Low-heat Portland cement and ground granulated blast furnace slag are widely used for the preparation of hydraulic concrete. Nevertheless, the effect and mechanism of corrosion on low-heat Portland cement paste mixed with ground granulated blast furnace slag need to be further explored. This paper investigated the impact of ground granulated blast furnace slag on the calcium leaching of low-heat Portland cement paste by evaluating its mass loss, porosity, leaching depth, compressive strength, and Vickers hardness, and comparing it with the leaching performance of ordinary Portland cement paste. Furthermore, the phase composition and morphology of low-heat Portland cement paste containing ground granulated blast furnace slag were analyzed by X-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy. The results indicate that, after 180 days of soaking in ammonium chloride solution, the mass loss rate, growth rate of porosity, leaching depth, and compressive strength loss rate of low-heat Portland cement paste were 8.0%, 43.6%, 9.1 mm, and 27.7%, respectively, while those of ordinary Portland cement paste were 7.4%, 37.8%, 8.4 mm, and 30.1%, indicating that low-heat Portland cement paste is slightly more damaging than ordinary Portland cement. The addition of ground granulated blast furnace slag could significantly improve the leaching resistance of low-heat Portland cement. For instance, after adding 20% ground granulated blast furnace slag, the above test values were 2.4%, 28.5%, 5.6 mm, and 20.8%, respectively. The reason for this is that ground granulated blast furnace slag has the potential to reduce the porosity of low-heat Portland cement paste, and it can also undergo the secondary hydration reaction with its hydration product Ca(OH)₂ to enhance the paste structure. Considering the cost performance, the suitable dosage of low-heat Portland cement paste for satisfactory leaching resistance is about 20%.

Hydraulic structures are frequently subjected to soft-water or acidic environments, necessitating serious consideration of the long-term effects of calcium leaching on the durability of concrete structures. Three types of common Portland cement (ordinary Portland cement, moderate-heat cement, and low-heat cement) paste samples widely applied to hydraulic concrete were immersed in a 6 mol/L NH₄Cl solution to simulate accelerated calcium leaching behavior. The mass loss, porosity, leaching depth, compressive strength, and Ca/Si ratio of the three types of pastes were measured at different immersion stages (0, 14, 28, 56, 91, 140, and 180 days). The Vickers hardness index was employed to compare cement samples subjected to erosion for 30 and 180 days. The microstructure and composition of the mineralogical phases of the leached samples were also determined by X-ray diffraction, thermogravimetric analysis, and scanning electronic microscopy. Accordingly, the time-varying behavior and deterioration mechanism of the different cements subjected to leaching were contrastively revealed. The results showed that the calcium leaching resistance of the low-heat cement was the best, followed by the moderate-heat cement and ordinary Portland cement, proving that the content and structure of Ca(OH)₂ and C-S-H gels were closely related to the leaching performance of the cement. The less Ca(OH)₂ and more aggregated C-H-S gels produced by C₂S led to better calcium leaching resistance in the cement. Therefore, the leaching performance of Portland cement could be effectively improved by reducing the content of C₃S and increasing the content of C₂S, and the dissolution rate of calcium ions under leaching could be reduced by controlling the low initial calcium content in cementitious materials. This paper offers theoretical guidance for mitigating the long-term effects of calcium leaching on hydraulic concrete structures by conducting a comprehensive comparative analysis of the damage behavior and deterioration mechanisms of various types of Portland cement under identical erosion conditions.