Mechanical properties and microstructure of nano-strengthened recycled aggregate concrete

Abstract

Abstract The surface adhesion mortar of recycled coarse aggregate (RCA) is the main factor leading to poor aggregate quality, and it also affects the internal structure and mechanical properties of recycled aggregate concrete (RAC). To improve the quality of RCA and mechanical properties of RAC, self-developed mortar removal equipment was used to strengthen the RCA. Then, the RCA was soaked in 1, 2, and 3% nano-silica solutions, and the vibration-mixing process was used to improve the quality of RAC. In addition, the microstructure of the RAC was examined via scanning electron microscopy to observe its improvement effect on the microstructure of the RAC. The results indicated that the quality of the RCA was improved by mechanical and physical strengthening, and the water-absorption rate and crushing value decreased by 32.9 and 23.9%, respectively. The improvement effect of nano-immersion on the RAC was obvious. The optimal condition was a combination of physical strengthening, 2 days of immersion in 2% NS solution, and vibration stirring. The 28 day compressive strength increased by 31.3%, the splitting tensile strength increased by 23%, and the flexural strength increased by 49%. The proposed strengthening method improves the mechanical properties and microstructure of RAC. The results of this study provided a technical reference for the mechanical strengthening of RAC and promotion of the application and popularization of RAC.