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

Chapter 2. Equipment, Materials, and Environment

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2.1 OVERVIEW

In this chapter, brands and makes of equipment are not specified; rather, the function of the equipment and the reason the equipment is required are described and explained. The successful operation of a petrographic laboratory is dependent on the skill, knowledge, and judgment of the petrographers and petrographic technicians, and the quality, sufficiency, and operating convenience of the equipment available to these people. The better the quality of the equipment, the more efficient and accurate the results of the petrographic examination. Table 1 is a list of the equipment found in a well-equipped petrographic laboratory. Not all of the equipment is necessary; however, its inclusion will permit the greatest flexibility in approaching a given problem. Much of this equipment is demonstrated in Walker (1988).

Table 1. Equipment for a petrographic laboratory.
For Sample Preparation Room:
  • Exhaust system
  • Table
  • Hood
  • Running water
  • Sink
  • Floor drains
  • Water-cooled drill press and diamond-edged drill bits
  • Rock trimmer
For Preparation of Slices:
  • Water-cooled, diamond-edged rotary saw with an overhand arm
  • Large oil-cooled, diamond-edged rotary saw
  • Diamond-edged trim saw
  • Lapping machines
  • Weights
  • Safety-approved container
  • Ultrasonic cleaner
For Production of Thin Sections:
  • Thin-sectioning equipment
  • Glass plate
  • Drying oven
  • Lapping machines
  • Vacuum oven
  • Set of clamps
  • Vibrating lap
For Examination of Specimens:
  • Stereomicroscope
  • Microtools
  • Equipment for determination of air-void parameters
  • Petrographic microscope
  • P/EF microscope
  • Ultraviolet lamp
  • Sieves
  • Hand lenses or loupes
  • SEM with energy-dispersive x-ray (EDX )
  • XRD
Expendable Materials:
  • Lapping oil or other vehicle
  • Degreasing agent
  • Ethanol
  • Grinding compounds, diamond pastes, abrasive discs, lapping film
  • Fluorescent or colored (e.g., blue) dye
  • Impregnating epoxy
  • Mounting epoxy
  • Flat glass petrographic slides
  • Carpet tape
  • Carnauba wax or colorless nylon fingernail hardener
  • Pens
  • 10 percent HCl acid
  • Notebooks
  • Glass trays
  • Dropper bottles or rods
  • Glass dishes
  • Absorbent cotton, paper towels, etc.
  • Index of refraction oils
  • Disposable 305-millimeter (mm) liners for vibrating lap
  • Disposable plastic petri dishes (60-mm diameter)
  • Equipment or materials (e.g., chemical stains) for specific tests
  • Reference specimens

2.2 FOR SAMPLE PREPARATION ROOM

2.2.1 General Comments

The initial sample preparation room is a "dirty" room because it is usually the room to which new specimens, complete with any adhering dust or soil, including concrete in all stages of disintegration, are brought and in which loose grinding compounds and lapping oils are stored and used. Water, oil, specimen fragments, mud, and grinding compounds may accumulate on the floor or other surfaces and may necessitate periodic cleaning and sorting to keep dirt and waste under control and make the room a practical and convenient space in which to work.

2.2.2 Equipment

The following equipment is needed in the sample preparation room:

  1. Exhaust system: For exchanging the air frequently and ridding the room of the chemical fumes and oil vapors produced from cutting, lapping, and cleaning specimens.

  2. Table: For sorting and labeling specimens and preparing them for additional preparation procedures. Equipment for marking specimens, paper, pens, and pencils should be available at this table.

  3. Hood with outside vent: For enclosing any area where strong solvents (e.g., acetone) and epoxy components are stored and used.

  4. Running water: For cooling and lubricating some of the saws and the drill press. Usually, it is most convenient to have adjustable, mixable, hot and cold water permanently supplied to each piece of equipment. Hoses that drape across the floor and must be reattached to each piece of equipment as it is put into use are a safety hazard and are inefficient. In many cases, the operator’s hands must stay in the running water for long periods. Thus, although the main purpose of the water is to remove heat from the specimen, it must be possible to adjust the water temperature so that the operator is comfortable and can maintain a firm grip on the specimen being shaped.

  5. Sink: For washing hands, pieces of equipment, and specimens.

  6. Floor drains: For draining spilled and splashed water. A large sump should be placed under the areas where oil may be spilled.

