Effect of limestone powder on sulfate resistance of sulfoaluminate cement concrete under semi-immersed condition

The durability of concrete structures in salt lake regions is severely threatened by sulfate attack. This study investigated the effect of incorporating limestone powder (LP) on the sulfate resistance of sulfoaluminate cement (SAC) concrete under a semi-immersed environment. Concrete specimens with varying LP dosages (0%, 5%, 10%, 15%, and 20% by cement mass) were exposed to a 5% Na₂SO₄ solution. The deterioration was evaluated through macroscopic properties (compressive strength, mass, and relative dynamic elastic modulus) and microstructural characterization (XRD, SEM, MIP) over 180 days. Results indicated that the performance was highly dependent on the LP content and the exposure zone. Specimens with 5–10% LP exhibited superior resistance, demonstrated by the most stable mass and the smallest reduction in compressive strength (5.16% and 5.03%, respectively) in the critical crystallization zone. Microstructural analysis revealed that, at optimal dosages (5–10%), LP acted as a micro-filler and participated in the hydration process, leading to a denser matrix with fewer harmful pores and microcracks. However, a higher LP content (15–20%) introduced a dilution effect, increasing porosity and compromising the durability. The findings confirm that an incorporation of 5–10% LP is a viable strategy for producing high-performance sulfate-resistant SAC concrete in aggressive environments.