Effects of superabsorbent polymers on the pore structure and coefficient of thermal expansion of cementitious materials

Internal curing is an effective method to reduce the autogenous shrinkage of cementitious materials. Besides, the increasing in relative humidity (RH) due to the internal curing also reduces the coefficient of thermal expansion (CTE), which is beneficial for enhancing the anti-cracking performance of cementitious materials. In this paper, effects of superabsorbent polymers (SAP) on the microstructure and performance of cementitious materials were investigated. The superabsorbent polymer (SAP) changes the time and spatial distribution of water in cementitious materials, so it should have an influence on the microstructure of cement matrix, thus affecting the performance of cementitious materials. Results indicate that the CTE of concrete increases over time, while that of concrete with SAP shows a completely different behavior. In 0.1 % SAP system, the CTE increases slowly over time after about 2days, while in 0.2 % SAP and 0.3 % SAP systems, the CTE is nearly stabilized during the test period. Low-field nuclear magnetic resonance (LF NMR) results indicate that the SAP decreases the number of empty capillary pores and increases the total porosity, which inhibits the increase of CTE over time. The dosage of SAP plays an important role in enhancing the internal curing performance. By increasing the dosage of SAP, the number of empty capillary pores decreases, the saturation degree of capillary pores rises, and consequently, the CTE and autogenous shrinkage of concrete are reduced.