Prefabricated Bridge Elements and Systems
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Connection Details for PBES
Appendix C: Sample Construction Specifications
Example 3: Maine DOT
Precast Integral Abutments and Piers
The following specifications were taken from a project that involved the reconstruction of a bridge in Maine. This project included prefabricated integral abutments, piers and approach slabs.
The following pages include:
- Prosecution of Work
- Incentive-Disincentive Specification
- Modifications to the standard precast concrete specifications
(PROSECUTION OF WORK)
To subsection 107.4.2 Schedule of Work Required, add the following:
"The Contractor shall plan and conduct his operations such that the Boom Birch Bridge will be closed for only a single period of time of up to 45 days between July 9th, 2007 and September 1st, 2007. While exact sequence of operations may vary from those found herein the following activities must be completed prior to opening both lanes to traffic:
- Existing bridge must be completely removed.
- All piles must be driven to meet the approval of the Resident.
- Abutment and pier caps must be erected, post-tensioned, and the socket fill placed prior to loading them.
- Superstructure must be erected and shear keys grouted.
- Shear key grout must be cured to a minimum strength of 3 ksi.
- Superstructure must be post-tensioned.
- Approach slabs must be placed.
- Curbs must be cast
- Bridge rail must be installed
- Permanent or temporary approach road guardrail must be installed
- Approach roadway gravel must be compacted and graded to a passable condition
The post-tensioning ducts in the abutments may be grouted under traffic. Fine grading of approaches, membrane, pavement, and permanent approach road guardrail may take place under single lane closures with traffic controlled through the work zone with flaggers.
A minimum of 30 days prior to the road closure, the Contractor shall provide the Department a Schedule of Work covering specifically each activity to take place during the closure in a Critical Path Method (CPM). In addition to either an activity on node or an activity on arrow diagram the contractor shall also provide the output from the CPM schedules in the form of a bar chart. At a minimum, the Schedule or Work shall show the major Work activities, milestones, durations, and a timeline. Durations within the schedule should be in hours.
The Department will review the Schedule of Work and provide comments to the Contractor within 7 days of receipt of the schedule. The Contractor will make the requested changes to the schedule and issue the finalized version to the Department.
(Incentive – Disincentive)
The Contractor shall plan and conduct operations in such a manner that the Route 116 in the vicinity of Boom Birch Bridge is closed to traffic for no more than forty-five (45) consecutive calendar days. The said road closure may only occur between Monday July 9th, 2007 and Saturday September 1st, 2007.
Once the Contractor commences work on this project, the work shall be continuous through completion. During the closure the Contractor shall maintain traffic on the detour route indicated in the Special Provision, Section 105, Use of Roads as Detours.
The closure period starts the moment the road is closed to through traffic for both lanes and ends the moment the road is opened to through traffic for both lanes. For the purposes of establishing incentive and disincentives the total closure period shall be the number of days both lanes of the road are closed to traffic.
Failure to open Route 116 to traffic across Boom Birch Bridge after a total closure period of 45 days will result in a disincentive of $1000/day. Opening Route 116 to traffic across Boom Birch Bridge within the forty-five (45) days total closure period will result in a daily incentive of $1000 per day for the number of days the road is open to traffic before the total closure period has elapsed.
The assessment of any disincentive charges to the Contractor will be in addition to the liquidated damages specified in Section 107 - Time, of the Maine Department of Transportation Standard Specifications.
Section 534, Precast Structural Concrete of the Standard Specifications is added as follows:
534.01 Description: This work shall consist of fabricating, delivering, and erecting the precast approach slabs, the precast/post-tensioned abutments and piers, and related material. Materials, work, inspection and documentation not specifically addressed by this Specification shall be done in accordance with the applicable sections of the PRECAST/PRESTRESSED CONCRETE INSTITURE (PCI), Manual for QUALITY CONTROL for Plants and Production of PRECAST AND PRESTRESSED CONCRETE PRODUCTS (MNL 116), including Commentary.
534.02 Materials. Materials for precast and prestressed concrete products shall meet the requirements of the following Sections:
|Air Entraininig Admixtures||701.03|
|Water Reducing Admixtures||701.04|
|High Range Water Reducing Admixture (HRWR)||701.0401|
|Calcium Nitrite Solution||701.11|
|Ground Granulated Blast Furnace Slag||701.13|
|Fine Aggregate for Concrete||703.01|
|Coarse Aggregate for Concrete||703.02|
|Welded Steel Wire Fabric||709.02|
|Steel Strand for Concrete Reinforcement||709.03|
|Post-tensioning Bar||see below|
The precast abutments and piers shall be post-tensioned with galvanized bars conforming to ASTM A722, Type II. Ducts for post-tensioning bars shall be galvanized, metal duct suitable for the intended purpose.
Portland cement shall conform to the requirements of AASHTO M85 (ASTM C150), Type I, Type II, or Type III. The Contractor shall supply the Department with copies of certified mill tests of the cement. The mill tests shall show the name of the manufacturer, location where produced, silo number and the person or agency conducting the test.
Coarse aggregate shall conform to the requirements of Section 703.02 - Coarse Aggregate for Concrete, Class A, Class AA or Latex.
Concrete that is to be placed in voids around the piling shall be self-consolidating with the addition of an approved high-range water-reducing admixture. The concrete shall also have an approved expansion agent such as intraplast-n or an approved shrinkage compensating admixture, to ensure a tight bond between the fresh concrete and the inside of the void. At the time of placement in the abutment voids, this concrete shall have a spread of between 20 inches and 25 inches with a Visual Stability Index of 1.5. Mix designs for all self-consolidating concrete shall be trial batched to: certify the standard specification requirements, including 28 day compressive strength; assure flowability considering reasonable transit time; and determine the curing time to reach intermediate compressive strengths of 1 ksi and 2.5 ksi. These curing times shall be reported to both the Department and the Contractor. Trial batch results must be acceptable to the Resident prior to the closure of the bridge to traffic. A technical representative from the admixture supplier must be at the production plant for trial and production batching.
534.03. Drawings: The Contractor shall prepare shop detail, erection and other necessary working drawings in accordance with Section 105.7 - Working Drawings. The drawings will be reviewed and approved in accordance with the applicable requirements of Section 105.7. Changes and revisions to the approved working drawings shall require further approval by the Fabrication Engineer.
Concrete mix designs shall be part of the shop drawing submittal. Mix designs shall include aggregate specific gravity, absorption, percent fracture, fineness modulus and gradation.
A copy of the Contractor's Quality System Manual (Q.S.M.) shall be submitted when requested by the Fabrication Engineer.
534.04 Plant: Precast, prestressed or post-tensioned concrete products shall be manufactured in a Precast/Pre-stressed Concrete Institute (PCI) Certified facility. An alternate facility certificate may be used at the discretion of the Engineer.
534.05 Inspection Facilities: The Contractor shall provide a private office at the fabrication plant for inspection personnel authorized by the Department. The office shall have an area not less than 9.3 m² [100 ft²] and shall be in close proximity to the work. The office shall be climate controlled to maintain the temperature between 18°C [65°F] and 30°C [85°F], lighted and have the exit(s) closed by a door(s) equipped with a lock and 2 keys which shall be furnished to the Inspector(s). The office shall be equipped with a desk or table having a minimum size of 1200 mm by 760 mm [48 in by 30 in], 2 chairs, a telephone, telephone answering machine, line data port, plan rack and 2-drawer letter size file cabinet with a lock and 2 keys which shall be furnished to the Inspector(s).
The facilities and all furnishings shall remain the property of the Contractor upon completion of the work. Payment for the facilities, heating, lighting, telephone installation, basic monthly telephone charges and all furnishings shall be incidental to the contract.
534.06 Notice of Beginning Work: The Contractor shall give the Fabrication Engineer a minimum of two weeks notice prior to beginning work. The Contractor shall advise the Fabrication Engineer of the production schedule and any changes to it. If the Contractor suspends work on a project, the Fabrication Engineer will require 48 hours notice prior to the resumption of work.
