Characterizing the effect of superabsorbent polymer content on internal curing process of cement paste using calorimetry and nuclear magnetic resonance methods

Internal curing (IC) is used to mitigate autogenous shrinkage in low water-to-cement ratio (w/c) concrete. Although, superabsorbent polymers (SAP) have been shown to work well for IC, their effects on the kinetics of the cement chemical reaction and the amount of water they provide have not been fully quantified. An experimental program was performed using isothermal calorimetry and nuclear magnetic resonance (NMR) to study the behavior of cement paste with various levels of IC using SAP. The results revealed that the higher the amount of IC the more susceptible the cement paste became to SAP overdosing resulting in a significant decrease in the heat of hydration (HOH) and therefore loss of IC efficiency. The mass of SAP to entrained water greater than 5\% led to particles agglomeration and a 65\% decrease in its IC efficiency. The HOH is observed to be linearly proportional to the entrained w/c, and that its development is limited by the initial porosity of the paste which controls the water diffusion from the SAP. The NMR signal corresponding to IC water showed that the SAP absorbs 4-7\% more mixing water than initially estimated, and that pre-wetted SAP has larger amount of entrained water in comparison with dry SAP.