Nonhydraulic Cements

In general, there are two main classes of constructional cements nonhydraulic, which do not set under water, and hydraulic. Their composition can be indicated by the following two examples ... 

Nonhydraulic cements were among the most common of the ancient cements. The relatively high solubilities of portlandite (Ca[OH]2) and gypsum means that they deteriorate rapidly in moist or wet environments. Many decades ago, the Romans used lime-based cements and mortars (cement plus sand) by ramming the wet pastes... 

Cement is a binder that sets and hardens by itself or binds other materials together. The most widely known application of cements is in construction a second one is the area of bone cements. Cements used in construction are characterized as hydraulic or nonhydraulic and mostly for the production of mortars and concrete. Hydraulic cements set and harden after combining with water. Most construction cements are hydraulic and based on Portland cement, which consists of calcium silicates (at least 2/3 by weight). Nonhydraulic cements include the use of nonhydraulic materials such as lime and gypsum plasters. Bone cements and bone cement composites refer to compounds that have a polymer matrix with a dispersed phase of particles. For instance, polymethylmethacrylate (PMMA) is reinforced with barium sulphate crystals (for radio-opacity) or with hydroxyapatite... 

Mortar masses on a purely inorganic basis consist of hydraulically setting components such as cement or gypsum that harden with water. In contrast to these products, there is nonhydraulically, that is, air-hardening mortar. 

Nonhydraulic cements are the most ancient type of cement. Most of these cements derive from the simple calcination of gypsum or calcium carbonates such as limestones. They harden when the calcine obtained is mixed with a given amount of water but the hardened products then produced when put in direct contact with water again are subject to dissolution and hence they are not resistant to water. Gypsum cement is still widely used in modern countries as plaster of Paris for interior applications like insulation panels. The transformation of natural gypsum to the calcium sulfate hemihydrate is obtained by moderate heat treating at 130-150 C and it is described by the following chemical reaction ... 

A better nonhydraulic cement type is quick lime or simply lime or calcia (CaO), which has been used extensively in Europe and the Middle East since Ancient Times, through the Middle Ages and well into the nineteenth century, and in Central America by the Mayas. Quicklime is obtained from the calcination of limestone in a vertical shaft kiln or rotary kiln by intense heating at 900-1000°C. The calcium carbonate (calcite) of the limestones gives off carbon dioxide leaving quicklime as follows ... 

Portland cement is termed a hydraulic cement because its hardness develops by chemical reactions with water. It is used primarily in mortar and concrete to bind aggregates of inert particles (sand and/or gravel) into a cohesive mass these are considered to be composite materials (see Section 16.2). Other cement materials, such as lime, are nonhydraulic—that is, compounds other than water (e.g., CO2) are involved in the hardening reaction. 

Cement A material that sets and hardens and can be used to bind materials together. A distinction is made between hydraulic and nonhydraulic binders. Hydraulic binders are able to set and harden under an excess of water (e.g. portland cement), while nonhydraulic binders require the removal of excess water to harden (e.g. lime). 

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