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Publication Number: FHWA-HRT-04-150
Date: July 2006

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Figure 1. Photo. Water-cooled drill press.

A core bit is mounted vertically under a press machine. The downward pressing of the core bit is done by way of the hand wheel attached vertically and to the side of the press for right hand operation. The hand wheel contains multiple knobs for easy grip on various points of the wheel. A water hose is connected to a water swivel above the core bit. The core bit is surrounded by a sheet-metal basin for water drainage control.

Figure 2. Photo. Rock trimmer

In a conceptual drawing, a chisel is mounted point-down on a hydraulic jack. The jack is held in place by a square metal frame. The jack is operated by a lever-arm and can apply a force of up to 4500 newtons.

Figure 3. Photo. Water-cooled, segmented, diamond-edged, rotary saw with overhead arm.

A 360-millimeter circular, diamond-edged blade with wide slotted teeth is mounted on a saw station bench. The blade is positioned vertically to allow the operator an easy sliding motion of the sample toward the blade. A large foot-pedal at the bottom of the bench controls the height of the saw.

Figure 4. Photo. Large, oil-cooled, continuous diamond-edged rotary saw

A man operating the saw provides a perspective on the size of the saw station; it is a little larger than a typical kitchen stove appliance. A cover encloses the entire unit to contain the splashing of oil.

Figure 5. Photo. The smooth edged blade, at least 610 millimeters in diameter, runs in an oil bath and vise that holds the specimen firmly and automatically moves it into the saw

This is a closer view of the saw shown in figure 4. A smooth-edged blade (with no visible teeth) and a vise are mounted on a frame such that a clamped horizontal concrete cylinder or core will be cut vertically at any chosen point while the vise automatically pushes the cylinder toward the blade. An oil bath keeps the blade lubricated.

Figure 6. Photo. Rotary saw with thin, continuous diamond-edged blade.

A 150 millimeter diamond blade is mounted vertically on a saw station such that cutting will be with a forward hand motion. A sliding push table, pointed to in the figure by a white arrow, is an integral part of the station and is used to brace the sample during cutting.

Figure 7. Photo. Bench lap.

. A turntable with a 200 millimeter disk used for rough grinding rock and concrete specimens. A jar for water or another lubricant is suspended approximately 0.3 meter above the disk and is used for dripping water or other lubricants during grinding. Grinding compounds may be added manually with plastic dispensers.

Figure 8. Photo. Lap. (diameter of 400 millimeters).

The photo has a footnote indicating the following parts that are identified on the photo by letters: A. rotating slotted specimen holder; B. cover plate to set on top of specimen; C. guide yoke that retains specimen holder; D. grit slurry cup mounted on its motor and containing spiral agitator pump; E. drain; and F. grooved lap. A turntable holds a horizontal grooved lap disk within a circular containment. Resting over the disk are three specimen-holder rings. Each ring has a cover plate and a guide yolk. The turntable is equipped with a grit-slurry cup mounted on its motor and containing a spiral agitator-pump that feeds a grit-slurry onto the lap disk. The spent grit-slurry is drained through a hole in the bottom of the containment.

Figure 9. Photo. Weights rest on the back of the slices, fitting loosely inside the rings to provide the downward force needed to produce smoothly lapped surfaces

Photo focuses on two of the specimen-holder rings in the previous figure. Here, ordinary coffee cans, filled with lead shot, have been inserted into each ring to keep the samples pressed against the horizontal lap wheel.

Figure 10. Photo. Automated grinding, lapping, and polishing machine.

A turntable machine has a rotating disk-holder positioned horizontally on which interchangeable discs can be attached for grinding, lapping or polishing. It has an overhead sample holder to keep the sample firmly pressed on the turning disks and a nozzle that dispenses water automatically for lubrication.

Figure 11. Photo. Ultrasonic cleaner.

The solvent tank or box is electric powered and made of a material able to resist most solvents used. Cyclic pressure waves are transmitted though the liquid to enhance the cleaning action. It also includes a cover.

Figure 12. Photo. Ingram-Ward thin-sectioning equipment: Diamond edged cutoff saw with very thin blade used to slice off excess specimen material.

A saw machine has a very thin diamond-edged blade disk for slicing thin sections. The blade disk, pointed out by a white arrow, is mounted vertically for a forward slicing motion.

Figure 13. Photo. Ingram-Ward thin-sectioning equipment: Diamond bearing, cupped ceramic grinder.

A cupped ceramic grinder disk with diamond bearing is pointed out in the photo by a white arrow. The grinder disk is both smaller and positioned just to the side of the blade to facilitate the alternation of use. A chuck holds the sample firmly in place during slicing or grinding and is moved longitudinally by a lever and handle. A small dial, positioned on the bottom-right of the machine and pointed out by a second arrow in the photo, adjusts the distance of the chuck relative to the blade or grinder.

Figure 14. Photo. Glass coated with grinding-compound slurry.

An ordinary flat pan is used to catch the grinding slurry that overflows the edge of the glass. The two plastic bottles have holes in the screw on covers and waxed paper cups for dust covers. Dry grit is shaken from the bottles and mixed on the plate with lubricant to produce a slurry.

Figure 15. Photo. Drying oven

A thermostatically controlled oven, approximately the size of a kitchen microwave oven, is set on a counter. The oven door is shown open with an intermediate level shelve and a vertical glass thermometer extending in from the top.

Figure 16. Photo. Vacuum oven: Thin-section stock in liquid-dyed epoxy in small disposable dishes

A square oven with a transparent glass front door is shown with the door open. Two sample trays, each containing a thin-section, are in the oven and ready to be vacuum-oven dried.

Figure 17. Photo. Closeup of bubbling of liquid epoxy as vacuum removes air and water from specimen.

A closeup of the thin section samples in the oven shows that foam has developed on the surface of the sample trays during the progress of the vacuum-heating operation.

Figure 18. Photo. Mounted set of clamps (small Lucite@reg; rectangles are used to distribute clamping force over the entire section surface).

Photo shows six thin section samples, each mounted on a rectangular glass surface that is held in place by a clamp. The six clamps, of uniform shape and size, are positioned in single file. The clamps hold the six individual plastic rectangles firmly on the specimens and hold the specimens firmly on a flat bracing surface. They are activated by the horizontal rotation of a hand lever. Reference is made to Walker and Marshall, 1979.

Figure 19. Photo. Syntron vibratory polisher and weights.

Photo shows a cylindrical vibratory machine that rests vertically on a countertop and is firmly positioned by a wider metal base. A lapping pad is mounted on the vibrating surface of the machine. Over the lapping pad are six individual circular metal weights, each holding a thin section in place for polishing. The weights are free to move over the surface of the lapping pad and have sponge rubber bumper rings mounted on them for shock absorption. A railing around the lapping surface keeps the weights and their samples from slipping off the surface of the vibrating pad. Reference is made to Walker and Marshall, 1979.

Figure 20. Photo. Stereomicroscope with light source and accessories.

A stereomicroscope is shown on a countertop along with a sample of hardened concrete positioned under the objective lens. Light is directed on the sample by two penlights mounted on their source with snake-arm adjustable positioning. Several small tool accessories are arranged on the countertop next to the microscope.

Figure 21. Photo. Microtools.

Photo shows an array of small tools for use under a microscope lens. These include needles, shovels and scrapers. Their points or heads are small enough to enter the cracks and crevices of the sample concrete surface. An arrow points to a small scale engraved on very thin, flexible metal mounted on a thin rod in turn attached to a handle. The scale has 5 millimeters marked into tenths of a millimeter on one side and one-tenth of an inch marked into 5 thousandths of an inch on the other.

Figure 22. Photo. Types of sieves used in examination of concrete and concrete materials .

Two sets of A S T M E 11 standard sieves are shown. One set is of 76-millimeter diameter frames and the other is of 203-millimeter diameter frames. Both sets have covers.

Figure 23. Diagram. Flowchart of petrographic examination process (adapted from Van Dam et al., 2002b).

The diagram shows a box at the top with "Problem" in it and a box at the bottom with "Diagnosis"in it. Seven circles in between are connected by lines and arrows in various directions showing the various steps and techniques that might be used to identify the type of deterioration. The circles start at the top with visual examination and then moving down to observation with the stereo optical microscope. Other options that might be used as needed are also included in circles: wet chemistry; staining techniques; use of the petrographic and/ or scanning electron microscope; and potentially X-ray diffraction analysis if needed to help make the diagnosis.

