Petrographic Methods of Examining Hardened Concrete: A Petrographic Manual

PDF files can be viewed with the Acrobat® Reader®

Table of Contents | Next

FOREWORD

Petrographic Methods of Examining Hardened Concrete: A Petrographic Manual was originally published in 1992 by the Virginia Transportation Research Council (VTRC) as Report VTRC-92-R14. Authored by Hollis N. Walker, it was the culmination of a quarter century of work by her in concrete petrography at the VTRC.

This edition, revised by D. Stephen Lane, senior research scientist at the VTRC, builds on the original work. It has been revised and updated to reflect recent advances in techniques and work in concrete petrography. Major additions to the manual include a new chapter (chapter 14, written by Paul E. Stutzman, physical scientist, National Institute of Standards and Technology) on the use of the scanning electron microscope to examine concrete and concretemaking materials, and additional information on the identification and classification of rocks and minerals in aggregates (appendix D). Chapter 10, Alkali-Aggregate Reactions, was reorganized to outline the process one would follow to investigate a case of concrete deterioration and illustrate the features that provide evidence of alkali-silica or alkali-carbonate reactions. It is hoped that the manual will be of great use both to those entering the field of concrete petrography and to the experienced petrographer.

This edition is an example of the continuing cooperation in infrastructure research and development between State and Federal agencies.

The following quotation from K. Mather (1966), serves as a mission statement for concrete petrographers:

The best petrographic examination is the one that finds the right questions and answers them with maximum economy in minimum time, with a demonstration clear to all concerned that the right questions were answered with all necessary and no superfluous detail. In practice, the approach to the ideal varies depending on the problem, the skill with which the questions are asked, and the skill of the petrographer. One measure of the petrographer’s skill is knowing when to stop, either because the problem is adequately solved, or, in some cases, because it has been shown to be insoluble under the circumstances.

Katherine Mather served as chair of the American Society for Testing and Materials Subcommittee on Petrography of Concrete and Aggregates for many years. She was an expert in the practice and use of petrography, contributed to many publications, and participated actively in cement and concrete research carried on by the U.S. Army Corps of Engineers, Vicksburg, Mississippi.

Gary L. Henderson, Director
Office of Infrastructure Research
and Development

NOTICE

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for its contents or use thereof. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trade and manufacturers’ names appear in this report only because they are considered essential to the object of the document.

