Internal curing of blended cement pastes with ultra-low water-to-cement ratio: Absorption/desorption kinetics of superabsorbent polymer

Internal curing by superabsorbent polymer (SAP) is an effective method to mitigate the autogenous shrinkage of cement-based materials with low water-to-cement ratio (w/c). In this study, the water absorption/desorption kinetics of SAP were studied quantitatively in blended cement pastes with ultra-low w/c. An absorption process at a rate of 0 to 6 g/(g h) was calculated at early ages. After that, SAPs showed mainly two distinct water desorption behaviors with a rate of 0 to 1.1 g/(g h), which was mainly governed by the osmotic pressure and capillary pressure triggered by the drop of internal relative humidity (IRH). The size and amount of SAP played a predominant role in controlling its absorption and desorption kinetics in the cement paste. Compared with ordinary Portland cement, a different desorption process with a higher release rate was noticed in binary and ternary cement pastes, primarily due to the changes in osmotic pressure resulting from the acceleration of cement hydration by silica fume at early ages. Overall, the mitigation of autogenous shrinkage is found to be highly dependent on SAP's absorption and desorption kinetics.