534.07 Inspection: Quality Control (Q.C.) is the responsibility of the Contractor. Quality Control Inspectors (QCIs) shall have a valid PCI Quality Control Certification Level I, Level II or Level III. Personnel performing concrete testing shall hold a current ACI Field Testing Technician Grade I Certification or equivalent, or work under the direct supervision of an ACI certified technician.
The QCI shall inspect all aspects of the work in accordance with the Contractor's QSM. The QCI shall record measurements and test results on the appropriate forms from APPENDIX E of MNL 116 or an equivalent form prepared by the user. Copies of measurements and test results shall be provided to the Quality Assurance Inspector (QAI) as follows:
|Type of Report||When Provided to Q.A.I*|
|Material certifications/stressing calculations/calibration certifications||Prior to beginning work (anticipate adequate time for review by QAI)|
|Pre-pour inspection report||Prior to the concrete placement|
|Concrete Batch Slips||The morning of the next work day|
|Results of concrete testing||The morning of the next work day|
|Results of compressive testing (for release)||The same work day|
|Concrete temperature records||Provide with compressive testing (for Release)|
|Non-conformance reports/repair procedures||Within 24 hours of discovery|
|Results of compressive testing (for design strength)||Prior to stopping curing/Prior to final Acceptance|
|Post-pour inspection report||Prior to final acceptance|
*The Contractor and QAI, by mutual agreement, may modify any part of the schedule; however, failure to provide the documentation when required will result in the product being deemed unacceptable.
The QCI shall reject materials and workmanship that do not meet contract requirements. The Contractor may perform testing in addition to the minimum required. The results of all testing shall be made available to the (QAI).
Quality Assurance (Q.A.) is the prerogative of the Fabrication Engineer. The QAI will verify documentation, periodically inspect workmanship, and witness testing. Testing deemed necessary by the Fabrication Engineer in addition to the minimum testing requirements shall be scheduled to minimize interference with the production schedule.
534.08 Inspector's Authority: The QAI will have the authority to reject material or workmanship that does not meet the contract requirements. The acceptance of material or workmanship by the QAI will not prevent subsequent rejection, if found unacceptable.
534.09 Rejections: Rejected material and workmanship shall be corrected or replaced by the Contractor. In the event that an item fabricated under this Specification does not meet the contract requirements but is deemed suitable for use by the Fabrication Engineer, said item will be paid for in accordance with Section 108.8.1 - Substantially Conforming Work.
534.10 Forms and Casting Beds: Form dimensions shall conform to the approved shop drawings. Forms shall be well constructed, carefully aligned and sufficiently tight to prevent leakage of mortar. Forms that do not maintain the plan dimensions within allowable tolerances during concrete placement shall be rejected.
Each abutment segment and each pier segment shall be match cast against the pieces to which they will be erected in their final position to ensure a precise fit up in the field.
Wood forms, if used, shall be sealed with a material to prevent absorption. The sealer shall be applied and cured in accordance with the manufacturer's recommendations.
Forms shall be cleaned of adherent material before each use. Forms shall be cleaned of all foreign matter and debris immediately prior to placing concrete. New forms shall be free from paint or other protective coatings.
Forms shall be treated with a non-staining bond breaking compound applied in accordance with the manufacturer's recommendations.
If the reinforcing steel or post-tensioning ducts have been contaminated with the bond-breaking compound, it shall be cleaned with solvent. No concrete shall be placed until the reinforcing steel and post-tensioning ducts has been inspected and accepted by the QCI.
534.11 Reinforcing Steel: Reinforcing steel shall be fabricated, packaged, handled, stored, placed, spliced, and repaired in accordance with Section 503 - Reinforcing Steel.
Reinforcing steel shall be accurately located and securely anchored to prevent displacement during concrete placement. All reinforcing steel shall be installed and secured before beginning the concrete placement.
The concrete cover shown on the approved shop drawings shall be the minimum allowable cover. The contractor shall use bar supports and spacers to maintain the minimum concrete cover. The bar supports and spacers shall be made of a dielectric material or other material approved by the Fabrication Engineer.
534.12 Voids and Inserts: Voids shall be non-absorbent. The out-to-out dimensions of the voids shall be within 2% of plan dimensions. Damaged voids shall be repaired in manner acceptable to the QAI. Voids shall be stored, handled and placed in a manner that prevents damage. Residue from void placement shall be entirely removed from the forms before beginning or continuing the concrete placement.
Voids shall be located accurately, anchored securely, capped and vented. Any portion of a void that is displaced beyond the allowable dimensional tolerances shall be cause for rejection of the abutment segment.
534.13 Conventional Concrete: Concrete mix designs shall be submitted to the Fabrication Engineer for approval a minimum of 30 days prior to beginning work. Mix designs previously approved for use shall not require qualification by trial batch if the mix design meets all the requirements of this Section. Only conventional concrete meeting this subsection shall be used for precast concrete.
New concrete mix designs shall be qualified by trial batches prepared in accordance with AASHTO T126 (ASTM C192). The test results shall demonstrate that the concrete meets the requirements of the Plans and this Section. If accelerated curing is to be used in production, the test specimens shall be similarly cured.
No concrete shall be placed until the mix design has been approved. Approval of the mix design does not relieve the Contractor of the responsibility of meeting the requirements of this Section during production.
The concrete mix design shall meet the following requirements:
|Maximum cement content||660 lb/yd3|
|Maximum cementitious material||685 lb/yd3|
|Water-cement ratio||0.42 maximum|
|Air entrainment||5½ % - 7½ %|
|Allowable slump||5 inch to 10 inch|
|Calcium Nitrite*||3 gal/yd3|
|Silica Fume (when required)||5% - 10% of cement content by weight|
|Fly Ash||40% of cementitious material maximum|
|Slag||50% of cementitious material maximum|
*The water in the Calcium Nitrite solution shall be included when calculating the water/cement ratio
The batching equipment, mixers and delivery equipment shall meet the requirements of MNL 116. Concrete shall be batched, mixed and handled in accordance with MNL 116.
534.135 Self-Consolidating Concrete: Self-consolidating concrete shall be trial batched to achieve the desired properties as discussed in 534.02 Materials.
534.14 Concrete Placement: The first two loads of concrete from each placement shall be tested by the QCI for temperature, air entrainment, and slump. If the first load is unacceptable, the second load shall be tested as the first. This process shall continue until two consecutive loads are found acceptable. After two consecutive loads are found acceptable, the frequency of testing shall be at the discretion of the QAI.
Concrete shall be tested if there is a change in the dosage rate of any admixture, a change of 2 inches or more in slump or a change of more than 5°F [3°C] in mix temperature.
Any load of 1 yd3 or less from a stationary mixer or 2 yd3 or less from a transit mixer shall be tested for air entrainment, slump, and temperature prior to being placed in the form.
Concrete shall be placed as nearly as possible to its final location. The depth of a lift shall be controlled in order to minimize entrapped air voids in conventional concrete castings. The maximum depth of an unconsolidated lift shall be 18 inches in conventional concrete castings. Concrete shall be vibrated with internal or internal and external vibrators in conventional concrete castings. External vibrators shall not be used alone. Internal vibrators shall be inserted vertically and penetrate the lower layer of concrete by at least 4 inches. The vibrators shall be inserted to assure that the radii of action of the vibrators overlap. The vibrators shall be held in position from 5 to 15 seconds. Vibrators shall not be used to move concrete horizontally. In concrete that is made self-consolidating, the amount of vibration and maximum depth of lifts shall be determined during the trial batching process with input from the Department, the Manufacturer's Technical Representative, and the Contractor.
When concrete placements are interrupted, no more than 60 minutes shall elapse from the time of the beginning of the placement and the resumption of the concrete placement when the concrete temperature is below 75°F. When the concrete temperature is above 75°F, the elapsed time shall be reduced to 30 minutes. Cold joints shall make the unit subject to rejection.
No water shall be added to the concrete after batching. HRWR may be added to the concrete after batching if that practice conforms to the manufacturer's published recommendations. Concrete that becomes unworkable shall be discarded.
