Optimal mix ratio and numerical simulation study of concrete modified by nano-silica synergistically reinforced with basalt fibers

Abstract

With the implementation of a series of national strategies, China's infrastructure construction is facing significant opportunities as well as considerable challenges. As one of the core building materials, concrete is required to meet increasingly stringent performance demands. Against this backdrop, this study focuses on developing a high-performance concrete with both high strength and high toughness. Basalt fiber (BF) and nano-silica (NS) were selected as the primary modifying materials. An orthogonal experimental design was employed to systematically investigate the effects of BF length, BF content, and NS content on the strength and toughness of concrete, in order to determine the optimal mix proportion. Experimental results show that as BF length, BF content, and NS content increase, both strength and toughness indicators initially increase and then decrease. The influence of each factor on performance indicators follows the order: BF content > BF length > NS content. Based on range analysis and variance analysis of the orthogonal tests, the optimal mix proportion was determined as BF length: BF content: NS content = 6 mm: 0.2 %: 2 %. Mechanical tests and microstructural observations were conducted on specimens prepared with the optimal mix. The results indicate that NS effectively fills micro-pores within the concrete, enhances density, and significantly improves mechanical performance. The coral-like micro/nano structures formed by NS modification significantly increase the surface roughness of BF. These structures highlight the excellent synergistic interaction between BF and NS, which jointly enhance the interfacial bonding performance. BF also provides a bridging effect within the concrete matrix, inhibits microcrack propagation, and markedly enhances toughness. Furthermore, numerical simulations were used to further elucidate the fracture behavior and energy evolution of flexural test specimens. The simulation results for peak stress, ultimate strain, and failure modes showed good agreement with experimental findings. The stress contour maps of nano-silica and basalt fiber-modified concrete (BFNSRC) and Part-BF were consistent with theoretical expectations. Energy–crack evolution analysis revealed that the cement matrix primarily absorbs and dissipates energy, while the presence of BF contributes additional dissipative capacity, thereby enhancing the material's toughness. The results of this study provide technical support and theoretical guidance for the preparation of high-strength, high-toughness, high-performance concrete.