Industrial Mineral-Based Ca-Rich Fly Ash Cement Mortars: 24-Month Durability Under Marine Exposure

This study investigates the long-term durability performance of Portland cement mortars incorporating 5% and 10% Ca-rich fly ash under 24 months of natural marine atmospheric exposure. An integrated experimental methodology was applied, combining gravimetric steel mass loss, half-cell potential monitoring (SCE), water-soluble chloride determination at reinforcement depth, carbonation depth evaluation interpreted through the diffusion-based square-root model (x = k√t), and pore structure characterization by MIP and SEM. After 24 months, cumulative steel mass loss decreased by 26.6% (FA5) and 33.6% (FA10) relative to the reference mortar. The water-soluble chloride concentration at reinforcement depth was reduced from 976 mg/L in CM-REF to 875 mg/L (−10.2%) and 805 mg/L (−17.5%) in CM-FA5 and CM-FA10, respectively. Carbonation depth after 24 months decreased from 5.97 mm in the reference mortar to 4.56 mm (−23.6%) and 2.48 mm (−58.5%) for FA5 and FA10, confirming a transport-controlled mitigation of carbonation progression. Within the investigated replacement range, moderate Ca-rich fly ash incorporation produces measurable reductions in chloride availability, carbonation rate, and cumulative corrosion damage under realistic coastal exposure conditions, demonstrating that limited clinker substitution can yield substantial long-term durability benefits. These findings demonstrate that Ca-rich fly ash incorporation (5%–10%) effectively enhances resistance to chloride ingress, carbonation progression, and reinforcement corrosion under natural marine exposure, supporting its use as a performance-oriented strategy for durable, low-clinker mortar design in coastal infrastructure.