Functional Polymer–Clay Composite Coating for Corrosion Protection in Concrete Sewer Structures

Concrete sewer structures are prone to severe degradation from sulfuric acid-induced corrosion, leading to high maintenance costs and shortened service life. This study develops an innovative functional polymer–clay composite coating, featuring kaolinite sheets dispersed in an epoxy matrix, specifically engineered to enhance concrete durability in highly corrosive environments. The coating was formulated using ultrasonic mixing techniques, which ensured the effective distribution of kaolinite sheets, resulting in improved mechanical strength, thermal stability, and chemical resistance. Notably, the optimized formulation containing 1 wt % kaolinite sheets exhibited outstanding durability, limiting mass loss to 6.99% following prolonged immersion in a sulfuric acid environment. This reflects a 69.74% improvement over unprotected concrete and a 60.11% improvement over neat epoxy. Moreover, water absorption was reduced to 0.16%, offering robust protection against moisture ingress. The coating's pull-off strength reached 5.7 MPa, marking a 42.5% enhancement compared to conventional epoxy coatings and confirming excellent bonding with the concrete substrate. The enhanced protective capability of the composite coating arises from the barrier-forming nature of kaolinite sheets, which obstruct the ingress of corrosive agents into the concrete. Density Functional Theory (DFT) simulations supported these findings by revealing improved electron-donating and accepting abilities of the composite system, which highlight its heightened resistance to corrosive degradation. This study presents a functional epoxy composite coating integrated with kaolinite sheets to effectively protect concrete sewer infrastructure against sulfuric acid corrosion.