Making Cement - November 14, 2007
Jeff Schalau, Associate Agent, Agriculture & Natural Resources, Arizona Cooperative Extension, Yavapai County

You may be wondering just what cement manufacturing has to do with gardening Ė actually very little. However, I will attempt to make a tenuous connection later in this column. We all benefit from cement. We use concrete to set fence posts, to construct hardscape elements, in the foundations of our homes, and roads. Most people probably donít think a lot about where cement comes from and how it is made.

As with any industry, the cement manufacturing industry has a history. The making of cement started in 1824 when Joseph Aspdin, a British stone mason, heated a mixture of finely ground limestone and clay in his kitchen stove. He ground the mixture to a powder and found when mixed with water it hardened into a hard, weather resistant mortar. He named it Portland cement because it resembled a stone quarried on the Isle of Portland off the British Coast.

Todayís Portland cement is the fundamental ingredient in concrete. It contains a combination of calcium, silicon, aluminum, and iron. Raw materials may include combinations of limestone, shells or chalk, and shale, clay, sand, or iron ore. These are usually are mined from quarries near the plant. Materials from the quarries are milled into small pieces (3/4 inch) and transported to the cement plant, proportioned to have a specific chemical composition, milled to a powder, and fed into a kiln. The kiln heats this material up to between 2,600 and 3,000 degrees F. A series of chemical reactions cause the material to fuse and create black pellets about the size of marbles. These are called clinkers. The clinkers are discharged red-hot from the lower end of the kiln and cooled to handling temperatures. The cooled clinker is combined with gypsum and ground into a fine gray powder called Portland cement.

Phoenix Cement in Clarkdale has been in operation since 1959 and continues to be a major employer in the Verde Valley. Regional and worldwide demand for cement continues to increase. This has led to two new cement plants being constructed in Yavapai County: one will be in Drake by Stirling Bridge Cement, LLC of Phoenix (north of Paulden) and the other in Seligman by Cemex of Mexico.

As you can imagine, cement manufacture requires lots of energy to fire the kilns in addition to electric motors and conveyor systems. Many cement plants have on-site power plants fueled by coal. In addition, cement plants (and other industrial manufacturers) are looking to use woody biomass from forest thinning projects and wood waste from sawmills to produce renewable energy. This creates new economic opportunities for small diameter timber and can ultimately help us utilize beetle-killed timber and manage wildland fuels that threaten Arizonaís forested communities. I believe we will begin to see these renewable fuels used more and more in manufacturing.

For those that held on for the gardening connection, natural processes also lead to the formation of cement-like deposits. Those that have gardened in the area may have heard of caliche. In Arizona, caliche refers to calcium carbonate that has been leached by precipitation from the upper soil layers and accumulated in lower soil layers where it has combined with soil particles, gravel, and rocks to form a hardpan. Caliche is very common in the arid southwest and can often be seen where road cuts have exposed subsoil layers. In Texas, caliche is mined and used in the manufacture of cement.

If you have heavy caliche deposits, it can interfere with your gardening/landscaping goals. The most common problem is poor drainage caused by a solid caliche layer. This can lead to salt accumulation and/or shallow rooting of plants. Another side effect is the general alkalinity of limey soils. Where there is caliche, there is lime and this causes soil alkalinity. Alkaline soil conditions can cause nutrient deficiency problems in plants that are not well adapted to these soil types. Nutrient deficiencies observed are often iron and sometimes phosphorus and zinc. All summed up, most gardeners realize the benefits of cement but usually donít appreciate caliche.

The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site:

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Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr. #C
Prescott, AZ 86305
(928) 445-6590
Last Updated: November 8, 2007
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