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Publication Number: FHWA-RD-97-146
Date: NOVEMBER 1997

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Petrographic Methods of Examining Hardened Concrete: A Petrographic Manual

Latest version available: FHWA-HRT-04-150

This manual was written by Hollis N. Walker while she was a research petrographer with the Virginia Transportation Research Council (VTRC). First published in 1992 as a Virginia SP&R report, it was intended as a reference and guide manual for those persons conducting petrographic evaluations of concrete and concrete materials. For those who have obtained a copy of the manual and used it, it has served that purpose well. Since its introduction, VTRC has continued to make the manual available to those who request it.

With the current downsizing of state highway agencies, and retirement of experienced staff of long time service, the Turner-Fairbank Highway Research Center of the Federal Highway Administration (FHWA) has noticed a steady increase in the number and extent of inquiries from the states regarding references and training in petrography. As a first step in responding to this growing need, the FHWA has joined with the VTRC to republish this manual for wider distribution and utilization.

The decision was made to republish the manual as it was written in 1992, without change. This was done not only to expedite printing and distribution, but also because the manual is still an excellent and timely document as written, with much of the equipment and procedures unchanged since that time. Where change has occurred, it is evolutionary rather than revolutionary, so that little technology advancement is forfeited by forgoing the re-write at this time. The excellent peer review group who helped finalize the original document (see acknowledgments) also ensured its initial quality.

Users of this document are encouraged to submit comments and suggested additions or changes to Dr. Stephen W. Forster, FHWA, 202 493-3070, or Mr. D. Stephen Lane, VTRC, 804 293-19S3, for inclusion in any future revisions to the manual.

TABLE OF CONTENTS


ACKNOWLEDGMENTS

1 INTRODUCTION
1.1 HISTORICAL BACKGROUND
1.2 CURRENT PRACTICES
1.3 HOW TO USE THIS MANUAL

2 EQUIPMENT, MATERIALS & ENVIRONS
2.1 OVERVIEW
2.2 FOR SAMPLE PREPARATION ROOM
2.2.1 General Comments
2.2.2 Equipment
2.3 FOR PREPARATION OF SLICES
2.3.1 General Comments
2.3.2 Equipment
2.4 FOR PRODUCTION OF THIN SECTIONS
2.4.1 General Comments
2.4.2 For Examination with Petrographic Microscope
2.4.3 For Examination with Polarizing/Epifluorescence Microscope
2.5 FOR EXAMINATION OF SPECIMENS
2.5.1 General Comments.
2.5.2 Equipment
2.6 EXPENDABLE MATERIALS
2.6.1 General Comments
2.6.2 Lapping Oil
2.6.3 Grinding Compounds
2.6.4 Dyes and Epoxies
2.6.5 Miscellaneous Supplies

3 GENERAL PROCEDURES

3.1 OVERVIEW
3.2 FORMAL RECEIPT OF SPECIMEN
3.3 INITIAL EXAMINATION
3.4 PRELIMINARY PLAN OF ANALYSIS
3.5 FILING OF APPROPRIATE DOCUMENTS
3.5.1 Permanent Case Files
3.5.2 Temporary and Archive Files

4 CRACKS
4.1 OVERVIEW
4.2 TYPES OF CRACKS
4.2.1 Microcracks
4.2.2 Crazing
4.2.3 Scaling
4.2.4 Cracks Due to Insufficient Air-Void Content
4.2.5 Cracks Due to Delamination at Reinforcement
4.2.6 Cracks Due to a Chemical Reaction
4.2.7 Cracks Due to Drying Shrinkage
4.2.8 Cracks Due to Plastic Shrinkage
4.3 DISTINGUISHING BETWEEN PLASTIC SHRINKAGE CRACKING AND DRYING SHRINKAGE CRACKING
4.3.1 Overview
4.3.2 Analogy with Clay Materials
4.3.3 Procedures