QUALITY ASSURANCE STATEMENT

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

Technical Report Documentation Page

Form DOT F 1700.7 (8-72 Reproduction of completed page authorized

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

• 1. INTRODUCTION
  • 1.1 Historical Background
  • 1.2 Current Practices
  • 1.3 How To Use This Manual
• 2. EQUIPMENT, MATERIALS, AND ENVIRONMENT
  • 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 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 Caused by Cycles of Freezing and Thawing While Concrete Is Critically Saturated
    • 4.2.5 Cracks Caused by Reinforcement Corrosion
    • 4.2.6 Cracks Caused by a Chemical Reaction
    • 4.2.7 Cracks Caused by Drying Shrinkage
    • 4.2.8 Cracks Caused by Thermal Volume Change
    • 4.2.9 Cracks Caused by 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 FOR OPTICAL MICROSCOPY
  • 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 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. 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 Entrapped Air Voids From Water Voids
    • 6.4.3 Distinguishing Entrained Voids From Entrapped Voids
    • 6.4.4 Procedures
  • 6.5 MEANING OF AIR-VOID PARAMETERS
• 7. QUANTITATIVE ANALYSES OF PASTE, AGGREGATE, AND OTHER COMPONENTS
  • 7.1 PASTE
    • 7.1.1 Overview
    • 7.1.2 Procedures
      • 7.1.2.1 Calculation From Mixture Design
      • 7.1.2.2 Estimation
      • 7.1.2.3 Microscopical Determination
  • 7.2 AGGREGATE AND OTHER COMPONENTS
• 8. EXAMINATION WITH THE STEREOMICROSCOPE
  • 8.1 OVERVIEW
  • 8.2 REVIEW OF AVAILABLE INFORMATION
  • 8.3 PREPARATION OF EQUIPMENT
  • 8.4 EXAMINATION AND MARKING OF SLICES
  • 8.5 ENHANCEMENT OF MARKED FEATURES
  • 8.6 PHOTOGRAPHING OF SLICES AND THE MAKING OF PHOTOMICROGRAPHS
    • 8.6.1 Photographs of Marked Slice
    • 8.6.2 Photomicrographs
  • 8.7 CHEMICAL SPOT TESTS AND STAINING TECHNIQUES
• 9. WATER-CEMENTITIOUS MATERIALS 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 REACTIONS
    • 10.2.1 Alkali-Silica Reaction
    • 10.2.2 Alkali-Carbonate Reaction
  • 10.3 Field Examination
    • 10.3.1 Cracking Pattern
    • 10.3.2 Structural Evidence of Expansion
    • 10.3.3 Exudations, Coatings, and Pore Fillings
    • 10.3.4 Sufficient Sampling
  • 10.4 Laboratory Examination
  • 10.5 ASSESSMENT
• 11. CEMENTITIOUS MATERIALS
  • 11.1 OVERVIEW
  • 11.2 PROCEDURES
    • 11.2.1 Cementitious Powders
    • 11.2.2 Hydraulic Cement Concrete
      • 11.2.2.1 Ground Granulated Blast-Furnace Slag
      • 11.2.2.2 Fly Ash
      • 11.2.2.3 Silica Fume
• 12. EXAMINATION WITH THE PETROGRAPHIC MICROSCOPE
  • 12.1 OVERVIEW
  • 12.2 USES OF THE PETROGRAPHIC MICROSCOPE
  • 12.3 PROCEDURES
• 13. EXAMINATION WITH THE POLARIZING/EPIFLUORESCENCE MICROSCOPE
  • 13.1 OVERVIEW
  • 13.2 USES OF THE P/EF MICROSCOPE
    • 13.2.1 Cracks
      • 13.2.1.1 In Aggregate
      • 13.2.1.2 In Paste
    • 13.2.2 Air-Void Parameters
    • 13.2.3 Porosity Related to Carbonation
    • 13.2.4 Water-Cement Ratio and Permeability
    • 13.2.5 Hydration
    • 13.2.6 Effect of Fine Aggregate
    • 13.2.7 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
• 14. SAMPLE PREPARATION FOR AND EXAMINATION WITH THE SCANNING ELECTRON MICROSCOPE
  • 14.1 OVERVIEW
  • 14.2 Scanning Electron Microscope
    • 14.2.1 Secondary Electron Imaging
    • 14.2.2 Backscattered Electron Imaging
    • 14.2.3 X-Ray Microanalysis
  • 14.3 Specimen Preparation
    • 14.3.1 Overview
    • 14.3.2 Materials for Sample Preparation
    • 14.3.3 Polished Sections of Cement and Pozzolan Powders
    • 14.3.4 Preparation of Cement Paste, Mortar, and Concrete Sections
    • 14.3.5 Cutting and Grinding
    • 14.3.6 Polishing
    • 14.3.7 Coating for Examination
  • 14.4 Imaging Strategies for SEM
  • 14.5 Quantitative Methods in Microscopy
    • 14.5.1 Point-Count Analysis
    • 14.5.2 Image Processing and Analysis
  • 14.6 Summary
• APPENDIX A. OBTAINING SPECIMENS OF HCC FOR PETROGRAPHIC EXAMINATION
  • A.1 OVERVIEW
  • A.2 TYPES OF SPECIMENS
  • A.3 SAMPLING PLAN
  • A.4 SAMPLING PROCEDURES
  • A.5 SPECIAL CONSIDERATIONS
    • A.5.1 Air-Void Samples
    • A.5.2 Overlay Material
      • A.5.2.1 Cracking
      • A.5.2.2 Delamination
    • A.5.3 Frozen Concrete
    • A.5.4 Unusual Conditions
    • A.5.5 Aggregate Specimens
  • A.6 COMPARISON OF FIELD AND LABORATORY SPECIMENS
  • REFERENCES
• APPENDIX B. CAUSES AND PREVENTION OF PLASTIC SHRINKAGE CRACKING
  • B.1 CAUSES
  • B.2 PREVENTION
  • B.3 LEGAL INVESTIGATIONS
  • REFERENCES
• APPENDIX C. RETEMPERING
  • C.1 OVERVIEW
  • C.2 LIKELY RETEMPERING SCENARIO
  • C.3 EFFECT OF RETEMPERING
    • C.3.1 On HCC Paste
    • C.3.2 On Air Voids
      • C.3.2.1 Quantity
      • C.3.2.2 Shape
      • C.3.2.3 Size
  • REFERENCES
• APPENDIX D. AGGREGATES USED IN HYDRAULIC CEMENT CONCRETE
  • D.1 OVERVIEW
  • D.2 COARSE AGGREGATE
  • D.3 FINE AGGREGATE
  • D.4 IDENTIFICATION OF MINERALS AND ROCKS
    • D.4.1 Mineral Identification
    • D.4.2 Rock Identification
    • D.4.3 Identification of Alkali-Silica Reactive Aggregates
    • D.4.4 Identification of Alkali-Carbonate Reactive Aggregates
  • D.5 AGGREGATE CONCERNS IN D-CRACKING
  • D.6 SPECIAL-PURPOSE AGGREGATES
    • D.6.1 Skid Resistance
    • D.6.2 Lightweight Aggregates
    • D.6.3 Radiation Shielding
  • REFERENCES
• APPENDIX E. EXAMPLES OF REASONS PETROGRAPHIC SERVICES ARE REQUESTED AND CORRESPONDING PLANS FOR ANALYSIS
• GLOSSARY
• ACKNOWLEDGMENTS
• REFERENCES
• READING LIST
  • Aggregates (also see Petrographic Methods)
  • Aggregate-Paste Reactions
  • Air-Voids
  • ASTM Standards
  • Cements
  • D-Cracking
  • Paste
  • Petrographic Methods
  • Reference Collections
  • Terminology

