Pub. 5 2015 Issue 1

15 MINING FOCUS Cement is critical to the construction industry – mixed with water and gravel it forms concrete, one of the key construc- tion materials in the world today. Cement is a direct derivative of the mining in- dustry and is produced by heating lime, silica, alumina, iron, and other materials at high temperature. The resulting sub- stance is a marble-like ball called clinker that is ground, mixed with limestone and gypsum, and used to create concrete. Varying the mix of cement, sand and aggregate enables concrete to be used in a range of applications. Products can be designed, colored and shaped to ac- commodate a variety of environmental conditions, architectural requirements and to withstand a wide range of loads, stresses and impacts. Famous concrete structures include the Hoover Dam, the Panama Canal and, incredibly, the Roman Pantheon. The ancient Romans are considered the earliest large-scale users of concrete technology, which was widely used in the Roman Empire as early as 300 B.C. The Colosseum in Rome was built largely of concrete, and the concrete dome of the Pantheon is the world's largest unrein- forced concrete dome. However, use of concrete can be traced back to ancient Egypt and Chi- na. For example, Egyptians mixed mud and straw to create dried bricks in 3000 B.C., and made a mortar combining lime and gypsum for use in building the Pyra- mids. About the same time, the Chinese combined materials that had the same characteristics as cement with bamboo, then used the combination to build the Great Wall, as well as boats. Today, the most widely used form of cement in the world is Portland ce- ment. Portland cement is a generic term for nearly all modern cement, ow- ing its name and origin to a British stone mason named Joseph Aspdin. Portland cement was developed from natural ce- ments made in Britain beginning in the middle of the 18th century. Its name is derived from its similarity to Portland stone, a type of building stone quarried on the Isle of Portland in Dorset, Eng- land. In the 1820s, Aspdin’s quest for a manufactured counterpart to natural or Roman cement (derived from volcanic ash and other naturally occurring min- erals) led to his discovery and patent of Portland cement. The name for Aspdin’s invention served two purposes. It distinguished the material from Roman cement, which existed for centuries, but it also was a marketing ploy. Concrete made from his new cement spoke to the highly prized building Portland stone quarried in England. Modern Portland cement is the product of high temperature conver- sion of finely ground materials—often as basic as blends of limestone, clay, and shale—containing four key ingredi- ents: calcium oxide, silica, alumina, and iron. Producers rely on native materi- als, and cement plants sit near quarries with rocks bearing some or all of these elements. When processed in a long horizontal furnace known as a rotary kiln, blends of raw materials reformulate into glass- like nodules called clinker. Suppliers then grind clinker and gypsum to ex - treme fineness to produce cement. The finished product is shipped to concrete producers in bags or in bulk. Cement’s natural chemistry comes to life in the presence of water, sand, and gravel or crushed stone—known as fine and coarse aggregate. Upon mixing with water, cement’s calcium compounds hy- drate to form new agents that bind the aggregates into concrete. Very little cement and concrete is traded and transported internationally. The relative expense of land transport usually limits cement and concrete sales. As a result, the manufacturing of con- crete supports local economies around the world. According to the Portland Cement Association, here in Utah the cement, concrete and related industries is re- sponsible for providing jobs to 5,519 employees with an annual payroll of $223.4 million. The state revenue from this industry is over $62.3 million each year. As we move into the second de- cade of the 21st century, it is clear that building and revitalizing infrastructure will be an overriding theme and an area of significant investment for the United States, and concrete – which begins at the mine, where raw materials like lime- stone, silica, aluminates, feric minerals and others are obtained – will continue to play a significant role. X