GB429015A - Improvements in and relating to aggregates for concrete or other cementitious masses - Google Patents

Abstract

Relates to the production of light weight aggregate for concrete by heating to fusion preformed bodies of ceramic material containing substances which on heating form gas to expand and vesiculate the bodies, and consists in preventing clinkering together of the bodies during firing by the provision or production, prior to or during the firing, of an outer coating or layer of less fusible material. The less fusible coating may be applied to the bodies before they are introduced into the kiln or refractory material in powdered or granulated form may be introduced together with the bodies, e.g. into a rotary kiln, so that it coats them during their passage through the kiln. In a modification the coating is produced by heating the bodies in an oxidizing atmosphere. All three methods may be used in combination. The basic raw material for the bodies is preferably an earth or clay containing one third alumina and two thirds silica. If the fusing point is substantially above 2000 DEG F. fluxes, e.g. lime, magnesia or iron compounds are added. To the clay or earth are added, unless already present, 3-6 per cent of carbonaceous material, e.g. coal or coke and 3-6 per cent of a readily reducible compound that will liberate a gas in the presence of carbon at temperatures around 2000 DEG F., e.g. calcium sulphate, oxides of iron, or mixtures thereof. Several compounds liberating gas at different temperatures may be used, e.g. magnesium and calcium sulphates. The mixture is moulded into rounded bodies from sand size to a size even larger than the coarsest aggregate in general use. Before being burnt, the bodies may be coated with relatively refractory material, e.g. silica, diatomaceous earth, or burnt or raw fireclay rich in silica. The firing may then take place in a rotary kiln.