534.15 Process Control Test Cylinders: All process control test cylinders shall be made and tested in accordance with the following Standards:
- AASHTO T23 (ASTM C31/C31M) Practice for Making and Curing Concrete Test Specimens in Field
- AASHTO T22 (ASTM C39) Test Method for Compressive Strength of Cylindrical Concrete Specimens
- AASHTO T119 (ASTM C143) Test Method for Slump of Hydraulic Cement Concrete
- AASHTO T141 (ASTM C172) Practice for Sampling Freshly Mixed Concrete
- AASHTO T152 (ASTM C231) Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method
- ASTM C1064 - Test Method for Temperature of Freshly mixed Portland Cement Concrete
A minimum of 8 concrete test cylinders shall be cast to represent each continuous concrete placement. Six of the cylinders from each test shall be cured under the same conditions as the units. Unit identification, entrained air content, water-cement ratio, slump and temperature of the sampled concrete shall be recorded by the Contractor at the time of cylinder casting. Testing shall be done in the presence of the QAI. The QAI will designate the loads to be tested. Cylinders made to determine handling strength shall be made during the last 1/3 of the placement.
At least once a week, the Contractor shall make four cylinders for use by the Department. They shall be cured in accordance with AASHTO T23 (ASTM C31/C31M).
If the Contractor fails to make enough cylinders to demonstrate that the product meets the contract requirements, the product will be considered unacceptable.
The standard size test cylinder for acceptance shall be 6 inches by 12 inches. If 4 inch by 8 inch cylinders are used for acceptance, the compressive strength values shall be reduced by 5%. The compressive strength of the concrete shall be determined by averaging the compressive strength of two test cylinders made from the same load.
For the purpose of acceptance, the average of two cylinders shall meet or exceed the design strength, and, neither cylinder shall be more than 500 psi. below the required strength.
534.16 Abutment and Pier Segment Curing: Immediately after the concrete has been finished, the product shall be covered with an impermeable barrier to prevent moisture loss. The barrier shall be tight to the form and securely fastened. The exposed surface of the concrete shall be kept moist. The Contractor shall monitor and record the concrete temperature during the initial curing cycle.
After the product has been removed from the form, moist curing shall continue until it has reached design strength. All surfaces of the product shall be kept moist and the product shall be placed in a moisture retention enclosure with a relative humidity not less than 80%. The product shall not be exposed to temperatures below 50°F until design strength is achieved.
Membrane curing compounds shall not be used without the approval of the Fabrication Engineer. If approved, the compound shall be applied in strict accordance with the manufacturer's published instructions. The Contractor shall provide the QAI with the product data sheet for the compound prior to application. The compound shall be applied immediately after stripping. Concrete shall have reached stripping strength prior to handling abutment and pier segments.
534.165 Curing Self consolidated concrete placed within voids, around piling: An approved membrane curing compound shall be applied in strict accordance with the manufacturer's published instructions.
534.17 Accelerated Curing (Optional): Accelerated curing shall begin after the concrete has attained its initial set. Initial set shall be determined in accordance with ASTM C403, Standard Test Method for Time of Setting of Concrete Mixtures by Penetration Resistance. A strength gain of 500 psi. indicates initial set. The Contractor shall provide documentation that the mix design being used has been tested in accordance with ASTM C403. Accelerated curing shall begin after the concrete has attained initial set. Application of heat more than 8 hours after initial set will not be considered accelerated curing.
The enclosure temperature may be increased by a maximum of 10°F/hour prior to initial set. The total temperature gain prior to initial set shall not exceed 40°F.
After initial set, the temperature gain of the concrete shall not exceed 40°F/hour. The concrete temperature shall attain a minimum temperature of 120°F and that temperature shall be maintained for a minimum of 8 hours. The maximum allowable concrete temperature shall be 180°F. Concrete temperature shall be measured near each end of the casting bed and at intervals not to exceed 100 feet.
The cooling rate from maximum accelerated curing temperature shall not exceed 40°F/hour. The cooling rate shall continue until the concrete temperature is within 40°F of the ambient air temperature.
Steam curing shall take place in an enclosure that allows the free circulation of steam. Steam jets shall provide a uniform distribution of steam without discharging directly on the product or the test cylinders.
When radiant heat is used, the Contractor shall take measures to assure that there is no moisture loss from the product. Free water shall be present on all exposed surfaces at all times.
Recording thermometers that indicate the time/temperature relationship shall be used by the Contractor until transfer/stripping strength has been achieved. Copies of the time/temperature records shall be made available to the QAI.
If the units have achieved 80% of design strength during the curing cycle, no further curing will be required.
534.20 Finishing Concrete and Repairing Defects: Products fabricated under this Section shall meet Standard Grade finish requirements as defined in MNL 116 when they are hidden from view in their final position by backfill or riprap, all other surfaces will be considered exposed to view and will require a special architectural finish.
For portions of product not exposed to view in their final position the recommendations of Standard Grade finish requirements shall be mandatory.
Portions requiring an architectural finish shall meet the following standards. No projections from the surface along the length of each piece will be allowed, uniform color and texture, no visible form tie holes patched or otherwise, all surface voids filled. In order to assure uniformity in appearance of the exposed abutment face, prior to any production work the Precaster shall prepare a sample measuring 24 inch by 24 inch by 6 inch for acceptance by the Department on an aesthetic and cosmetic basis; this piece shall be used throughout production as the standard by which all abutment surfaces exposed to view in their final position are compared for acceptance of the finish.
Structural defects shall be repaired by a method approved by the Fabrication Engineer. Structural defects shall include, but not be limited to exposed reinforcing steel or strand, cracks in bearing areas, through cracks and cracks 0.0125 inches or more in width that extend more than 12 inches. The Contractor shall submit a proposed repair procedure for structural repairs to the Fabrication Engineer. No structural repairs shall be made without the QAI being present. The QAI shall be given adequate notice before beginning repairs.
Chamfers and drip notches shall be made smooth and uniform. Keyways shall be sandblasted to remove mortar paste.
On surfaces not exposed to view in their final position honeycombing, ragged or irregular edges and other cosmetic defects shall be repaired using a product from the MDOT Prequalified List for Patching Materials. The repair, including preparation of the repair area, mixing, application, and curing of the patching material shall be in accordance with the manufacturer's published instructions. Edges not exposed in the final product may be ground smooth with no further repair necessary if the depth of the defect does not exceed one-half inch. Form ties shall be removed to a depth of not less than 1 inch from the face of the concrete and patched using a cementitious mortar or patching compound.
534.22 Tolerances: Tolerances for precast units shall be in conformance with the latest edition of MNL 116, as applicable.
534.23 Transportation and Storage: The precast products may only be handled, moved or transported after the 28 day design strength has been attained. Prestressed products shall be stored and transported so that the reactions with respect to the unit shall be approximately the same during transportation and storage as the product in its final position. The product shall be handled so that only a vertical force is applied to the lifting devices.
Stored products shall be supported above the ground on dunnage in a manner to prevent twisting or distortion. Products shall be protected from discoloration and aesthetic damage.
Units damaged by improper storing, hoisting or handling shall be replaced by the Contractor.
534.26 Post-Tensioning and Pile Socket Filling: Immediately before post-tensioning abutment segments and pier segments, the match cast joint shall be coated with an adhesive epoxy, Sikadur 32 or approved equal, in accordance with the manufacturer's published recommendations. A lockoff tension of 166,000 pounds per bar shall be applied to lateral post-tensioning bars.
Recesses at ends of lateral post-tensioning ducts shall be filled with grout using the same type cement as that in the abutment segments. Prior to installing the grout, the stressing pockets shall be clean of any dirt, grease, oil, or other material that may prevent bonding. Grouting shall be completed within 10 days of lateral post-tensioning. Backfill of abutments and erection of precast superstructure shall not be allowed until posttensioning of all substructure caps is complete.
After the post-tensioning of a precast unit is complete, fill the socket for the tops of the piles with self-consolidating concrete. Test cylinders cured in the same environment as the socket fill concrete must demonstrate that the fill concrete has reached 2.5 ksi prior the application of any gravity loads on the precast segments. Backfilling of abutments may proceed once the abutment socket fill concrete has reached 1.0 ksi.
