Cement clinkers are formed by the heat processing of cement elements in a kiln. Limestone, clay, bauxite, and iron ore sand in specific proportions are heated in a rotating kiln at 2,770° Fahrenheit (1,400° Celsius) until they begin to form cinder lumps, which are also known as cement clinkers. These are usually ground with gypsum to produce the fine powder later mixed with liquid to produce cement, although some manufacturers ship clinkers in their lump form to cut down on dust.
Cement is heavily relied upon to produce mortar, grouts, and concrete, and cement clinkers are the first stage, post firing, in making cement. Cement has strong bonding qualities when mixed with gypsum and water to form a hydration reaction, and it forms approximately one tenth of concrete, mixed with rocks, sand, and other materials and used in building construction all over the world. Concrete's high versatility makes it an ideal tool for building projects of all shapes and sizes, from skyscrapers to pool sides. Concrete can also be recycled when it has outlived its usefulness and converted back into cement clinkers through careful processing.
The most commonly used cement in the world is Portland cement, which is formed at high temperatures that chemically combine the ingredients into new components, including calcium silicates and calcium aluminates. When the cement clinkers are ground with approximately 5% gypsum, they form Portland cement. These compounds allow cement to set when combined with water and to form strong bonds that can withstand pressure, water immersion, and other elements.
Natural raw materials can be utilized in a kiln to form cement clinkers, although other materials with the proper chemical composition are also used, such as fly ash from coal burning, furnace slag, and other industrial byproducts. Depending upon the purpose for which the cement is intended, slightly different chemical formulations are used to increase strength, add sulfate resistance, make cement that is tolerant to low temperatures, form expansion cement that will not shrink after setting, or create masonry cement, which is not intended for concrete mixtures. If consumers are unsure about which cement formulation is appropriate for a project, they should consult a knowledgeable source to confirm that they are using the most suitable material for their needs.
Manufacture of cement clinkers has environmental ramifications, beginning with the dust, noise, and vibration caused by mining for natural raw materials. Cement kilns also eat through a substantial amount of fuel, and polluting equipment is used at most stages of cement manufacture. However, some of these effects are offset by the reuse of slag, fly ash, and silicate byproducts. Furthermore, many cement manufacturers use other agricultural and industrial byproducts to fuel the kilns, helping to dispose of these materials.
Cement, when mixed with water, forms a very strong alkaline solution. Gloves and eye protection should be worn at all times when working with cement, and cement should be washed from the skin immediately to prevent skin injury. Once cement hardens, it can be handled without precautions.