Figure 24. Photo. Core with P number

The original construction number is not obscured, and the P number is marked with a felt marker and graphite. The photo shows a cylindrical concrete core with a P-number on its surface. The number is written clearly below the original construction number in felt marker and also in graphite, and it is easily distinguished from other designations on the core.

Figure 25. Photo. Page from V T R C logbook.

The photo shows an example page of V T R C logbook. Each specimen is logged on a separate row. The leftmost column shows the P-number of each specimen in ascending order. Other information on each specimen includes date received and type of test performed

Figure 26. Photo. V T R C Request for Petrographic Services Form.

The photo shows an example of a completed, hand-printed form with a project title "Deterioration of Bridge Deck" and sections for the charge number, county, route number, and section. Other spaces in the form are provided for the file number, person submitting the samples, reason for the request, analyses desired, list of samples received, numbers assigned to them, and preparation requested by the petrographer.

Figure 27. Photo. Scaling caused by cycles of freezing and thawing (occurred in concrete unprotected by a proper air-void system).

To photograph the cracking, the specimen was glued back together with a dark glue, and then cut vertically across the layered cracking. The photo shows a longitudinal cross section of a cylindrical concrete core showing sections of the aggregates and cement paste. No entrained air is apparent, and the top portion of the core shows several horizontal layers that have cracked and produced scaling and spalling

Figure 28. Photo. Cracking on surface and side of core with associated corrosion and expansion of the reinforcing bar.

The photo shows a view of the top and side of a cylindrical core concrete revealing a rusted transverse reinforcing bar at about middepth in the core, a crack extending vertically over the bar to the top surface, and another horizontal crack at the top of the reinforcing bar creating a delamination plane parallel to the top surface.

Figure 29. Photo. Delamination around reinforcing bars (there is no cracking on the surface).

The photo shows a cylindrical concrete core with an embedded transverse reinforcing bar. A delamination is formed horizontally at the location of the reinforcement. The top and bottom surfaces of the delamination are tangent respectively to the top and bottom of the reinforcement bar. Within the delamination there is another horizontal crack that begins at the bar and extends to the edge of the core.

Figure 30. Photo. Fragments of concrete destroyed by freezing before final setting

The sample of damaged concrete shown (60 millimeters length) is fragmented into multiple clumps by freezing action. Also, the clumps do not have the appearance of a normally hardened concrete. Instead, they are packed with ice crystal patterns in the form of streaks, each less that 1 millimeter apart.

Figure 31. Photo. Surface sawed through concrete slab that froze before final setting.

Molds of ice crystals are quite visible and generally parallel with the concrete surface. The molds, now empty, create zones of weakness throughout the concrete. Field width is 75 millimeters.

Figure 32. Photo. Core marked with identification, cutting planes, and match marks.

A core of hardened concrete is shown resting up side down and marked with identification numbers. The original bottom of the core has an irregular surface resulting from a continuity failure. Two parallel lines spaced apart 12.7 millimeters are drawn vertically along the side from the smooth bottom to the irregular top. The identification numbers are shown also between the parallel lines. Near the original top of the core, three essentially parallel short lines "match marks" are drawn crossing one of the vertical lines. Also near the original top and near the match marks, an arrow is drawn pointing to the original top surface of the concrete.

Figure 33. Photo. Plastic shrinkage cracking was covered up by mortar filling over it on top of a 100-millimeter core.

The top section of a broken concrete core is shown with areas of finer mortar material noticeable near the surface. The mortar was worked into surface plastic shrinkage cracks while the concrete was still plastic. These weaker areas of the hardened concrete cracked again. A near-vertical crack is shown with a crack branching off at a lower angle. Chunks of the top surface have broken off.

Figure 34. Photo. Plastic shrinkage cracking occurred before a surface texture was formed.

The top section of a concrete core is shown with a crack and void noticeable below a surface layer of mortar leaving a void about 10 millimeters below the finished concrete surface.

Figure 35. Photo. Plastic shrinkage cracking occurred in a latex-modified concrete overlay.

The top view of a core section taken through the exposed top surface of the concrete showing an irregular plastic shrinkage crack with small threads of latex spanning the crack.

Figure 36. Photo. Plastic shrinkage cracking: Small bridges of latex paste connect sides of crack.

Vertical cross section cut down through the core shows the irregular crack going down about 25 millimeters below the surface of the concrete.

Figure 37. Photo. Small bridge of paste across a crack caused shrinkage that took place while the ordinary portland cement was not hardened.

Photo shows a crack on the surface of a 100-millimeter core. The crack formed during the concrete’ s plastic stage.

Figure 38. Photo. Bridge of paste across plastic shrinkage crack: Closeup of bridge.

A closeup of the crack shows a bridge of paste between its two sides.

Figure 39. Photo. Tortuous path of a plastic shrinkage crack.

Photo shows a section through hardened concrete with the tortuous path of a plastic shrinkage crack. In this case the crack has not completely separated, showing how bridges of material form as the plastic concrete is stretched.

Figure 40. Photo. Plastic shrinkage crack on lapped surface (wearing surface is at the top of the photograph

Photo shows a typical plastic shrinkage crack that is wider at the concrete surface and has an irregular shape as the crack becomes narrower toward the bottom of the vertical cross section shown.

Figure 41. Drawing. Undercutting

A conceptual drawing shows the cross section of a lapped concrete sample. The lapped surface is cut deeper in the softer areas (the paste) than in the harder areas (the aggregate). The disparity in the depth of the cut will expose more of the harder material than with a theoretical even-depth cut.

Figure 42. Photo. Well-prepared surface viewed in ordinary illumination.

The lapped surface of a concrete sample is shown at approximately a 30-degree incident angle under ordinary light conditions. The surface appears smooth and flat.

Figure 43. Photo. Well-prepared surface viewed at a very low angle toward a source of illumination

The same surface as in figure 42 is viewed at about a 5 degree incident angle and toward a light source. The clear reflection of a distant object or image is an indication of the flatness of the lapped surface

Figure 44. Photo. Properly finished slice

The surface of a properly finished slice (same as that shown in figures 42 and 43) is able to reflect a scenic view outside the room. The camera was focused on the reflection; thus, to the camera, the slice is out of focus. The human eye sees both in focus.

Figure 45. Slice cut at right angles to original slice

View shows the edges of three thin sections of top surfaces of a concrete core embedded in epoxy and repotted in mortar in a mold 152 millimeters in diameter and then re-sliced and finely lapped to allow examination of the vertical surface. In this case, the concrete was slightly etched with weak hydrochloric acid to delineate the depth of carbonation.

Figure 46. Slice cut at right angles to original slice: Left portion of middle slice shown in figure 45 is enlarged.

The carbonated area is above the lower edge of the whiter area near the wearing surface. An undulating dashed line shows the separation between the carbonated area on top and the noncarbonated area below the dashed line.

Figure 47. Photo. Thin section wedged to one end.

A thin section, shown in a glass mount, was cut to standard thickness on one end and tapered to zero thickness on the opposite end. This wedge form allows for the optimum thickness necessary to reveal dolomite rhombs in micrite as indicators of possible alkali-carbonate reactivity. The photo shows the rock thin section as whitish on the top (thicker) end grading to gray and then black as the section becomes thinner. Glass mount is 27 by 46 millimeters

Figure 48. Photo. Stages in preparing this section to show details of wearing surface

. Photo shows two samples with ridges of a wearing surface.

Figure 49. Photo. Stage in the preparation of this section to show the details of the wearing surface: (2) Blocks cemented to microscope slide

The photo shows a section mounted on a microscope slide prior to cutting to a thin section.

Figure 50. Photo. Stage in preparation of this section to show the details of the wearing surface: (3) Thin section of blocks.

The photo shows the final thin section that remains mounted on the slide. This section was made to about 50 micrometers in thickness because the study for which it was fabricated was concerned with the profile of the wearing surface and not with the identity and interrelationship of the component materials.

Figure 51. Drawing. Specimen mounted between work glasses and final slide.

A cross section conceptual drawing shows a specimen that is clamped for a proposed cut along its entire length to produce a thinner section. The specimen is held by layers of glued work glass on one side and by a final well slide and trimmer chuck on the other side. A dotted line indicates the plane the saw will cut parallel to the working glass and through the impregnated specimen.

