Effect of SAP on the properties and microstructure of cement-based materials in the low humidity environment

In this study, environments of 60 % and 33 % relative humidity have been chosen to investigate the effect of internal curing of pre-absorbed superabsorbent polymers (SAPs) on the resistance of cementitious materials to the harsh environment of external drying, which will be analyzed experimentally in terms of mechanical properties, volumetric stability, degree of hydration and pore structure. The results showed that 2 parts per thousand SAP improved the hydration of cementitious materials, enhanced the ability of the cement paste to resist low humidity environments, effectively increased the compressive strength and reduced the drying shrinkage deformation of the cement mortar. The relevant tests including FTIR, XRD and TG also prove this from multiple angles. It was also discovered that a moderate amount of pre-absorbed SAP was able to reduce the drying shrinkage of the cement mortar. However, the pore structure analysis revealed that the preabsorbed SAP increased the cement paste porosity, leading to accelerated dissipation of pore water in the cement paste. In the end, the critical pore size (Dc) micromechanical model showed that the shrinkage reduction mechanism of the pre-absorbed SAP in low humidity environment is that the maximum pore size of the SAP group forming the meniscus during the drying process generates less shrinkage stress.