534.27 End anchorage, Ducts & Grout: End anchorage shall be the plate anchorage detail as manufactured by Dywidag-Systems International or approved equal. They shall be shown in detail on the working drawings, and shall be formed in such a manner that 2 inches of cover is provided to the ends of the post-tensioning bar in the final product. Grout tubes shall be installed at each duct in each end of each segment for a total of: 8 grout tubes required for each abutment post-tensioning duct; and 6 grout tubes required for each pier post-tensioning duct. Ducts shall be galvanized corrugated metal ducts. Grout for post-tensioning ducts shall be either Five Star Special Grout 400 or Masterflow 1205. Alternate high strength specially graded pumpable cable grouts will be considered for approved by the engineer upon request.
534.28 Method of Measurement: Precast structural concrete will be measured by the lump sum.
534.29 Basis of Payment: All work done under Precast Structural Concrete will be paid for at the contract lump sum price. Payment will be full compensation for furnishing all materials in the precast unit including, precast concrete, reinforcing steel, posttensioning bars, ducts and related materials and work. Related materials and work will include, but not be limited to, erecting the products, grouting of ducts, post-tensioning operations, providing and applying adhesive epoxy, providing and placement of socket filling, and any concrete admixtures used. The quantity shown on the Plans for estimating purposes is both the precast concrete and the socket filling concrete.
Payment will be made under:
|Pay Item||Pay Unit|
|534.76||Precast Abutment||Lump Sum|
|534.7601||Precast Approach Slab||Lump Sum|
|534.7602||Precast Pier||Lump Sum|
Example 4: Texas DOT
Precast Column Connections
The following pages contain portions of a Texas DOT research project for the connection of precast bent caps using grouted post-tensioning sleeves. The research report for this work is as follows:
Development of a Precast Bent Cap System 
Authors: E.E. Matsumoto, M.C. Waggoner, M.E. Kreger, S.L. Wood and J.E. Breen
The University of Texas at Austin, Center for Transportation Research
Published: January 2001
Design Methodology: Pages 251-309
The following pages include:
- Chapter 7 – Development of a Precast Connection Specification
- A sample specification for this connection
DEVELOPMENT OF A PRECAST CONNECTION SPECIFICATION
This chapter summarizes the development of a connection specification for a precast bent cap system, referred to as a precast connection specification. Major components of the specification are developed based on results from Phases 1-3. The following areas are addressed: 1) materials, 2) precast bent cap placement plan, 3) grouting operations, and 4) additional items.
To ensure selection of a proper grout, the connection specification should include a grout specification. In addition, properties of connectors and connection hardware should be carefully specified.
7.2.1 Non-Shrink Grout
Table 7.1 is a modified version of Table 2.6, the grout specification for a precast bent cap system. Based on Phase 1-3 tests, the properties specified in Table 2.6 were modified to address mechanical, compatibility, constructability, and durability properties. The reader is referred to Chapters 2 through 5 for background information on construction and grouting issues.
126.96.36.199 Mechanical Properties
The compressive strength requirement for grout is intended to: 1) provide for transfer of forces between connectors, grout, ducts, and/or concrete, 2) provide timely strength gain for rapid construction, and 3) ensure the grout is not the weak link in the connection system. Phase 1-3 tests indicated adequate grout strength for transfer of connection forces, even for the majority of cases in which the grout strength was less than that of the surrounding concrete. All of the tested grouts were expected to satisfy the strength gain requirements of Table 2.6, although this did not always occur. Masterflow 928 (MF928) exhibited the most consistency in achieving strength gain. Although the grout specification provides a reasonable minimum requirement for strength gain, project-specific requirements may be more or less stringent. Thus, the engineer should not rely solely on the grout specification, but should specify in the plans the required minimum grout strength for beam placement and the final grout strength. The contractor, in turn, is required to select a grout that achieves the necessary strength at the critical stages.
Only in one test was the grout considered to be the weak link in the system (Phase 2, VD04, Euclid Hi- Flow [EHF]). In the VD04 pullout tests, the grout strength was just 55% of the strength of the surrounding concrete (3.1 ksi, modified grout cube strength compared to a concrete strength of 5.6 ksi). As mentioned in Chapter 1, others have reported excellent anchorage and response for grouted vertical duct connections when the grout strength was approximately equal to or as much as 1.4 ksi greater than the concrete strength [1.30,1.31].
Based on the previous discussion, it is recommended that: 1) the grout cube compressive strength satisfy the requirements of Table 7.1, and 2) the modified grout cube strength at 28-days, based on a 0.8 factor, exceed the specified 28-day concrete compressive strength by a minimum of 1000 psi. Many prepackaged grouts satisfy these two requirements. A 1000-psi margin accounts for the likelihood that the actual concrete strength will exceed the specified strength as well as the possibility of a low grout strength. The 28-day grout cube strength was increased to 5800 psi in Table 7.1 to provide a 1000-psi margin for Class C concrete.
If a bent cap uses 5000-psi concrete, then grout with a 28-day (unmodified) cube strength of at least 7500 psi is required. A number of such grouts are available. Engineers should be careful to ensure that they select a grout with a compressive strength based on the water required for fluid consistency. Grouts mixed to a flowable or plastic consistency in accordance with ASTM C 230 achieve a higher compressive strength but inadequate fluidity for grouting voids in a precast bent cap system. Manufacturers' data sheets typically list compressive strengths for all three consistencies.
Compatibility requirements are related to volume stability, modulus of elasticity, and coefficient of thermal expansion. Table 7.1 uses the same values as those defined in Table 2.6. The values for the modulus of elasticity and coefficient of thermal expansion provide a fairly close match for grout and the surrounding concrete. As mentioned in Chapter 2, ASTM C 1107 allows three grades of shrinkagecompensating grouts (Table 2.5): Grade A—prehardening volume-controlled type, Grade B—posthardening volume-controlled type, and Grade C—combination volume-controlled type. MF928 is a Grade B grout, whereas EHF and Sika 212 are Grade C. Tests confirmed that for connections using Grade B and Grade C grouts, cracking did not develop in the connection region prior to loading. No deficiencies in behavior were attributed to Grade type. Thus, Table 7.1 lists either Grade B or Grade C as acceptable grout types. Grade A grouts were eliminated because they can produce as much as a 4-percent volume expansion before the grout hardens, possibly causing a reduction in density of the hardened grout, as well as larger shrinkage stresses.
Proper grout flowability is a key to successful construction of a precast bent cap system. Table 7.1 specifies a fluid consistency for grout, with an efflux time, or flow, between 20 and 30 seconds as determined by the Flow Cone Method per CRD-C 611 and ASTM C 939. The lower limit has been changed from Table 2.6, which specified a flow between 10 and 30 seconds.
In tests that used grouts with a flow that longer than 30 seconds, the greater grout viscosity slowed down the venting of air bubbles from the grout, often resulting in an air void at the top of the pocket. This could provide a moisture path into the connection and threaten durability. On the other hand, a grout with too short of a flow time may be indicative of segregation. This was observed particularly with Sika 212 grout in Phases 2 and 3. Segregation resulted in a denser grout at the bottom of connections, but pasty, weak material near the top surface. To prevent segregation, the lower range has been increased to 20 seconds. When needed, ice or warm water may be used in grout mixing to help adjust the flow. For some temperature ranges, this will also increase the working time. No problems with set time were observed in the test program. Thus, the range was not changed from Table 2.6.
The working time, or pot life, of the grout is a crucial consideration in grout selection. Based on Phase 2 and 3 grouting, it is expected that a contractor will require approximately 15 minutes to gravity-flow grout a 30-in. deep cap with a double line grout pocket connection or a connection with four ducts. Although longer times should be estimated for deeper caps or additional ducts, grouting of an individual connection is not expected to require more than 30 minutes. Pumping of grout is expected to reduce grouting time. It is important that the estimate of the total grouting time account for: 1) conducting the flow cone test, 2) transferring grout from the mixer to dispensers, 3) transporting grout to point of placement, and 4) grouting one or more connections. Water and air temperatures at the jobsite must also be considered.
