Microwave Hydrothermal Assessment for CSH Formation in Silica-Lime-Water Systems

Abstract

Microwave energy as a fast technique was utilized for the preparation of calcium silicate hydrates using hydrothermal reaction of silica quartz and/or silica fume with active lime in a solution. The silica/lime ratio was selected to be 60/40 in a mix as compared with the composition of sand-lime-based construction industries. The CSH formation was assessed after treatment at 140 and 160 °C under saturated steam microwave hydrothermal conditions. Moreover, the CSH formation was studied at 160 °C for periods up to 180 min. The prepared samples were characterized through XRD and FTIR. Further, DSC and SEM tools were used to investigate selected samples. The results led to the conclusion that the complete reaction of lime with the available silica sand was pronounced for samples prepared under saturated steam at 160°C/2 h, forming cross network needle structure morphology as seen from SEM results. Moreover, the results confirm the conversion phenomenon of CSH compounds changing in reaction time or in reactive silica percentage into another form of CSH. An amorphous structure like tobermorite is formed in samples containing silica fume as source of silica and microwave hydrothermally cured at 160 °C/2 h.