HYDROTHERMAL CHARACTERISTICS OF SAND-LIME BRICK PRODUCTION

The chemical reaction of calcium hydroxide with silica at high tempera ture and pressure forms the basis for the production of sand-lime bric ks. The principal requirements of the lime and sand are that both shou ld be sufficiently reactive to yield a binder (calcium silicate hydrat e) of sufficient quality at competitive costs. The reaction velocity, the formation of the binder, and the properties of the sand-lime produ cts were found to depend on many factors: Raw materials (composition a nd reactivity) including SiO2-source: quartz, sand, fly ash, shale fin es, slag, etc.; the CaO-source: lime, cement, mixtures of lime and cem ent, etc.; added modifiers, accelerators. Preparation conditions: slak ing, mixing, water content and moulding pressure. Autoclaving conditio ns: pressure/temperature, time of autoclaving. The usual autoclave pre ssure in the industry lies between 64 to 120 bar . h. In recent years there has been a trend to reduce the autoclaving pressure while retain ing standard properties. The aim is to lower the cost and increase the life time of the autoclaves in old plants. A review is given of the c urrent knowledge and hypotheses concerning the compositions and struct ures of raw materials and of the resultant reaction. products in relat ion to the properties of sand-lime products.