In order to study the basic mechanical properties of basalt fiber reinforced recycled aggregate concrete, the concrete mix ratio, the length and the volume mixing ratio of chopped basalt fiber yarn are designed for changing factors. A total of 324 specimens have been completed for this investigation. The compressive strength, splitting tensile strength, elastic modulus and axial compressive strength of basalt fiber recycled concrete have carried on the experimental study and theoretical analysis as 81 specimens, respectively. In all specimens, coarse aggregate were replaced by recycled aggregate with a replacement rate of 100%. Experimental results show that the failure process and failure pattern of basalt fiber recycled concrete and ordinary concrete are similar; With the improvement of concrete strength grade; When the volume mixing ratio of chopped basalt fiber yarn is 0.2%, the mechanic performance can effectively improve, and the length of chopped basalt fiber has less effect on the mechanical indexes; The conversion relation between common concrete mechanics index is no longer suitable for basalt fiber recycled concrete, new conversion formulas for basalt fiber recycled concrete between the mechanics index were presented through fitting experimental data.

This paper describes an experimental investigation to evaluate the shear performance of basalt Fiber-reinforced Polymer (BFRP)-reinforced recycled aggregate concrete deep beams without stirrups. A total of 13 beams were tested under four-point loading until failure: nine were reinforced with BFRP bars, and four were reinforced with steel bars. The parameters of this experiment included the shear-span-to-depth ratio (a/d), reinforcement ratio of the longitudinal bar (ρ), sectional effective depth (d) and compressive strength of the recycled concrete (f_c′). The shear behavior of the beams was described in terms of the crack type, failure mode, shear strength and load-deformation relationship. The effects of the experimental variables on shear capacities and deflections of the tested beams were also investigated. The experimental results showed that the shear capacity of BFRP-reinforced beams was smaller than that of steel-reinforced beams. Additionally, the deformation of BFRP-reinforced beams was larger than that of steel-reinforced ones. The shear capacity of BFRP-reinforced recycled concrete beams without stirrups showed a linear relationship with the sectional effective depth d and was proportional to (d/a)^4/3, (ρ)^1/5 and (f_c′)^1/3. Meanwhile, four existing codes were used to predict the shear strength of test beams and the CSA806-02 gave the better results.

In order to investigate the bond stress-slip constitutive relation between BFRP bar and basalt fiber recycled-aggregate concrete, 81 central pullout specimens were tested. Basalt fiber volume percent, fiber length and concrete strength grade were considered to be experimental variables to obtain the bond stress-slip curves. The results showed that adding basalt fiber into recycled-aggregate concrete will reduce the bond stress between BFRP bar and recycled-aggregate concrete but enhance the ductility of bond property; the bond stress increases with the increasing of fiber length and concrete strength grade. The bond stress-slip constitutive model was proposed and the results showed that the model is good in effect of fitting. The constitutive model can reflect the bonding mechanism between BFRP bar and basalt fiber concrete well, it also can provide reference for theoretical analysis and engineering applications of the bond and anchor property between BFRP bars strengthened recycled concrete.

In enhancing the high-temperature resistance of concrete, incorporating fiber materials was established as an effective approach. This study focused on evaluating the cubic compressive strength, splitting tensile strength, prism compressive strength, and flexural strength of plain concrete, nano-SiO₂ concrete, and basalt fiber nano-SiO₂ concrete when subjected to elevated temperatures. Subsequently, a concrete strength prediction model was established, and a microstructure analysis of the specimens was conducted. The results indicated that after exposure to 800°C, the cubic compressive strength, splitting tensile strength, prism compressive strength, and flexural strength of basalt fiber-reinforced nano-SiO₂ concrete increased by 33.7%, 15.6%, 10.4%, and 17.2%, respectively, compared to plain concrete. Furthermore, the fitting values of the strength prediction model were all above 0.9. Microstructure analysis revealed that the filling effect of nano-SiO₂ made the concrete matrix denser, while the basalt fiber effectively restrained the formation of cracks in the concrete matrix. Additionally, nano-SiO₂ promoted the formation of hydrated calcium silicate from Ca(OH)₂(CH) and adhered to the basalt fiber, enhancing bonding and reducing the risk of concrete spalling.

The use of short cylinders of recycled aggregate concrete (RAC) reinforced with basalt fiber-reinforced polymer (BFRP) circumferential strips and polyvinyl chloride (PVC) tubes has been proven effective in previous studies. However, BFRP circumferential strips are cumbersome to install and do not ensure the integrity of the BFRP strips. Therefore, this study investigates axial compression experiments on RAC short cylinders reinforced with BFRP spiral strips and PVC tubes. A combination of experimental studies, finite element simulations, and theoretical analyses revealed that the winding angle and spacing of BFRP strips significantly affect the load-bearing capacity and ductility of the restrained specimens. Additionally, an improved strength model was developed based on an existing model. When evaluated using both computational and experimental results, the equations generated in this study showed an average error of less than 10%. The findings indicate that the composite structure provides effective reinforcement and offers valuable reference information for practical applications.