout cap for permanent restoration.
  2. If a grout sample is removed from the anchor head, patch the area of the missing grout with an approved hydraulic cement grout mortar prior to reinstalling the grout cap. In cases where the whole grout is removed, regrout the cap cavity by gravity feed after the cap is installed.
  3. For a partially cored grout cap, patch the area of the grout taken for a sample with grout mortar and the original cored piece reinstalled. Seal the perimeter of the piece with epoxy (see figure 76).
  4. Reapply the elastomeric coating over the cap.
  5. For cantilever or other tendons with a pour-back present, restore the pour-back with epoxy concrete.
Figure 76 through figure 78 show the permanent restoration process of a grout cap, including elastomeric coat application.

Figure 76. Photo. Completed restoration of a partially cut grout cap prior to coating. This photo shows a restored tendon grout cap that had been partially cut open prior to application of a protective coating.
Source: Parsons Brinckerhoff
Figure 76. Photo. Completed restoration of a partially cut grout cap prior to coating.

Figure 77. Photo. Applying elastomeric coating over a grout cap. This photo shows a worker applying an elastomeric coating to a previously opened grout cap on an internal tendon.
Source: Parsons Brinckerhoff
Figure 77. Photo. Applying elastomeric coating over a grout cap.

Figure 78. Photo. Completed permanent restoration of a grout cap. This photo shows a completely restored tendon end cap subsequent to opening
Source: Parsons Brinckerhoff
Figure 78. Photo. Completed permanent restoration of a grout cap.

RESTORATION MATERIAL

It is recommended that approved material from the bridge owners be used in the restoration of tendons after invasive testing. For grout restoration, after the existing grout is removed for a test sample, the grout should be patched with an approved prepackaged grout mortar/hydraulic cement grout mortar applied to both internal and external tendons.

Basic materials used for external tendon restoration include the following:

Basic materials used for internal tendon restoration include the following:

CHAPTER 9. INTERPRETATION OF RESULTS AND COURSES OF ACTION

Background

Grout issues fall into the following categories:

Compounding factors that contribute to determining response actions are presence of free water, the extent of any strand corrosion, and occurrence of strand fractures. This chapter presents a generalized course-of-action decision guide based on a categorization of Cl and extent of strand corrosion and fractures considering the grout issues and compounding factors. It is recognized that “no one size fits all” and that this guide may be modified, supplemented, or even supplanted by an alternative approach. Specifically, sound engineering judgment must be employed. Ongoing research under FHWA sponsorship is investigating implications of Cl contaminated PT grout on strand performance.(43) Once available, results from this research could modify recommendations made in this report.

Evaluation Approach and Interpretation

Table 32 lists CD classifications and recommended actions, respectively, for option 1 inspections according to the determined condition of individual tendons. This considers that strands are embedded in sound grout and only CDs, as expressed in terms of four Cl, are at issue. Conversely, option 2 inspections consider that the same CD classifications for option 1 are an issue as well as PDs (grout structure and presence of any air voids, strand corrosion, or strand fractures), as listed in table 33. Based on findings for either inspection option, individual tendons are assigned a grade from 1 to 10—the higher the grade, the more problematic the tendon condition.

For option 2, assigning a tendon grade based on the determined CDs and PDs and projecting any resultant action requires multiple considerations. For example, if it is determined that Cl is less than or equal to 0.08 wt percent cement (CD1) and a grout air pocket is noted (PD1), then a grade of 2 is assigned, and no action (A1) is recommended (see table 33). If the air pocket is long and larger than 0.5 inches, action A6 may be considered by regrouting the void. However, if strands also exhibit surface corrosion but no section loss (PD4), then the grade 6 is assigned and actions A3 and A6 result. In other words, the highest PD determines the grade and recommended action. The term “section loss” refers to any reduced cross section for all strands in a particular tendon, as affected by fractures. For example, if a tendon has 22 strands and 1 has fractured but the others remain load bearing, then section loss is 4.5 percent (PD5 in table 33) in combination with other deficiencies. If grade 8 CD3 is selected, actions A2, A4, A5, and A6 are recommended. Conversely, if there are 18 strands, then 1 fracture translates to 5.6 percent section loss (PD6), which is a grade of 10, and actions A2 and A4 through A8 should be taken.

