Rheological Behaviour and Flow Properties of Alkali-Activated Materials

Great efforts are being made by researchers concerning the development of cement-less concrete to reduce both greenhouse gas emissions and energy use. Alkali-activated materials (AAMs) are one of the viable alternatives which are attracting increasing attention in practice and research due to their lower CO₂ emissions. In this paper, the rheological behaviour of binary blended alkali-activated fly ash/slag pastes is investigated. Various rheological measurements were conducted such as paste fluidity, viscosity, yield stress and thinning index. The effect of different parameters was assessed including the slag content, SiO₂/Na₂O ratio as well as the solution/binder ratio. The experimental results revealed that increasing the slag content increases the viscosity and yield stress and reduced the overall paste fluidity at elapsed times. The viscosity of AAM pastes was in the range of 0.77–7.55 Pa.s. The AAM pastes behaved like a shear-thinning fluid, where the apparent viscosity decreased by increasing the shear rate. The SiO₂/Na₂O ratio in the activator had no significant effect on shear thinning parameters and fluidity. The thinning index, which is the ratio between viscosity at low and high shear rates, of AAM pastes was found to be in the range of 1.92–4.01. The volumetric solution-to-binder ratio was shown to effectively influence the thinning index. The findings of this study confirm that the fluidity and thinning index are independent of the chemical composition of the used activator but depend upon the changes done in the volume of both slag and activation solutions.