Improving the freeze-thaw resistance of mortar by a combined use of superabsorbent polymer and air entraining agent

Abstract

Air entraining agent (AEA) is often used to improve the freeze-thaw (F-T) resistance of concrete, but with the deterioration of compressive strength. In this paper, the combination of AEA and superabsorbent polymer (SAP) was used to improve the F-T resistance of mortar without sacrificing its compressive strength. The mass loss and relative dynamic elastic modulus were measured after the rapid F-T cycles test. Meanwhile, the change in the pore structure of mortar was observed. Results showed that the air entraining effect of AEA was better than that of SAP, and the effect of the mixture of SAP and AEA on the compressive strength of mortar was nonlinear. Compared to mortar containing 0.2 wt‰ AEA alone, the combination of 0.05 wt‰ AEA and 0.2 wt% SAP can improve the compressive strength of mortar by around 10% with comparable F-T resistance. The mechanisms behind the phenomenon were unveiled based on the quantitative analysis of the air void characteristics of mortar. Furthermore, the combination use of AEA and SAP increases the air content and porosity of mortar, and the addition of SAP leads to redistribution of air void, the pores with a diameter larger than 200 μm increase, and those with a diameter less than 100 μm reduce.