In the D 7370 procedure, lab technicians first place the fine aggregate sample in the metal pycnometer. After 30 minutes, they will have the data to calculate the sample's absorption and specific gravity.
The technician divides a sample of fine aggregate, dried to a constant mass, into two sample splits. He places one sample in the special volumetric flask filled with water to the calibrated line and then weighed. The technician mounts the flask to the mixing platform of the AVM, which automatically mixes the water and material with vacuum air from the sample chamber until the sample has reached the Apparent Specific Gravity condition. The flask is removed, refilled with water to the calibration line, and weighed.
While the first sample is being tested, the second is placed in the special bowl the manufacturers provide. This sample and bowl are weighed, then mounted to the mixing platform of the SSD device. The apparatus injects small amounts of water into the sample, mixes the material, and absorbs water until reaching the saturated surface dry (SSD) condition.
An infrared detector monitors the sample during the mixing/water injection process for trace amounts of water to begin building on the aggregate surface. The unit will automatically stop when a stable SSD condition is reached. The technician weighs the test bowl to determine the net weight of the sample at SSD.
The D 7370 procedure uses a vacuum to calculate the rapid saturation of dry aggregates. Each test involves two representative dry aggregate samples of the same material. One sample is evacuated inside the vacuum chamber inside a plastic bag and opened under water for rapid saturation of the aggregate. The dry mass and submerged mass of the sample are used to calculate apparent relative density.
The second sample of the same aggregate is tested in a known volume metal pycnometer. The known mass of the pycnometer with water, mass of the dry aggregate, and mass of the aggregate and pycnometer filled with water is used to calculate unsaturated density. Results from the samples tested are used to calculate absorption and specific gravity.
To buy either test procedure, visit ASTM at www.astm.org. You can also learn more about the specific equipment by visiting the manufacturers' Web sites.
For D 7172, visit Barnstead International at www.barnsteadthermolyne.com. (The device is listed under the material testing tab.)
For D 7370, visit InstroTek at www.instrotek.com.