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| Types of Cement |
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Although only certain types of cement are commonly utilized today, there are several different types of cement that can be created. Various types of cement are possible by blending different proportions of gypsum, clinker, and other additives. Cements that are used for construction fall into two main categories based on cement properties, hydraulic or non-hydraulic. In addition to the two main cement forms, there are several different forms of hydraulic cement. Of the many varieties of hydraulic cement, the most commonly used cement today is Portland cement. Non-Hydraulic Cement Of the two main types of cement, non-hydraulic cement is more basic, and was the first form of cement invented by early scientists, thousands of years ago. Non-hydraulic cement is cement which cannot harden while in contact with water, as opposed to hydraulic cement which can. Non-hydraulic cements are created using materials such as non-hydraulic lime and gypsum plasters, and oxychloride, which has liquid properties. After non-hydraulic cement is utilized in construction, it must be kept dry in order to gain strength and hold the structure. When non-hydraulic cement is used in mortars, those mortars can set only by drying out, and therefore gain strength very slowly. Due to the difficulties associated with waiting long periods for setting and drying, non-hydraulic cement is rarely utilized in modern times. Hydraulic Cement Hydraulic cements are cements that have the ability to set and harden after being combined with water. As a result of chemical reactions, after hardening hydraulic cement mixtures retain strength and stability even when in contact with water. Due to the fact that hydrates that are formed when hydraulic cement is initially in contact with water the new mixture becomes essentially insoluble in water. That gives hydraulic cement a strength and stability that makes it distinct from non-hydraulic cement. Hydraulic cement is made primarily from limestone, certain clay minerals, and gypsum, which are burned together in a high temperature process that drives off carbon dioxide and chemically combines the primary ingredients into new compounds. Setting and hardening of hydraulic cements is caused by the formation of water-containing compounds, which are formed during reactions between cement components and initial contact with water. That reaction produces the hydrates which give hydraulic cement strength and stability. As a result of the immediate start of the reactions, stiffening can be observed which is initially slight but which increases with time. The compressive strength of the material grows steadily over a period that can range from a few days in the case of ultra-rapid-hardening cements to several years in the case of primitive hydraulic cements. The ability to withstand continuous contact with water, in addition to the ability to set and harden quickly, and greater relative strength makes hydraulic cement the main cement utilized in modern day construction. Portland Cement In addition to the two main forms of cement which exist, hydraulic and non-hydraulic, there are also several types of hydraulic cements that can be made and used in construction. The main form of cement used in construction worldwide today is the hydraulic cement called Portland cement. Portland cement is a type of hydraulic cement made by heating a limestone and clay mixture in a kiln and pulverizing the materials. It is a fine, grey or white powder that is made by grinding Portland cement clinker, a limited amount of calcium sulfate which controls the set time, with other minor constituents. Portland cement is the most common type of cement in general usage in many parts of the world. The cement is used as the basic ingredient of concrete, mortar, stucco and most non specialty grout. Invented in the 19th century, Portland cement has become the staple form of cement produced and used worldwide. All references to cement worldwide refer to Portland cement, as it constitutes virtually all cement produced. |