LIST OF FIGURES

• Figure 1. Water-cooled drill press.
• Figure 2. Rock trimmer (with chisel points and hydraulic jack to apply up to 4500 newtons (N)).
• Figure 3. Water-cooled, segmented, diamond-edged rotary saw with overhead arm (360-mm blade is diamond-edged and slotted into wide teeth; foot pedal controls the height of the saw).
• Figure 4. Large, oil-cooled, continuous diamond-edged rotary saw.
• Figure 5. The smooth-edged blade, at least 610 mm in diameter, runs in an oil bath and vise that holds the specimen firmly and automatically moves it into the saw.
• Figure 6. Rotary saw with thin, continuous diamond-edged blade (diameter of 150 mm; arrow points to the sliding table on which the specimen can be braced).
• Figure 7. Bench lap (diameter of 200 mm, for rough-grinding rock and concrete specimens; suspended bottle is for water or another lubricant; grinding compounds may be shaken like salt from plastic bottles with a pierced cover).
• Figure 8. Lap (diameter of 400 mm).
• Figure 9. Weights rest on the back of the slices, fitting loosely inside the rings to provide the downward force needed to produce smoothly lapped surfaces. (Here, cans of an appropriate diameter, weighted with lead shot, are used.).
• Figure 10. Automated grinding, lapping, and polishing machine uses interchangeable grinding and polishing discs to simplify specimen preparatio.
• Figure 11. Ultrasonic cleaner (tank is of a material that will resist most solvents).
• Figure 12. Ingram-Ward thin-sectioning equipment: Diamond-edged cutoff saw with very thin blade (see arrow) used to slice off excess specimen material.
• Figure 13. Ingram-Ward thin-sectioning equipment: Diamond-bearing, cupped ceramic grinder (see arrow).
• Figure 14. Glass coated with grinding-compound slurry.
• Figure 15. Drying oven (thermostatically controlled).
• Figure 16. Vacuum oven: Thin-section stock in liquid dyed epoxy in small disposable dishes.
• Figure 17. Closeup of bubbling of liquid epoxy as vacuum removes air and water from specimen.
• Figure 18. Mounted set of clamps (small Lucite® rectangles are used to distribute clamping force over the entire section surface) (Walker and Marshall, 1979).
• Figure 19. Syntron vibratory polisher and weights (weights have sponge rubber bumpers) (Walker and Marshall, 1979).
• Figure 20. Stereomicroscope with light source and accessories.
• Figure 21. Microtools (including needles, shovels, and scrapers small enough to be useful in the cracks and crevices of concrete and to fit in the working distance under the stereomicroscope).
• Figure 22. Types of sieves used in examination of concrete and concrete materials (203-mm and 76-mm sizes).
• Figure 23. Flowchart of petrographic examination process (adapted from Van Dam, et al., 2002b).
• Figure 24. Core with P-number.
• Figure 25. Page from VTRC logbook.
• Figure 26. VTRC Request for Petrographic Services form.
• Figure 27. Scaling caused by cycles of freezing and thawing (occurred in concrete unprotected by a proper air-void system).
• Figure 28. Cracking on surface and side of core with associated corrosion and expansion of the reinforcing bar.
• Figure 29. Delamination around reinforcing bars (there is no cracking on the surface).
• Figure 30. Fragments of concrete destroyed by freezing before final setting.
• Figure 31. Surface sawed through concrete slab that froze before final setting.
• Figure 32. Core marked with identification, cutting planes, and match marks.
• Figure 33. Plastic shrinkage cracking was covered up by mortar filling over it on top of a 100-mm core.
• Figure 34. Plastic shrinkage cracking occurred before a surface texture was forme.
• Figure 35. Plastic shrinkage cracking occurred in a latex-modified concrete overlay (top view of core (small threads of latex span the crack)).
• Figure 36. Plastic shrinkage cracking: Small bridges of latex paste connect sides of crack.
• Figure 37. Small bridge of paste across a crack caused by shrinkage that took place while the ordinary portland cement concrete was not hardened (100-mm core, road surface at right).
• Figure 38. Bridge of paste across plastic shrinkage crack: Closeup of bridge.
• Figure 39. Tortuous path of a plastic shrinkage crack in a concrete that has not completely separated.
• Figure 40. Plastic shrinkage crack on a lapped surface (wearing surface is at the top of the photograph).
• Figure 41. Undercutting.
• Figure 42. Well-prepared surface viewed in ordinary illumination.
• Figure 43. Well-prepared surface viewed at a very low angle toward a source of illumination (an illuminated screen).
• Figure 44. Properly finished slice (same as that shown in figures 42 and 43).
• Figure 45. Slice cut at right angles to original slice: Edges of thin top surfaces of a concrete core embedded in epoxy and repotted in mortar in a mold 152 mm in diameter and then resliced and finely lapped to allow examination of the vertical surface.
