Study on compressive mechanical properties of recycled aggregate concrete with silica fume at different strain rates

Treating waste concrete to produce recycled aggregate concrete (RAC) is an important measure to save resources and protect environment. Studies have shown that adding silica fume to RAC can improve the mechanical properties of RAC. Based on the experiment, the uniaxial compressive mechanical properties of RAC specimens with silica fume content (S) for 0%, 5% and 9% at strain rates of 10(-5)/s, 10(-4)/s, 10(-3)/s and 10(-2)/s were studied. From the mesoscopic point of view, the damage and failure mechanisms of RAC were analyzed based on the statistical damage constitutive model. The results showed that with the increase of strain rate, the peak stress, elastic modulus and brittleness of RAC were on the rise. In addition, the peak stress and elastic modulus of RAC with high silica fume content were higher than those of RAC with low silica fume content. Considering two damage evolution modes of mesoscopic fracture and yield, the variation characteristics of mesoscopic damage parameters were obtained. From the perspective of effective stress, the whole process of damage evolution and accumulation induced catastrophe of concrete was expounded. The critical state and peak nominal stress state were distinguished, and it is considered that the critical state should be the limit state of the stress process of concrete material. These results were evaluated and analyzed by acoustic emission (AE), scanning electron microscope (SEM) and nuclear magnetic resonance (NMR) tests.