Figure 52. Photo. Concrete that increased in volume because of corrosion of aluminum fragments.

After it was cast in the cylinder mold, the concrete increased in volume as hydrogen gas evolved from the chemical reaction of aluminum (from an aluminum delivery pipe) with the alkaline fluids of the fresh cement paste. The photo shows two 150 by 300 millimeter heavy steel cylinder molds with concrete rising above the top rim of the molds. To give scale a hand is shown holding a pen on the top rim of one of the molds to show that the concrete has risen about 10 millimeters.

Figure 53. Photo. Surface of finely lapped slice of concrete containing 5.6 percent total air voids.

The concrete surface shown has many very fine air voids spaced throughout. It also has a few larger voids, including a 2 millimeter void (larger than an entrained air void), which is shown marked by a white arrow. The void is in the mortar phase, between two coarse aggregate pieces. The void content of this concrete is in the middle of the specification range.

Figure 54. Photo. Surface of finely lapped slice of concrete containing 17 percent total air voids.

The concrete surface shown can be characterized by large numbers of voids of approximately 1 millimeter diameter as well as smaller voids. The area of darker paste (lower left) has a lower void content. If an H C C contains more than one kind of paste, this generally indicates that the mixture had begun to hydrate before additional water was added. The void content of this concrete is much greater than the upper limit of the specification range. An example 1 millimeter void is shown marked with an arrow.

Figure 55. Photo. Concrete core with about 4 percent large, irregularly shaped voids.

The surface of the concrete cross section shown has irregularly shaped voids. In this instance, the concrete, which had not yet been consolidated, became hard and unworkable while repairs were being made on the paving equipment. The specimen is 100 millimeters across, and some of the large voids exceed 5 millimeters in size.

Figure 56. Photo. Partially automated linear traverse equipment for determining air-void parameters

The photo shows a stereoscopic microscope with a polished sample set on the stage. Either linear traverse or point count software can be used to control the motion of the stage and collect data. A video camera is also mounted on the microscope so that the image of the polished surface can be shown on a screen.

Figure 57. Photo. Image analysis equipment

Photo shows an assembly of video camera with magnifying lens mounted vertically and scanning a concrete slice. A computer screen in the background shows the progress of the analysis. (Photograph by R.H. Howe, courtesy of the Pennsylvania Department of Transportation.)

Figure 58. Drawing. Illustration of various sizes of sections that may be expressed on a randomly placed plane.

Drawing illustrates that the area of a plane intersecting a sphere will vary in size depending on how close it may be to the center of the sphere. The top of the drawing shows similar size spheres intersecting a plane. The spheres are located at different distances from the plane, resulting in a smaller projected area on the plane as the sphere center is gradually moved away from the plane. The bottom of the drawing shows how different size spheres can project the same area on the plane if cut by the plane at the correct distance from the sphere center, as long as the sphere is equal to or larger in diameter than the diameter of the intersected circle.

Figure 59. Drawing. Two equally spaced arrays of voids.

A drawing shows two separate arrays of spheres. The top set has small spheres; the bottom set has large spheres. Each set is arranged in seven rows across and six rows down. Each array of voids is crossed by a randomly oriented plane. There is the same number of voids in a unit area in each array. The plane touches more voids when the voids are larger than when the voids are small. Only one of the small spheres is intersected by a random plane, but four of the large spheres are intersected.

Figure 60. Photo. Void system produced by early types of high-range water reducers

The concrete surface shown can be characterized by a high number of large voids (in the 0.5 to 1.0 millimeter range). Such large voids do not add to the resistance of the concrete to cycles of freezing and thawing but do lower the compressive strength.

Figure 61.Photo A. Finely lapped slice of concrete with normal paste content:

Rounded to sub-angular quartz gravel coarse aggregate and sand fine aggregate. By visual inspection of the naked eye, the paste occupies about one-quarter of the total surface area.

Figure 62. Photo. Finely lapped slice of concrete with normal paste content

In contrast to figure 61, this photo shows angular crushed granite coarse aggregate and sand fine aggregate. In both cases, by visual inspection of the naked eye, the paste occupies about one-quarter of the total surface area.

Figure 63. Photo. Finely lapped slice of concrete with abnormal paste content: High paste content.

Photo is of high paste content with a coarse and medium sized aggregate of a fine-grained metamorphosed shale, and a fine aggregate of quartzose sand. By visual inspection of the unaided eye, the paste covers about 40 percent of the total surface area

Figure 64. Photo. Finely lapped slice of concrete with abnormal paste content:

In contrast with figure 63 this photo is of low paste content with a coarse aggregate of a granitic gneiss, and a fine aggregate of river sand. By visual inspection of the unaided eye, the paste covers about 20 percent of the total surface area.

Figure 65. Drawing. Lapped surface

Shown is a conceptual drawing of the cross section of a polished concrete surface showing a true, flat matte lapped surface, matte aggregate surfaces flat and level with the polished paste surface on the lapped concrete surface. The cross section has a smooth, neat line surface.

Figure 66. Drawing. Flaws in lapped surface.

Conceptual drawing of lapped sample cross sections is shown, each with delineated aggregate. This cross section shows two types of surface flaws caused by aggregate that is fragile. These flaws, marked A and B, interrupt the neat line on the polished surface. Flaw A is of a chipped piece of aggregate and leaves a jagged but rather planar surface on the remaining stone. Flaw B is of a complete or near complete loss of aggregate leaving a cavity shaped surface of paste exposed.

Figure 67. Photo. Knot of cement exposed on finely lapped slice.

The lapped surface shown has a knot of cement (or sometimes called a ball of cement) that can be confused with coarse aggregate. Its rounded shape was caused by tumbling in the mixer.

Figure 68. Photo. Etched slice: Etched surface on concrete fabricated with quartz sand fine aggregate.

Photo is a section of the mortar phase of concrete, and it shows the etched surface on a concrete with quartz sand fine aggregate in which the paste was undercut. The outline of the quartz sand particles is easily identified. The width of the image is 10 millimeters.

Figure 69. Photo. Etched slice: Etched surface on concrete fabricated with crushed limestone fine aggregate.

The photo can be compared to figure 68. Again this is a section of the mortar phase of concrete, and it shows the etched surface on a concrete with crushed limestone fine aggregate in which the limestone and paste were cut level. The boundary between limestone and paste is not very clear. The width of the image is 10 millimeters.

Figure 70. Drawing. Cross section of surface demonstrating problems of boundary distinction.

A conceptual drawing shows the cross section of a lapped concrete sample that was matte lapped and acid etched. The etched paste has exposed some of the aggregate below the planar matte line. Of the total exposed aggregate only the portions that are matte-lapped should be counted as aggregate.

Figure 71. Photo. Varying amounts of aggregate size fractions: concrete fabricated without larger sizes of coarse aggregate

The photo shows the surface of a concrete slice with an estimated maximum aggregate size of 13 millimeters. No larger size aggregate is present.

Figure 72. Photo. 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

The photo shows the surface of a concrete slice with aggregate as large as 40 millimeters.

Figure 73. Photocopy. Two-page Petrographic Examination of Hardened Concrete form used by the Ontario Ministry of Transportation.

The form calls for the following information:

Location: Highway, Crossing Over/Under, County Site Number, District, Region Details of Structure: Year of Construction, Contract Number, Description of Structure, Description of Deterioration/Problem Concrete Description: Concrete description is divided into seven parts.Part 1 has several categories with descriptions to check for each. They are:Hit with Hammer—oes it ring or is it dull.Break with Fingers—is it powdery, friable, or particles not dislodged.Strength—very strong, strong, weak, or very weak.During Sawing—clean cut or tears easily.Unusually West or Dry Areas—Yes or no.Cement/Coarse Aggregate Bond—Good or bad.Cement/Fine Aggregate Bond—Good or bad.

Part 2 also has several categories, some fill in, some check boxes, and table to fill in.Source (fill in).Percentage of Total (fill in).Material Type—gravel, quarried, or mixture.Shape—rounded, partly crushed, or 100 percent crushed.Distribution—even or uneven.Grading—even or uneven.Maximum Size in millimeters—10, 15, 20, 25 or fill in the blank.Preferred Orientation—present or not observed.Other—fill in

These are followed by a table to fill in the columns. The columns are labeled lithological types, percent of coarse aggregate, reaction rims/gel/fractures, and remarks.

