Study of the influence of the secondary raw materials on microstructure and properties of calcium silicate composite

Abstract

Calcium silicate composites are a widely used building material, especially autoclaved aerated concrete or sand-lime bricks. The physico-mechanical properties of these materials depend on their microstructure. Microstructure is characterized by the content of crystalline calcium silicate compounds that arise during autoclaving. This is in particular the tobermorite mineral, which carries the mechanical strength of the composite. This paper focuses on the influence of secondary raw materials on properties and microstructure of the calcium silicate composite. Secondary raw materials were selected as slag from the combustion of lignite and ground glass. Mixtures of composites were selected with respect to the required C/S molar ratio of 0.73. The hydrothermal treatment was carried out at a temperature of 190 °C and a residence time of 4, 8 and 16 hours. The microstructure of calcium silicate composites and autoclaved aerated concrete was studied. The use of slag resulted in an increase in the intensity of the diffraction line of tobermorite by X-ray diffraction analysis as well as the use of glass. The difference was particularly evident in the shape of the tobermorite crystals. Long strong crystals were detected in the sample with slag, while the sample with glass exhibited low tobermorite leaves. Porous structure of autoclaved aerated concrete with slag was uniform, unlike samples with glass. Both materials have a positive effect on the increase in compressive strengths of the samples.