• Figure 46. Slice cut at right angles to original slice: Left portion of middle slice shown in figure 45 is enlarged.
• Figure 47. Thin section wedged to one end to observe dolomite rhombs in micrite as an indicator of possible alkali-carbonate reactivity (glass mount is 27 by 46 mm).
• Figure 48. Stage in the preparation of this section to show the details of the wearing surface: (1) Small blocks of wearing surface.
• Figure 49. Stage in the preparation of this section to show the details of the wearing surface: (2) Blocks cemented to microscope slide.
• Figure 50. Stage in the preparation of this section to show the details of the wearing surface: (3) Thin section of blocks.
• Figure 51. Specimen mounted between work glasses and final slide (dotted line indicates the plane the saw will cut).
• Figure 52. Concrete that increased in volume because of corrosion of aluminum fragment.
• Figure 53. Surface of finely lapped slice of concrete containing 5.6 percent total air voids.
• Figure 54. Surface of finely lapped slice of concrete containing 17 percent total air voids.
• Figure 55. Concrete core with about 4 percent large, irregularly shaped voids.
• Figure 56. Partially automated linear traverse equipment for determining air-void parameters.
• Figure 57. Image analysis equipment.
• Figure 58. Illustration of various sizes of sections that may be expressed on a randomly placed plane.
• Figure 59. Two equally spaced arrays of voids.
• Figure 60. Void system produced by early types of high-range water reducers.
• Figure 61. Finely lapped slices of concrete with normal paste content: Rounded to subangular quartz gravel coarse aggregate and fine sand aggregate.
• Figure 62. Finely lapped slices of concrete with normal paste content: Angular crushed granite coarse aggregate and fine sand aggregate.
• Figure 63. Finely lapped slices of concrete with abnormal paste content: High paste content.
• Figure 64. Finely lapped slices of concrete with abnormal paste content: Low paste content.
• Figure 65. Lapped surface.
• Figure 66. Flaws in lapped surface.
• Figure 67. Knot of cement exposed on finely lapped slice (rounded shape was caused by tumbling in the mixer).
• Figure 68. Etched slice: Etched surface on concrete fabricated with quartz sand fine aggregate.
• Figure 69. Etched slice: Etched surface on concrete fabricated with crushed limestone fine aggregate .
• Figure 70. Cross section of surface demonstrating problems of boundary distinction.
• Figure 71. Varying amounts of aggregate size fractions: Concrete fabricated without larger sizes of coarse aggregate.
• Figure 72. Varying amounts of aggregate size fractions: Concrete fabricated with coarse aggregate that is larger than what is now considered to be normal for bridge deck concrete.
• Figure 73. Two-page Petrographic Examination of Hardened Concrete form used by the Ontario Ministry of Transportation.
• Figure 74. Excess air at surface of concrete (top).
• Figure 75. Clustering of voids apparently caused by excess air-entraining admixture and incomplete mixing (field width is 50 mm).
• Figure 76. Overwatered concrete: Rain and snow occurring after the concrete was placed caused overwatering near the surface (top). (The aggregate sunk out of the overwatered zone..
• Figure 77. Cement coating on aggregate.
• Figure 78. Fly-ash particles on the surface of a lapped slice of concrete.
• Figure 79. Cracks at the bond between the aggregate, rebar, and paste (see arrows).
• Figure 80. Cracks typical of damage caused by cycles of freezing and thawing.
• Figure 81. Microcracks: Smoothly lapped surface (A) with ink-marked microcracks.
• Figure 82. Microcracks: Wearing surface near figure 81.
• Figure 83. Finely lapped surface of beam tested for resistance to cycles of freezing and thawing.
• Figure 84. Finely lapped surface of beam tested for resistance to cycles of freezing and thawing: Mixtures in figures 83 and 84 were identical except that the mixture shown here contained an experimental admixture.
• Figure 85. Lapped surface of slice of concrete containing prestressing strand.
• Figure 86. Cracking just below the bond in the concrete deck with latex-modified concrete overlay.
• Figure 87. Sheet used in VTRC stereomicroscopy photograph notebook.
• Figure 88. Specimen treated with phenolphthalein (high-alkalinity, uncarbonated paste stains pink; carbonated paste does not stain).
• Figure 89. Specimen from retaining wall with destructive ASR treated with uranyl acetate: Ordinary light.
• Figure 90. Specimen from retaining wall with destructive ASR treated with uranyl acetate: Ultraviolet illumination causes silica gel to fluoresce (darkroom photograph).
• Figure 91. Polished specimen treated with sodium cobaltinitrite, which stains the potassiumbearing compounds yellow.
• Figure 92. Fractured surface treated with BaCl-KMnO4 (secondary deposits containing sulfate are stained pink).
• Figure 93. Idealized sketch of cracking pattern in concrete mass caused by internal expansion as a result of AAR.