  7. Water-cooled drill press and diamond-edged core bits (figure 1): For fabricating small cores of rock or concrete. Bits should be of the internal-diameter sizes required for any tests using small cores of rock. This item will not be required unless the preparation of rock specimens for tests such as those specified in ASTM C 586 is a function of the petrography laboratory. Quantity: 1.

  8. Rock trimmer (figure 2): Hydraulic press that by means of opposing chisel points produces controlled cracks in rock, concrete, and similar materials.

Figure 1. 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. Rock trimmer (with chisel points and hydraulic jack to apply up to 4500 newtons (N)).

 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.

2.3 FOR PREPARATION OF SLICES

2.3.1 General Comments

Apparatus and materials for the preparation of surfaces of HCC specimens for microscopic observation are described in ASTM C 856, "Apparatus." Other apparatus may be equally suitable. Water should be used as little as possible on portions of HCC that are to be examined microscopically. Water dissolves particular components of HCC (see section 6.3.3). With this in mind, whenever a choice is possible, equipment for sawing concrete that uses an oil bath should be selected rather than equipment that uses running water or a water bath containing a rust inhibitor. The diameters listed for the rotary saw blades reflect the fact that the depth of the cuts made with a rotary saw cannot exceed the distance from the supporting central plate to the edge, a distance that is always less than half the diameter of the saw blade. Some blades thicken or bow in the middle and cause binding.

2.3.2 Equipment

The following equipment is needed for shaping and lapping slices:

  1. Water-cooled, diamond-edged rotary saw with an overhand arm (figure 3): For reducing large fragments and long cores and cylinders to sizes that may be held in the vise of the next saw. The 360-mm diamond-edged blade is usually slotted into wide teeth. The saw is cooled with running water to allow specimens to be hand-held for quick setup and to obviate the need for a cover. Both hands are often needed to hold the specimen and roll the table. The foot pedal for adjusting the height is a necessity. Quantity: 1.
  2. Large oil-cooled, diamond-edged rotary saw (figures 4 and 5): For cutting specimens. The 610-mm (minimum) diamond-edged, continuous-rim blade produces a smooth cut with few ridges and minimizes the difficulty of producing finely lapped surfaces. A vise that holds the specimen firmly and automatically moves it into the saw is an integral part of this equipment. The saw blade should be flat and true, and carefully aligned in the saw so that it is parallel to the travel of the vise. The saw is covered to contain the splashing oil and oil vapors. Quantity: 1 (minimum).
  3. Diamond-edged trim saw: For shaping small specimens of rock or concrete, such as thin-section blanks. The saw in use at VTRC (figure 6) is water-cooled; however, an oil-cooled saw is preferable so that specimens are not exposed to water that might dissolve particular phases in the concrete. The diamond-edged blade should be 200 mm or less in diameter. Quantity: 1.
  4. Bench lap (figure 7): For smoothing surfaces of hand-held specimens of rock or concrete. The usual lubricant is water added by hand or dripped from an overhead container. The grinding compounds are usually dispensed from small shakers. Quantity: 1.

    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).

    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. 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. 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.

    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. 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).

    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. 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).

    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.
  5. Rotating laps: For producing finely lapped surfaces for microscopic examination and air-void analysis. The laps should be fabricated of cast iron with radial grooves cut in the surface to provide drainage. The equipment includes an adjustable timer and automatic feed for the slurry of lapping oil and grinding compound. A lap 400 mm in diameter will handle three 100-mm specimens or two 150-mm specimens. The lapping equipment includes slotted, rotating, sample-holding rings (sized to fit common slice sizes), yokes to hold the rings, and cover plates to rest between the slice and its weight. The lapping of concrete or rock slices is time-consuming. Two laps speed up operations. If there is only one horizontal lap wheel, great care must be taken to clean the iron wheel and the associated equipment carefully (such as the feeder for grinding compound) whenever a change is made to a finer compound. A very small amount of coarser grit left in the equipment can significantly damage a lapped surface produced with fine grit. The finest grinding compound should be used on one lap, and all coarser grit on the other. The lap wheels (figure 8) should be sturdy and have durable bearings to withstand the stresses of unbalanced samples and heavy weights. Quantity: 2.

    Figure 8. Lap (diameter of 400 mm).

