Abstract
This study elaborate on the collective impact of simultaneous sulphate–chloride ingress, cyclic wetting–drying and crystallization-induced microcracking, in the long-term degradation of concrete infrastructures in marine-like exposure conditions. This paper offers a comprehensive mechanistic assessment of the durability of self-compacting engineered cementitious composites (SC-ECC) exposed to sulphate, chloride, and combined sulphate–chloride exposure under a partial-immersion condition for 270 days. The developed blended SC-ECC having Class F fly ash and 1.5 vol% PVA fibres was evaluated by compressive strength, water and Rapid chloride penetration (RCPT) tests, half-cell potential (HCP) and scanning electron microscopy (SEM) analyses. At elevated sulphate concentrations, progressive but controlled degradation was observed from the experimental results. Water penetration was low (≤2.0 mm at 7.5% Na₂SO₄ after 270-days) suggesting that limited pore coarsening occurred even with microcrack generation. Across all regimes, the RCPT values remained ≤ 1500 C, further establishing the low ionic conductivity properties of SC-ECC compared with typical high-performance concrete with a similar exposure (Fig. 12). The most aggressive sulphate condition saw compressive strength retained about 80% of its water-cured reference even at 270 days. The measured corrosion potential (HCP) measurements (−120 to −430 mV vs. CSE) indicated low to moderately passive corrosion risk under chloride-only and sulphate-only exposures but more negative shifts were only developed under combined sulphate−chloride attack. SEM observations demonstrated a mechanistic degradation pathway driven by ettringite/gypsum crystallization in microcracks and ITZ widening, leading to enhanced ionic connectivity but not significant global porosity. Results corroborated from mechanical, transport, electrochemical, and microstructural aspects emphasize the excellent restrained resistance of fibered SC-ECC over long-term multiion, which exemplifies its high applicability for coastal and partially submerged structural use.