Development of Ambient-Cured Low-Alkali High-Strength Geopolymers

The present work demonstrates that ambient-cured geopolymer pastes and mortars can be fabricated without the need for high alkalinity activators or heat curing, provided the ratio of Class F fly ash (40-90 wt%), blast furnace slag (10-60 wt%), and low-alkalinity sodium silicate (Ms = 1.5, 1.7, 2.0) is appropriately balanced. These compositions were characterised in terms of the setting time and compressive strength. These data were used to generate predictive models for the initial and final setting times as well as for the ultimate curing time and ultimate compressive strength. These projections indicate that compressive strengths in excess of 100 MPa can be achieved with geopolymer compositions with ≥40 wt% slag after ambient curing of 56 days.The effects of curing temperature (25°C, 40°C, 60°C for 24 h), Ms value (1.5, 1.7, 2.0), and slag content (10, 20, 30, 40 wt%) on the compressive strength development (1, 7, 14, 28 days) of the geopolymer mortars were analysed. These data were used to generate predictive models for 28-day compressive strength as a function of curing temperature and slag content at fixed Ms value. While the 1-day compressive strength was dependent largely on the curing temperature, the slag content dominated the 28-day strength. The ratio of the 1-day and 28-day compressive strengths as a function of curing temperature, Ms value, and slag content allows prediction of the maximal possible curing temperature of 65°C, above which no further advantage is to be gained. This predictive model also revealed that cold-weather casting of