Red mud-modified acrylic composite coatings for durable concrete applications

This study investigated the durability and protective performance of acrylic coating modified with red mud (RM) applied on cement mortar specimens and exposed to aggressive environments. Coated specimens were exposed to 2% sulfuric acid for up to 60 days and to wet/dry cycling in 3.5% NaCl solution for 90 days. Visual inspection, compressive strength evaluation, X-ray diffraction (XRD) and Fourier transmission infra-red (FTIR) analysis were carried out to assess the mechanisms of degradation and performance trends of red mud-modified acrylic coating. Specimens coated with pure acrylic coating deteriorated rapidly under acid exposure, with severe corner debonding and loss of surface protection. The incorporation of red mud in acrylic coating significantly enhanced performance of concrete, with 5% RM-modified coating exhibiting optimum performance by enhancing the adhesion strength, decreasing porosity, delaying gypsum formation, and improving the residual compressive strength by ∼46% compared to the control specimens after 60 days. Although the acrylic coating with 10% RM further improved the acid resistance, formation of blisters and localized debonding limiting its long-term stability. Under chloride-rich wet/dry cycles, both acrylic and RM-modified coatings prevented structural damage, but RM blends exhibited superior strength retention and minimized discoloration. Overall, the findings establish that the incorporation of red mud, particularly at 5%, provides an effective and sustainable route to improve the durability of acrylic-based protective coatings in aggressive chemical environments.