Iowa's Cement Industry
by Robert M. McKay
Devonian limestone quarried along the Mississippi Valley is converted into various portland cements at this cement production facility, Lafarge Corporation's Davenport Cement Plant located near Buffalo, Iowa.
Photo courtesy of Lafarge Corporation.The cement industry in Iowa is geographically restricted to four sites, but these sites account for about one-third of the total value of non-fuel mineral production in the state. In 1993 these four plants produced and marketed 2.5 million tons of portland cement valued at 136 million dollars. Lehigh Portland Cement Company and Holnam Inc. both operate plants at Mason City in Cerro Gordo County. Lafarge Corporation operates a plant near Buffalo in Scott County, and Monarch Cement Company in Des Moines grinds cement clinker, an intermediate product, received from another facility in Humboldt, Kansas. In 1992 Iowa ranked 10th in both production and value among the 37 portland cement-producing states.
The majority of cement produced in Iowa and worldwide is called "Portland cement." This product consists of finely ground powder composed of limestone and clay which, when mixed with water, makes a binding paste for masonry mortar and construction concrete that will harden or "set" to an insoluble, rock-like solid. The name "Portland cement" was coined by its inventor Joseph Aspdin, a brick layer and mason from Leeds, England. He patented this process of making artificial stone in 1824 and named it for the well-known building stone quarried from the nearby Isle of Portland, a peninsula in southern England.
The raw materials used in the production of Portland cement consist principally of limestone and clay, resources which occur abundantly in Iowa. Calcium-rich limestones and clay-rich glacial deposits are utilized as these raw-mix sources. Production begins with quarrying and crushing the stone and clay, followed by a dry-process blending of these materials in specified proportions. After preheating the blended mix to about 1600 degrees F, the mixture enters the top end of a slightly inclined, coal- or gas-fired rotary kiln where the mix temperature continues to rise to 2500 degrees F.
Temperature-driven chemical reactions occur at various times during this firing process. Carbon dioxide and water are driven from the limestone and clay minerals at lower temperatures, while reactions between the elements of calcium, oxygen, aluminum, and silica take place at higher temperatures where partial melting and liquidization also occur. This latter phase generates the final cement compounds (calcium silicates and aluminates) which combine into black, glistening nodules of various sizes. This material is known as "Portland cement clinker." After the clinker drops from the kiln and cools, it is ground with a small percentage of gypsum (calcium sulfate) to a fine powder. This final product is then readied for shipping via rail, barge, or truck.
Portland cement has been produced in Iowa since the beginning of this century. The industry has grown steadily in the volume of production even though the number of plants has remained about same. Modern Portland cements are manufactured in large, multimillion-dollar industrial plants capable of producing several thousand tons of cement per day. Nearly all construction concrete used today incorporates Portland cement as its basic binding ingredient. Various "types" of cement can be produced to meet needed project-design engineering specifications.
Significant trends in the industry in Iowa, as well as nationally, include efforts to increase production and energy efficiency. While the U.S. cement industry has made progress in energy efficiency and productivity, it continues to rank low in energy efficiency when compared to other industrialized nations.
The continued growth of the north-central United States construction markets, combined with Iowa's raw materials, geographic position, and innovative plant operations, ensures that the cement industry in Iowa will endure well into the next century.
Adapted from Iowa Geology 1989, No. 14, Iowa Department of Natural Resources