Recycled aggregate concrete (RAC) exhibits inferior mechanical and durability properties owing to the deterioration of the recycled coarse aggregate (RCA) surface quality. To improve the surface properties of RCA, the reinforcement efficiency of RAC, and the maneuverability of the surface treatment method, this study used magnesium phosphate cement (MPC), a clinker-free low-carbon cement with excellent bonding properties, to precoat RCA under three-day pre-conditioning. Moreover, variable amounts of fly ash (FA) or granulated blast furnace slag (GBFS) were utilized to partly substitute MPC to enhance the compressive strength and chloride ion penetration resistance. Subsequently, FA–MPC and GBFS–MPC hybrid slurries with the best comprehensive performance were selected to coat the RCA for optimal reinforcement. The crushing value and water absorption of RCA, as well as the mechanical strengths and durability of RAC, were investigated, and microstructures around interfaces were studied via BSE-EDS and microhardness analysis to reveal the strengthening mechanism. The results indicated that the comprehensive property of strengthening paste was enhanced significantly through substituting MPC with 10% FA or GBFS. Surface coating resulted in a maximum reduction of 8.15% in the crushing value, while the water absorption barely changed. In addition, modified RAC outperformed untreated RAC regarding compressive strength, splitting tensile strength, and chloride ion penetration resistance with maximum optimization efficiencies of 31.58%, 49.75%, and 43.11%, respectively. It was also evidenced that the improved MPC paste properties enhanced the performance of modified RAC. Microanalysis revealed that MPC pastes exhibited an excellent bond with RCA or new mortar, and the newly formed interfacial transition zone between MPC and the fresh mortar exhibited a dense microstructure and outstanding micro-mechanical properties supported with an increase in the average microhardness value of 30.2–33.4%. Therefore, MPC pastes incorporating an appropriate mineral admixture have enormous potential to be utilized as effective RCA surface treatment materials and improve the operability of RCA application in practice.

Masonry structures are highly vulnerable to collapse when subjected to blast shock waves. However, existing research primarily concentrates on the response of masonry walls under blast loading, with limited investigation into the response of three-dimensional full-size masonry structures. Therefore, this paper investigates the effects of blast distance and blast equivalent on masonry structure damage using the continuum-discontinuum element method (CDEM). The integration of the HJC element constitutive model, fracture energy contact surface constitutive model, and shock wave fast imposition algorithm into CDEM enables efficient calculation of the damage process of masonry structures under the influence of shock waves. Initially, the blasting process of a masonry wall was numerically simulated, yielding results consistent with experimental findings. Subsequently, the entire damage process of a 3D full-size masonry structure under blast loading was simulated. The findings indicate that at short distances from the blast, the wall may detach directly from the concrete frame due to shock wave overpressure reaching the material’s ultimate compressive strength, leading to structural instability. As the distance increases beyond a critical value, the shock wave’s effect weakens, and wall damage transitions gradually to bending damage.