The engineering properties of alkali-activated slag pastes exposed to high temperatures

Abstract Alkali cementations material is a recent and new type of environmentally friendly and economical material that is produced from industrial waste (e.g., fly ash and slag). This material possesses many excellent engineering properties, including a high compressive strength, light weight and low thermal conductivity. This study used different liquid–solid ratios, alkaline solutions and slag to produce pastes. The findings showed that the slump and slump flow of the alkali-activated slag pastes increased with the alkaline solutions and liquid–solid ratio. Without any slow setting additive, the setting rate could be reduced by reducing the alkaline solutions. After different curing ages at high temperatures, residual compressive strength, ultrasonic pulse velocity and thermal imaging tests. The findings showed that the ultrasonic pulse velocity and compressive strength of the alkali-activated slag pastes increased with the increase in the alkali-activated solution. The engineering properties declined as the liquid–solid ratio increased, but the workability improved. The increase in the alkaline solutions could enhance the compressive strength at high temperatures; the compressive strength of 0.5% alkali-activated at 500 °C was 30–50% of that of 1% alkali-activated. The ultrasonic pulse velocity at the high temperature of 500 °C was 2171–3322 m/s; the ultrasonic pulse velocities of 0.75% and 1% alkali-activated at 800 °C were 2605 m/s and 2812 m/s, respectively, but the ultrasonic pulse velocity of 0.5% alkali-activated 0.5% was only 2211 m/s. The alkaline solutions of 0.75% alkali-activated and 1% alkali-activated were sufficient to finish the polyreaction within a short period of time to afford a material that possessed low porosity and high strength material. The results show that research on alkali-activated slag significantly contributes to energy saving and carbon reduction.