Aggregates

Aggregates are all the products of a pit or quarry; including sands, gravels, and crushed stone.

Typically, a pit contains loose sands and gravels that are immediately excavated, screened, and transported. A quarry contains bedrock that must first be drilled and blasted before it can be crushed into smaller fragments, then screened and processed into the final products.

Sand and gravels are naturally occurring, usually found in pits, and are typically rounded in appearance; whereas crushed rock comes from the blasting and crushing of stone, in a quarry, and is typically cubicle in shape.

Limestone is Missouri’s most abundant commercial mineral. It was created 320-500 million years ago by the deposition of calcium and magnesium on ocean floors. Almost all limestone formations in the state contain fossils of animals that lived in the ocean, providing evidence of interesting land-sea changes which this part of the country has undergone in the geologic history.

Limestone is commonly white or gray in color with angular edges. Gravel has several different colors and is generally smooth and rounded.

Sand and gravel used to be bedrock that was crushed by movement and melting of glaciers during the last ice age. Deposits are typically now found near river deltas and at expansions in rivers where flow slows and solids fall out.

Riprap is large pieces of rock which have undergone only initial crushing and sizing, or are larger uncrushed pieces. These pieces of rock range in size from 6 to 30 inches in diameter. Riprap is generally used to stabilize slopes, creek beds, and shorelines and to construct erosion-control structures.

A base product is comprised of a crushed or naturally coarse rock and sand that is well graded to create, when compacted, a strong stabilized sub grade for parking lots, streets, concrete slabs, or highways.

Aggregates range from small grains of sand to huge boulders.

First, the stone is drilled and blasted into smaller pieces. The material then goes through various stages of crushing and screening to produce the sizes and specifications desired by customers. The aggregates are then stored in separate stockpiles to avoid segregation, mixing, and product pollution.

Aggregates come from three sources: 1) unconsolidated rock, sand and alluvial materials; 2) solid rock, limestone and hard rock; and 3) recycled materials.

Every time you see a work crew on a residential, commercial or public project, it's virtually guaranteed that aggregates are being put to use. In Missouri, aggregates are most often found in the form of crushed limestone. Limestone is mined in 92 of Missouri's 114 counties, and the industry employs more than 2,500 people.

The following facts about aggregates point out the importance of this resource and why it is beneficial to have a quarry or pit nearby. Construction of a typical home requires 300 to 400 tons of aggregates. Up to 80% of the concrete in roads and other structures is comprised of aggregates; up to 95% of asphalt roads and parking lots is aggregates. One mile of a two-lane concrete highway requires 7,200 tons of aggregates; one mile of a two-lane asphalt highway requires 10,300 tons of aggregates.

About one-half of all aggregates production is used for publicly-funded projects, such as highways, bridges, water/sewer systems, government buildings, airports, etc.

Most aggregates are used within 40 miles of where they are extracted and are typically hauled by dump truck. After a truck loaded with aggregate travels about 20 miles, freight charges usually begin to exceed the cost of the materials it carries.

Millions of tons of aggregates are produced in Missouri each year -- roughly 10 tons for each resident. Aggregates are essential to maintaining our quality of life because they are a major part of the roadways and bridges we utilize to go to work, school, and entertainment. They are the foundations and building blocks for our homes, our churches, our learning institutions, and our medical facilities.

Natural processes and agricultural practices tend to make Missouri soils used for crops and pastures become acidic. Acidic soil limits grain production, plant growth, and forage quality. The cure is agricultural limestone (aglime), which is readily available throughout the state.

The use of nitrogen-containing fertilizers (ammonia nitrate and anhydrous ammonia) is extensive in agriculture, and this practice is a leading contributor to soils becoming acidic. Other contributors are decomposition of organic matter, leaching of soil components, rainwater, and plant uptake of calcium and magnesium.

Aglime is a natural substance since it is merely finely ground limestone and is available throughout the state. It is usually broadcast dry on the surface of fields using a spreader truck.