(ASTM C-109, 2" cubes)
|Compressive strength (psi)
(ASTM C 827 & ASTM C 1090)
Modulus of elasticity
Coefficient of thermal expansion
|Grade B or C—expansion per ASTM C 1107
(CRD-C 621/ASTM C-939)
Set Time (ASTM C-191)
efflux time: 20-30 seconds
Freeze Thaw (ASTM C-666)
|300 cycles, RDF 80%
expansion at 26 weeks < 0.1%
As mentioned in Chapter 2, grout durability should be at least equal to that of the surrounding concrete, and proprietary grouts are often formulated to achieve this. Because examination of grout durability was beyond the scope of this research, specific properties of proprietary grouts were not investigated. Requirements listed in Table 7.1 should be checked against project-specific requirements. In addition, manufacturers should be consulted for available properties, such as resistance to freeze-thaw, chlorides, sulfates, and scaling.
In some cases, specially-modified grouts such as latex-modified grouts may be useful. Such grouts cannot be recommended based on the scope of this research. However, future research may show other alternatives to be viable. Specifying durability requirements for a cementitious grout is generally expected to eliminate lesser quality grouts. However, engineers should be careful that grouts do not satisfy durability requirements at the expense of other required properties.
The following minimal provisions are recommended in selecting durable grouts: 1) grouts should be chloride-free, 2) grouts should use non-metallic formulations. Bleed properties should also be reviewed, if available.
Provisions for durability enhancement of the connection region are discussed in Chapter 6.
7.2.2 Connection Hardware
Connection hardware refers to connectors, ducts, anchor plates, shims, and other similar items required for connection construction. Connector and duct requirements are discussed in Chapter 6. Connectors should conform to the requirements of the Materials section of the Precast Connection Specification.
The engineer should specify in the plans any requirements for plates and other items necessary for anchorage of bolted connections. These items were not addressed in a detailed way in Phases 2 and 3.
Shims were found to be a reliable means for cap support. In Phase 2, both steel and plastic shims were effective for cap placement. Shims were glued together and to the column or pile surface to prevent movement. In Phase 3 the contractor did not glue individual shims together or glue shimpaks in place. Workers thus found steel shims to provide better stability than plastic shims.
It is recommended that both steel and plastic shims be permitted. Plastic shims should be an engineered multipolymer high-strength plastic. Specific measures to prevent movement of shims during cap placement should be detailed in the plan sheets. Prior to cap placement, the underside of the cap should be checked to ensure a flat bearing surface. Two shims may be used at exterior columns or piles to ensure bearing on at least three of the four shims. To facilitate complete grouting of the bedding layer, the total shim plan area should be limited to approximately 10% of the pile or column top area. Limiting individual shims to an aspect ratio of two may also help. Shims should be sized to ensure the allowable bearing stress at both concrete surfaces is not exceeded. In addition, shims should be placed at least 2 in. away from surface edges to help ensure grout completely surrounds shims. Additional cover may be required for corrosion protection of steel shims.
7.3 PRECAST BENT CAP PLACEMENT PLAN
To ensure the contractor uses an appropriate construction sequence and carefully plans all operations associated with cap placement, the contractor should submit a Precast Bent Cap Placement Plan to the engineer for approval prior to mixing a trail batch of grout. This plan should include: 1) a step-by-step description of the construction sequence, 2) a step-by-step description of grouting operations, 3) the method for cap support prior to and during grouting, 4) manufacturer's literature for a minimum of two candidate connection grouts, and 5) manufacturer's literature for connection hardware.
7.3.1 Construction Sequence
Example construction sequences for a precast bent cap system are discussed in Section 2.2. The contractor should completely describe the proposed construction sequence. In addition, a description of other pertinent information should be outlined, such as the method to provide anchorage holes in the piles or columns (i.e., embedded sleeves vs. drilled holes) or the use of special devices to assist in threading the cap over connectors.
7.3.2 Grouting Operations
A detailed description of grouting operations should address formwork, air venting, grouting method, and sequence of steps. These issues are discussed in Section 7.4.
7.3.3 Cap Support
The contractor should indicate the method and hardware for cap support prior to and during grouting. Hardware will likely consist of shims, friction collars, bearing plates and leveling nuts, shoring or other systems. The contractor should define the support systems and provide product information, material descriptions, and drawings, as appropriate.
7.3.4 Manufacturer's Literature for Candidate Grouts
The contractor should identify two candidate grouts for connections and provide the manufacturers' literature. Selected grouts should satisfy the grout criteria listed in Table 7.1. In addition, literature should indicate mixing requirements, working time, curing requirements, and other pertinent information. Two grouts should be selected in the event that the first grout is found unacceptable during the trial batch.
7.3.5 Manufacturer's Literature for Connection Hardware
The contractor should also provide manufacturers' literature for all connection hardware to be used.
The precast connection specification should include specific requirements for all grouting operations, including: 1) a trial batch, 2) formwork, 3) presoaking, 4) pre-grouting meeting, and 5) grouting methods. The following sections discuss these requirements.
7.4.1 Trial Batch
The trial batch of grout should be prepared a minimum of two to four weeks prior to connection grouting. The requirement for a trial batch is especially important because a trial batch enables contractor personnel to assess the suitability of a grout for constructability and strength, and also provides the contractor valuable experience. During Phase 3, the contractor confirmed the importance of a trial batch. As mentioned in Section 188.8.131.52, the specific purposes of a trial batch are:
- To determine the required amount of water to be added to a particular grout brand to achieve acceptable flowability using the CRD-C 611/ASTM C 939 Flow Cone Method under the temperature conditions expected in the field
- To determine the grout cube strength corresponding to the flow achieved
- To examine grout for undesirable properties such as segregation
- To establish the adequacy of proposed grouting equipment such as the mixer, tremie tubes, funnels, buckets, and vent tubes
- To provide jobsite personnel experience in mixing and handling grout prior to connection grouting
- To help the contractor to make a judicious decision regarding grout brand
The following sections highlight important lessons learned during Phase 1-3 grouting, which should be applied in trial batches.
The contractor should use the proposed grouting equipment in all mixing and grouting operations. Equipment such as a mortar mixer, tremie tubes, funnels, buckets, and vent tubes should be carefully selected. The proposed mixer for actual grouting should be used for mixing trial batches. High-speed hand drills mix grout more thoroughly, but cannot produce a sufficient volume for connection grouting. The inside diameter of the tremie tube should be large enough for grouting in a timely manner, but small enough to drain the funnel volume gradually so that a continuous grout flow is maintained. In addition, the outside diameter of the tube should be small enough to fit between the duct walls and connectors. Funnels should be large enough to ensure a continuous flow of grout within the tube. A minimum funnel size of 4 quarts is recommended. A pinch valve in the tube is recommended and should be required for cases in which an interruption in grouting operations may occur. Bucket volume should be at least 5 gallons. The inner diameter of air vent tubes should be at least 0.5 in. Transparent vent tubes will accommodate visual inspection of air venting better than opaque tubes or vent holes. A 0.5-in. minimum wire mesh (hardware cloth) should be used as a filter to remove potential clumps when dispensing grout from the mixer.
184.108.40.206 Grout Flowability
A main purpose of the trial batch is to determine the required amount of water to be added to a prepackaged grout to achieve acceptable flowability in the field. The trial batch of grout should be mixed using water at a temperature corresponding to that expected for field grouting, and also at the expected ambient air temperature. This is important, as some grouts only achieve the fluidity and strength stated in the literature when mixed at an ideal temperature of 70 degrees Fahrenheit. The manufacturer's recommended amount of water to achieve fluid consistency may be used in the first batch.
After mixing in accordance with manufacturer's recommendations, the grout should be inspected for undesirable properties such as segregation or clumps. A minor amount of settlement of grout solids during mixing is acceptable, but grouts exhibiting significant segregation (e.g., clear separation between mix water and fine aggregate) should not be used. Grout segregation may lead to the formation of gaps at the bedding layer or produce cavities at the top of the cap. Gaps or cavities may threaten connection durability and/or reduce the ability of the connection to transfer forces. Clumps may result when a lowspeed mortar mixer is used with a large volume of grout.
