Effect of drying temperature on the properties of alkali-activated binders - Recommendations for sample preconditioning

Various durability tests require a drying step to remove free water without altering the chemistry or microstructure of the materials. However, little is known about the effects of drying on alkali-activated materials (AAMs). This study focusses on the drying stage to assess the behaviour of four alkali-activated binders compared with conventional binders: a metakaolin-based geopolymer, ground granulated blast-furnace slag (GGBS) activated by sodium silicate or by sodium carbonate, and a mixture of metakaolin-GGBS activated by sodium silicate. After a 28-day autogenous cure, mortar and paste samples were dried at temperatures ranging between 20 °C and 125 °C. Micro-structural damage was observed in metakaolin-based AAMs dried at temperatures above 40 °C, but occurred only between 40 and 60 °C for GGBS-based AAMs. SEM observations and MIP porosimetry coupled with mineralogical analyses, allowed AAMs drying mechanisms to be better understood, and recommendations to be made for the preconditioning of these materials.