Part 3 is Fine Aggregates with the following categories and boxes to check.Percent of total—fill in.Material type—natural, manufacture, or mixture Shape—rounded, subangular, or angular Distribution—even or uneven. Grading—even or uneven. Preferred Orientation—present or not observed. Other—fill in.

The same table described above appears after this group of information.

Part 4 is Cement Paste with the following categories: Percent of total—fill in. Appearance in Broken Concrete—substranslucent, dull, or chalky.Colour—grey, light grey, white, or blue green.Colour Distribution—even, mottled, or gradational.Strength—strong, friable, or powdery.Bleeding—observed or not observed.Carbonation—outer skin only, along fractures, partial or total.lag cement (greenish blue, greenish)—observed or not observed.Evidence of retempering—yes or no.Other—fill in.

Part 5 is Voids with the following categories:Percent of total —fill in.Grading —even, uneven,very large, well air —entrained, poorly airentrained.Interior luster—dull or shining.Interior condition—empty, lined, partly filled, or filled Percent voices with mineralization —most, about half, few, or none Mineralization —alkali—silica gel, ettringite, portlandite, or calcium carbonate.Other —fill in.

Part 6 is Cracks:Amount—frequent, occasional, or none.Continuity and Distribution —fill in.Location —through aggregate particles or around aggregate particles.Width in millimeters —fill in.Filling Material—alkali —silica gel, ettringite, portlandite, or calcium carbonate.Associate with embedded items —yes or no Other —fill in.

The last section is Embedded Items:Description —fill in.Location —fill in.Condition—clean, corroded, or decayed.Associated voids, cracks, mineralization, etc.—fill in.Other —fill in.

At the end there is a space to write conclusions followed by a signature and date line. Courtesy of Christopher A. Rogers, Ministry of Transportation, Ontario, Canada

Return to Figure73

Figure 74. Photo. Excess air at surface of concrete (top).

This cross section of a concrete core is representative of a placement in which water was added to facilitate the finishing. It shows elongated, angular coarse aggregate, which caused the mixture to be difficult to place. Angular voids are present to a depth of 10 millimeter. The deteriorated, originally finished surface is at the top of the picture.

Figure 75. Photo. Clustering of voids.

The concrete section shown has clusters of voids, probably resulting from a combination of excess air entraining admixture and incomplete mixing. Field width is 50 millimeters.

Figure 76. Photo. Overwatered concrete: Rain and snow occurring after the concrete was placed caused overwatering near the finished surface (top).

The concrete core shown has a typical 19-millimeter nominal maximum size coarse aggregate. However, the top 50 millimeter of the core is devoid of any coarse aggregate. This occurred because of rain and snow falling after the placement but before the concrete had set. The coarse aggregate sunk out of the overwatered zone leaving a top zone of mortar.

Figure 77. Photo. Cement coating on aggregate.

A polished surface of concrete shows a piece of coarse aggregate that is coated with cement that is not hydrated. This occurred because the aggregate was damp and came in contact with dry cement. This layer is much denser than the zone surrounding the aggregate in figure 54

Figure 78. Photo. Fly-ash particles on surface of lapped slice of concrete

. Photo shows the magnified surface of a lapped slice. Fly-ash particles can be recognized by their glassy interiors. They are generally rounded and about one-quarter millimeter or smaller in size. The photo points out the lighter colored particles with arrows and encircles the black colored ones. Etching the slice would reveal even more fly-ash particles.

Figure 79. Photo. Cracks at bond between aggregate, rebar, and paste

On a polished cross section slice of concrete, arrows point to cracks and voids at component interfaces. In this instance, the bond cracks occur most frequently on the underside of the aggregate and rebar, and therefore, can probably be attributed to bleeding or poor consolidation. The specimen is 100 millimeters in width.

Figure 80. Photo. Cracks typical of damage caused by cycles of freezing and thawing.

Three polished concrete cross section slices are shown with cracks emphasized in ink. The cracks are quite visible (about 1 millimeter thick) and typically found in non-air-entrained concrete that has been exposed to freezing and thawing and often to deicers as well in a wet-freezing environment. Such cracks tend to be parallel to each other and parallel to the surface or joint where moisture and deicing salts may be available to cause critical saturation.

Figure 81. Photo. View A. Microcracks: Smoothly lapped surface with ink-marked microcracks

This view is of a smoothly lapped surface with ink marked microcracks generally going in random directions.

Figure 82. Photo. View B. Microcracks: Wearing surface (B) near figure 81.

The cracks were followed over the edge of the slice. The crack pattern seen in view A was used to guide the finding of the cracks in view B. A careful study of these views shows that the two crack patterns are related. The specimen is 100 millimeters in diameter.

Figure 83. Photo. Finely lapped surface of beams tested for resistance to cycles of freezing and thawing.

This lapped surface is closely related to the one shown in figure 84 on the same page. Each one is approximately 25 by 50 millimeters. Both have been marked with ink to establish boundaries on portions of interest. The cracks have been marked as well. This section shows fewer cracks than figure 84 with an experimental admixture.

Figure 84. Photo. Finely lapped surface of beams 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.

This lapped surface is closely related to the one shown in figure 83 on the same page. Each one is approximately 25 by 50 millimeters. Both have been marked with ink to establish boundaries on portions of interest. The cracks have been marked as well. This sample contains an experimental admixture that caused a greater number of cracks, particularly around aggregate particles.

Figure 85. Photo. Lapped surface of slice of concrete containing prestressing strand.

The cracks on the slice are marked, and they radiate from the perimeter of the cross section of the prestressing strand. These cracks were visible with the stereomicroscope, but the relationship of all of the cracks to the reinforcing cable could not be noted until the cracks had been marked and the crack pattern examined without magnification. The field of view (the portion of the slice) seen at the magnification necessary for observation of the fine crack system is about the size of one wire of the cable.

Figure 86. Photo. Cracking just below bond in concrete deck with latex-modified concrete overlay.

The slice of concrete shown is a cross section of concrete bridge deck with a stratum of latex-modified concrete overlay placed above a substrate of normal concrete. Cracking has formed, not exactly at the strata boundary but slightly below it. Also, a vertical crack in the substrate continues through the latex concrete and up to the wearing surface. The specimen is 100 millimeters in width.

Figure 87. Photocopy. Sheet used in V T R C stereomicroscopy photograph notebook.

Form included here to show an example of the information about photos taken through the stereomicroscope that may be helpful to record. Information to be completed includes: photomicrographic data sheet number, date, film roll number, frame number, film type and speed, as well as other information as desired concerning the camera and microscope settings. Also recorded is the specimen identification, and a space is provided to draw a sketch of the object or feature photographed. At the bottom there are several places to complete information about the photo settings if needed.

Figure 88. Photo. Specimen treated with phenolphthalein (high-alkalinity, uncarbonated paste stains pink; carbonated paste does not stain).

The photo is a magnified view of a specimen treated with phenolphthalein. The lower half has stained pink due to its contents. The upper half contains carbonated paste and did not stain. The specimen is a vertical cross section through concrete with the exposed top surface at the top of the photo.

Figure 89. Photo. Specimen from retaining wall with destructive A S R treated with uranyl acetate: Ordinary light.

See description for figure 90.

Figure 90. Photo. Specimen from retaining wall with destructive A S R treated with uranyl acetate: Ultraviolet illumination causes silica gel to fluoresce (darkroom photograph).

The two views in figure 89 and 90 show a concrete slice treated with uranyl acetate figure 89 is under ordinary artificial light and displays no particular visual effect. The same section in figure 90 is under ultraviolet illumination and much of the surface fluoresces showing an iridescent blue color.

Figure 91. Photo. Polished specimen treated with sodium cobaltinitrite, which stains potassium-bearing compounds yellow.

The portions of the specimen surface that contain potassium-bearing compounds are shown stained yellow by the sodium cobaltinitrite treatment.

Figure 92. Photo. Fractured surface treated with barium chloride—potassium permanganate (secondary deposits containing sulfate are stained pink).

A closeup of a mortar section from concrete is shown with several linear features stained pink. The features are about a millimeter wide and several millimeters long.

Figure 93. Drawing. Idealized sketch of crack pattern in concrete mass caused by internal expansion due to A A R.