The flow time should be determined using the CRD-C 621/ASTM C 939 Flow Cone Method. When collecting grout for the flow cone test, a representative portion of the grout should be used. Grout should not be obtained by skimming the top surface of grout from a mixer, as grout tends to be more fluid at the top. A 0.5-in. mesh should be used to eliminate clumps from grout used for the flow cone test. Two flow cone tests should be conducted: one immediately after mixing and a second at the expected pot life of the grout. The second test is intended to confirm that a batch of grout will maintain a suitable flowability throughout grouting operations.
If the flow time falls outside of the 20 to 30 second range, then one of the following actions should be taken: 1) slightly change the amount of water, as long as it is still within manufacturer's recommendations, or 2) use cold or warm water to adjust the flow. If this does not produce an acceptable flow, another brand of grout should be used. In each case, a new batch of grout should be mixed. Remixing, or retempering, of grout mixtures should not be permitted, as it can change grout properties and introduce extra air into the mix. In some cases, slightly increasing the amount of water (e.g., 10%) may significantly increase the flow. However, this will also reduce the grout strength.
A TxDOT Materials representative should assist in conducting the flow cone test, and should prepare and cure a minimum of nine grout cubes for each candidate grout that achieves a suitable flow. A commercial testing laboratory approved by the engineer or a TxDOT Materials representative should test the grout cube specimens. At least two cubes should be tested at 1 day, 3 days, 7 days and 28 days.
220.127.116.11 Trial Grouting Operation
Only grouts that achieve a suitable flow should be used in a trial grouting operation. All equipment proposed for actual grouting operations should be used in a simple, mock grouting operation. Grouting operations should test the suitability of tremie tubes, funnels, vent tubes, and other equipment proposed for use. This allows the grout to be further inspected for workability, segregation and excessive bleeding.
Tamping of grout is recommended instead of vibrating. However, if a vibrator is proposed for use, it should be approved by the grout manufacturer and tested during the trial grouting operation. Care must be exercised in using vibrators because excessive agitation can entrap air in the grout.
Depending on the project requirements, grouting operations may encompass a wide range of activities, from forming and grouting a mock-up of an actual connection detail to grouting a simple box or circular form. It is left to the discretion of the engineer to judge what is reasonable and prudent. However, the trial grouting operation should closely simulate the actual field conditions, including physical constraints, temperature, etc.
18.104.22.168 Scheduling, Weather Restrictions, Admixtures
22.214.171.124.1 Scheduling of Trial Batch
It is recommended that trial batches be completed at least two weeks prior to actual grouting operations. This time is necessary to conduct the trial batch, determine grout strength and strength gain, and conduct an additional trial batch if the strength or strength gain does not satisfy the specification.
126.96.36.199.2 Weather Restrictions
Grouting should be conducted under the same limitations as casting concrete. Grouting during rainy weather may not only add water to grout mixes but may also rush workers as they conduct grouting operations. To prevent poor durability or other undesirable properties, manufacturer's recommendations for cold weather limitations should be followed. In addition, cold and warm weather practices may be necessary for flowability.
Prepackaged grouts are proprietary mixes, and thus no additives should be used in the grout. Additives may adversely affect grout properties and void manufacturer warranties.
Any grout conforming to the following should be acceptable for use:
- Satisfies all of the parameters of the grout specification of Table 7.1
- Achieves an acceptable grout flow in field conditions during the trial batch immediately after mixing and at the pot life
- Attains compressive strength and compressive strength gain based on grout cube tests using trial batch grout
- Possesses a working time suitable for connection grouting
- Performs reliably in trial grouting operation
- Possesses other properties, including durability, required for a project-specific application
To ensure successful grouting, the bedding layer must be properly formed. As shown in Chapter 5, flexible fiberglass forms are readily available and may be tightly wrapped around and bolted on round columns. Wood may be used to form around the bedding of square or rectangular piles or columns. Care should be exercised to ensure forms are tight and properly sealed. Presoaking is a vital step to ensure forms are sealed. Custom-made forms may be more reliable in sealing rectangular and square sections. Formwork should accommodate air vent tubes or holes. Supplementary vents may be formed into the bent cap.
Connections should be presoaked with water for a minimum of two hours prior to grouting. Presoaking connections should be conducted for two reasons: 1) to verify tightness of forms at the bedding layer, and 2) to minimize loss of moisture from the grout into the surrounding concrete that can lead to grout shrinkage. Verification of form tightness is particularly critical to successful connection grouting. An overnight or 24-hour presoaking of the connection is preferable. Residual water left in the connection after presoaking must be drained prior to grouting. This may be accomplished with auxiliary water ports provided at the bottom of the bedding layer formwork or by vacuuming.
7.4.4 Pre-Grouting Meeting
Because of the difficulty in correcting field problems after grouting, special care and oversight should be exercised prior to and during initial grouting operations. An on-site pre-grouting meeting between the contractor and a TxDOT representative should be conducted just prior to actual grouting operations to review the details of the grouting procedure and ensure lessons learned during the trial batch are incorporated. In addition, the TxDOT representative should be available for consultation during initial grouting operations and periodically thereafter. All grouting operations should be observed by a TxDOT representative for compliance with the Precast Bent Cap Placement Plan.
7.4.5 Grouting Methods
Grout should be deposited in the connection in such a way that all voids are completely filled. Both gravity-flow and pressure grouting may achieve this objective. As mentioned in Chapter 2, gravity-flow grouting involves simpler operations overall and may be less expensive. However, additional effort may be required to ensure connection voids are completely filled. Grouting using a low pressure pump requires a higher level of skilled labor in the field, but would likely result in a connection free of voids and can expedite grouting operations, especially on large projects. Both approaches can be economical, depending on specific project constraints.
This section discusses gravity-flow grouting, which was used in Phases 1 through 3. Gravity-flow grouting should be conducted using either a bucket or tremie tube.
188.8.131.52 Bucket Approach
Placement of grout with a bucket is a viable alternative for grout pocket connections, which use relatively large openings at the cap top. As discussed in Chapters 4 and 5, five-gallon buckets are recommended for placement. After mixing the grout, buckets are filled and lifted to the cap top. The grout is poured into the pocket in lifts and tamped after each lift. A flat object such as a shovel or plywood can be used to help direct grout into the pocket with minimal agitation of the grout or air entrapment. Any grout sediments remaining at the bottom of the bucket should be removed and placed into the pocket prior to tamping.
184.108.40.206 Tremie Tube
Tremie-tube grouting should be used for grouted vertical duct and bolted connections, and may also be used for grout pocket connections. One of three variations may be used: 1) continuous-flow, 2) modified, and 3) decanting. Continuous-flow tremie-tube grouting should be conducted by lowering a flexible tube to the bottom of the bedding layer and filling the connection from the bottom upward with a continuous flow of grout. With this approach, it is crucial that grout fill the tube continuously to avoid entrapping air in the connection. This requires that a sufficient amount of grout be mixed prior to grouting and that the funnel connected to the tube have adequate capacity. A pinch valve may be used to stop the flow during grouting. This allows for refilling the funnel and tamping the voids. The tube should remain within the grout, but may be gradually withdrawn as the level of grout rises in the ducts or pockets. This approach should be used when possible, as it will likely prevent air entrapment.
The modified tremie tube and decanting approaches do not require a continuous flow of grout. The modified tremie tube approach should be used in cases where the tube cannot extend to the bottom of a connection due to small clearances or other reasons. The tremie tube should always be kept above the top of the grout, and the tube should direct the flow of grout against either a connector, sidewall, or duct. The decanting approach should be conducted by pouring grout against connectors to direct the flow to the bottom of the connection. This limits grout agitation and helps prevent air entrapment. Voids should be tamped several times during grouting.
220.127.116.11 Pressure Grouting
Pressure grouting involves pumping grout into connections under low pressure. This approach may be used for all connection types, and is required for grouted sleeve couplers. The trial batch and manufacturer's guidelines should be used to establish the pressure for grouting. To prevent entrapped air, grout should not be placed at too high a rate. Voids may be lightly tamped.
