A novel expansion-tolerant strategy to improve the sulfate resistance of cementitious materials: Guided formation of CaSO4 within superabsorbent polymers (SAPs) pores

During the sulfate attack process, the expansion of CaSO₄ formation in dense cement matrix resulted in the mechanical deterioration of cementitious materials. In this research, a novel expansion-tolerant strategy was proposed to mitigate the expansion pressure by guiding the formation of CaSO₄ within the preset pores introduced by superabsorbent polymers (SAPs). The experimental results showed that the compressive strength of cement paste (C₃A content: 5.61 wt%) with 0.1 wt% addition of SAPs can be sustained after 240 d of sulfate attack, whereas the one without SAPs showed a 21 % reduction with obvious surface spalling and cracking. In addition, the numerical simulation results indicated that the expansion pressure of CaSO₄ formation was correspondingly reduced by 41 %, which beneficially increased the sulfate resistance of cement paste by 170 %. Such a remarkable enhancement was built on the enrichment of Ca(OH)₂ within SAPs pores, which were previously dispersed randomly throughout the cement matrix. During the sulfate attack, sufficient Ca²⁺ provided by Ca(OH)₂ facilitated the in-situ formation of CaSO₄ in micro-scaled SAPs pores, which offered space for accommodating the CaSO₄ crystallization therefore reducing the expansion pressure. In conclusion, the current study presents a novel strategy to guide the formation of CaSO₄ in SAPs pores, effectively mitigating expansion-related damage and opening new frontiers for improving the sulfate resistance of cementitious materials.