Influence of Nano-CaCO₃ on the Strength and Fatigue Behavior of Concrete with 30% or 50% Recycled Coarse Aggregates

Abstract

Recycling construction demolition waste as recycled coarse aggregate (RCA) is a value-added process. However, the utilization rate of recycled aggregate concrete (RAC) is greatly reduced due to the poor material properties of RCA itself, so it is necessary to improve the related performance of RAC for its practical engineering application. Herein, taking natural aggregate concrete (NAC), recycled aggregate concrete (RAC), recycled aggregate concrete modified with nano-CaCO 3 (NC-RAC) and natural aggregate concrete with nano-CaCO 3 (NC-NAC) as the targets, the slump test, compressive strength test, flexural strength test, static axial compressive strength test and fatigue test under different stress levels were carried out. Combined with SEM images, the basic mechanical properties and fatigue characteristics of the test concrete are analyzed, and the effects of RCA and NC are evaluated. The results indicate that the replacement of natural coarse aggregate (NCA) by RCA has a significant negative impact on the mechanical properties and fatigue properties of concrete, and the negative impact increases with the increase of RCA replacement rate. However, the incorporation of nano-CaCO 3 can significantly improve the compressive strength, flexural strength, elastic modulus and fatigue life of RAC, and effectively improve the performance of RAC materials. The recommended amount of nano-CaCO 3 is 1%. In addition, the fatigue life of the test concrete conforms to the Weibull distribution. The S-N-P fatigue equation considering the survival probability is established by fitting analysis, which has guiding significance for the application of RAC and NC-RAC in structures that need to withstand cyclic loads.