Shrinkage mechanisms of alkali-activated slag

In this work, the physical and chemical changes of alkali-activated slag (AAS) after a prolonged drying treatment under various relative humidity (RH) conditions were studied. The results show that the shrinkage kinetics of AAS is strongly dependent on the RH, but irrespective of the moisture loss. At high RH, AAS exhibits a pronounced viscous characteristic, which is likely due to the rearrangement and reorganization of calcium-alumina-silicate-hydrate (C-A-S-H). Meantime, micropore closure, silicate polymerization, and new interlayer formation were observed during microstructure rearrangement, indicating a strong interaction between adjacent C-A-S-H particles. The large shrinkage in AAS may be attributed to the structural incorporation of alkali cations in C-A-S-H, which reduces the stacking regularity of C-A-S-H layers and makes the C-A-S-H easier to collapse and redistribute upon drying.