Production of autoclaved aerated concrete with silica raw materials of a higher solubility than quartz Part II: Influence of autoclaving temperature

This study examines the effects of autoclaving temperature on the mechanical and microstructural properties of autoclaved aerated concrete (AAC) containing calcined diatomaceous earth (C-DE) as the main silica source. The autoclaving process was conducted using an autoclave at various temperatures of T = 134-192 °C and a corresponding steam pressure of P = 2-12 bar for 6 hours. The resultant phases were characterized using quantitative and qualitative X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The compressive strength of samples containing C-DE as the main silica source increased by 30% when the autoclaving temperature decreased by around 60 °C. This is in complete opposition to samples containing quartz as the only SiO2 source. The compressive strength of the latter decreased by 85% when the autoclaving temperature decreased by approximately 60 °C. For all samples, changes in compressive strength corresponded with changes in tobermorite formation.