Repair Behavior of Magnesium Phosphate Cement-Emulsified Asphalt Composites under Different Liquid Ratios

With the increasing work of highway maintenance in China, pavement rapid rehabilitation materials that can realize rapid opening to traffic gradually have become an important research focus. This study developed a novel rigid-flexible composite material, magnesium phosphate cement (MPC)-emulsified asphalt (MPC-EA). We systematically evaluated its repair behavior under various liquid ratios (A/C and W/C) for pavement crack applications. Using volume stability tests, mechanical strength assessments, and microstructural characterization, key findings revealed that the volume of MPC-EA gradually expands, contrary to the change of elastic modulus. Although higher EA content (A/C>0.20) reduced flexural bonding strength, AC30 maintained bonding strength >2.5 MPa due to EA’s interfacial adhesion. Excessive W/C (>0.20) weakened hydration product morphology, decreasing bond strength by 40%. Microstructural analysis confirmed EA’s dual role in enhancing adhesion yet inhibiting MPC hydration. Optimized proportions (AC10–AC20 and WC18–WC20) achieved balanced performance: injectability depths >17 mm, water resistance >90%, and elastic moduli (2.5–3.2 GPa) suitable for coarse-grained pavements. Effective bonding of MPC-EA to the substrate through synergistic mechanical embedding, chemical bonding, and interfacial adhesion mechanisms was found. The proposed five-dimensional radar evaluation model provided a framework for tailoring MPC-EA formulations to specific repair scenarios, advancing its application in durable pavement maintenance.