ALKALI-ACTIVATED CEMENT BASED ON NATURAL SiO2-CONTAINING MATERIAL. PT.1. STRENGTH, HYDRATION, MICROSTRUCTURE AND DURABILITY

An alkali-activated cement (AAC) based on natural SiO2-containing materials, namely, 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 cured in an autoclave at 1.6 MPa and 205 C. It was shown that the strength of the cement and the microstructure of its hydration products depend on the composition and content of coarse Pr particles. The autoclave-cured cementing material comprises secondary quartz, while the matrix consists of sodium hydrated silicates along with the initial Pr crystal phases. After two years storage under water, 15% Na2SO4 and Dead Sea water, the strength 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. 16 refs.