Cement, and Plasters

Lime is made by heating limestone, including chalk, to a temperature between 1100°C and 1200°C in a current of air, at which point carbon dioxide is driven off to produce quicklime (CaO). Approximately 56 kg of lime can be obtained from 100 kg of pure limestone. Slaking and hydration of quicklime take place when water is added, giving calcium hydroxide. Carbonate rocks vary from place to place both in chemical composition and physical properties so that the lime produced in different districts varies somewhat in its behaviour. Dolostones also produce lime however, the resultant product slakes more slowly than does that derived from limestones. 

Portland cement is manufactured by burning pure limestone or chalk with suitable argillaceous material (clay, mud or shale) in the proportion 3 1. The raw materials are crushed and 

When gypsum (CaS04.nH20) is heated to a temperature of 170°C, it loses three quarters of its water of crystallization, becoming calcium sulphate hemi-hydrate, or plaster of Paris. Anhydrous calcium sulphate forms at higher temperatures. These two substances are the chief materials used in plasters. Gypsum plasters have now more or less replaced lime plasters. 

---

Potassium alum, which also occurs naturally as the mineral kalinite [7784-24-9], KAl(SO 2 12H20, sp gr 1.75, is used ia tanning skins, as a mordant ia dyeiag, and ia the pharmaceutical and cosmetic iadustries (see Pharmaceuticals Cosmetics). It is used as a styptic pencil and as a hardening agent and set accelerator for cement and plaster. The ACGIH threshold limit value TWA is 2 mgAl/m (1 ). 

Hydraulic cements. These cements are formed from two constituents one of which is water. Setting comprises a hydration and precipitation process. Into this category fall Portland cement and plaster of Paris. 

The two other main types of human-made building cements, lime cement and gypsum cement, have been and still are used in many areas of the world. Both these cements require quite elaborate thermal procedures for producing their main components, which are slaked lime in lime cement and plaster of Paris in gypsum cement. Making them involves the calcination of an appropriate type of stone, a process that has been practiced since prehistoric times. Slaked lime is made by the calcination of limestone plaster of Paris, by the calcination of gypsum (see Textbox 33) (Cobum et al. 1990 Lea 1962). 

Casting involves filling molds with molten glass in much the same manner as cement and plaster of Paris molded objects. Art glass objects are often made by casting. 

We can confirm this point of view by looking at paramagnetic shifts and rs (for water) in the complexes of supposedly different water coordination. We find that in the Ln(III) series of complexes, LnY, anomalies often occur at around Tm(III) especially. We conclude that the exact structures of Ln(III) complexes like those of Na(I), K(I) and Ca(II) can not be represented by single simple pictures and we must refer to statistical populations of complexes of different structure at equilibrium. The complexity of the structural and dynamic features of this A-subgroup chemistry has been used to functional advantage both by man in cements and plasters and by biology in shells and bones and in messengers. 

Hydraulic cements are another class of technologically important materials. Examples include Portland cement, calcium aluminate cement, and plaster of Paris. They harden at room temperature when their powder is mixed with water. The pastes formed this way set into a hard mass that has sufficient compression strength and can be used as stmctural materials. Their structure is generally noncrystalline. 

What is milk of lime Mortar Cement Plaster Slaked lime Explain the hardening of mortar, cement, and plaster. 

The rate of curing depends primarily on the reactivity of the resin and curing agent. It is also dependent on the quantity of mix and on temperature. The materials used in the construction industry that can be bonded with epoxy resin adhesives are metals and metal alloys, concrete, natural stone, fibre cement and plaster, ceramic materials, glass, china and porcelain and wood. 

To write the formula for a hydrate, write the formula for the compound and then place a dot followed by the number of water molecules per formula unit of compormd. The dot in the formula represents a ratio of compound formula emits to water molecules. For example, CaS04 2H2O is the formula for a hydrate of calcium sulfate that contains two molecules of water for each formula unit of calciiun sulfate. This hydrate is used to make portland cement and plaster of paris. To name hydrates, follow the regular name for the compound with the word hydrate, to which a prefix has been added to indicate the number of water molecules present. Use Table 5.5 to find the correct prefix to use. The name of the compound with the formula CaS04 2H2O is calcium sulfate dihydrate. 

This chapter commences with advice on the cleaning of zinc surfaces. The major corrosion interests are then considered in five groups (a) inorganic chemicals and their aqueous solutions, (b) organic materials and fuels, (c) concretes, cements, and plaster, (d) bitumen, and (e) other building materials. 

The sectors Manufacture of Weapons Ammunition (25.4) and Other First Processing of Steel (24.3) show the highest hazard ratio and can be regarded as the most risky sectors to work in. The top 10 high-hazard sectors features three branches of the metals industry, two mining branches and two branches closely related to construction Demolition site preparation (43.1) and Manufacture of articles of concrete, cement and plaster (23.6). Various branches in the construction sector show hazard ratios ranging from 4.0 to 5.2. 

SETARAM, File 2, Cements and Plasters, Sheet 1, p. 188, Caluire Cedex,... 

---