    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.
    1. Rotating slotted specimen holder
    2. Cover plate to set on top of specimen
    3. Guide yoke that retains specimen holder
    4. Grit-slurry cup mounted on its motor and containing spiral agitator-pump
    5. Drain
    6. Grooved lap
  6. Weights (figure 9): For lapping slices smoothly. Weights fit on the back of the slices, loosely inside the rings. The weights press the specimen firmly against the lap to prevent the lapping away of the softer material and the leaving of the hard material as high spots. The weight increases the wear on the high (hard) portions of the specimen and prevents a buildup of grinding compound on the softer portions. Without the weights, the softer portions would be worn away more deeply. The weights should cover nearly all of the back of the specimen and should weigh 6 to 7 kilograms (kg) for a specimen 100 mm in diameter and 7 to 8 kg for a specimen 150 mm in diameter. Coffee cans of appropriate diameter weighted with lead shot have been found to be satisfactory. Quantity: Equal to the number of specimens it is possible to lap at one time.
  7. Automated combination grinding, lapping, and polishing machines: Machines such as those shown in figure 10 (Abramin by Struers, Inc.) are available and are in use at the Turner-Fairbank Highway Research Center (TFHRC) and the Missouri Department of Transportation (DOT). This equipment uses easily interchangeable grinding and polishing discs together with a continuously variable pneumatic system for applying downward force on the specimen, thus eliminating the need for loose abrasives and weights.

    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.)

    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. Automated grinding, lapping, and polishing machine uses interchangeable grinding and polishing discs to simplify specimen preparation.

    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.
  8. Safety-approved container: For cleaning specimens. Specimens are cleaned in solvents (such as isopropyl alcohol (99 percent) or acetone) to remove oil and grinding compound accumulated during lapping.
  9. Ultrasonic cleaner (figure 11): For cleaning specimens. The cleaner should be of sufficient size to easily submerge the largest lapped specimen that will require cleaning. The cleaner bath must be of a material that can hold acetone or isopropyl alcohol. Quantity: 1.

Figure 11. Ultrasonic cleaner (tank is of a material that will resist most solvents).

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.

CAUTION: It has been reported that the use of ultrasonic cleaning equipment may be harmful to the surface of concrete specimens; therefore, such treatment should be used with care and only after experimentation with the specific frequencies of the equipment (ASTM C 457).

2.4 FOR PRODUCTION OF THIN SECTIONS

2.4.1 General Comments

To fabricate a specimen chip of concrete or rock that will fit the glass to be used to support the thin section will usually require the use of at least one of the two large saws and the small trim saw. The room used for further fabrication of thin sections should be isolated from the area where lapped slices are prepared, and it must have an efficient exhaust system or two hoods because the cutting and grinding of thin sections to the required thickness produce an oil vapor and the production of thin sections requires the use of epoxy (which is toxic in large quantities). The method any particular laboratory uses to produce thin sections will depend on the equipment available and the preference of the technical personnel. Pacific Northwest Laboratories of Battelle in Richland, WA, recommended the use of a belt sander and a bench lapping machine with diamond-impregnated laps (Beauchamp, Williford, and Gafford, 1972). Wilk, Dobrolubov, and Romer (1974) recommended the use of a diamond-tooled milling machine.A variety oftechniques are described by St. John, et al. (1998). VTRC has Ingram-Ward thin-section machines; TFHRC uses PETROTHIN® by Buehler, Inc.; and the U.S. Bureau of Reclamation has equipment from Microtec Engineering Laboratories, Inc. The preparation of thin sections requires skilled technicians, and when experienced personnel are not available, it may be more practical to have them prepared by a laboratory that specializes in making thin sections.

