Abstract <p>In this study, an efficient, sustainable, and low-carbon slag-based rapid repair mortar (SBRRM) was developed to overcome the inherent limitations of slow hardening and insufficient early strength in conventional rapid repair materials. Response surface methodology (RSM) was employed to systematically optimize the composition, investigating the effects of varying cement substitution rates on setting time, mechanical performance, and bonding strength. Microstructural analyses were conducted using X-ray diffraction (XRD), scanning electron microscopy (SEM), and nitrogen adsorption-desorption (BET) techniques. The optimal composition identified through the model comprised a cement substitution rate of 24.82%, a water glass modulus of 1.5, an alkali equivalent of 8.1%, and a water-to-binder ratio of 0.54. Under these optimized conditions, the deviation between the predicted and experimental results was merely 3.82%, highlighting the model’s high predictive accuracy. After 28 days of curing, the optimized SBRRM exhibited significantly enhanced mechanical properties, achieving a compressive strength of 67.88 MPa and a bending bond strength of 4.9 MPa, corresponding to respective improvements of 16.5 and 54.84% compared to the pure slag system. Moderate incorporation of cement promoted the formation of calcium silicate hydrate (C–S–H) gels, refined the microstructure, reduced the number of large pores, and substantially improved the compactness and stability of the mortar. Additionally, nitrogen adsorption capacity decreased notably from 18.5326 to 14.1033 mmol/g, further confirming a denser and more cohesive microstructure. This study provides valuable theoretical insights into the design and practical application of eco-friendly rapid repair materials featuring high slag utilization and reduced cement content. The findings align closely with contemporary sustainable development goals, demonstrating significant potential for practical engineering applications and environmental benefits.</p>