. A conceptual drawing shows a concrete cube with cracks. The cracks on the surface are not parallel to either side of the cube and form a random map-cracking pattern due to the volume near the surface expanding less (or even shrinking) compared to the volume deeper in the concrete where A A R expansion is active.

Figure 94. Photo. Map cracking with preferred longitudinal trend in continuously reinforced concrete pavement.

The surface of the concrete structure shown has cracks that are parallel with its length showing that the concrete has expanded transversely but not longitudinally.

Figure 95. Photo. Typical destructive A S R in plain or lightly reinforced pavement.

Photo shows the surface of a concrete slab with significant transverse and map cracking. To provide a perspective on the spacing of the cracks, a cigarette pack rests on the slab. A typical spacing between cracks is less than 50 millimeters.

Figure 96. Photo. Destructive A S R in anchor block.

. Photo shows a massive concrete anchor block for support cables that has experienced significant cracking in random directions.

Figure 97. Photo. Cracking of pavement due to A C R.

Photo shows a portion of the surface of a slab with a construction joint (or gap) separating two parts. Cracking has formed throughout the slab. The cracks are irregular in shape and pattern, except near the construction joint where they approach perpendicular to the joint.

Figure 98. Photo. Upper portion of back wall sheared by expansion of bridge deck.

The upper portion of a bridge abutment wall is sheared by expansion of the bridge deck.

Figure 99. Photo. Expanding median barrier crushes itself.

Expansion caused by A S R of quartzose coarse aggregate caused a median barrier to crush itself. A large crushed concrete zone with a diagonal crack is shown in a Jersey-type median barrier. Other random cracking due to A S R is present as well.

Figure 100. Photo. Closing of joint caused by bridge deck expansion as a result of A C R.

The photo shows an engineer measuring the relative positions of each side of the joint at the end of a concrete bridge deck.

Figure 101. Photo. Bridge deck.

Photo shows the surface of a concrete deck with cracking.

Figure 102. Photo. Extracted core.

The photo shows a concrete core extracted from the deck. The core is positioned vertically and shows the profile of a crack, which is about 60 millimeters deep. Damaged coarse aggregate particles are situated in the area of the crack and below. This aggregate is quartzose gravel susceptible to A S R.

Figure 103. Photo. A S R in longitudinally reinforced pavement constructed with dark metabasalt aggregate.

This figure shows an irregular pattern of cracks on the surface of a concrete slab.

Figure 104. Photo. A S R in longitudinally reinforced pavement constructed with dark metabasalt aggregate: 100-millimeter diameter core that fractured on this surface upon removal from the pavement.

The photo shows the surface of a concrete section cored from the same slab in figure 103. There is a dried, white deposit around each piece of aggregate.

Figure 105. Photo. Fractured face of splitting tensile specimen is shown with the coarse aggregates visible on the fractured surface. Aggregate fracture and deterioration as well as secondary deposits can be seen.

Figure 106. Photo. Destructive A S R in pavement.

The view is of a pavement with pattern cracks throughout the photo.

Figure 107. Photo. Destructive A S R in pavement: Alkali-silica gel in a 2-millimeter void in a lapped slice from the pavement in figure 106 (dark aggregate is siltstone).

This view is of a magnified lapped slice from the pavement in figure 106 and shows alkali silica gel in a 2 millimeter void. That void is rounded and appears white in the photo. It is contained in the mortar with dark coarse aggregate particles nearby.

Figure 108. Photo. A S R damage expressed on lapped slab (cracks highlighted in yellow, deposits of reaction products highlighted in red).

The lapped surface shows some cracks around the perimeter of coarse aggregate, while others cut through coarse aggregate. Reaction products are present in about a dozen locations throughout the paste.

Figure 109. Photo. Lapped surface showing type of aggregates and A S R products.

The surface includes the following: a 25-millimeter diameter light brown quartzite coarse aggregate particle with black streaks; a 19-millimeter black chert aggregate. Alkali-silica gel is visible in white deposits in pockets up to 13 millimeters in size as well as within small cracks.

Figure 110. Photo. Lapped surface of specimen affected by A C R rim and areas of altered paste

Darkened rims on the coarse aggregate particles extend from the aggregate edges to 2 or 3 millimeters into the particles.

Figure 111. Photo. Paste cracking and alteration of paste.

A crack is shown along the perimeter of a coarse aggregate and one also through the paste.

Figure 112. Photo. Lapped surfaces of A C R specimens showing aggregate cracking and alteration of paste.

The photo shows a magnified view of a section of dark coarse aggregate with mortar on one side. The texture of the aggregate is extremely fine-grained.

Figure 113. Photo. Internal cracking of aggregate particle.

The photo shows a magnified view of a section of dark coarse aggregate. The texture of the aggregate is extremely fine-grained.

Figure 114. Photo. Thin section showing void containing crystallized A S R product

A crack and A S R product in an air-void are shown in the magnified view.

Figure 115. Photo. Thin section prepared from concrete sample showing aggregate crack

in one of the aggregate particles as observed through a petrographic microscope.

Figure 116. Photo. Thin section in plane polarized light.

The reaction product exhibits birefringence. Voids appear bright white and any crystallized A S R products within them stand out clearly.

Figure 117. Photo. Thin section with crossed polars.

The voids and A S R products can be distinguished with some effort.

Figure 118. Photo. Backscattered electron image of A S R-damaged concrete.

In a magnified view of a concrete lapped surface, a crack filled with reaction product extends from within a coarse aggregate particle through mortar.

Figure 119. Photo. Optical image of lapped section showing A S R product associated with damaged chert particles.

Under conventional lighting a void in the mortar filled with reaction product stands out in bright white. Other features around it include mortar with distributed fine aggregate and cracks running to and through coarse aggregate particles nearby.

Figure 120. Photo. Similar feature in backscattered electron image and associated E D X elemental plots for potassium, silicon, and calcium.

The void is seen in varied colors for the different elements shown, and other features around the void stand out as well.

Figure 121. Photo. Thin section of A C R rock (lower left of image) and adjacent altered paste in plane polarized light.

In the plane polarized light, the adjacent altered paste is seen in bright white circles and streaks that border the A C R rock.

Figure 122. Photo. Thin section of A C R rock (lower left of image) with crossed polars.

In the crossed polars view the same circles and streaks are seen in black with a white fragmented border.

Figure 123. Photo. Backscattered electron image of polished thin section showing area of altered paste adjacent to A C R rock in lower left.

The altered paste is seen in patches of gray bordering the A C R rock.

Figure 124. Photo. Thin section of fracture in A C R rock at low magnification.

In two separate views (figures 124 lower magnification and 125 higher magnification) the fracture in the rock is seen as a hollow, dark streak.

Figure 125. Photo. Thin section of fracture in A C R rock at high magnification.

In two separate views (figures 124 lower magnification and 125 higher magnification) the fracture in the rock is seen as a hollow, dark streak.

Figure 126. Photo. Backscattered electron images of outer rim of reacting A C R rock.

There are two magnified views (figures 126 and 127), each approximately 50 by 70 microns. Figure 126 shows a spot within the boundaries of the actual rim.

Figure 127. Photo. Interior of same reacting A C R rock particle.

The photo is figure 126 but it is within the interior of the particle. At this magnification, the color tones differ slightly. While both are primarily of light and medium gray, the view of the rim shows a greater number of black patches.

Figure 128. Photo. Powder mount of A S R product in plane polarized light.

Shown are light colored crystalline-looking particles on a light gray background. Birefringence is exhibited with crossed polars and is indicative of developing crystallinity. Compare figures 128 and 129, which are of the same material.

Figure 129. Photo. Powder mount of A S R product in crossed polarized light.

Compare figures 128 and 129, which are of the same material. Shown here are light colored translucent particles on a very dark background. Birefringence is exhibited with crossed polars and is indicative of developing crystallinity.

Figure 130. Photo. Polished specimen treated with sodium cobaltinitrite solution.

Potassium in secondary deposits in void and paste are stained yellow.

Figure 131. Drawing. Integration of field observations with laboratory investigations.

Shown is a diagram with two text boxes. The top one is for field observation rating and states Features: extent, severity. The bottom box is for the laboratory investigation rating and states: Damage: extent, severity; aggregate involvement; mechanisms involvement. Large arrows from each of these boxes point to a third diamond-shaped box showing some example conclusions from an investigation: damage extent, severity; aggregate involvement; identify mechanisms involved; apportion responsibility to mechanisms

Figure 132. Photo. Immersion mount of portland cement in plane polarized light showing alite crystals.

