Cement manufacturing is truly unique. It requires technology ranging from mega-machines in mines and quarries to nano-needles in research centers. A 24/7 continuous process of dynamic chemical and physical transformations, cement manufacturing uses temperatures in cement kilns that easily reach one-quarter the surface temperature of the sun.

That spectrum of technology represents literally dozens of science and engineering disciplines: ceramics engineering, civil engineering, control engineering, combustion engineering, electrical engineering, environmental engineering, mechanical engineering, and process engineering. Natural sciences like geology, organic, inorganic, and analytical chemistry, and physics are also represented, and of course today's manufacturing relies heavily upon computer automation.

Take a look at what's happening in our industry and we think that you'll agree that this is an incredibly fascinating process with unlimited career opportunities. The Cement 101, Version 4.0: A Guide to Careers in the Cement Industry supplement is a cooperative effort between the Portland Cement Association's Manufacturing Technical Committee and Cement Americas magazine.

You'll find articles spotlighting the industry's environmental excellence in areas of outreach, environmental performance, innovation, land stewardship, and energy efficiency. You'll also read about carbon dioxide reduction initiatives in the cement industry and get a glimpse into the world of virtual cement and concrete.

Cement 101 offers a resource and reference guide that will direct you to the companies and organizations you can contact for employment opportunities in the cement industry.

Want to find out more?

Go to our website at www.cement.org/manufacture.

Cement Manufacturing: The History, The Process

In 1824, Joseph Aspdin, a British stone mason, obtained a patent for a cement he produced in his kitchen. The inventor heated a mixture of finely ground limestone and clay in his kitchen stove and ground the mixture into a powder to create a hydraulic cement — one that hardens with the addition of water. Aspdin named the product portland cement because it resembled a stone quarried on the Isle of Portland off the British Coast.

Portland cement, the fundamental ingredient in concrete, is a calcium silicate cement made with a combination of calcium, silicon, aluminum, and iron. Producing a cement that meets specific chemical and physical specifications requires careful control of the manufacturing process.

The first step in the process is obtaining raw materials. Generally, raw materials consisting of limestone, shells or chalk, and shale, clay, sand, or iron ore are mined from a quarry near the plant. At the quarry, the raw materials are reduced by primary and secondary crushers. Stone is first reduced to 5-in. (125-mm) size, then to 3/4-in. (19-mm).

Once the raw materials arrive at the cement plant, the materials are proportioned to create a cement with a specific chemical composition. Two different methods, dry and wet, are used to manufacture portland cement.

In the dry process, dry raw materials are proportioned, ground to a powder, blended together and fed to the kiln in a dry state. In the wet process, a slurry is formed by adding water to the properly proportioned raw materials. The grinding and blending operations are then completed with the materials in slurry form.

After blending, the mixture of raw materials is fed in to the upper end of a tilted rotating, cylindrical kiln. The mixture passes through the kiln at a rate controlled by the slope and rotational speed of the kiln. Burning fuel consisting of powdered coal or natural gas is forced into the lower end of the kiln. Inside the kiln, raw materials reach temperatures of 2,600°F to 3,000F° (1,430°C to 1,650°C). At 2,700°F (1,480°C), a series of chemical reactions cause the materials to fuse and create cement clinker — grayish black pellets, often the size of marbles. Clinker is discharged red-hot from the lower end of the kiln and transferred to various types of coolers to lower the clinker to handling temperatures.

Cooled clinker is combined with gypsum and ground into a fine gray powder. The clinker is ground so fine that nearly all of it passes through a No. 200-mesh (75-micron) sieve. This fine gray powder is portland cement.