5 PREPARATION OF SPECIMENS
5.1 OVERVIEW
5.2 SLICES
5.2.1 Basic Lapped Slice
5.2.1.1 Overview
5.2.1.2 Procedures
5.2.2 Vertical Section of Horizontal Slice (or Vice Versa)
5.2.3 Acid-Etched Slice
5.2.3.1 Overview
5.2.3.2 Procedures
5.3 THIN SECTIONS
5.3.1 Basic Thin Section
5.3.1.1 Overview
5.3.1.2 Procedures
5.3.2 Thin Section for Detecting Alkali-Reactive Textures in Carbonate Aggregate Rock
5.3.2.1 Overview
5.3.2.2 Procedures
5.3.3 Thin Section Showing Profile of Wearing Surface
5.3.3.1 Overview
5.3.3.2 Procedures
5.3.4 Thin Section for Epifluorescent Illumination
5.3.4.1 Overview
5.3.4.2 Procedures
5.4 GRAIN MOUNTS
5.4.1 Overview
5.4.2 Procedures
5.4.2.1 Temporary Mount
5.4.2.2 Permanent Mount
5.5 AGGREGATE SPECIMENS
5.5.1 Overview
5.5.2 Procedures
5.5.2.1 Hand Specimen and Large Fragment of Rock
5.5.2.2 Sand, Gravel, Crushed Stone, and Slag

6 THE VOIDS
6.1 OVERVIEW
6.2 TYPES OF VOIDS
6.2.1 Capillary Voids
6.2.2 Entrained Air Voids
6.2.3 Entrapped Voids and Water Voids
6.3 QUANTITATIVE DETERMINATION OF AIR-VOID PARAMETERS
6.3.1 Overview
6.3.2 Methods and Equipment
6.3.2.1 Overview
6.3.2.2 Linear Traverse
6.3.2.3 Point Count
6.3.2.4 Image Analysis
6.3.2.5 Other Considerations
6.3.3 Preparation of Specimens
6.3.4 Technician Considerations
6.4 CLASSIFICATION OF VOIDS
6.4.1 Overview
6.4.2 Distinguishing Between Entrapped Voids Caused by Air and Those Caused by Water
6.4.3 Determination of Size Break Point Between Entrained and Entrapped Voids
6.4.4 Procedures
6.5 MEANING OF AIR-VOID PARAMETERS

7 PERCENTAGE ANALYSES OF PASTE, AGGREGATE & OTHER SUBSTANCES
7.1 PASTE
7.1.1 Overview
7.1.2 Procedures
7.1.2.1 Calculation from Design of Mixture
7.1.2.2 Microscopical Determination
7.2 AGGREGATE AND OTHER SUBSTANCES

8 EXAMINATION WITH THE STEREOMICROSCOPE
8.1 OVERVIEW
8.2 REVIEW OF DATA
8.3 PREPARATION OF EQUIPMENT
8.4 EXAMINATION ANT) MARKING OF SLICES
8.5 ENHANCEMENT OF MARKED FEATURES
8.6 PHOTOGRAPHING OF SLICES AND MAKING OF PHOTOMICROGRAPHS
8.6.1 Photographs of Marked Slice
8.6.2 Photomicrographs

9 WATER-CEMENT RATIO
9.1 OVERVIEW
9.2 PROCEDURES
9.2.1 Estimation
9.2.2 Chemical Determination

10 ALKALI-AGGREGATE REACTIONS
10.1 OVERVIEW
10.2 ALKALI-SILICA REACTION
10.2.1 Overview
10.2.2 Field Examination
10.2.2.1 Crack Pattern
10.2.2.2 Structural Evidence of Expansion
10.2.2.3 Aggregate Lithology
10.2.2.4 Exudations, Coatings, and Pore Fillings
10.2.2.5 Sufficient Sampling
10.2.3 Laboratory Examination
10.2.4 Testing of Siliceous Aggregate
10.3 ALKALI-CARBONATE REACTION
10.3.1 Field Examination
10.3.3 Testing of Carbonate Aggregate

11 PARTICULATE MATERIALS OTHER THAN PORTLAND CEMENT
11.1 OVERVIEW
11.2 PROCEDURES
11.2.1 Ground-Granulated Blast Furnace Slag
11.2.2 Fly Ash
11.2.3 Silica Fume