This image shows alite crystals. The only portion of these crystals that stands out clearly is their outline

Figure 133. Photo. Immersion mounts of belite cluster with darker interstitial aluminate and ferrite.

CThis image is of a belite cluster with darker interstitial aluminate and ferrite that stands out sharply

Figure 134. Photo. Immersion mount of fly ash showing spherical particle shape.

The fly ash particles are spherical.

Figure 135. Photo. Immersion mount of agglomerate of minute silica-fume particles.

The silica-fume particles are very small and agglomerated.

Figure 136. Photo. Immersion mount of natural pozzolan (calcined shale).

The natural pozzolan is about 35 micrometers on its longest dimension and has very dark spots. Other small particles are present as well.

Figure 137. Photo. Immersion mount of slag.

Slag particles are up to about 25 micrometers in longest dimension and appear rather translucent and glassy.

Figure 138. Photo. S E M images illustrating the size difference of various cementitious material particles.

The four views include cement, fly ash, silica fume and ultra-fine fly ash. The cement particle has rough edges and measures about 15 micrometers in its longest dimension. The fly ash particles are essentially spherical with diameters ranging between 8 and 20 micrometers. The ultra-fine fly ash particles are also spherical with diameters ranging from a fraction of a micrometer to about 3 micrometers. Silica fume particles are smaller than 1µm and appear irregular shaped and somewhat agglomerated.

Figure 139. Photo. Cut surface on H C C containing slag exposed to air for 6 months.

In this view, the paste is of a uniform color.

Figure 140. Photo. Interior of beam of H C C containing slag, illustrating the partially dry two color stage.

. In this view, the majority of the paste is dark greenish gray while a small section on the top is a lighter beige color.

Figure 141. Photo. Thin section of concrete containing slag: At 28 days hydration (note the angularity of the slag fragments).

Compare figures 141–143. In all the slag concentration is 65 percent of the cementitious material.

Figure 142. Photo. Thin section of concrete containing slag: At 56 days hydration (note the slight rounding of the slag fragments).

Figure 143. Photo. Thin section of concrete containing slag: At 6 months hydration (note the further rounding of the slag fragments).

Figure 144. Photo. Etched area of lapped surface of concrete containing fly ash.

Partial fly-ash particles are pointed out in the photo and categorized in three types. A frothy fly-ash agglomeration is hazy white. Cenospheres filled with froth or many cenospheres are small black circles. Cup shaped portions of cenospheres are white circles with black in the concave center.

Figure 145. Photo. Fly ash in thin section of H C C, viewed in plane polarized light with a petrographic microscope (note the broken fly-ash particle that is composed of dark and light glass, magnified 100 times).

Figure 146. Photo. Fly ash in thin section of H C C, viewed in plane polarized light with a petrographic microscope (cenospheres of fly ash filled with smaller circular cenospheres, magnified 400 times).

Figure 147. Photo. Petrographic microscope.

On this microscope, the stage positioning is manually operated. The nosepiece holds three objective lenses. Light can be transmitted up from the bottom through thin translucent specimens, which can be observed through the eyepieces, or a picture can be taken using the camera mount on top.

Figure 148. Schematic. Light paths and features of the P/ E F microscope.

The schematic shows 15 components of the P/ E F microscope: 1. Camera back, 35 mm; 2. automatic exposure meter; 3. binocular tube; . analyzer and Bertrand lens; 5. dichroic mirror and barrier filter selector; 6. light shield; 7. point counter stage; 8. rotating stage that can be centered; 9. polarizing condenser; 10. auxiliary lens system; 11. swing out mount for B G-12; 12. stand modification; 13. mercury burner, 200 Watts, for incident illumination; 14. exciter filter turret; and 15. halogen light for transmitted illumination. It also shows the path of the three types of illumination. The combined illumination can be viewed from both the binocular tubes in front of the microscope and the exposure meter/camera on the top. The incident illumination enters from a mercury burner in the back and joins the transmitted illumination at the objective lens. The transmitted illumination enters from a halogen light built in the lower back. This light goes through the polarizing condenser. Located below the stage mount and meets the other light stream at the stage mount.

Figure 149. Photo. P/ E F microscope.

The microscope is positioned in the center of the photo. In the right foreground are two pushbutton counters. The camera and exposure meter are on top of the microscope. The control for the exposure meter is between the microscope and the automatic point counter keyboard in the left background.

Figure 150. Graph. Relationship of filters to dye emittance spectrum.

A graph with wavelength (nanometers) from 400 to 650 on the horizontal X axis and percent transmitted on the vertical Y-axis from 0 to 100 percent. It shows the relationship of the filters B G-12, D M-455, and Y-495 to the florescent dye emittance spectrum. The fluorescent light is shown coming from above. The fluorescent dye starts at 30 percent transmitted at 400 nanometers. The line dips to 12 percent at 475 nanometers then rises sharply to its peak of100 percent at 530 nanometers. The line declines to 55 percent where it leaves the chart at 650 nanometers. B G-12 starts 400 nanometers at 62 percent transmitted and declines at an even rate to 0 at 480 nanometers. By contrast, both the D M-455 and Y-495 rise with nearly parallel ascents starting at different wavelengths. The D M-455 starts at 410 nanometers and the Y-495 starts at 460 nanometers. The D M-455 peaks at 85 percent transmitted and the Y-495 peaks slightly higher at 91 percent. The D M-455 gradually descends to 78 percent and then rises again steadily to exit the graph at 89 percent at 650 nanometers. The Y-495 does not waver and maintains the 91 percent transmitted all across the chart.

Figure 151. Photo. Swing-out filter over light port on base of microscope.

A filter holder fabricated in the V T R C shop is mounted so it can swing over the light port.

Figure 152. Drawing. Cracks in the thin section of the concrete.

The drawing is of a cross section of a thin section on a glass mount and under an objective lens. The thin section has a crack through the paste that runs through the thickness of the thin section and is perpendicular to the surface. Only a crack in this position is visible with transmitted illumination. Conversely, impregnation with a fluorescent dye and illumination with ultraviolet light would make possible the observation of the fluorescence of the dye in the other cracks, regardless of their positioning. The thickness of the concrete thin section is shown as 0.015 millimeter.

Figure 153. Photo. Fluorescence from porous clay pocket shining through edge of quartz particle.

The photo is at high magnification. Paste is seen as cloudy white and approximately 15 by 40 micrometers. A clay pocket bordering the paste particle is a cloudy gray and slightly bigger. Quartz aggregate, seen as black, surrounds both the paste and clay pocket on three sides and covers most of the surface area of the photo. The focus plane is within the section. The reference cited is Walker, 1981.

Figure 154. Photo. Void in thin section with focus plane on top surface of section.

A thin section is shown at two different planes of focus (figures 154 and 155) with the same magnification. One is focused on the top surface of the section, the other on the bottom surface. Each view accentuates different features of the section.

Figure 155. Photo. Void in thin section (same as figure 154) with focus plane on bottom surface magnified 100 times.

A thin section is shown at two different planes of focus (figures 154 and 155) with the same magnification. One is focused on the top surface of the section, the other on the bottom surface. Each view accentuates different features of the section.

Figure 156. Photo. Thin section of exterior portion of H C C: Surface exposed to the air is at the top.

Three views of the thin section are shown in figures 156 to 158. This figure 156 is of the surface exposed to the air at the top.

Figure 157. Photo. 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. Photo. Same view as figures 156 and 157, but viewed with ultraviolet light, causing fluorescence of the pore structure of the H C C (note that there is more porosity indicated by fluorescence in the portion of the H C C farthest from the surface than there is in the carbonated zone).

Figure 159. Photo. Thin section of interior portion of H C C: Viewed with crossed nicols (bright area shows the high birefringence of the calcite of the carbonated area).

Figure 160. Photo. Thin section of interior portion of H C C: Same area as figure 159, but viewed with ultraviolet light causing fluorescence of the pore structure within the carbonated area.

Figure 161. Photo. 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).

This photo is with plane polarized illumination under which the particulars do not stand out very vividly. At the center is the remnant of a very large cement grain. Modern cement is usually smaller. The arrow is pointing to a small cement grain in relation to the large grain, which is about 25 times larger.

