Study of the Dynamic Splitting Tensile Mechanical Properties and Damage Evolution of Steel Fiber–Reinforced Recycled-Aggregate Concrete Based on Acoustic Emission Technology

Aiming at effectively utilizing recycled coarse aggregate (RCA) in sustainable construction, it is necessary to study the internal damage evolution of steel fiber–reinforced recycled-aggregate concrete (SFRAC) under dynamic tensile loads and the reinforced mechanism of steel fiber. The influences of the steel fiber content, the recycled-aggregate replacement ratio, and the loading rate on the mechanical properties and dynamic damage of SFRAC were studied using the Brazilian disc splitting test and acoustic emission (AE) technology. Then, the mechanism of crack evolution was investigated by means of the parameter analysis method. The results indicate that the existence of RCA makes the mechanical properties of recycled-aggregate concrete worse than those of normal concrete and weakens the strain rate effect of splitting tensile strength, whereas this negative influence can effectively be improved by steel fiber. The preferable steel fiber contents obtained from the splitting tensile strength and peak displacement are 1.0% and 1.5%, and under these conditions, the SFRAC replaced by 30% RCA has a mechanical performance superior to that of normal concrete. It is also found that the damage degree and energy absorbing capacity of SFRAC can be identified by analyzing the ring and energy counts of the AE signal. Furthermore, the evolution of the crack pattern of SFRAC under dynamic axial tensile load is well reflected by the rise angle and average frequency. Increased steel fiber content and recycled-aggregate replacement ratio can change the failure mode to a complex tensile-shear mixed failure, and the shear crack gradually becomes the main crack with increasing loading rates.