• Figure 94. Map cracking with preferred longitudinal trend in continuously reinforced concrete pavement.
• Figure 95. Typical destructive ASR in plain or lightly reinforced pavement.
• Figure 96. Destructive ASR in anchor block.
• Figure 97. Cracking of pavement as a result of ACR.
• Figure 98. Upper portion of backwall sheared by expansion of bridge deck.
• Figure 99. Expanding median barrier crushes itself.
• Figure 100. Closing of joint caused by bridge deck expansion as a result of ACR.
• Figure 101. Bridge deck.
• Figure 102. Extracted core.
• Figure 103. ASR in longitudinally reinforced pavement constructed with dark metabasalt aggregate.
• Figure 104. ASR in longitudinally reinforced pavement constructed with dark metabasalt aggregate: 100-mm core that fractured on this surface upon removal from the pavement.
• Figure 105. Fracture face of splitting tensile specimen: Examine for aggregate fracture and deterioration, as well as secondary deposits.
• Figure 106. Destructive ASR in pavement.
• Figure 107. Destructive ASR in pavement: Alkali-silica gel in a 2-mm void in a lapped slice from the pavement in figure 106 (dark aggregate is siltstone).
• Figure 108. ASR damage expressed on lapped slab (cracks highlighted in yellow, deposits of reaction product highlighted in red).
• Figure 109. Lapped surface showing type of aggregates and ASR products.
• Figure 110. Lapped surface of specimen affected by ACR exhibiting rim and areas of altered paste at corners of aggregate.
• Figure 111. Paste cracking and alteration of paste.
• Figure 112. Lapped surfaces of ACR specimen showing aggregate cracking and alteration of paste.
• Figure 113. Internal cracking of aggregate particle.
• Figure 114. Thin section showing void containing crystallized ASR product.
• Figure 115. Thin section showing aggregate crac.
• Figure 116. Thin section in plane polarized light.
• Figure 117. Thin section with crossed polars.
• Figure 118. Backscattered electron image of ASR-damaged concrete.
• Figure 119. Optical image of lapped section showing ASR product associated with damaged chert particles.
• Figure 120. Similar feature in backscattered electron image as associated EDX elemental plots for K, Si, and Ca.
• Figure 121. Thin section of ACR rock (lower left of image) and adjacent altered paste in plane polarized light.
• Figure 122. Thin section of ACR rock (lower left of image) with crossed polar.
• Figure 123. Backscattered electron image of polished thin section showing area of altered paste adjacent to ACR rock in lower left.
• Figure 124. Thin section of fracture in ACR rock at low magnificatio.
• Figure 125. Thin section of fracture in ACR rock at high magnification.
• Figure 126. Backscattered electron images of outer rim of reacting ACR roc.
• Figure 127. Interior of same particl.
• Figure 128. Powder mount of ASR product in plane polarized light.
• Figure 129. Powder mount of ASR product in crossed polarized light.
• Figure 130. Polished specimen treated with sodium cobaltinitrite solution.
• Figure 131. Integration of field observations with laboratory investigations.
• Figure 132. Immersion mount of portland cement in plane polarized light showing alite crystals.
• Figure 133. Immersion mount of belite cluster with darker interstitial aluminate and ferrite.
• Figure 134. Immersion mount of fly ash showing spherical particle shape.
• Figure 135. Immersion mount of agglomerate of minute silica-fume particles.
• Figure 136. Immersion mount of natural pozzolan (calcined shale).
• Figure 137. Immersion mount of slag.
• Figure 138. SEM images illustrating the size difference of various cementitious materials.
• Figure 139. Cut surface on HCC containing slag exposed to air for 6 months.
• Figure 140. Interior of beam of HCC containing slag, illustrating the partially dry twocolor stage.
• Figure 141. Thin section of concrete containing slag: At 28 days hydration (note the angularity of the slag fragments).
• Figure 142. Thin section of concrete containing slag: At 56 days hydration (note the slight rounding of the slag fragments).
• Figure 143. Thin section of concrete containing slag: At 6 months hydration (note the further rounding of the slag fragments).
• Figure 144. Etched area of lapped surface of concrete containing fly ash.
• Figure 145. Fly ash in thin section of HCC, viewed in plane polarized light with a petrographic microscope (note the broken fly-ash particle that is composed of dark and light glass, 100X).
• Figure 146. Fly ash in thin section of HCC, viewed in plane polarized light with a petrographic microscope (cenospheres of fly ash filled with smaller cenospheres, 400X).
• Figure 147. Petrographic microscope.
• Figure 148. Light paths and features of the P/EF microscope.
• Figure 149. P/EF microscope.
• Figure 150. Relationship of filters to dye emittance spectrum.
• Figure 151. Swing-out filter over light port on base of microscope.
• Figure 152. Cracks in the thin section of the concrete.
