Effect of drying procedures on pore structure and phase evolution of alkali-activated cements

This study reports the effects of different drying procedures on the pore determination and phase evolution of alkali-activated cements based on metakaolin (AAMK), fly ash (AAFA) and slag (AAS), as characterized by N2 adsorption and XRD and FTIR analysis, in comparison with ordinary Portland cement (OPC) paste. The selected drying methods are: (1) 65 °C/24 h vacuum drying, (2) 105 °C/24 h oven drying, (3) solvent-exchange with ethanol for 3 days then 50 °C/24 h oven drying, and (4) freeze-drying with liquid nitrogen. The pore structures of AAMK and AAFA, with zeolite-like sodium aluminosilicate gel phases and little bound water, are less sensitive to drying conditions than are AAS and OPC, which consist of calcium (alumino)silicate hydrates. The drying procedures have less impact on the phase compositions of alkali-activated cements than OPC in general. Nonetheless, caution must be applied in selection of appropriate drying procedures to obtain reproducible and meaningful information regarding the pore and phase structure of alkali-activated cements.