Carbon-Absorbing Inorganic Coating with Ultrahigh Bonding Strength for Concrete: Bonding, Durability Performances, and the Underlying Mechanisms

Inorganic coatings are widely used to protect concrete structures due to their high durability. However, improving the antipenetration performance and bonding strength of these coatings remains a challenge. This study aims to develop an inorganic coating with excellent performances using high-carbonation reactivity γ-dicalcium silicate (γ-C2S) and delve into the underlying mechanisms. This γ-C2S coating exhibits an excellent bonding strength of 5.25 MPa to the concrete substrate by absorbing CO2 and demonstrates great durability, with a bonding strength retention of 90% after 28 days of irradiation. Compared to the noncoated concrete, the capillary water absorption of the coated concrete has decreased by 58%, while the contents of free and total chloride ions in the coated concrete substrate have decreased by 68 and 60%, respectively. Furthermore, the phase assembly and pore structure of the γ-C2S coating were investigated to understand the antipenetration and bonding mechanism. A connecting section was revealed, which positively impacts the bonding strength between the coating and the substrate. This coating-to-substrate interface interaction was further explored to elucidate the underlying mechanisms of the bonding performance of the γ-C2S coating to the concrete substrate.