Effects of Chloride and Sulphate Exposure on the Strength of Basaltic Pozzolanic Cements

This study evaluates the durability, mechanical performance, and physical characteristics of Portland-pozzolana and pozzolanic cements that contain basaltic pozzolana under various exposure scenarios. Five cement types (CEM I, CEM II/A-P, CEM II/B-P, CEM IV/A, and CEM IV/B 42.5 N) were evaluated for flexural and compressive strength up to 365 days under water, chloride, sulphate, and combined chloride–sulphate curing regimes. Under standard water curing, compressive strength at 365 days ranged from 53.9 MPa (CEM I) to 46.1 MPa (CEM IV/B), corresponding to 113–108% of their 28-day values. Chloride exposure reduced strength retention to 82% for CEM I and 61% for CEM IV/B, while sulphate curing caused 8–25% losses, with CEM IV/B retaining only 75% of its 28-day strength. Combined chloride–sulphate exposure produced the most severe deterioration: CEM I preserved 87% of its 28-day strength, compared with 73% for CEM IV/B. The results confirm that higher pozzolana content enhances sustainability but increases vulnerability to ionic ingress due to reduced Ca(OH)₂ and coarser pore structures. In summary, the pozzolanic blends achieved between 77% and 93% of the strength of the reference Portland cement mortar, demonstrating a clear inverse relationship between pozzolana content and mechanical performance. Nevertheless, their durability under aggressive environments remains a key challenge, highlighting the need for further optimization of pozzolanic compositions and hybrid SCM systems to enhance resistance while supporting carbon reduction objectives.