Effect of temperature on the fresh and hardened state properties of alkali-activated slag/fly ash mixtures

Abstract

The effect of ambient temperature on the engineering properties of alkali-activated materials (AAM) needs to be further investigated due to the high variety of activating solutions in the AAM technology. This paper presents the rheological behavior, structural build-up, reaction kinetics and mechanical properties of GGBFS-FA mixtures activated by sodium hydroxide, sodium silicate, sodium carbonate and sodium sulfateinvestigated under different ambient temperature conditions. It was found that the effect of ambient temperature on the rheology and reaction kinetics was highly dependent on the activator type. Under room temperature conditions, the highest and lowest yield stress values were obtained in sodium hydroxide and sodium silicate mixtures, respectively. The increase in temperature did not affect the yield stresses and viscosities of sodium carbonate and sodium sulfate mixtures; however, the yield stresses of sodium hydroxide and sodium silicate mixtures significantly increased. This effect was more pronounced in mixtures with high Ms values. Higher storage modulus values were obtained with an increase in temperature, indicating initial structuration with temperature. The increasing temperature enhanced the compressive strength of alkali-activated GGBFS-FA mixtures. This improvement was more pronounced at early ages for the sodium silicate mixture, and at later ages for the sodium carbonate and sodium sulfate mixtures, while it was very limited in the sodium hydroxide mixture. The SEM images and calorimetric measurements showed the formation of a denser microstructure and enhancement in the exothermic peak with a shorter induction period with an increase in temperature.