Figure 162. Photo. Same location as figure 161, but viewed with crossed nicols. Note the original birefringence still present in the unhydrated central portion of the large cement grain.

Figure 163. Photo. 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).

The ultraviolet light causing fluorescence of the dye allows the original external boundary of the cement grain to be seen more clearly.

Figure 164. Photo. Thin section of 25-year-old concrete viewed with plane polarized light.

The cement grains here are completely hydrated. Some cement grain centers are empty. Others contain secondary mineralization.

Figure 165. Photo. View of the section in figure 164 with incident ultraviolet illumination, causing fluorescence of the dye-filled space.

Figure 166. Photo. Thin section of H C C made with smooth, rounded sand.

View with plane-polarized light reveals much of the texture of the fine aggregate and paste.

Figure 167. Photo. Thin section of H C C made smooth, rounded sand: same view as figure 166, but with ultraviolet illumination, causing fluorescence in the pore structure impregnated with dye. There is an even texture of the paste.

In comparison to this photo, figure 166 has the effect of neutralizing the internal fine aggregate texture, but it does add fluorescence in the pore structure of the paste that is impregnated with dye showing an even texture of the paste with dark specks in a gray matrix

Figure 168. Photo. Thin section of H C C made with angular, dirty sand.

There are numerous reentrant angles. The thin section is viewed with plane-polarized lighting that shows the texture of the components.

Figure 169. Photo. Thin section of H C C made with angular, dirty sand: same view as previous figure, but with ultraviolet illumination, causing fluorescence that delineates the pore structure.

With ultraviolet illumination of the same section shown in figure 168, the fluorescence delineates the pore structure in the paste. The clumping of the cement grains, abundance of pores (shown by the fluorescence) at the edge of the sand, structure of the clay coatings, and general uneven texture of the paste are noticeable. Such uneven texture indicates zones of weakness through the H C C.

Figure 170. Photo. Thin section of porous, iron-stained particle of sand: Viewed with plane polarized light.

Figure 171. Photo. Thin section of porous, iron-stained particle of sand: Viewed with incident ultraviolet illumination.

In this photo, the incident ultraviolet illumination causes fluorescence of the dye in the pore structure of the sand grain and indicates a zone of water accumulation (a cause of weakness). This cannot be seen in the plane polarized light view in figure 170.

Figure 172. Photo. Page from V T R C P/ E F photomicroscopy notebook.

Picture of a form used by V T R C in their photomicroscopy notebook. It is titled, “Photomicrographic Data Sheet,” with spaces to fill in the appropriate information about the specimen or section being photographed, the camera and microscope settings, and the lighting conditions for the photograph. The form is included here to show an example of the information about photos taken through the petrographic microscope that may be helpful to record. Information to be completed include: photomicrographic data sheet number, date, film roll number, frame number, film type and speed, as well as other information as desired concerning the camera and microscope settings. A space is provided to draw a sketch of the view of object or feature photographed. At the bottom there are several places to complete information about the photo settings if needed

Figure 173. Photo. Scanning electron microscope.

The equipment includes a computer station with two monitors and various controls surrounding the keyboard in the foreground and the electron column, specimen chamber, and X-ray detector in the background.

Figure 174. Photo. S E image showing platy or foil-like C S H, fine bundles of C S H fibers and platy C H.

Image shows the plate-like C H morphology and fine fiber like bundles of C S H.

Figure 175. Photo. S E image showing platy C H and ettringite needles and also plate-like C H morphology.

Figure 176. Equation. Equation to estimate backscatter coefficient from Goldstein, et al. (1992).

The backscatter coefficient (eta) is equal to negative 0.0254 plus 0.016Z minus 1.86 times 10 to the negative 4 times Z squared plus 8.3 times 10 to the negative 7 times Z cubed.

Figure 177. Equation. Equation to estimate the backscatter electron coefficient (eta) of a multielement phase.

Eta is equal to the sum of the products of all the individual constituent eta values multiplied by the mass fraction of that constituent.

Figure 178. Equation. Equation to calculate contrast between constants.

C equals the produce to eta sub 2 minus eta sub 1 divided by eta sub 2.

Figure 179. Photo. Stereomicroscope image.

The stereomicroscope, at low magnification, shows the colors of each component, but not so much the texture.

Figure 180. Photo. Backscattered electron image.

At a slightly higher magnification, the backscattered electron image of the same specimen as that shown in figure 179 is black and white and shows more of the texture.

Figure 181. Photo. Secondary electron image of a fresh-fracture surface from concrete.

The secondary electron image is also in black and white, but at much higher magnification and shows minute details of the fracture such as cavities where small aggregate particles were dislodged.

Figure 182. Photo. Top. Paired images at successively greater magnification of stereomicroscope (white light) images and S E M B E images.

The three pairs, in this pair and the next two figure pairs, have field widths of 11 millimeters, 3 millimeters, and 1.5 millimeters respectively.

Figure 183. Photo. Middle. Field width is 3 millimeters.

In each of the three pairs (figures 182, 184, and 184) the S E M B E images show greater texture and clarity than the stereomicroscope images.

Figure 184. Photo. Bottom. Field width is 1.5 millimeters.

The difference becomes more pronounced at the higher magnification, where the conventional stereomicroscope image is cloudy.

Figure 185. Photo. Backscattered electron image of an epoxy-impregnated, polished cross section of concrete (field width is 2 mm).

Image at high magnification shows the particulars of residual cement, calcium hydroxide, two forms of calcium-silicate-hydrate, inner-product and outer-product as well as aggregate.

Figure 186. Photo. Backscattered electron image of an epoxy-impregnated, polished cross section of concrete (field width is 1 millimeter).

Image of a close up of figure 185 at higher magnification, show the more detail of residual cement, calcium hydroxide, two forms of calcium-silicate-hydrate, inner-product and outer-product as well as aggregate.

Figure 187. Graph. E D X spectrum.

On a graph called an energy-dispersive X-ray spectrum (E D X), peak positions along the horizontal axis are specific to a particular element; the intensity (height on the vertical axis) is proportional to its relative abundance. The graph shown, from ettringite, has three high peaks in increasing order and a smaller peak on either side of the trio. This spectrum exhibits that mineral’s characteristic composition with oxygen, aluminum, sulfur, and calcium.

Figure 188. Graph. E D X spectra for ettringite (top left graph), monosulfate (top right graph), calcium hydroxide (bottom left), and calcium-silicate-hydrate (bottom right) aid in phase identification characteristics.

Example of actual E D X output patterns. The lower horizontal axis is in kiloelectronvolts (shown as K E V on the output). It is the voltage energy of the individual electrons shown as a spectrum of the intensity at different kiloelectronvolts. Each element has characteristic spectra at particular kiloelectronvolt fluorescence energy. The symbols at the peaks are the symbols for the individual elements represented at that K E V level: C (carbon), C A (calcium), O (oxygen), F E (iron), A L (aluminum), S I (silicon), and S (sulfur).

Figure 189. Photo. Fence diagram created by collecting a series of E D X spectra along an emplacement of A S R gel

A graph shows the amount of calcium, silicon, aluminum, and potassium between two spots on a magnified section. The gel composition rapidly becomes much like the bulk C S H once outside the aggregate and source of reaction. The figure shows a picture (below the graphical diagram) of an A S R-filled void in a concrete section with the spots number 1 and number 10 shown.

Figure 190. Photo. Plots of element spatial distribution are generated through X-ray imaging.

Nine images labeled A L K, S I K, C A K, S K, T I K, K K, M G K, O K, and R T 64 Pavement, show a variety of patterns and colors. All nine images are of the section of concrete (Route 64 pavement) with each showing by color intensity the relative amounts of the following elements, with each element having its own color: aluminum, silicon, calcium, sulfur, titanium, potassium, magnesium, oxygen.

Figure 191. Graph. Effects of different accelerating voltage on X-ray spectra of ettingite show loss of low-energy peaks at high accelerating voltages and the opposite effect at low voltages.

This graphical diagram shows the typical peak pattern for ettringite. At lower-accelerating beam voltages 6 and 12 K E V (kiloelectronvolts), the low-energy kilo electron volts X-ray peaks at the left side of the horizontal axis are higher and the high-energy peaks lower. The reverse is true for higher accelerating voltage.

Figure 192. Photos. B E images of unimpregnated, sawed surfaces.