• Figure 153. Fluorescence from porous clay pocket shining through edge of quartz particle.
• Figure 154. Void in thin section with focus plane on top surface of section.
• Figure 155. Void in thin section (same as figure 154) with focus plane at bottom of section, 100X.
• Figure 156. Thin section of exterior portion of the HCC: Surface exposed to the air is at the top.
• Figure 157. Same view as figure 156, but viewed with crossed nicols: Bright area shows the high birefringence of the calcite of the carbonated area.
• Figure 158. Same view as figures 156 and 157, but viewed with ultraviolet light, causing fluorescence of the pore structure of the HCC (note that there is more porosity indicated by fluorescence in the portion of the HCC farthest from the surface than there is in the carbonated zone.
• Figure 159. Thin section of interior portion of HCC: Viewed with crossed nicols (bright area shows the high birefringence of the calcite of the carbonated area).
• Figure 160. Thin section of interior portion of HCC: Same area as figure 159, but viewed with ultraviolet light, causing fluorescence of the pore structure within the carbonated area.
• Figure 161. Thin section of 50-year-old concrete. At the center is the remnant of a very large cement grain (cement was more coarsely ground then). Modern cement is usually about the size of the completely hydrated and filled cement grain indicated by the arrow (viewed with plane polarized illumination).
• Figure 162. Same location as figure 161, but viewed with crossed nicols. Note the original birefringence still present in the unhydrated central portion of the grain.
• Figure 163. Same location as figure 161, but viewed with ultraviolet light, causing fluorescence of the dye in the pore structure. The structure indicates that the original external boundary of the cement grain was the thin line (indicated by the arrows).
• Figure 164. Thin section of 25-year-old concrete viewed with plane polarized light.
• Figure 165. Thin section of 25-year-old concrete viewed with incident ultraviolet illumination, causing fluorescence of the dye-filled space.
• Figure 166. Thin section of HCC made with smooth, rounded sand: Viewed with plane polarized light.
• Figure 167. Thin section of HCC made with smooth, rounded sand: Same view as figure 166, but with ultraviolet illumination, causing fluorescence in the pore structure impregnated with dye (note the even texture of the paste).
• Figure 168. Thin section of HCC made with angular, dirty sand: Viewed with plane polarized light (there are numerous reentrant angles).
• Figure 169. Thin section of HCC made with angular, dirty sand: Same view as figure 168, but with ultraviolet illumination, causing fluorescence that delineates the pore structure.
• Figure 170. Thin section of porous, iron-stained particle of sand: Viewed with plane polarized light.
• Figure 171. Thin section of porous, iron-stained particle of sand: Viewed with incident ultraviolet illumination, causing fluorescence of the dye in the pore structure of the sand grain and indicating a zone of water accumulation and weakness.
• Figure 172. Page from VTRC P/EF photomicroscopy notebook.
• Figure 173. Scanning electron microscope.
• Figure 174. SE image showing platy or foil-like CSH, fine bundles of CSH fibers and platy CH (top).
• Figure 175. SE image showing platy CH and ettringite needles and also plate-like CH morphology (bottom).
• Figure 176. Equation to estimate backscatter coefficient from Goldstein, et al. (1992).
• Figure 177. Equation to estimate BE coefficient of a multielement phase.
• Figure 178. Equation to calculate contrast between constituents.
• Figure 179. Stereomicroscopic image.
• Figure 180. Backscattered electron image (same specimen).
• Figure 181. Secondary electron image of a fresh-fracture surface from concrete.
• Figure 182. Top. Paired image at successively greater magnification of stereomicroscope (white light) images and SEM BE images: Field width is 11 mm.
• Figure 183. Middle. Field width is 3 mm.
• Figure 184. Bottom. Field width is 1.5 mm.
• Figure 185. Backscattered electron image of an epoxy-impregnated, polished cross section of concrete (field width is 2 mm).
• Figure 186. Backscattered electron image of an epoxy-impregnated, polished cross section of concrete (field width is 1 mm).
• Figure 187. EDX spectrum.
• Figure 188. EDX spectra for ettringite (top left), monosulfate (top right), calcium hydroxide (bottom left), and calcium-silicate-hydrate (bottom right) aid in phase identification characteristics.
• Figure 189. Fence diagram created by collecting a series of EDX spectra along an emplacement of ASR gel (the gel composition rapidly becomes much like the bulk CSH once outside the aggregate and the source of reaction).
• Figure 190. Plots of element spatial distribution are generated through x-ray imaging.
• Figure 191. Effects of different accelerating voltage on x-ray spectra of ettringite show the loss of low-energy peaks at high accelerating voltages and the opposite effect at low voltages.
