Color‐compatible repair method for the restoration of concrete structures using magnesium phosphate cement mortar and inorganic pigments

Abstract The aesthetic integrity of repaired concrete structures is often affected by the visible “patch” effect caused by color differences between repair materials and the original substrate. To address this issue, this study proposes a digital color‐compatibility repair model for concrete structures based on magnesium phosphate cement (MPC) mortar, aiming to coordinate functional repair and color consistency. Color characterization ( L *, a *, and b *) and color difference (Δ E *) were performed in the CIE 1976 ( L *, a *, b *) color space. Through single‐pigment calibration using six inorganic pigments, a color coefficient matrix were obtained, forming a linear inverse model to determine the pigment dosage matrix . Long‐term color stability monitoring showed that the 28‐day MPC color, mainly located in the black–red–yellow quadrant, can serve as a stable reference for color adjustment. Multi‐pigment blending experiments verified the feasibility of matching MPC and concrete color systems within a linear range, with prediction errors below Δ E * <3. Field application on full‐scale pier columns of the Ruian Bridge achieved satisfactory color matching between repaired and existing areas, confirming the model's effectiveness for engineering use. This study provides a practical framework for material design and application in color‐compatible concrete repairs.