2.4.2 For Examination With Petrographic Microscope

The following equipment is needed for examination with a petrographic microscope:

  1. Thin-sectioning equipment: For producing thin sections of rock and similar materials for examination with the petrographic microscope. This manual describes the use of Ingram-Ward equipment (figures 12 and 13). The instructions can probably be adapted for use with any type of thin-sectioning equipment that permits variability in section thickness and thus will make possible ultrathin and extra-thick sections. Part A of the set is a rotating cutoff saw with a very thin blade used to slice off excess specimen material, thus reducing the specimen chip (mounted on a glass slide and held in a vacuum chuck)from 50 to 30 micrometers (µm) in thickness. Generally, the thinner the slice of specimen chip remaining on the glass slide, the better. Part B of the set holds the specimen in another similar vacuum chuck and permits it to be moved carefully and evenly over a rotating, diamond-bearing, cupped ceramic grinder to grind it to nearly the desired thinness. The relative position of the chuck to the saw or grinder can be adjusted with a small dial at the right-hand end of each piece of equipment. The lubricant (denatured kerosene with 1/10th motor oil) is collected in the surrounding tank and pumped to the top of the saw or wheel to cool and lubricate the work. Quantity: 1 set.
  2. Glass plate firmly supported in a flat pan (figure 14): For catching spilling slurry when thin sections are hand-lapped after they have been cut and ground on the Ingram-Ward equipment. Ordinary window glass is usually sufficient. Used for final grinding of ordinary and intermediate grinding of fluorescent ultrathin sections for use with the petrographic and P/EF microscopes. Quantity: 1.
  3. Drying oven (figure 15): For evaporating water or lapping oil from slices, thin sections, or rock fragments and curing the epoxy of specimens impregnated for thin sections. Vented to allow the escape of vapors. A thermometer is mounted near the center of the oven. Steam must not form in the HCC; therefore, the temperature in the oven must be thermostatically controllable (adjustable to less than 100 degrees Celsius (°C)). Quantity: 1.

Figure 12. Ingram-Ward thin-sectioning equipment: Diamond-edged cutoff saw with very thin blade (see arrow) 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. Ingram-Ward thin-sectioning equipment: Diamond-bearing,cupped ceramic grinder (see arrow).

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.

The handle and chuck permit the specimen to be moved carefully and evenly over the rotating, diamondbearing, cupped ceramic grinder. The relative position of the chuck to the saw or grinder can be adjusted with a small dial (bottom arrow) at the right-hand end of each piece of equipment.

Figure 14. 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.

The pan used to catch the grinding slurry, which 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 a lubricant to produce a slurry.

Figure 15. Drying oven (thermostatically controlled).

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.

2.4.3 For Examination With Polarizing/Epifluorescence Microscope

The following equipment is needed for examination with a P/EF microscope:

  1. Vacuum oven (figures 16 and 17): For vacuum-impregnating thin-section stock with epoxy and slow, even drying of specimens. For fluorescence, fluorescent dye is added to the epoxy. Quantity: 1.
  2. Set of clamps mounted on a sturdy metal plate (figure 18): For cementing an impregnated thin-section chip to the final glass slide. Quantity: 1.
  3. Vibrating lap with weights (figure 19): For producing the final surface of thin sections. The thin sections are attached to the bottom of the weights. The circular pan is lined with Pellon Pan-W, a specially formulated lapping pad, which is coated with diamond paste thinned with thin oil. Quantity: 1.

Figure 16. 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. 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. Mounted set of clamps (small Lucite® rectangles are used to distribute clamping force over the entire section surface) (Walker and Marshall, 1979).

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. Syntron vibratory polisher and weights (weights have sponge rubber bumpers) (Walker and Marshall, 1979).

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.

2.5 FOR EXAMINATION OF SPECIMENS

2.5.1 General Comments

The room in which specimens are examined is also where the microscopes are stored and used and should be as close to a "clean" room as can be managed without the use of special clothing. A worker whose hands or clothing are contaminated with grinding compounds, excessive dust, lapping oil, grease, soil, or materials used to mix concrete should remove the contaminants from his or her person before approaching a microscope. It is best if the air in the room is under positive pressure and an anteroom is equipped with an exhaust system to create the concomitant negative pressure. The room should be furnished with tables and microscope benches and a number of adjustable-height stools and chairs.

2.5.2 Equipment

The following equipment is needed for examination of specimens:

  1. Stereomicroscope (figure 20): For conducting a general examination of specimens. May also be used in the quantitative determination of air-void parameters. This is the instrument most used by concrete petrographers. The stereomicroscope should have a magnification variable between 25 and 120 diameters. The higher magnifications may be attainable with a 2X accessory lens below the objective. It is most convenient to have a zoom objective; however, excellent observations can be made with turret-mounted objectives. It is tedious and annoying to have to change objectives by dismounting them and remounting them. The eyepieces should be the wide-field type. A measuring reticle in one eyepiece can be convenient (must be calibrated for each magnification). Video-imaging systems are available with integral or separate software packages that have measurement tools. Measurement calibrations can be saved to match the various magnifications used for easy application during an examination. By the use of thismicroscope, decisions are made concerning concrete quality and the planning of further testing. If there is a difference in the quality of the microscopes available, the one with the least distortion and the widest field of view should be the one used in the quantitative determination of air-void parameters. Quantity: At least 2.