12 EXAMINATION WITH THE PETROGRAPHIC MICROSCOPE
12.1 OVERVIEW
12.2 USES
12.3 PROCEDURES

13 EXAMINATION WITH THE POLARIZING/EPIFLUORESCENCE MICROSCOPE
13.1 OVERVIEW
13.2 USES
13.2.1 Cracks
13.2.1.1 In Aggregate
13.2.1.2 In Paste of Concrete
13.2.2 Air-Void Parameters
13.2.3 Hydration
13.2.4 Effect of Fine Aggregate
13.2.5 Photomicrographs
13.3 PROCEDURES
13.3.1 General Techniques
13.3.2 Cracks
13.3.3 Air-Void Parameters
13.3.4 Porosity Related to Carbonation
13.3.5 Water-Cement Ratio and Permeability
13.3.6 Hydration
13.3.7 Quality of Fine Aggregate
13.3.8 Photography

REFERENCES
SUGGESTED READING SECTION

APPENDICES
APPENDIX A: GLOSSARY
APPENDIX B: OBTAINING SPECIMENS OF HCC FOR PETROGRAPHIC EXAMINATION
APPENDIX C: CAUSES AND PREVENTION OF PLASTIC SHRINKAGE CRACKING
APPENDIX D: RETEMPERING
APPENDIX E: AGGREGATES USES IN HCC
APPENDIX F: PREVENTION OF A DESTRUCTIVE ALKALI-SILICA REACTION
APPENDIX G: QUESTIONS AND SUGGESTIONS FOR FURTHER RESEARCH

LIST OF TABLES
Table 2-1
Equipment for Petrographic Laboratory
Table 2-2 Reference Specimens of Materials Used in Fabricating HCC
Table 2-3 Reference Specimens of Various Conditions of HCC
Table 3-1 Reasons Petrographic Services Are Requested and Corresponding Plans for Analysis
Table 3-2 Typical Types of Specimens
Table 3-3 Procedure-Formal Receipt of Specimen in Laboratory
Table 3-4 Procedure-Initial Examination of Specimen
Table 3-5 Procedure-Preliminary Plan of Analysis of Specimen
Table 3-6 Sample of Typical Analysis
Table 3-7 Sample of Typical Analysis
Table 3-8 Sample of Typical Analysis
Table 4-1 Procedure-Distinguishing Between Plastic and Drying Shrinkage Cracking
Table 5-1 Procedure-Production of Basic Lapped Slice
Table 5-2 Procedure-Etching of Slice
Table 5-3 Procedure-Preparation of Basic Thin Section
Table 6-1 Types of Voids
Table 7-1 Procedure-Determining Percentage of Paste
Table 8-1 Procedure-Examination with Stereomicroscope
Table 8-2 Checklist for Examination with the Stereomicroscope
Table 9-1 Procedure-Estimation of Water-Cement Ratio
Table 10-1 Silica Minerals in Order of Decreasing Reactivity
Table 10-2 Rocks in Order of Decreasing Reactivity
Table 10-3 Factors to Be Considered in Field Examination for Alkali-Aggregate Reactions
Table F-1 Methods of Preventing Destructive Alkali-Silica Reaction

