Hydrothermal solidification of siliceous and calcareous wastes into building materials: A generic mix design framework

The presence of inactive components in siliceous and calcareous wastes tends to cause a misunderstanding in their mix design for hydrothermal solidification. The contents of typical reactive elements (i.e. Ca act , Si act and Al act ) in raw materials are quickly determined by simulating hydrothermal conditions. A generic mix design framework is proposed, which utilizes the molar ratio of Ca act /Si act as the controlling parameter. The framework was demonstrated through a series of studies, which involved the production of granular materials using a mixture of clayey soil with slaked lime, as well as the production of compacted cylinders using a mixture of clayey soil with either slaked lime or calcium carbide slag. Experimental results showed that the hydrothermal samples achieved their maximum strength when the molar ratio of Ca act /Si act in raw materials approached the theoretical Ca/Si molar ratio (i.e. 0.83) in tobermorite, provided that the molar ratio of Al act /(Al act + Si act ) remained below 21%. • Reactive Ca act and Si act in raw solid wastes are quantified. • A Ca act /Si act molar ratio-controlled mix design framework is proposed for material synthesis. • An optimal Ca act /Si act molar ratio of 0.83 is found for hydrothermal synthesis in CaO-SiO 2 -H 2 O reaction system. • Densification occurs to the pores between 0.1 and 10 μm.