    Figure 20. 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.
  2. Microtools: For measuring, manipulating, and removing portions of slices of concrete and manipulating the grains of grain mounts under any kind of magnification. The most useful microtools will probably be those that have been fabricated in the petrographic laboratory (figure 21). Sets of microtools are commercially available; however, they often do not meet the needs of the concrete petrographer. The best sets have a variety of needles, shovels, and scrapers. The tiny tools must be small enough to use in the cracks, crevices, and voids of the concrete; however, they must be strong and resilient to resist breaking. Some of these sets are constructed with the microtools as detachable pieces that screw or clamp into a handle. Such sets should have more than one handle. The needles used for biological dissection are usually strong enough; however, the point thickens so rapidly that the tool may not be of use in tight cracks and voids. Sewing needles with the handle of a section of a small dowel rod can be very useful. They are strong and sharp and come in a variety of sizes. Often what is required is an assortment of needles with bends of different radii, well within the working distance of the microscope, to allow the needle to attack the concrete from a variety of angles. Such needles are commercially available for biological microscopy; however, they may not be strong enough to pick out reaction products and small pieces of aggregate from the concrete. Duplicate tools should be obtained so that breakage will not cause a delay in the progress of the work.

    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).

    Photo shows an array of small tools for use under amicroscope 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.

    The arrow indicates a small scale engraved on very thin, flexible metal attached to a thin rod that is attached to a handle. The scale has 5 mm marked into tenths of a millimeter on one side and 0.1 inch arked into five thousandths of an inch on the other.

    The most irreplaceable, commercially available microtool is a small scale engraved on very thin flexible metal attached to a thin rod, which is attached to a handle. The scale may have 5 to 10 mm marked into tenths of a millimeter on one side and 0.1 to 0.2 inch marked into five thousandths of an inch on the other side. This flexibility allows better positioning of the scale. The thinness allows the scale to be more nearly in the same focal plane as the item examined. Unfortunately, the solder joint between the flexible metal and the stiff rod connection to the handle may be fragile. It is good to have a replacement scale available. For less precise measurements, a transparent scale (usually the International System of Units (SI) (metric system)), used by the microscopist viewing through the scale with the markings down on the concrete (to allow for the best focus) is useful. Such scales may be found in stationery and variety stores.

    Excellent picks, miniature knives, shovels, and scrapers can usually be obtained from most dentists if a request for used tools is made. These tools are strong and designed for approaching the work area in close quarters. They may require sharpening and reshaping to suit the needs of the concrete petrographer. For this purpose, a stick or two of abrasive dressing compound is useful. These tools may corrode in the presence of chemicals and must be kept clean and sharp. Quantity: Minimum of 1 each.

  3. Equipment for air-void determinations: An example of this equipment is described in chapter 6.
  4. Petrographic microscope: An example of this microscope is described in chapter 12.
  5. P/EF microscope: An example of this microscope is described in chapter 13.
  6. Sieves (figure 22): For sorting aggregate particles (pebbles, sands, and crushed fragments) by size and preparing specimens for microscopic examination. Sieves should comply with the requirements of ASTM E 11. Two sizes of frames are required: 203 mm and 76 mm. Both sets of sieves should include standard covers and pans. The 203-mm size is used for sizing and sorting aggregate material to determine compliance with the client’s specifications and to prepare aggregate specimens for various testing procedures. The 203- mm set should include the mesh sizes necessary to determine the compliance of an aggregate with the client’s specifications. If other laboratories concerned with aggregates are on the premises, this size of sieve will probably be available. The smaller 76-mm frame size is used to prepare sands and rock and concrete fragments for grain mounts or other microscopic studies. The 76-mm set should include the mesh sizes of the 203-mm set that are smaller than 9.5 mm and an assortment similar to those listed in table 2.

    Figure 22. Types of sieves used in examination of concrete and concrete materials (203-mm and 76-mm sizes).

