BaCO3-shelled phase change microcapsules for enhancing sulfate resistance of cement paste: Sulfate immobilization and multiscale deterioration analysis

BaCO 3 -shelled phase change microcapsules improve sulfate resistance of cement paste. • The BaCO 3 shell immobilizes sulfate ions through in-situ ion exchange. • BMPCM regulates sulfate-attack products and pore-network deterioration. • Optimal BMPCM dosage reduces eroded area by 69.9% and enhances strength. Sulfate attack is one of the major degradation mechanisms responsible for expansion cracking, surface spalling, and long-term performance deterioration of cementitious materials. To improve the durability of cementitious materials in sulfate environments, a functional microcapsule (BMPCM) with a BaCO 3 shell and tetradecane core was prepared, and its effect on sulfate resistance was systematically evaluated. Cement paste specimens incorporating different BMPCM dosages were separately immersed in deionized water and MgSO 4 solution for up to 360 d. The deterioration behavior and underlying mechanisms of cement paste incorporating BMPCM were elucidated at multiple scales through macroscopic damage characterization, microstructural observation, hydration/sulfate-attack product analysis, pore connectivity assessment, and compressive strength testing. Results showed that the BaCO 3 shell reacted with invading SO 4 2− to form insoluble BaSO 4 , thereby chemically immobilizing sulfate ions. This process reduced the effective sulfate activity within the matrix, suppressed the formation of expansive products such as gypsum and ettringite, and mitigated the leaching of soluble hydration products such as Ca(OH) 2 . Compared with controls, specimens with an appropriate BMPCM dosage exhibited a 69.9% reduction in the severely deteriorated area, a 24.4% decrease in interconnected porosity, and a 44.9% increase in compressive strength after 360 d. In contrast, excessive BMPCM incorporation promoted microcapsule agglomeration and introduced initial defects, thereby weakening sulfate resistance. In addition, thermal analysis confirmed that BMPCM retained its phase-change response near the freezing point, suggesting its potential for further application in sulfate-resistant cementitious materials exposed to complex temperature-fluctuation service environments.