Table 32. CD classifications as determined by grout Cl levels from an option 1 inspection and resultant recommended actions.

CDa

CD1 Cl ≤ 0.08 X      
CD2 0.08 < Cl ≤ 0.20   X    
CD3 0.2 < Cl ≤ 0.50b     X  
CD4 Cl > 0.50b       X
Action Grade
1 5 7 9
A1 None      
A2 Expand sampling      X
A3 Reinspect in 5 years      
A4 Reinspect in 2 years     X X
A5 Tendon monitoring     X X
a Chloride concentration units are wt percent cement.
b If strand corrosion or fracture(s) are found (PD5 or PD6 under option 2 in table 33 ), then
grade 9 or 10 should be assigned as appropriate per option 2 actions.

AMENDED January 7, 2014

 

Table 33. CD and PD classifications as determined by grout Cl levels and in-place grout structure by an option 2 inspection and resultant recommended actions.

CDa
CD1 Cl ≤ 0.08 X X X X            
CD2 0.08 < Cl ≤ 0.20         X X        
CD3 0.2 < Cl ≤ 0.50             X X    
CD4 Cl > 0.50                 X X
PD
PD0 Sound grout X                  
PD1 Grout air pocket   X X X X X X X X X
PD2 Exposed strand/tendon     X X X X X X X X
PD3 Soft or segregated grout       X X X X X X X
PD4 Tendon surface corrosion (no section loss)           X X X X X
PD5 Tendon surface corrosion (< 5 percent section loss)               X X X
PD6 Tendon with partial or full fracture (≥ 5 percent section loss)                   X
Action Grade
1 2 3 4 5 6 7 8 9 10
A1 None X X                
A2 Expand sampling             X X X X
A3 Reinspect in 5 years       X X X        
A4 Reinspect in 2 years             X X X X
A5 Tendon monitoring             X X X X
A6 Consider repairing deficiency as necessaryb   X X X X X X X X X
A7 Structural evaluation/load rating                   X
A8 Tendon replacement                   X
a Chloride concentration units are wt percent cement.
b This applies to PD1, PD2, and PD3.

AMENDED January 7, 2014

 

The protocol is simpler in the option 1 inspection case in that the determined Cl translates directly to a respective grade as indicated in table 32 and table 33. However, if strand corrosion and/or fractures are observed as part of option 1 grout sampling activities, then, as indicated, this reverts the action recommendation from table 32 to that in table 33. Figure 79 and figure 80 summarize these decision processes for options 1 and 2, respectively.

Figure 79. Flowchart. Inspection, sampling, evaluation, and actions for levels 1 and 2 inspections for option 1. This flowchart starts with a box on the left labeled “Option 1 level 1 or 2.” An arrow points to the right to a box labeled “Use table 33 for grade evaluation.” Two arrows point to two boxes from this one. The one on the top is labeled “Discontinue inspection; actions A1, A3.” The box on the bottom is labeled “Expand sampling,” which has an arrow pointing to a box labeled “Use table 33 for grade evaluation.” This points to a final box labeled “Actions: A1, A3, A4, A5.”
Figure 79. Flowchart. Inspection, sampling, evaluation, and actions for levels 1 and 2 inspections for option 1.

Figure 80. Flowchart. Inspection, sampling, evaluation, and actions for levels 1 and 2 inspections for option 2. This flowchart starts with a box on the left labeled “Option 2 level 1 or 2.” An arrow points to the right to a box labeled “Use table 36 for grade evaluation.” Two arrows point to two boxes from this one. The one on the top is labeled “Discontinue inspection; actions A1, A3, A4.” The box on the bottom is labeled “Expand sampling,” which has an arrow pointing to a box labeled “Use table 36 for grade evaluation.” This points to a final box labeled “Actions: A1, A2, A3, A4, A5, A6, A7, A8.”
Figure 80. Flowchart. Inspection, sampling, evaluation, and actions for levels 1 and 2 inspections for option 2.

