Shrinkage prevention

Ozone is being investigated for shrinkage prevention (182). Wool and blends of wool, cotton, and polyester have been finished to provide improved flame-retardant, durable-press, and shrinkage properties (183,184). Fabrics of these types are often used for uniforms or protective clothing (185). 

R. W. Moncrieff, Wool Shrinkage and Its Prevention, National Trade Press, London, 1953. 

A number of modifiers are employed to prevent most of the shrinkage of gypsum when it is heated above 300°C. Among these are boric acid (118) and sodium and other chlorides (119,120). A review of the development and composition of some investments is given (121). 

When concrete hardens, the cement paste shrinks. The gravei, of course, is rigid, so that smaii shrinkage cracks are created. It is found that air entrainment (mixing small bubbles of air into the concrete before pouring) helps prevent the cracks spreading. 

There are certain basic rib-design guidelines that should be followed (Fig. 3-9). The most general is to make the rib thickness at its base equal to one-half the adjacent wall s thickness. With ribs opposite appearance areas, the width should be kept as thin as possible. In areas where structure is more important than appearance, or with very low shrinkage materials, ribs are often 75 or even 100 percent of the outside wall s thickness. As can be seen in Fig. 3-10, a goal in rib design is to prevent the formation of a heavy mass of material that can result in a sink, void, distortion, long cycle time, or any combination of these problems. 

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