Enhancing mechanical properties of high-strength recycled concrete with basalt fiber and nano-calcium carbonate: Experimental and numerical investigations

In structural engineering applications, the use of recycled aggregate (RA) is often limited due to its relatively low mechanical properties, particularly in high-performance environments where its suitability is critical. This limitation has driven the need for improvements to ensure RA can be used effectively in high-strength concrete applications. In order to make it more suitable for demanding engineering applications while promoting sustainability by utilizing recycled materials, this study investigates the modification effects and modification mechanisms of basalt fiber (BF) and nano-calcium carbonate (NC) on the static mechanical properties of high-strength recycled concrete (HSRC). Through static uniaxial compression experiments, the macroscopic effects of different dosages of BF and NC on the stress-strain curve, failure mode and mechanism, elastic modulus, and compressive strength of HSRC were systematically analyzed. Scanning electron microscopy was used to investigate the microstructure and reveal the microscopic enhancement mechanism of BF and NC in the interface transition zone and matrix. Additionally, a constitutive model of modified high-strength recycled concrete (MHSRC) was developed, which quantified the effects of three material dosages of RA, BF, and NC on the material stress-strain relationship. The fitting results show that it has good applicability. Moreover, mesoscopic model of MHSRC was established. By comparing the numerical simulation results with the experimental results, the reliability of the model in predicting the macroscopic mechanical properties of MHSRC and the accuracy of the constitutive model in estimating its stress-strain relationship were verified. The results show that the synergistic effect of BF and NC significantly improves the mechanical properties of HSRC, and the best combination is 0.5 % BF and 2.5 % NC, which increases the compressive strength by 6.4 % compared with the unmodified HSRC. Microscopic analysis shows that the interaction between BF and NC improves the interface transition zone between RA and matrix, as well as between BF and matrix. The two produce a synergistic mechanism at appropriate dosages, which is manifested explicitly as a comprehensive improvement in strength and ductility. This finding provides important insights into understanding fiber-nanomaterials to improve the mechanical properties of HSRC and its structural engineering applications and contributing to the development of more sustainable, high-performance concrete for structural applications.