Kansas Geological Survey, Public Information Circular (PIC) 6
Next Page--Lightweight Aggregate, Sand and Gravel
David A. Grisafe
The average American uses more than a million pounds of cement, sand, gravel, and crushed stone over the course of a lifetime. These geologic materials are used throughout society, from concrete in buildings to crushed stone for roads. Much of the demand for these materials comes from areas of growing population where new construction and road-building are most common. Because sand, gravel, and other geologic commodities come from the earth, their production often raises a conflict between people's desire for an undisturbed landscape and the demand for these resources.
Mines and quarries that produce sand, gravel, and crushed stone are extremely common in Kansas. However, most people know very little about such operations. To help provide information about these resources, this circular discusses sand, gravel, crushed stone, and lightweight aggregate, a man-made material manufactured from shale. This publication describes the type and amount of these materials used in Kansas; their source, processing, and usage; and environmental issues related to their production.
These materials--sand, gravel, crushed stone, and lightweight aggregate--are known collectively as aggregate. By definition, aggregate is a construction material that is hard and inert (that is, it does not react chemically with materials around it). It is used to make concrete, mortar, asphalt, or similar products. Buildings nearly always include concrete, concrete block, and mortar. Most roads are constructed from concrete or asphalt that contain sand and crushed stone. Alone, aggregate is used as the support for railroad beds, road covering, or fill; large quantities of sand and gravel and crushed stone are used on unpaved county roads throughout the state.
Limestone, dolomite, and sandstone--the rocks used to make crushed stone--occur naturally, as do sand and gravel. Lightweight aggregate is manufactured from shale, a soft rock composed mostly of clay minerals that occurs naturally. Sand, gravel, and crushed stone require little processing compared to many commodities, but vast quantities are used in construction. Thus, they are high volume/low-unit-cost commodities. That is, sand, gravel, and crushed stone are sold in large quantities at a low cost per ton. Over two billion tons of sand, gravel, crushed stone, and lightweight aggregate were used or sold in the U.S. during 1994. In Kansas, nearly 23.6 million tons of crushed stone and 12.3 million tons of sand and gravel, worth over $130 million, were produced in 1994; that's an average of about 14 tons of aggregate per person in the state.
Crushed stone is used throughout Kansas, but most of it is quarried from limestone in the eastern third of the state. Smaller amounts are also produced from dolomite (a rock that looks similar to limestone) and sandstone in central Kansas, and from relatively soft limestones in northwestern and north-central Kansas. In addition, some crushed stone is produced in northwestern Kansas where the Ogallala Formation is naturally cemented together. In general, Kansas counties with larger annual production of crushed stone are found around the state's larger cities, especially in the highly developed corridor from Topeka to Kansas City and in an area east of Wichita (fig. 1).
Figure 1--Surface geology of Kansas, showing counties producing aggregate.
Crushed stone is produced by blasting rock from quarry or mine walls and then crushing and screening the rock to the desired sizes for different applications. Many producers collect the extremely fine, dust-like material remaining from the crushing operation and sell it to farmers for agricultural lime, which helps reduce the acidity of their soil.
Crushed limestone, crushed clay or shale, and other ingredients are mixed together and baked in kilns to produce a coarse material that is ground, then bagged for sale as cement (fig. 2).
Figure 2--Cement plant in Allen County.
Gypsum is often added to cement as a retarding agent to keep it from setting too rapidly. About 1.8 million tons of cement, valued at more than $100 million, were produced in Kansas in 1994. Water, crushed stone, sand, and gravel are added to the cement to make concrete. To make mortar (the material that is used to cement bricks or concrete blocks together), finer grains of sand are used instead of gravel in the mixture, producing a smoother finish.
Over time, the state has used more and more crushed stone, although the amount varies depending on economic and construction activity. Based on annual production reported to the U.S. Bureau of Mines and census figures, consumption of crushed stone in Kansas has risen from about 800 pounds per person in 1920 to about 18,500 pounds in 1994, more than a tenfold increase. At the same time, the state's population has grown, so that total production has jumped from about 700,000 tons in 1920 to 23.6 million tons in 1994.
Next Page--Lightweight Aggregate, Sand and Gravel
Kansas Geological Survey, Public Outreach
1930 Constant Ave., Lawrence, KS 66047-3726
Phone: (785) 864-3965, Fax: (785) 864-5317
Web version Jan. 1997