Setting and curing of mortars obtained by alkali activation and inorganic polymerization from sodium silicate and silica aggregate

This research is focused on sodium silicate bonded silica aggregates for making sustainable construction materials such as bricks and precast products. Different compositions are investigated to produce castable mortars. The mortars are cured at temperatures ranging from 150 to 300 °C and characterized, in particular microstructural and mechanical properties are investigated. Very high compressive strength of 100 MPa and elastic modulus of 5 GPa are obtained for samples with optimized compositions and heat treatments. Solubility and degradation study of the samples in water demonstrate that alkali silicates are prone to be soluble if not treated at 200 °C or above. Transformation of Si-OH to Si-O-Si not only increases the strength but also makes it insoluble in water. It is concluded that sodium silicate bonded bricks and blocks are very promising and affordable materials for construction. They represent an alternative to Portland cement concrete bricks and to sintered clay bricks, providing higher strength and representing an eco-friendly material.