LIST OF FIGURES
Figure 2-1 Water-Cooled Drill Press
Figure 2-2 Rock Trimmer
Figure 2-3 Water-Cooled, Diamond-Edged, Rotary Saw with Overhand Arm
Figure 2-4 Large, Oil-Cooled, Diamond-Edged, Rotary Saw
Figure 2-5 Rotary Saw with Thin, Diamond-Edged, Smooth-Edged Blade
Figure 2-6 Bench Lap
Figure 2-7 Lap
Figure 2-8 Weights
Figure 2-9 Safety-Approved Container for Cleaning of Specimen
Figure 2-10 Ultrasonic Cleaner
Figure 2-11 Ingram-Ward Thin-Sectioning Equipment
Figure 2-12 Glass Coated with Grinding Compound Slurry
Figure 2-13 Drying Oven
Figure 2-14 Vacuum Oven
Figure 2-15 Mounted Set of Clamps
Figure 2-16 Syntron Vibratory Polisher and Weights
Figure 2-17 Stereomicroscope with Light Source and Accessories
Figure 2-18 Microtools
Figure 2-19 Sieves
Figure 3-1 Core with P-Number
Figure 3-2 Page of Logbook
Figure 3-3 VTRC Request for Petrographic Services Form
Figure 3-4 Scaling Caused by Freezing and Thawing
Figure 3-5 Cracking on Surface and Side of Core
Figure 3-6 Delamination Around Reinforcing Bars
Figure 3-7 Fragments of Concrete Destroyed by Freezing Before Final Setting
Figure 3-8 Surface Sawed Through Concrete Slab That Froze Before Final Setting
Figure 3-9 Core Marked with Identification, Cutting Planes, and Match Marks
Figure 4-1 Plastic Shrinkage Cracking
Figure 4-2 Plastic Shrinkage Cracking
Figure 4-3 Plastic Shrinkage Cracking
Figure 4-4 Bridge of Paste Across Plastic Shrinkage Crack
Figure 4-5 Plastic Shrinkage Crack
Figure 4-6 Plastic Shrinkage Crack
Figure 5-1 Undercutting
Figure 5-2 Well-Prepared Surface
Figure 5-3 Properly Finished Slice
Figure 5-4 Slice Cut at Right Angles to Original Slice
Figure 5-5 Thin Section Thinned to Nothing on One End
Figure 5-6 Steps in Preparing Thin Section to Show Details of Wearing Surface
Figure 5-7 Specimen Mounted Between Work Glass and Welled Slide ; 80
Figure 6-1 Concrete That Increased in Volume Due to Incorporation of Aluminum Fragments
Figure 6-2 Surface of Finely Lapped Slice of Concrete Containing 5.6% Total Air Voids
Figure 6-3 Surface of Finely Lapped Slice of Concrete Containing 17% Total Air Voids
Figure 6-4 Concrete Core with About 4% Large Irregular Voids
Figure 6-5 Partially Automated Linear Traverse Equipment for Determining Air-Void Parameters
Figure 6-6 Fully Automated Equipment for Determining Air-Void Parameters
Figure 6-7 Image Analysis Equipment6
Figure 6-8 Illustration of Various Sizes of Sections That May Be Expressed on Randomly Placed Plane;100
Figure 6-9 Two Equally Spaced Arrays of Voids
Figure 6-10 Type of Voids and Paste Texture Produced by Early Types of High-Range Water Reducers
Figure 7-1 Finely Lapped Slices of Concrete with Normal Paste Content ;108
Figure 7-2 Finely Lapped Slices of Concrete with Nonstandard Paste Content
Figure 7-3 Flaws in Paste
Figure 7-4 Knots of Cement Exposed on Finely Lapped Slice
Figure 7-5 Etched Slices
Figure 7-6 Cross Section of Surface Demonstrating Problems of Boundary Distinction
Figure 7-7 Varying Amounts of Aggregate Size Fractions
Figure 8-1 Excess Air at Surface of Concrete
Figure 8-2 Voids Occurring in Bunches
Figure 8-3 Overwatered Concrete
Figure 8-4 Cement Coating on Aggregates
Figure 8-5 Fly Ash Particles on Surface of Lapped Sliced of Concrete
Figure 8-6 Cracks at Bond Between Aggregate and Paste
Figure 8-7 Typical Cracks Due to Freezing and Thawing
Figure 8-8 Microcracks
Figure 8-9 Finely Lapped Surfaces of Beams Tested for Resistance to Freezing and Thawing
Figure 8-10 Lapped Surface of Slice of Concrete Containing Reinforcing Cable
Figure 8-11 Cracking Just Below Bond in Concrete with Latex Concrete Overlay
Figure 8-12 Sheet Used in VTRC Stereomicroscopy Photograph Notebook
Figure 10-1 Idealized Sketch of Broken Honeycomb Pattern
