Effect of Steel Fiber Coupled with Recycled Aggregate Concrete on Splitting Tensile Strength and Microstructure Characteristics of Concrete

The main objective of this paper is to investigate the impact splitting tensile property and microstructure characteristics of steel fiber recycled aggregate concrete (SFRAC) based on the split Hopkinson pressure bar (SHPB) and scanning electron microscope (SEM). The effects of fiber content, strain rate, and recycled aggregate replacement ratio on the mechanical parameters (static and dynamic splitting tensile strength, peak strain and ultimate strain, peak toughness and ultimate toughness) were analyzed. Then the microstructure characteristics of SFRAC at different interfaces were observed via SEM, and energy spectrum analysis of the interface transition zone (ITZ) was carried out. The results show that SFRAC is a strain-rate sensitive material whose mechanical properties are affected by the strain rate and improved with its increase. It is also found that steel fibers play a role in improving dynamic splitting tensile strength and toughness, and the optimal fiber content is about 1.0%. However, increasing the recycled aggregate replacement ratio will weaken the good effect of steel fibers on the mechanical properties. Furthermore, it can be seen by means of SEM that the fracture area of steel fiber is mostly pulled out. Also, there are more cracks and pores in the cement paste of recycled aggregate concrete (RAC) compared with normal concrete (NC), and the hydration products in the ITZ are significantly decreased. With the incorporation of steel fibers, the calcium content of the ITZ can be reduced.