U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000


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Aggregate and Petrographic Laboratory

 

Laboratory Capabilities

Aggregate

The Aggregate and Petrographic Laboratory characterizes and classifies aggregate types based upon their mineralogical makeup and physical characteristics of the rock types and provides quantitative data for each rock types present in the aggregates in accordance with procedures set in American Society for Testing and Materials (ASTM) C 295. If aggregates are found marginal or poor quality by petrography, additional testing is recommended in the report.

the two images show stereomicroscope photographs of representative dense and porous chert particles from the materials retained on the No. 8 sieve size of the fine aggregate. The length of field of view in each image is 26 mm. The first image shows 6 dense chert particles, 3 particles on the top and 3 on the bottom. The second shows 5 porous particles. Three particles on the left and 2 particles on the right.
Figure 1a. Dense chert particles.
the two images show stereomicroscope photographs of representative dense and porous chert particles from the materials retained on the No. 8 sieve size of the fine aggregate. The length of field of view in each image is 26 mm. The first image shows 6 dense chert particles, 3 particles on the top and 3 on the bottom. The second shows 5 porous particles. Three particles on the left and 2 particles on the right.
Figure 1b. Porous and moderately soft chert particles.

 

Figure 1a and b. Stereomicroscope photographs of representative dense and porous chert particles from the materials retained on the No. 8 sieve size of the fine aggregate. Length of field of view from left to right in each image is 26 mm.

 

The image shows microcrystalline quartz, featuring a wavy black and cream-colored pattern.
Figure 2a. Chalcedonic chert.
The image shows microcrystalline quartz, featuring a wavy black and cream-colored pattern.
Figure 2b. Chalcedonic chert.

 

Figure 2a and b. Transmitted light (crossed-polarized light), thin section photomicrographs of potentially reactive chalcedonic chert particles (microcrystalline quartz) from a fine aggregate.  Length of field of view from left to right is 5 mm in 2a and 2 mm in 2b.

 

Concrete

The Aggregate and Petrographic Laboratory provides troubleshooting of performance problems/inferior qualities and investigates degradation (distress) mechanisms of concrete from highway and other concrete structures in accordance with procedures set in ASTM C 856. The laboratory also performs condition assessment and evaluates conditions of quality control concrete cylinder and mortar bars.

The figure shows a stereo-optical image of a lapped concrete section showing a crack filled with alkali-silica reaction (ASR) gel between the two reactive chert particles, which is shown by yellow arrows.
Figure 3a. Stereo-optical image of a portion of a lapped concrete section showing a crack filled with alkali-silica reaction (ASR) gel bridging the two reactive chert particles (shown by arrows). Length of field of view from left to right is approximately 4.5 mm.

 

The figure shows a transmitted light thin section photomicrograph showing a crack filled with alkali-silica gel (ASR) that extends from the reactive chert particle to the cement paste (shown by yellow arrows).
Figure 3b. Transmitted light (cross-polarized light) thin section photomicrograph showing a crack filled with alkali-silica gel (ASR) extends from the reactive chert particle to the cement paste (shown by arrows).

 

Air-Void System

The Aggregate and Petrographic Laboratory also evaluates and measures concrete air-void properties in accordance with procedures set in ASTM C 457. Air content and other air-void parameters (including spacing factor and specific surface) are critical to predict the freeze-thaw durability of concrete structures that will be or were exposed in different weathering regions.

The figure shows an image of a lapped section of a concrete core showing the air-void system in hardened concrete.
Figure 4. Lapped section of a concrete core showing the air-void system in a hardened concrete. The length of field of view from left to the right is approximately 9 mm.

Asphalt Pavement

The Aggregate and Petrographic Laboratory also helps in forensic investigations of problems related to asphalt pavement polishing/slipperiness, as well as sources of admixtures (e.g., lime) in hot-mix asphalt pavement.

The figures show stereomicroscope photomicrographs showing polished limestone aggregates (shown by yellow arrows) on the surface of an asphalt pavement.
Figure 5a. Very smooth and polished coarse aggregate from the middle portion of a core extracted from an asphalt pavement.
The figures show stereomicroscope photomicrographs showing polished limestone aggregates (shown by yellow arrows) on the surface of an asphalt pavement.
Figure 5b. Polished Aggregates (shown by arrows).

 

Figure 5a and 5b. Stereo-optical photomicrographs showing polished and smooth exposed aggregates along the top surface of a core extracted from an asphalt pavement. Scale shown in both images is in one-sixty-fourths of an inch increment.

 

The figures show stereomicroscope photomicrographs showing partially polished limestone aggregates (shown by yellow arrows) on the surface of an asphalt pavement.
Figure 6a. Note the portion of the aggregate shown by red arrows is still covered with asphaltic material.
The figures show stereomicroscope photomicrographs showing partially polished limestone aggregates (shown by yellow arrows) on the surface of an asphalt pavement.
Figure 6b. Middle portion is still covered with asphaltic materials (shown by red arrows).

 

Figure 6a and 6b. Partially polished limestone aggregates (shown by yellow arrows). Broken yellow lines mark an inferred outline/edge of the aggregate particles in the portion where it is still covered by asphaltic material. Scale shown is in one-sixty-fourth-of-an-inch increment.

 

 

Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000
Turner-Fairbank Highway Research Center | 6300 Georgetown Pike | McLean, VA | 22101