Figure 10-2 Symbol from Coat of Arms of Rulers of Isle of Man
Figure 10-3 Typical Destructive Alkali-Silica Reaction in Pavement
Figure 10-4 Destructive Alkali-Silica Reaction in Anchor Block
Figure 10-5 Wheel Guard Sections Destroying Each Other
Figure 10-6 Upper Portion of Back Wall Sheared by Expansion of BridgeDeck
Figure 10-7 Destructive Alkali-Silica Reaction in Pavement
Figure 10-8 Alkali-Silica Reaction in Longitudinally Reinforced Pavement Constructed with Dark Metabasalt Aggregate
Figure 10-9 Alkali-Silica Gel
Figure 10-10 Alkali-Silica Gel on Back Wall
Figure 10-11 Electric Hammer Removing Carbonated Surface of HCC
Figure 10-12 Testing for Alkali-Silica Gel
Figure 10-13 Specimen Treated with Uranyl-Acetate from Pavement with Destructive Alkali-Silica Reaction
Figure 10-14 Thin Section of Highly Strained Quartzite
Figure 10-15 Destructive Alkali-Carbonate Reaction in Walkway Pavement
Figure 10-16 Deterioration Due to a Combination Alkali-Silica Reaction and Alkali-Carbonate Reaction
Figure 10-17 Destructive Alkali-Carbonate Reaction in Bridge Deck
Figure 10-18 Fine Cracks in Reactive Carbonate Aggregate in Mortar Bar with High-Alkali Cement
Figure 10-19 Alkali-Reactive Microtexture in Four Carbonate Rocks
Figure 10-20 Nonreactive Microtextures of Carbonate Rocks
Figure 10-21 Reacted Dolomite Crystal
Figure 10-22 Reaction of Dolomitic Rock
Figure 11-1 HCC Containing GGBFS
Figure 11-2 Thin Sections of Concrete Containing GGBFS
Figure 11-3 Etched Area of Lapped Slice Containing Fly Ash
Figure 11-4 Fly Ash in Thin Section of HCC
Figure 12-1 Petrographic Microscope
Figure 13-1 Light Paths in P/EF Microscope
Figure 13-2 P/EF Microscope
Figure 13-3 Relationship of Filters to Dye Emittance Spectrum
Figure 13-4 Swing-Out Filter Over Light Port on Base of Microscope
Figure 13-5 Cracks in Thin Section of Concrete
Figure 13-6 Fluorescence from Porous Clay Pocket Shining Through Edge of Quartz Particle
Figure 13-7 Void in Thin Section
Figure 13-8 Thin Section of Exterior Portion of HCC
Figure 13-9 Thin Section of Interior Portion of HCC
Figure 13-10 Thin Section of 50-Year-Old Concrete
Figure 13-11 Thin Section of 25-Year-Old Concrete
Figure 13-12 Thin Section of HCC Fabricated with Smooth, Rounded Sand
Figure 13-13 Thin Section of HCC Fabricated with Angular, Dirty Sand
Figure 13-14 Thin Section of Porous, Iron-Stained Particle of Sand
Figure 13-15 Page from VTRC P/EF Photomicroscopy Notebook
Figure B-1 Popout
Figure C-1 Effect of Ambient Climatic Conditions on Rate of Evaporation
Figure E-1 Shaly Particle Shape
Figure E-2 Aggregate Particles from Fissile Gneiss
Figure E-3 D-Cracking
Figure E-4 Traffic-Worn Rounded Surface of Feldspar Aggregate Particle
Figure E-5 Traffic-Worn Surface of Granite Aggregate Particle
Figure E-6 Lapped Slice of HCC Fabricated with Expanded Lightweight Aggregate

LIST OF ACRONYMS
ACI. American Concrete Institute.
ASTM. American Society for Testing and Materials.
BF. Barrier filter.
DM. Dichroic mirror.
GGBFS.Ground-granulated blast furnace slag.
HCC. Hydraulic cement concretev
P/EF. Polarizing/epifluoresence.
RH. Relative humidity.
SI. International System of Measurements, i.e. metric.
VDOT. Virginia Department of Transportation.
VTRC. Virginia Transportation Research Council.

 

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The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT).
The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). Provide leadership and technology for the delivery of long life pavements that meet our customers needs and are safe, cost effective, and can be effectively maintained. Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
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