18.104.22.168 Air Venting, Plan Sheets, Grout Handling
22.214.171.124.1 Air Venting
Air should be vented at the bedding layer using a minimum of four vent tubes or holes, distributed uniformly around the perimeter of the column or pile formwork. Vent tubes or holes should be located at the top of the bedding layer. When gravity flow grouting is used, multiple grout pockets or vertical ducts should be grouted from a single pocket or from a corner duct. Vents should be plugged sequentially when a steady stream of grout flow out without air. For connections with ducts or pockets, grout will eventually flow up the ducts or pockets. After the grout level in the pocket or ducts rises near the cap top, a tremie tube should be used to top off the openings.
126.96.36.199.2 Plan Sheets
It is highly recommended that plan sheets include a step-by-step list of procedures to be followed during grouting operations. This is considered a key to successful grouting operations. The contractor involved in Phase 3 construction strongly felt that this will help ensure grouting procedures are properly conducted.
188.8.131.52.3 Grout Handling
Precautions should be taken to minimize air entrapment when pouring grout from the mixer into dispensers and when grouting connections.
7.5 OTHER ITEMS
Additional items related to the precast connection specification are discussed in this section, including recommended tolerances, grout sampling for test cubes, grout curing, post-grouting inspection, and verification of connector anchorage in columns and piles.
7.5.1 Recommended Tolerances
As discussed in Chapter 6, horizontal tolerances for grout pocket connections should be +/-1 in. in the longitudinal direction and +/-2 in. in the transverse direction. Grouted vertical duct and bolted connections using ducts should provide for a horizontal tolerance of +/-1 in. in both directions. If possible, however, the engineer should size pockets and ducts to provide tolerances of at least +/-1.5 in. in both directions. These tolerances must account for combined tolerances associated with placement of connectors in piles or columns and fabrication and placement of pockets and ducts in the bent cap. Vertical tolerances should be +/-1 in.
When specifying connections using grouted sleeve couplers, the engineer should verify the available horizontal and vertical tolerances provided by a particular coupler. Different tolerances are available for different manufacturers and for couplers housing different bar sizes. In determining the suitability of such a connection, the engineer should ensure that available tolerances are compatible with tolerances of +/-1/8 in. in the horizontal direction and +/-3/8 in. in the vertical direction for placement of the coupler within the bent cap.
To ensure adequate clearances are provided, ducts should be cast in the bent cap in such a way that a vertical orientation is achieved after setting of the bent cap. This must be carefully considered during bent cap fabrication, and may be especially critical when tight tolerances are necessary such as for grouted sleeve couplers. Cross slope can be achieved by use of variable depth pedestals.7.5.2 Grout Sampling for Test Cubes
During grouting operations, a TxDOT representative should witness the flow cone test and preparation of a minimum of six grout cubes for each batch of grout. A commercial testing laboratory approved by a TxDOT representative should test the grout cube specimens. To verify grout strength, cubes should be tested at 1 day, 3 days, and for approval of beam setting and final strength.
For cases in which inadequate strength is indicated, additional grout cubes should be tested and the average strength calculated. The engineer should determine the course of action in the event of inadequate strength, including additional grout cube testing, a review of structural calculations and durability provisions, and grout removal and re-grouting of the connection.
7.5.3 Grout Curing
All exposed grout surfaces should be cured in accordance with manufacturer's recommendations. This will typically involve covering exposed grout with clean wet rags and maintaining moisture for a minimum of 6 hours, followed by the application of an approved membrane curing compound.
7.5.4 Post-Grouting Inspection
After grout curing and form removal, all exposed grout surfaces at the top and sides of the cap and at the bedding layer should be carefully examined. If voids appear at any surface, external sealants should be applied to prevent a moisture path into the connection. In extreme cases, epoxy injection or other measures may be recommended by the engineer. In addition, external sealants should be applied to all surfaces for which enhanced durability is required.
7.5.5 Verification of Anchorage
For specific projects, the engineer may require that a pullout test be conducted to verify the adequacy of connector installation in columns, drilled shafts or piles. The connector should be loaded to less than the yield force to limit potential damage. The number of connectors to be tested is left to the engineer's discretion. The minimum force required to demonstrate adequacy of connector installation should be shown in the plans. Adequate anchorage should be assumed when an applied load equal to 85% of the specified yield strength of the connector is applied without slippage or pullout of the connector.
XXXX.1. Description. This item shall govern for connection of precast concrete bent caps to cast-inplace columns, drilled shafts and prestressed concrete piles.
XXXX.2. Materials. All materials shall conform to the pertinent requirements of the following Items except as otherwise required herein:
- Item 420, "Concrete Structures"
- Item 421, "Portland Cement Concrete"
- Item 425, "Prestressed Concrete Structural Members"
- Item 435, "Elastomeric Materials"
- Item 440, "Reinforcing Steel"
- Item 442, "Metal for Structures"
- Item 447, "Structural Bolting"
- Item 449, "Anchor Bolts"
(1) Hydraulic Cement Grout (Non-Shrink)
All grout for precast connections shall consist of prepackaged, cementitious, non-shrink grout in accordance with ASTM C-1107 and the additional performance requirements listed in Table 1, including mechanical properties, compatibility, constructability, and durability. Table 1 requirements shall govern over ASTM C-1107 requirements. Grout using metallic formulations will not be allowed. Grout shall be free of chlorides. No additives shall be added to prepackaged grout.
(2) Connection Hardware
All connection hardware, connectors, and ducts shall be in accordance with the requirements shown in the plans.
XXXX.3. Contractor Submittals. At least one month prior to the start of precast bent cap placement, the Contractor shall submit to the Engineer a Precast Bent Cap Placement Plan. Caps shall not be set until the Engineer has approved all required submittals. At a minimum, the plan shall contain the following items:
- Step-by-step description of bent cap placement for each bent, including proposed method to form the connection and ensure grout is properly consolidated in the connection and bedding layer.
- Method and description of hardware used to hold bent cap in position prior to connection grouting. Hardware may consist of plastic shims, steel shims, friction collars, shoring or other support systems. Total shim area for each connection shall not exceed 10% of the cross sectional area of the column, drilled shaft or pile. Individual shims shall be limited to a ratio of length to width of 2:1. Hardware submittal shall consist of product information for plastic shims and friction collars, drawings and material description for steel shims, and shop drawings for shoring if used.
- Method of installing connectors. Manufacturer's literature for connector hardware and adhesives used to install the connectors in the columns, drilled shafts or piles. Literature shall include step-by-step installation instructions for adhesives used to install connectors and material properties of the adhesive. Connector hardware shall conform to the type, coating, and installation requirements shown in the plans. Submittals for connectors shall include design calculations showing that the embedment depth exceeds that required to yield connectors. Installation of anchors shall be in accordance with Item 420.11 (9) "Installation of Dowels and Anchor Bolts".
- Manufacturer's product information for two candidate grouts, to include a description of the performance characteristics as specified in Table 1, mixing requirements, working time, curing requirements, and other information related to grouting of precast connections utilizing ducts or grout pockets.
- Other required submittals shown on the plans or requested by the Engineer relating to successful installation of precast bent caps and associated hardware.
XXXX.4. Construction Methods.
The Contractor shall follow the Precast Bent Cap Placement Plan, including all manufacturer's recommendations for anchorage installation and grouting operations. At the request of the Engineer, a pre-grouting meeting shall be held to review grouting procedures.
When grout pocket connections are used, tolerance for placement of columns, drilled shafts and piles shall be +/-1 in. in the longitudinal direction and +/-2 in. in the transverse direction. Horizontal tolerances shall be taken with respect to the centerline of the bridge. When connectors are embedded in ducts, tolerance for placement of columns, drilled shafts and piles shall be +/-1 in. Size, type, location and orientation of ducts to account for cap slope shall be as shown in the plans. When connectors are installed in preexisting columns, drilled shafts or piles, the tolerance for connector placement shall be +/-1/4 in. with respect to plan location. All connectors shall be installed plumb. Vertical tolerance for cap placement shall be +/-1 inch. Tolerances for grouted sleeve couplers, if used, shall be as shown in the plans. Out-of-tolerance substructure elements shall be subject to structural review by the Engineer.
All form release agents and curing membranes shall be completely removed from areas of the cap that will be in contact with bearing seat and connection grout.
(2) Cap Placement.
