Relation between the molecular structure and the efficiency of superabsorbent polymers (SAP) as concrete admixture to mitigate autogenous shrinkage

摘要

Superabsorbent polymers (SAP) were studied as admixtures for mitigating the autogenous shrinkage of a high-strength concrete. The presence of Ca~(2+) ions in the alkaline solution modified the kinetics of the liquid uptake and release when compared to that in other saline solutions and distilled water. SAP with high density of anionic functional groups took up the cement pore solution quickly, but greatly released it subsequently. The cross-linking density had no pronounced influence on the behaviour of such SAP. SAP with lower density of anionic groups did not release the liquid over the time of experiment. All SAP counteracted autogenous shrinkage during the acceleration period of cement hydration. For the materials which released the absorbed pore solution no effect on autogenous shrinkage was found beyond the initial period. SAP materials which did not release the absorbed solution in the experiments with liquids continued the mitigation of autogenous shrinkage during the deceleration period. The internal curing had no negative effect on the compressive strength of the mortar.