RAPID HARDENING ALKALI-ACTIVATED PORTLANDCEMENTS FOR EMERGENCY RECONSTRUCTION OF BUILDINGS

Abstract

Modern construction trends drive the current need to develop repair and rehabilitation materials to increase the durability of building structures. The use of alkali-activated Portland cements in these materials requires that ways be found to maximize early strength. The current production of these cements by one-component technology results in the use of sodium silicate, the most effective activator, in the solid state (e.g., sodium metasilicate pentahydrate). The factors influencing the early strength of such alkali-activated Portland cements have been determined. The increase in both initial setting time by 30 % and final setting time by 67 % as well as the increase in strength from class 42.5 N to 42.5 R and is due to the use of a complex additive of the system “surface-active agent – sodium salt” in alkali-activated Portland cement. The decrease in water content and the acceleration of hydrate crystallization are the cause of this increase in strength. The effectiveness of the aluminosilicate constituent has been further enhanced by increasing the specific surface area and adding nano-silica. Increasing the dispersion of granulated blast furnace slag from 450 to 530 m²/kg and introducing an amorphous silica nano-additive (Aerosil) helps increase strength to class 52.5 R by densifying the microstructure of the cement matrix.