The Contractor is solely responsible for insuring the stability of the bent cap prior to and during grouting operations.
All grades, dimensions and elevations shall be verified and/or determined before the bent cap is placed. The contractor shall verify proper alignment between the columns, drilled shafts or piles, including connectors, grout pockets, post-tensioning ducts, and other connection hardware cast into the bent cap. The precast cap may be set and used as a template for drilling anchorage holes at the Contractor's option.
All loose material, dirt and foreign matter shall be removed from the tops of columns, drilled shafts or piles before the cap is set.
A pullout test shall be used to verify the adequacy of the grout or adhesives used to anchor connectors into columns, drilled shafts or piles. The minimum force required to demonstrate adequacy of anchor installation shall be 85% of the nominal force required to yield the connector.
(4) Grouting of Connections.
Grout shall be used in strict accordance with manufacturer's recommendations.
Admixtures, including retarders, shall not be added to grout, but the temperature of mixing water may be adjusted or ice may be added to increase working time and pot life.
Addition of water to previously mixed grout or remixing of grout shall not be permitted. Water exceeding manufacturer's recommendations shall not be added to the grout to increase flowability.
(a) Trial Batch At least two weeks prior to grouting of connections, a trial batch of grout shall be prepared to demonstrate grout properties and adequacy of equipment and to familiarize job site personnel with grouting procedures.
A batch of grout is the amount of grout sufficient to complete an entire connection or number of connections and is limited to the amount of grout that can be placed within the pot life determined in the trial batch. Partial batches will not be allowed and shall be discarded. For continuous placement using a grout pump, a batch shall be defined as one connection or one bent cap.
The Contractor shall establish grout flowability by measuring efflux (flow) time of with a standard flow cone according to the Corps of Engineers Flow Cone Method, CRD-C 611 and ASTM C 939.
Test flow shall be determined immediately after mixing and at the expected working time to establish pot life. The ambient temperature and mixing water temperature at the time of trial batch mixing shall be the same as that expected at the time of grout placement. The Contractor shall establish that the grout flow time satisfies the limits prescribed in Table 1.
Observation of segregation or large clumps of grout in the final trial batch shall be cause for rejection of the proposed brand of grout. Samples used for testing shall be taken from the middle of the batch.
One set of six (6) grout cubes shall be prepared as specified under Section 4 (c), Grout Testing, to verify the compressive strengths shown in Table 1.
The Contractor shall validate the proposed grout placement technique by using the trial batch grout and grout equipment in a sample grouting operation similar to the proposed connection grouting. Adequacy of mixer, pump, tremie tubes, funnels, buckets, and vent tubes shall be established. The contractor shall demonstrate that the equipment provided for grouting is adequate for mixing the grout and grouting the connection within the pot life of the batch and does not introduce air into the grout or connection. A square mesh with an opening no larger than 0.5 in. shall be used to filter out potential clumps when transferring grout from the mixer to buckets.
(b) Grout Placement
Tremie tubes shall be small enough to enable grout to be placed between the connectors and corrugated ducts. Funnels shall be large enough to keep the tremie tube full at all times. The tremie tube shall be equipped with a pinch valve to stop flow in the event that grouting is interrupted.
All equipment necessary to properly perform grouting operations shall be present before actual grouting operations begin. All grouting operations shall be performed in the presence of the Engineer in accordance with the Precast Bent Cap Placement Plan. Grouting operations shall be performed under the same weather limitations as cast-in-place concrete and as required by the manufacturer. Grout pumping shall be required for connections that cannot be completed using buckets within the pot life established for the grout during the trial batch.
Forms shall be drawn tight against the existing concrete and sealed water tight to avoid grout loss or offsets at the joint. The connection shall be presoaked with water for a minimum of two hours prior to grouting. After presoaking, the connection shall be drained of all water just prior to placement of grout.
Forms for the closure pour between the cap and column shall be adequately vented to allow air to escape during grouting. Vent tubes shall have a minimum ½-in. inner diameter and shall be flush with the top of the bedding layer. Vents shall not be plugged until a steady stream of grout flows out.
Grout shall be deposited such that all voids are completely filled. Grout shall be consolidated at intervals during placement operations for all connection types. Vibrators shall not be used. All connections shall be grouted in a manner that deposits grout from the bedding layer or bottom of the connection upward. Grout shall be placed through connection ducts and/or grout ports located at the top or side of the precast cap. When grout pocket connections are used, grout may also be deposited against the side of the pocket. When insufficient pressure is available to completely fill the duct from the bottom up, the final portion of grout may be placed from the cap top.
The Contractor shall validate the proposed grout placement technique by using the trial batch grout and grout equipment in a simple grouting operation. Adequacy of tremie tubes, funnels, buckets, and vent tubes shall be established.
All equipment necessary to properly perform grouting operations shall be present before actual grouting operations begin. All grouting operations shall be performed in the presence of the Engineer in accordance with the Precast Bent Cap Placement Plan.
Forms shall be drawn tight against the existing concrete to avoid grout loss or offsets at the joint. All previously hardened concrete surfaces that will be in contact with the grout shall be pre-watered to a surface-saturated moist condition when the grout is placed. Drain ports or holes shall be provided to allow residual water from prewatering to drain prior to grouting. Forms for the closure pour between the cap and column shall be adequately vented to allow air to escape during grouting.
Grout shall be deposited such that all voids are completely filled. Grout shall be consolidated at intervals during placement operations for all connection types. All connections shall be grouted in a manner that deposits the grout from the bedding layer or bottom of connection upward. Grout shall be placed through connection ducts and/or grout ports located at the top or side of the precast cap. When insufficient pressure is available to completely fill the duct from the bottom up, the final portion of grout may be placed from the cap top. In such cases, care shall be taken to prevent introducing air into the previously placed grout.
Care shall be taken to prevent introducing air into previously placed grout by monitoring tremie tube placement, grout flow, and rate of pour.
All exposed grout surfaces shall be cured in accordance with manufacturer's recommendations.
(c) Grout Testing. The compressive strength of the grout for "Beam Setting Strength" and "Final Strength" shall be determined using grout cubes prepared and tested in accordance with ASTM C-109. The contractor will prepare a minimum of six (6) cubes per batch. A Commercial Testing Laboratory approved by the Engineer shall test the specimens for "Beam Setting Strength" and "Final Strength." Grout failing to meet the minimum required compressive strength may be cause for rejection of the connection, grout removal, and re-grouting of the connection by means approved by the Engineer.
(5) Beam Placement.
Bearing seat build-ups, when required, shall be placed in accordance with Item 420.18. The top surface of the precast cap anchorage shall be finished in accordance with Item 420.18 or waterproofed as shown in the plans. Lifting loops shall be burned off 1 in. below the surface of surrounding concrete and patched using anchorage grout, bearing seat buildup grout or other material approved by the Engineer.
Beams shall not be set until the connection grout has reached a compressive strength equal to the "Beam Setting Strength" shown on the plans. Final acceptance of the connection shall be after the grout has reached the "Final Strength" shown in the plans and after the connection has been waterproofed, if required.
XXXX.5. Measurement. Precast connections of the type specified shall be measured by each precast connection.
XXXX.6. Payment. The work performed and materials furnished in accordance with this Item and measured as provided under "Measurement" shall be paid for at the unit price bid for each precast connection of the type specified. This price shall be full compensation for furnishing hardware to support the bent cap prior to grouting; for installation of the precast connection anchorage devices; for furnishing and mixing grout; for placing, finishing and curing the grout; waterproofing the connection; and for all labor, tools, equipment and incidentals necessary to complete the work.
(ASTM C-109, 2" cubes)
|Compressive strength (psi)
5800 and 1.25(f'ccap+1000)
(ASTM C 827 & ASTM C 1090)
Modulus of elasticity
Coefficient of thermal expansion
|Grade B or C—expansion per ASTM C 1107
(ASTM C-939; CRD-C 611 Flow Cone)
Set Time (ASTM C-191)
|fluid consistency efflux time: 20-30 seconds
Freeze Thaw (ASTM C-666)
|300 cycles, RDF 90%
expansion at 26 weeks < 0.1%
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