    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.
    Table 2. Useful sieves for petrographic laboratory using 76-mm frames.
    Alternate DesignationASTM E 11 (SI) Standard Designation
    No 30600 µm
    No 40425 µm
    No 60250 µm
    No 100150 µm
    No 20075 µm
    No 40038 µm
  7. Other equipment: Various instrumental methods of analysis (e.g., x-ray diffraction (XRD), elemental analysis by x-ray dispersion (EDX), SEM, differential thermal analysis, infrared spectroscopy, x-ray fluorescence (XRF), and analytical chemical methods) may be employed in the identification of the raw materials and reaction products and deleterious substances that may be associated with HCC. XRD, SEM, and EDX are discussed in chapter 14.

2.6 EXPENDABLE MATERIALS

2.6.1 General Comments

WARNING: Persons unfamiliar with the hazards of these compounds, or any chemicals and materials used or examined, are referred to the Chemical Safety Data Sheets published by the Manufacturing Chemists Association, Inc., 1825 Connecticut Avenue, NW, Washington, DC 20009, or to the Materials Safety Data Sheet that may be obtained from the supplier of the particular compound, chemical, or material.

2.6.2 Lapping Oil

Water should not be used on any surface of an HCC specimen that is to be examined under magnification. The lubricant used for cutting and lapping specimens should be low-viscosity, water-free lapping oil, such as denatured kerosene (e.g., Exxon Isopar M) mixed with 1/10th 30-weight motor oil. The motor oil lessens the production of vapors from the kerosene. A number of light oils are sold specifically as lubricants for cutting with diamond saws. Specialized lubricants are required for grinding and polishing thin sections with diamond grinding compounds (an example of such a lubricant is Formula C (Glennel Corporation, Chester Springs, PA)).

Oil-based lubricants will not dissolve reaction products and secondary minerals as readily as will water-based lubricants. It is convenient to use a lapping lubricant that will evaporate and leave the surface of the specimen oil-free. At magnifications such as those used in the analysis of concrete, an oil film can obscure the exact edges of voids and aggregate particles. The evaporation of the oil may be hastened by treatment in a warm (< 70 °C), not hot, drying oven. High heat can crack the concrete specimen or heat the oil to its flash point. The oil drained from the laps may be reused after filtering and decanting.

2.6.3 Grinding Compounds

For preparing finely lapped surfaces on concrete specimens. The grit numbers and sizes listed are given only as a guide. The grinding compounds produced by one manufacturer may vary from those produced by another.

2.6.4 Dyes and Epoxies

The following dyes and epoxies are needed:

  1. Fluorescent dye: For inclusion in the impregnating epoxy of sections to create fluorescence in the voids and cracks. This is available only as samples (believed to be a paint ingredient). The dye currently used is Fluorol Yellow 088, available as samples from BASF Wyandotte Corp., Holland, MI. This dye dissolves completely in epoxy; no dye particles can be seen at 600X magnification and the epoxy is evenly colored by the dissolved dye. An ultraviolet light source is required for the use of this material.
  2. Colored dye: For use in impregnating thin sections when observations will be made with transmitted light. A blue-colored dye is commonly used to highlight voids and cracks.
  3. Impregnating epoxy: For strengthening thin-section stock and carrying fluorescent or colored dye. EPO-TEK 301-2 from Epoxy Technology, Billerica, MA, is a good impregnating epoxy. It dissolves the dye completely. It has sufficient shelf life to be useful after a year or so, although it may have to be warmed a little. It has a sufficient pot life to remain fluid through several hours of vacuum impregnation and can be formulated to cure with a little heat treatment over several days to a hard brittle substance that shows no plasticity. When properly cured, the hardened epoxy is not soluble or softened in oil, alcohol, or acetone. LR White is a one-part epoxy with extremely low viscosity and is routinely used to impregnate specimens for SEM examination.
  4. Mounting epoxy: For attaching the smoothed thin-section stock to the final supporting glass slide. The mounting epoxy currently used can be either Epoxide from A.B. Buehler, Lake Bluff, IL, or Section-Lok epoxy mounting medium from Microtech Engineering Laboratory, Inc., Clifton, CO. Of the two, the Section-Lok product has the longer shelf life.