Evaluation of test and inspection results should be performed by treating tendons of a common type as a group and assigning a grade to individual tendons of that group according to the protocol provided in table 32 for option 1 inspection and table 33 for option 2. An option 1 inspection may be either level 1 with no further sampling required or expanded to level 2, which involves additional sampling depending on the table 32 grading. Typically, for an option 2 level 2 inspection, all tendons of the types considered are inspected.

Examples
  1. Typical Span-by-Span Segmental Bridge with Complete Grouting Records
  2. Preliminary information is as follows:

    Inspection Results:
    Inspection results are as follows:

    Recommended Course of Action:
    Table 32 should be used as follows:

    Conclusions:
    Discontinue inspection and reinspect all tendon types in group 1 in 5 years.

  3. Typical Span-by-Span Segmental Bridge
  4. Preliminary information is as follows:

    Inspection Results:
    Inspection results are as follows:

    Recommended Course of Action:
    Table 33 should be used as follows:

    Conclusions:
    Based on the examples, the following procedure was created:

    1. Expand inspection to all tendon types in groups 1 and 2.
    2. Reevaluate the results of the new samples, including the previous samples.
    3. Make a decision based on the combined results either to inspect all tendons or discontinue inspection.
    Probable final course of actions could be the combination of the following items:

    Reinspections, Non-Destructive Testing (NDT), and Monitoring

    It is intended that the term “reinspect” in table 33 refers to further inspection and sampling, as described in chapters 5 through 8 of this report, in order to either increase reliability of the findings or determine if any deterioration has progressed since an earlier inspection and sampling. In addition, consideration can be given to adapting one or more of the following NDT technologies that are available:

    Each of these has attributes, but a common limitation is that section loss or fracture of wires or strands within internal tendons and within deviation blocks and anchorages of external tendons, which is where problems are most likely to occur, cannot currently be detected by these methods. Improvement in these NDT techniques remains an area of active ongoing research.

    Monitoring tendons for wire and strand breaks is an option for assuring that any fractures are detected in a timely manner. Passive acoustic emission instrumentation with remote monitoring is an option in this regard, and commercial systems are available for implementation.

APPENDIX A TYPICAL BALANCED CANTILEVER BRIDGE PLANS

Figure 81. Illustration. Segment layout—part 1. This figure shows the bridge superstructure segment layout and segment numbers from span 1 to the middle of span 5. Pier numbers are shown from end bent 1 to pier 5.

Figure 81. Illustration. Segment layout—part 1.

Figure 82. Illustration. Segment layout—part 2. This figure shows the bridge superstructure segment layout and segment numbers from the middle of span 5 to span 10. Pier numbers are shown from pier 6 to end bent 11.

Figure 82. Illustration. Segment layout—part 2

Figure 83. Illustration. Bulkhead details. This figure shows the typical bulkhead of a precast concrete segment with shear keys in the webs and alignment keys in the flanges, including cantilever tendon ducts and post-tensioning anchorages.

Figure 83. Illustration. Bulkhead details.

Figure 84. Illustration. Longitudinal PT layout—part 1. This figure shows part 1 of the longitudinal post-tensioned (PT) layout. It shows cantilever, top continuity, bottom continuity and erection tendon layout in plan and elevation views for span 1 to part of span 2.

Figure 84. Illustration. Longitudinal PT layout—part 1.

Figure 85. Illustration. Longitudinal PT layout—part 2. This figure shows part 2 of the longitudinal post-tensioned (PT) layout. It shows cantilever, top continuity, bottom continuity and erection tendon layout in plan and elevation views for part of spans 2 and 3.

Figure 85. Illustration. Longitudinal PT layout—part 2.

Figure 86. Illustration. Longitudinal PT layout—part 3. This figure shows part 3 of the longitudinal post-tensioned (PT) layout. It shows cantilever, top continuity, bottom continuity and erection tendon layout in plan and elevation views for part of spans 3 and 4.

Figure 86. Illustration. Longitudinal PT layout—part 3.

Figure 87. Illustration. Longitudinal PT layout—part 4. This figure shows part 4 of the longitudinal post-tensioned (PT) layout. It shows cantilever, top continuity, bottom continuity and erection tendon layout in plan and elevation views for part of spans 4 and 5.

Figure 87. Illustration. Longitudinal PT layout—part 4.

