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 degrees C and 125 degrees C. Micro-structural damage was observed in metakaolin-based AAMs dried at temperatures above 40 degrees C, but occurred only between 40 and 60 degrees 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.

Automated summary

The study found that drying at different temperatures can result in varying degrees of microstructural damage for different alkali-activated materials, highlighting the importance of preconditioning for these materials.