2.6.5 Miscellaneous Supplies

The following miscellaneous supplies are needed:

  1. Flat glass petrographic slides (27 by 46 mm): For mounting thin sections and grain mounts for examination with the petrographic microscope. A standard item in most scientific catalogs. The slides used for temporary grain mounts can be cleaned and reused.
  2. Carpet tape or other strong, double-sided tape: For attaching thin sections to the bottom of weights.
  3. Carnauba wax or colorless nylon fingernail hardener: For impregnating fragile concrete.
  4. Pens: For fine marking of concrete slices. The pen used should be such that when the inky point is positioned on a crack a very small portion of the ink will flow into the crack and be drawn along the crack and will thus indicate the next direction of the crack.
  5. 10 percent HCl: For etching entire slices or portions of slices.
  6. Notebooks: For recording observations.
  7. Glass trays: For etching or other chemical treatment of finely lapped specimens.
  8. Dropper bottles or glass rods: For dropping acid and water.
  9. Glass or ceramic dishes: For use in chemical tests.
  10. Absorbent cotton, tissues, paper towels, lintless cloth, etc.
  11. Index of refraction oils: For determining the optical properties of minerals and other translucent substances with polarized light microscopy. The oils should range in index from 1.40 to 1.50 in steps of 0.04, from 1.500 to 1.600 in steps of 0.002, and from 1.600 to 1.700 in steps of 0.01. Index oils change with age and must be checked periodically with a refractometer or standard solids.
  12. Disposable 305-mm liners for the vibrating lap: Pellon Pan-W polishing pads.
  13. Disposable plastic petri dishes, 60 mm in diameter, 20 mm in depth: For potting thin-section specimens in fluorescent- or color-dyed epoxy.
  14. Equipment and materials for specific tests: Examples are the concrete molds and the length comparators required by particular ASTM procedures. The equipment required for the uranyl acetate fluorescence test for the presence of alkali-silica gels is listed in section 10.2.3. Chemicals needed for staining techniques.
  15. Reference specimens: For comparison between materials under study and carefully labeled and documented specimens in a reference collection. Two general kinds of materials should be included in such a collection: (1) raw materials from which concrete is fabricated and (2) various kinds of HCC in both rough fragments and finely lapped slices. If storage space is limited, photographs may have to be substituted for the larger specimens. Ideally, enough of each specimen should be available for various destructive testing procedures. Some of the items to be included are listed in tables 3 and 4.
Table 3. Reference specimens of materials used in making hydraulic cement concrete.

Aggregates

  • Coarse
  • Fine
  • Those known to have caused problems (e.g., alkali-reactive aggregates, unsound aggregates, aggregates that create a high water demand)

Cementitious materials approved for use (in moisture-resistant containers)

  • Portland cement
  • Portland cement blended with slag, fly ash, silica fume, etc
  • Other cements, such as ground slag
  • Fly ash
  • Silica fume
  • Natural pozzolans
  • Other

Note: Specimens should include as many types of each as are available locally. They should be labeled as to source and type, and stored in transparent containers.

Table 4. Reference specimens of hydraulic cement concrete representing various conditions or features.
  1. Each of the materials listed in table 3 used in the proper manner in hardened HCC mixtures.
  2. Materials used in varying amounts:
    • Several lapped slices of HCC with a high water-cementitious materials ratio (w/cm)
    • Several lapped slices of HCC with a normal w/cm
    • Several lapped slices of HCC with a low w/cm
    • Lapped slices of HCC subjected to moist curing of varying duration
    • Lapped slices of inadequately cured HCC
    • Lapped slice of HCC with a normal amount of visible cement ferrites
    • Lapped slice of HCC with a less-than-normal amount of visible cement ferrites
  3. Various forms of distress (in large fragments) according to occurrence in the area and accompanied by photographs of the surface condition:
    • Examples of deterioration caused by lack of resistance to cycles of freezing and thawing resulting from an insufficient air-void system (including layered scaling)
    • Examples of deterioration caused by expansive alkali-aggregate reaction (generally alkali-silica, but also alkali-carbonate if such rocks occur in the region)
    • Examples of concrete deteriorated by D-cracking caused by aggregate susceptibility
    • Examples of plastic shrinkage cracking (including specimens with lapped surface cutting across the cracks)
    • Examples of shrinkage (drying or thermal) cracking

 

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