The next series of Fun Fact Friday posts will be an aggregate of knowledge about aggregates!
What makes aggregates so important? Well, as an important component of concrete, their quality matters. (You can read about why concrete testing is essential for new construction projects by clicking here.) Aggregates (which is pretty much a fancy word for gravel, sand, crushed stone, recycled concrete, slag, and other materials used in construction) are also used in the construction of roads and paved areas and in drainage application, so it’s important to be sure that they will behave as expected when put under a load, exposed to moisture, and other factors.
As with concrete, aggregates must be tested to ensure that that particular aggregate is the right choice for the project or application. The material being considered can be evaluated based on factors including the size of the individual pieces that make up the aggregate mixture, the texture that the aggregate provides to the finished product, resistance to chemicals or climate, and what aggregate will be used for. The range of testing used also depends on the specifics of the building codes the project is subject to, and the preferences of the project owner.
Aggregates can be sampled during production, or from stockpiles. Production sampling most commonly takes samples directly from conveyor belts moving the material from place to place. At least three samples are taken from the moving belt in order to get an accurate cross-section of the material being used.
Stockpile sampling, the method commonly used on jobsites, involves the use of the front-end loader to dig into the stockpile and remove a small pile of material, as if the material were being loaded into a truck, with samples from various stockpiles on the site being combined into a single, mixed up sample pile. (ASTM guidelines provide very specific procedures for how to do this, in order to obtain consistent representative samples.)
Once the sample pile is properly mixed, the sample is taken at the center, and approximately one-third down the height of the pile. At least six full shovels of aggregate are taken at equal increments around the pile, and collected in a bag, sampling tube, or other container for transport. The same general methods can be used for sampling from trucks, rail cars, barges, or other means of aggregate transportation.
How many samples are enough, and how big do they need to be? That depends on the aggregate size, what the aggregate is being used for, and what properties of the aggregate are being tested. The requirements can also vary by locality.
Once we’ve got our samples, we need to take them back to the lab. Don’t be aggravated, though – come back next week to learn about aggregate moisture content testing! We promise it won’t be a dry subject!
Need aggregate sampling, or other materials testing services? Contact Encorus Group’s Civil Laboratory Supervisor Jeremy Lake at 716.592.3980, ext. 133 or [email protected].