Alkali-activated cement based on natural SiO2-containing material: Part I. Strength, hydration, microstructure and durability

An alkali-activated cement (AAC) based on natural SiO₂-containing materials—grounded porcellanite (Pr) and highly dispersed pure quartz sand—was examined. Sodium hydroxide was used as an alkali activator. The pressed specimens were prepared and were cured in an autoclave at a pressure of 1.6 MPa and a temperature of 205 °C. It was shown that the strength of cement as well as compound and the microstructure of its hydration products depend on the cement composition. It was distinguished that autoclave-cured cementing matter comprises secondary quartz and the mass of sodium hydrated silicates along with the initial Pr crystal phases. After a 2-year storage under water, 15% Na₂SO₄, and Dead Sea water, the strength of specimens decreased by 17.5-20%. Control specimens, prepared with Portland cement and immersed in a 15% Na₂SO₄ solution for 2 weeks, were broken up completely. Positive results of long-term durable tests suggest that an AAC based on natural raw material would be stable in other salt solutions.