Two photos show the sawed surface is rough with residual particulate matter, yielding poor contrast and shadowing that make interpretation of B E and E D X images difficult. The top picture is at a lower magnification image than the bottom picture.

Figure 193. Photos. BE images of the impregnated, polished surfaces from same concrete.

The same concrete in figure 192 now shows polished surfaces that present optimum B E and E D X imaging characteristics. The top picture is at a lower magnification image than the bottom picture.

Figure 194. Photo. Polished section of hardened portland cement paste imaged using the B E signal clearly shows the constituent phases.

In the top image, the residual cement (R C) appears brightest, followed by C H, C S H, and other hydration products. The E D X images (bottom four images in the figure) show regions of intermediate-intensity calcium (blue), intermediate-intensity aluminum (purple) and high-intensity sulfur (yellow) defining locations of monosulfate that could not be distinguished on a rough surface. The field width is 73 microns.

Figure 195. Equation. Equation for percent error in the point-count method (at the 96-percent confidence level) based on the proportion of points on the phase of interest and the total number of all points counted.

The absolute error in percent (lower case delta) equals 2.0235 times the square root of the product of P times the product of 100 minus P, all divided by N.

Figure 196. Photo and Graph. B E image of carbonate aggregate composed of darker gray dolomite rhombs in fine-grained matrix containing lighter gray calcite.

. The gray-level intensity of calcite and dolomite is distinct, and they can also be distinguished on the basis of E D X spectra (shown in the graph) where the dolomite shows a large magnesium peak and the calcite does not. Field width approximately 100 microns.

Figure 197. Photo. B E image of carbonate aggregate in concrete magnified 15 times.

Uniformity and shape are useful in distinguishing carbonate aggregate from a mortar matrix that contains phases of similar gray-level intensity.

Figure 198. Photo. B E image of carbonate aggregate in concrete magnified 400 times.

This photo is the same as figure 196 but more highly magnified, Again, uniformity and shape are useful in distinguishing carbonate aggregate from a mortar matrix that contains phases of similar gray-level intensity.

Figure 199. Graph. Gray-level histogram of hardened cement paste.

The graph shows the spectrum of number of pixels up the left-hand vertical axis in relation to the gray level in the image, along the lower horizontal axis where the range is from zero (for black) to a maximum of 255 (for white), for a hardened cement paste.

Figure 200. Photo. BE image of hardened cement paste.

The photo corresponds to the graph in figure 199.

Figure 201. Photo and Graph. Pseudocolored image.

The image is based on B E gray scale of figures 199 and 200 showing residual cement as red, C H as blue, C S H as black, and coarse porosity as green. The graph below shows the pixels for each color. Counting the number of pixels for each color allows an estimate of the phase area fractions for this field of view.

Figure 202. Photo. Processing of B E and calcium X-ray images here highlights the C H location.

Four X-ray images are shown. Analysis of the binary image of C H distribution calculated 12 percent of the image field to be occupied by C H.

Figure 203. Photo. Giant popout caused by a piece of glass.

The surface diameter is about 20.4 centimeters. Accompanying it are several small popouts of a more usual size (about 3.8-centimeters surface diameter) caused by porous chert particles.

Figure 204. Photo. Glass particle.

The photo shows the glass particle that caused the giant popout in figure 202.

Figure 205. Graph. Effect of concrete temperature, air temperature, wind velocity, and relative humidity on the rate of evaporation of surface moisture from a concrete surface.

This is a reproduction of the classic A C I nomograph chart for estimating the rate of evaporation from freshly placed concrete based on the air temperature, the relative humidity of the air, the concrete temperature, and the wind velocity.

Figure 206. Photo. Shaley particle shape of crushed slate aggregate.

Several coarse aggregate particles of a crushed slate are shown. They are gray and rather flat and angular.

Figure 207. Photo. Aggregate particles from a fissile gneiss.

Each aggregate has a rough and porous surface. A particle shape such as this can cause a high water demand.

Figure 208. Graph. Mohs comparative hardness scale.

The scale plots 10 materials in sequence from least to greatest hardness. They are talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum and diamond. The first nine material names fall along a rising straight line. The much steeper line between the last two (corundum and diamond) shows the step to the mineral diamond as being much more than the other increments because diamond is much harder. The graph also makes reference to five common methods of scratching materials: fingernail is positioned between talc and gypsum; penny is between gypsum and calcite; knife and window glass are in sequence between apatite and orthoclase; and a steel file is between orthoclase and quartz.

Figure 209. Photo. Cubic habit, brassy yellow color, metallic luster of pyrite.

In this magnified view, the cubic pyrite stands out in an earthy yellow from the other formations around it.

Figure 210. Photo. Granite aggregate exhibiting cleavage traces at right angles in orthoclase and no cleavage in quartz.

The portion with cleavage has a rippled surface. The other portion has smooth surface. Scratch test with metal tool leaves metal on both quartz and orthoclase, which are harder than the metal.

Figure 211. Photo. Metal tool scratches upper limestone (calcite) aggregate and leaves metal on lower quartzite particle.

A section of concrete is shown with a piece of limestone coarse aggregate, a piece of quartzite coarse aggregate, and air-entrained mortar between the two larger aggregate particles.

Figure 212. Photo. Immersion mount of chert in plane polarized light.

Here small particles of the mineral chert are immersed in a liquid of a selected index of refraction, mounted between glass slides, and light is passed through the specimen and observed using a petrographic microscope.

Figure 213. Photo. Immersion mount of chert with crossed polars, showing microcrystalline texture.

The crossed polars darkens most of the object but accentuates certain crystals. Refractive index matches that of quartz.

Figure 214. Photo. Thin section of marble (calcic schist) in plane polarized light.

Here light is passed through a very thin section of rock, showing the individual mineral grains and their relative color and shape.

Figure 215. Photo. Thin section of marble (calcic schist) in crossed polarized light.

This photo is the same as figure 213. There are elongated quartz grains (white-gray in polarized image) set apart from the predominant calcite crystals by their low birefringence and high negative relief. Undulose extinction of quartz seen in the plane polarized light image indicates strain of crystal and suggests increased susceptibility to A S R.

Figure 216. Graph. Quantitative X R D analysis to determine mineral composition of aggregate shown in figures 182, 183, and 184.

This is an example of the output graph that shows percentages of anorthite, augite, albite, hornblende, epidote, chlorite, and quartz. The phase concentration is proportional to the phase pattern intensity.

Figure 217. Photo. Coupling the knowledge of the mineral present (figure 215) with the elemental E D X maps.

The E D X maps are shown here, which are related to figure 215 differentiate between silicon, sodium, aluminum, potassium, magnesium and titanium. This allows one to identify the minerals present at specific locations within the fine-grained rock.

Figure 218. Photo. Thin section of strained quartzite.

The photo is a magnified view using crossed polars. It consists of jagged patches of white and black in several bands. The white patches are predominant.

Figure 219. Photo. Alkali-reactive microtexture in four carbonate rocks.

Four magnified images show the typical texture and spacing between individual crystalline phases in reactive A C R rock.

Figure 220. Photo. Nonreactive microtextures of carbonate rocks.

Two magnified images show the difference between individual crystalline textures and the partially crystalline reactive textures shown in figure 218. They are close together with little or no fine material or spacing between them.

Figure 221. Photo. D-cracking of a pavement due to destruction of the aggregate by cycles of freezing and thawing.

Photo shows the surface of a concrete slab that has two joints (gap or spacing) crossing each other perpendicularly. D-cracking is present. This cracking is parallel with each joint and wraps around at their juncture.

Figure 222. Photo. Pavement surface with a flaw (a popout) caused by freezing and thawing of water trapped in the aggregate particle.

A portion of the concrete surface has popped out. The resulting hole is conical shape about the size of a pocketknife with folded blade.

Figure 223. Photo. Traffic-worn rounded surface of feldspar aggregate particle.

A magnified view of pavement surface centers on a 5-millimeter aggregate particle. The surface of the particle is rounded and almost polished. This surface will not provide good skid resistance.

Figure 224. Photo. Traffic-worn surface of granite aggregate particle.

A magnified view of pavement surface centers on a 6-millimeter aggregate particle. It has zones of weakness to provide an irregular skid resistant surface. This surface is good for skid resistance.

Figure 225. Photo. Lapped slice of H C C containing expanded-shale lightweight aggregate.

The aggregate particles on this specimen are highly porous.

 

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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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