Performance of nano-modified silica, alumina, and titania concrete coatings under combined cyclic environments, carbonation, and calcium chloride

In cold regions, transportation infrastructure (e.g., concrete pavements and bridges) undergo complex degradation due to the combined effects of freeze-thaw cycles (FT), wet-dry cycles (WD), and carbonation with chloride-based de-icers; however, the effectiveness of plain and nano-modified coatings as a mitigation or rehabilitation strategy under such combined conditions remains largely unexplored. This study examines methyl methacrylate (MMA) and silane coatings, modified with 0–5 % nano-alumina or nano-titania, and evaluates colloidal silica as an alternative coating for a rehabilitation strategy. Coatings were applied to concrete with 0.4 and 0.6 w/b ratios and exposed for 12 months to combined FT, WD, carbonation (10 %), and calcium chloride (13.6 % and 21.9 %) conditions to stimulate chemical and physical damage. In addition to initial fluid transport, performance was assessed through mass change, expansion, relative dynamic modulus ( REd ), mineralogy, microstructure, and corrosion tests. Uncoated, colloidal silica, and MMA-coated specimens failed within 4–5 months, while silane and its nanocomposites showed minimal expansion (0.01–0.03 %) and superior durability. MMA nanocomposites offered moderate improvement through barrier, pozzolanic, and nucleation effects but were limited by low chloride-binding capacity; silane nanocomposites outperformed them due to synergistic hydrophobic, pore-lining, and microstructural densification effects.