• Figure 192. BE images of unimpregnated, sawed surface (the sawed surface is rough with residual particulate matter, yielding poor contrast and shadowing that make interpretation of BE and EDX images difficult).
• Figure 193. BE images of the impregnated, polished surface from the same concrete (polished surface presents optimum BE and EDX imaging characteristics).
• Figure 194. Polished section of hardened portland cement paste imaged using the BE signal clearly shows the constituent phases (residual cement (RC) appears brightest, followed by CH, CSH, and other hydration products) (top); EDX image (bottom) shows regions of intermediate-intensity calcium (blue), intermediateintensity aluminum (purple), and high-intensity sulfur (yellow), defining locations of monosulfate that could not be distinguished on a rough surface (field width is 73 µm).
• Figure 195. Equation for percent error in the point-count method (at the 96-percent confidence level) based on the the proportion of points on the phase of interest and the total number of all points counted.
• Figure 196. BE image (right) of carbonate aggregate composed of darker gray dolomite (1) rhombs in fine-grained matrix containing lighter gray calcite (6) (the gray-level intensity of calcite and dolomite is distinct, and they can also be distinguished on the basis of the EDX spectra (left); field width is approximately 100 µm).
• Figure 197. BE images of carbonate aggregate in concrete at 15X (field width of 8 mm).
• Figure 198. BE images of carbonate aggregate in concrete at 400X (field width of 300 µm.
• Figure 199. Gray-level histogram of hardened cement paste.
• Figure 200. BE image of hardened cement paste (field width is 73 µm).
• Figure 201. Pseudocolored image based on BE gray scale of figures 198 and 199 (red = residual cement, blue = CH, black = CSH, and green = coarse porosity). Counting the number of pixels for each color allows an estimate of the phase area fractions for this field of view.
• Figure 202. Processing of BE and calcium x-ray images here highlights the CH location (analysis of the binary image of CH distribution calculated 12 percent of the image field to be occupied by CH).
• Figure 203. Giant popout caused by a piece of glass (accompanying it are several small popouts of a more usual size caused by porous chert particles).
• Figure 204. Glass particle.
• Figure 205. Effect of concrete temperature, air temperature, wind velocity, and relative humidity on the rate of evaporation of surface moisture from a concrete surface.
• Figure 206. Shaley particle shape of crushed slate aggregate.
• Figure 207. Aggregate particles from a fissile gneiss (a particle shape such as this can cause a high water demand).
• Figure 208. Mohs comparative hardness scale.
• Figure 209. Cubic habit, brassy yellow color, metallic luster of pyrite.
• Figure 210. Granite aggregate exhibiting cleavage traces at right angles in orthoclase (right box) and no cleavage in quartz (left box) (scratch test with metal tool leaves metal (arrows) on both quartz and orthoclase, which are harder than the metal).
• Figure 211. Metal tool scratches upper limestone (calcite) aggregate and leaves metal on lower quartzite particle.
• Figure 212. Immersion mount of chert in plane polarized light.
• Figure 213. Immersion mount of chert with crossed polars, showing microcrystalline texture (refractive index matches that of quartz).
• Figure 214. Thin section of marble (calcic schist) in plane polarized light.
• Figure 215. Thin section of marble (calcic schist) in crossed polarized light.
• Figure 216. Quantitative XRD analysis to determine mineral composition of aggregate shown in figures 182 through 184.
• Figure 217. Coupling the knowledge of the mineral present (figure 215) with the elemental EDX maps shown here allows identification of the minerals present at specific locations within the fine-grained rock.
• Figure 218. Thin section of strained quartzite: Crossed polars.
• Figure 219. Alkali-reactive microtexture in four carbonate rocks.
• Figure 220. Nonreactive microtextures of carbonate rocks (examples are shown to illustrate the difference between these crystalline textures and the partially crystalline reactive textures shown in figure 218).
• Figure 221. D-cracking of a pavement caused by destruction of the aggregate by cycles of freezing and thawing (cracking parallel to the joint and wrapping around at the juncture of joints defines D-cracking).
• Figure 222. Pavement surface with a flaw caused by freezing and thawing of water trapped in aggregate particle.
• Figure 223. Traffic-worn rounded surface of feldspar aggregate particle (this will not provide good skid resistance).
• Figure 224. Traffic-worn surface of granite aggregate particle (zones of weakness provide an irregular skid-resistant surface).
• Figure 225. Lapped slice of HCC containing expanded-shale lightweight aggregate.

