Why is limestone used as an aggregate?

Answer 1

Crushed limestone course aggregate for concrete is typically sold in competition with natural river gravel. River gravel is usually dug from deposits found in the bends of major rivers which have flowed out of rocky terrain. These stones are usually very hard and typically round because they have been broken away from the hills and then water currents literally "polish" them as they roll down the river. This gravel is found in deposits that also contain sand most of the time. Usually there is more sand than gravel. Many gravel deposits contain stones that are about the correct size to make concrete, so the only prep work necessary is to separate the sand from the gravel and remove any clay, wood or other foreign material. Because it is relatively easy to produce river gravel as compared to crushed limestone, usually the first source of aggregates developed for a community is gravel. As the gravel deposits are depleted and people learn the advantages of crushed aggregate, the use of crushed limestone in concrete increases.

Crushed limestone has several important advantages over river gravel as an aggregate for concrete. First, for a given amount of cement in the mix, crushed limestone concrete will have an approximately 10% strength advantage. This strength advantage comes from the fact that cement bonds tighter to limestone than to a slick/smooth gravel and the strength that is derived from the sharp angular faces of the crushed aggregate. Second, because crushed limestone has a lighter unit weight than gravel, it will require about 12% less crushed limestone than gravel to mix a cubic yard of concrete. Additionally, crushed limestone concrete is easier to saw through than gravel concrete. This is because most gravel is silica. Silica is almost impossible to cut with a steel saw.

Crushed limestone concrete also has a lower thermal coefficient of expansion than gravel concrete. This means that slabs poured with limestone concrete will expand and contract less than gravel concrete for a given change in temperature. Studies have shown that this thermal stability coupled with limestone's superior curing properties results in greater crack spacing, and less crack width in limestone concrete slabs.

Answer 2

Limestone is used as an aggregate in construction because it is a durable and strong material that can provide stability and support to structures. It is also readily available and cost-effective, making it a popular choice for various construction projects. Additionally, limestone's natural properties, such as its ability to compact well and drain water, make it a versatile material for use in different applications.