Figure 88. Illustration. Longitudinal PT layout—part 5. This figure shows part 5 of the longitudinal post-tensioned (PT) layout. It shows cantilever, top continuity, bottom continuity and erection tendon layout in plan and elevation views for part of spans 5 and 6.

Figure 88. Illustration. Longitudinal PT layout—part 5.

Figure 89. Illustration. Longitudinal PT layout—part 6. This figure shows part 6 of the longitudinal post-tensioned (PT) layout. It shows cantilever, top continuity, bottom continuity and erection tendon layout in plan and elevation views for part of spans 6 and 7. It is also applied for spans 7 and 8.

Figure 89. Illustration. Longitudinal PT layout—part 6.

Figure 90. Illustration. Longitudinal PT layout—part 7. This figure shows part 7 of the longitudinal post-tensioned (PT) layout. It shows cantilever, top continuity, bottom continuity and erection tendon layout in plan and elevation views for part of spans 8 and 9.

Figure 90. Illustration. Longitudinal PT layout—part 7.

Figure 91. Illustration. Longitudinal PT layout—part 8. This figure shows part 8 of the longitudinal post-tensioned (PT) layout. It shows cantilever, top continuity, bottom continuity and erection tendon layout in plan and elevation views for part of spans 9 and 10.

Figure 91. Illustration. Longitudinal PT layout—part 8.

 

APPENDIX B. TYPICAL SPLICED GIRDER BRIDGE PLANS

Figure 92. Illustration. Plan and elevation—main channel unit. This figure shows a three-span unit of a spliced girder bridge in plan and elevation views. The main span crosses over a navigation channel. The vertical and horizontal clearances are below the main span.

Figure 92. Illustration. Plan and elevation—main channel unit.

Figure 93. Illustration. Bridge section. This figure shows typical I-girder sections positioned over a pier cap, columns and foundations. The bridge deck over the I-girders are also shown.

Figure 93. Illustration. Bridge section.

Figure 94. Illustration Pier cap PT details. This figure shows a post-tensioned (PT) pier cap, including tendon profiles, anchorages detail, and anchor zone reinforcement.

Figure 94. Illustration. Pier cap PT details.

Figure 95. Illustration. Tendon profile—main channel unit. This figure shows an elevation view of typical girders and tendon profiles.

Figure 95. Illustration. Tendon profile—main channel unit.

Figure 96. Illustration. Modified Florida bulb-T78 beam end segment. This figure shows modified Florida bulb-T78 beam end segment with tendon profiles, reinforcement details, and typical sections.

Figure 96. Illustration. Modified Florida bulb-T78 beam end segment.

Figure 97. Illustration. Modified Florida bulb-T78 beam haunch segment. This figure shows modified Florida bulb-T78 beam haunch segment with tendon profiles, reinforcement details, and typical sections.

Figure 97. Illustration. Modified Florida bulb-T78 beam haunch segment.

Figure 98. Illustration. Modified Florida bulb-T78 beam drop-in segment. This figure shows modified Florida bulb-T78 beam drop-in segment with tendon profiles, reinforcement details, and typical sections.

Figure 98. Illustration. Modified Florida bulb-T78 beam drop-in segment.

Figure 99. Illustration. Modified Florida bulb-T78 beam end block detail. This figure shows modified Florida bulb-T78 beam end block detail with tendon profiles, reinforcement details, and typical sections.

Figure 99. Illustration. Modified Florida bulb-T78 beam end block detail.

Figure 100. Illustration. Typical sections—haunch segment. This figure shows typical sections of haunch segment, tendon ducts, and reinforcement.
Figure 100. Illustration. Typical sections—haunch segment.

REFERENCES

  1. Merrill, B.D. (2011). TxDOT PT/Grout Issues, Presented to the American Segmental Bridge Institute Board of Directors, Washington, DC.
  2. Corven Engineering, Inc. (2002). “New Directions for Florida Post-Tensioned Bridges,” Post-Tensioning in Florida Bridges, 1, Florida Department of Transportation, Tallahassee, FL.
  3. Pearson-Kirk, D., Collard-Jenkins, S.J., Theryo, T., and Chandra, V. (2004). Improving the Durability of Segmental Bridges, Parsons Brinckerhoff, New York City, NY.
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