Siliceous rocks can be an excellent alternative for making such types of building materials as ceramic bricks, lightweight aggregates for concrete and the like.
Sedimentary and volcanic-sedimentary siliceous rocks in bulk consist of opal (diatomite, spongolite, etc.), flasks and trefoils. The mentioned siliceous rocks are three-component minerals. Along with the siliceous component, there is necessarily a clay material. In ordinary diatomites, flasks, trefoils, the content of silica (opal-cristobalite) varies from 60 to 80%, clay material – from 10 to 40%. In clayey varieties, the clay content increases to 30-60%. Quartz, glauconite, etc. are also present as usual impurities in different amounts.
Siliceous rocks are porous materials since sintering, and the resulting shrinkage only partially reduces the natural porosity of the sedimentary rock under glass transition conditions. If the sintering process is completed, a vitreous, almost non-porous mass can be obtained. The sintering experience indicates the possibility of regulating the porosity, bulk density, and strength of the calcined rock. The sintering process that occurs when firing various stones is one of the primary methods in ceramic technology. The most important properties of products: strength, hardness, frost resistance, acid resistance, fractiousness increase with increasing sintering.
When firing siliceous rocks, the wintering process occurs at a relatively low temperature (about 800 ° C). The phenomenon of vitrification is strongly pronounced at a temperature of 1200-1300 ° C. In some cases, the interval between sintering and melting is 50-70 ° C. To understand the sintering process, it is worth considering that fine-grained siliceous rocks have high porosity (25-55%).