Production of autoclaved aerated concrete with silica raw materials of a higher solubility than quartz part I: Influence of calcined diatomaceous earth

This study examines the effects of calcined diatomaceous earth (C-DE) as a silica raw material of a higher solubility than quartz, on the mechanical and microstructural properties of autoclaved aerated concrete (AAC) produced at the steam curing temperature of 192 °C for 6 h. Quartz within an AAC mixture was replaced at various replacement ratios by C-DE. The resultant phases were characterized using quantitative and qualitative X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA), and thermogravimetric analysis (TGA). In the mixtures with more than 50% substitution of quartz with C-DE, the autoclaving temperature of 192 °C with a duration of 6 h prevented the crystallization of amorphous calcium silicate hydrate (C-S-H) to tobermorite. The optimum strength was obtained at the substitution ratio of 75% despite having the lowest tobermorite content. By substituting quartz with C-DE for higher than 50%, plate-like tobermorite was changed to grass-like and amorphous C-S-H with low CaO/SiO₂.