Tailored surface energetics and interfacial adhesion in hydrophobic cementitious composites: SHAP-based mechanistic insights into corrosion resistance

The deterioration of concrete structures in aggressive marine and chloride-laden environments necessitates the development of durable, water-repellent cementitious materials to enhance service life and reduce maintenance costs. This study addresses this need by formulating a hydrophobic composite using fly Ash (Class F), silica Fume, metakaolin, and zinc stearate. Among 30 trial mixtures, the optimised Mix M4 exhibited superior hydrophobic performance, with a maximum water contact angle of 110° and a significantly reduced surface energy of 16 mJ/m2 (dispersive: 12 mJ/m2, polar: 4 mJ/m2). Potentiodynamic polarisation analysis revealed a corrosion rate of just 0.000132 mm/year and a polarisation resistance of 316.989 Ω·cm2, confirming enhanced corrosion resistance. Furthermore, the work of adhesion was minimised to 48 mJ/m2, indicating a 19.5% reduction in water affinity. SHAP sensitivity analysis highlighted zinc stearate as the primary contributor to hydrophobicity (+40°), while fly Ash and metakaolin refined mechanical properties, microstructure and decreased corrosion susceptibility by up to 78%. These results position Mix M4 as a robust, durable composite ideal for coastal, wastewater, and marine infrastructure applications.