Properties study of cement pastes synergistically reinforced with chloride salts: The damaging effect of negative temperature and sulfate erosion on mechanical properties

This study elucidates the hydration characteristics and durability modulation mechanisms of cement paste subjected to the combined influences of low-temperature curing and sulfate attack, focusing on the synergistic role of a CaCl 2 –BaCl 2 binary admixture system. CaCl 2 acted as a cryoprotectant, accelerating hydration under subzero conditions by promoting Friedel’s salt formation, which in turn enhanced early-age strength development. At an optimized dosage of 12.5 % CaCl 2 , the 54-day compressive strength exhibited an 86.99 % improvement compared with the control, verifying its hydration-promoting efficiency. The co-incorporation of BaCl 2 further contributed to durability enhancement through a dual-protection mechanism: externally, Ba 2 + reacted with SO 4 2- to form dense BaSO 4 barrier layers that hindered ionic penetration; internally, Ba 2+ consumed infiltrating SO 2- , suppressing the generation of expansive phases such as gypsum and ettringite. This process effectively alleviated sulfate-induced deterioration while simultaneously maintaining hydration continuity under freezing conditions. Although CaCl 2 addition facilitated faster ion migration during subzero curing, this effect diminished during subsequent ambient-temperature exposure, as hydration recovery occurred in reference samples. Nevertheless, excessive CaCl 2 led to structural degradation through dissolution channel formation and crystallization stress-induced microcracking, underscoring the importance of dosage control. Overall, the combined use of CaCl 2 and BaCl 2 was shown to significantly enhance both low-temperature hydration kinetics and long-term sulfate resistance. The findings provide valuable theoretical insight and practical guidance for the durability design of cementitious materials exposed to aggressive sulfate-bearing permafrost environments.