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Evaluating the Quality of Aggregate: 5 Important Things to Look For
Rocks are rocks, right?
Wrong. In fact, there are vast differences between different types of rock, and those differences can change (for better or worse) the quality of aggregate made from them. Not all rock makes good aggregate; sites for potential quarries must be extensively evaluated for the quality of their rock before any digging, drilling, or blasting can take place. If the rock is weak or corrosive, the aggregate will be bad. If it's hard and cohesive, the aggregate will be better.
Here are five standards you should look for when evaluating the quality of rock for aggregate.
Till. Till is the accumulation of pieces of eroded rock, usually located somewhere downstream from a major rock deposit. Geologists study till to determine the quality of aggregate that can be made from the rock. Bigger pieces in the till indicate stronger and more cohesive rocks, since the elements haven't been able to wear them down. Strong and more cohesive rocks make better quality aggregate. Smaller pieces of rock and lots of sediment indicate corrosive, erodible rocks, which will make a worse quality aggregate.
Fracture frequency. The more cracks and fissures one finds in a rock deposit, the weaker the rock. Weak rock is easier to mine, but it adversely affects the quality of aggregate. For aggregate, a quarry wants to mine harder, stronger rock. Numerous cracks and fractions are a sure sign that the rock will be unsuitable for aggregate.
Shape and surface texture. Geologists can determine the quality of a rock by applying pressure or splitting it open. If the rock cracks into rough, angular pieces, it's strong and will make better quality aggregate. If the rock splits into round, smooth pieces, it's weaker and more corrosive, and will make lower quality aggregate.
Abrasion resistance. The rock used to make aggregate must be difficult to break. Hard rock is more difficult to mine, but it provides the best quality aggregateit won't crumble or collapse under pressure. Resistance to abrasion is another sign of quality aggregate.
Resistant to breakdown. Geologists and quarry managers must make an assessment of how easily and quickly a rock erodes. If it erodes rapidly when exposed to water, air, or pressure, it's low quality rock and will produce low quality aggregate. If it resists erosion and doesn't break under pressure, then it's probably higher quality rock, and will produce higher quality aggregate.
Geologists and quarry managers have other criteria for rocks. In general, though, all rocks aren't the same. Some rocks are definitely better than others, especially in the manufacturing of aggregate.
