Sulfate attack mechanism and service life prediction of concrete under drying-wetting cycles synergistically regulated by hybrid fibers and CaO-MgO-based expansive agent

Abstract

To address the durability degradation of concrete exposed to sulfate-rich dry-wet environments, this study investigated the synergistic effects of modified polyester fibers (PF), basalt fibers (BF), and their hybrid system (PB) combined with a calcium-magnesium composite expansive agent (CMEA). Damage evolution during exposure to a 15% Na 2 SO 4 solution was characterized in terms of, electrical response, phase assemblage, pore structure (PS), and microstructure. Layered damage and service-life prediction models were also developed. The mechanical performance (MP) and mass changes of the specimens exhibited three distinct stages: early enhancement, intermediate deterioration, and gradual late-stage degradation. The composite containing BF and 4% CMEA (BF-4E) exhibited the best overall durability, with a compressive strength retention ratio of 54.17% after 50 cycles. Although the composite containing PB and PB-4E provided a more balanced improvement in splitting tensile resistance and resistance to surface spalling. Its splitting