LIST OF TABLES

• Table 1. Equipment for a petrographic laborator.
• Table 2. Useful sieves for petrographic laboratory using 76-mm frame.
• Table 3. Reference specimens of materials used in making hydraulic cement concret.
• Table 4. Reference specimens of hydraulic cement concrete representing various conditions or feature.
• Table 5. Typical types of specimen.
• Table 6. Procedure for formal receipt of a specimen in the laborator.
• Table 7. Procedure for initial examination of specime.
• Table 8. Procedure for preliminary analysis of specime.
• Table 9. Outline of typical low strength analysi.
• Table 10. Outline of typical laboratory deterioration analysi.
• Table 11. Outline of typical rain damage analysi.
• Table 12. Procedure for distinguishing between plastic and drying shrinkage crackin.
• Table 13. Procedure for producing lapped slic.
• Table 14. Procedure for etching slic.
• Table 15. Types of void.
• Table 16. Procedure for determining paste percentag.
• Table 17. Stereomicroscopic examination procedur.
• Table 18. Checklist for examination with the stereomicroscop.
• Table 19. Procedure for estimating w/c.
• Table 20. Paste characteristics reflective of w/c.
• Table 21. Silica minerals in order of decreasing reactivit.
• Table 22. Potentially alkali-silica reactive rock.
• Table 23. Visual features and rating indices from field observations (British Cement Association, 1992; Lane, 2001.
• Table 24. Petrographic features and weighting factors for ASR distress (Lane, 2001.
• Table 25. Damage categorization to provide neutral assessment (Lane, 2001.
• Table 26. Cement and hydration product constituents, chemical composition, and backscattered electron coefficient (?.
• Table 27. Equipment and supplies for preparation of polished section.
• Table 28. Typical SEM settings for routine examination.
• Table 29. Keys to mineral identificatio.
• Table 30. Selected properties of common minerals (FHWA, 1991.
• Table 31. Keys to rock identificatio.
• Table 32. Igneous rock classificatio.
• Table 33. Classification of carbonate rock.
• Table 34. Classification of clastic sedimentary rock.
• Table 35. Classification of metamorphic rock.
• Table 36. Alkali-silica reactive constituent.

LIST OF ACRONYMS AND ABBREVIATIONS