Silica-Concrete Products

precast structural members, such as inner wall panels, floor slabs, wall units, columns, and beams, made from silica concrete. Silica-concrete products are used in modern construction along with reinforced-con-crete structures and products; the former may sometimes be reinforced with a steel framework (reinforced silica concrete). The production processes for silica-concrete products and their use in construction were first developed by Soviet specialists (Lenin Prize, 1962).

In the USSR the most widely used silica-concrete products are prepared from lime-quartz and lime-slag binders and natural sand. The production processes for the manufacture of silica-concrete products are (1) the preparation of the raw materials, including the preparation of a mix composed of a binder, underground sand, and water, (2) the molding of the products, either with or without a framework, (3) autoclave processing, (4) cooling, (5) removal from the molds, and (6) storage.

Two methods are used to prepare the mix. In the first method, unslaked lime is ground in a ball mill together with quartz sand or slag; admixtures of cement, a small amount of gypsum, or surface-active agents may also be added. The resultant binder is added to the unground sand at a ratio of 300–450 kg per cubic meter of concrete, together with the amount of water necessary to ensure complete slaking of the lime and the formation of a mix that can be easily poured into molds by means of vibration consolidation. In the second method, the binder is prepared by mixing slaked lime with ground sand.

The processing, or steaming, of silica-concrete products in an autoclave typically involves raising the temperature and pressure inside the autoclave to maximum values for 2–3 hr, isothermal heating of the products for 4–8 hr, and purging of the steam and cooling of the products for 2-3 hr.

Silica-concrete products are used in housing, industrial, and agricultural construction. The use of silica-concrete products to replace structures and products of equivalent performance characteristics made from cement concrete results in a cost reduction of 10-15 percent. In silica-concrete products designed for external sections of buildings and for interiors where relative humidity exceeds 60 percent, the framework and insertion elements should be protected from corrosion, for example, by coating or metallization.