A new method to improve the properties of recycled aggregate concrete: Composite addition of basalt fiber and nano-silica

Use of recycled aggregate manufactured from waste concrete to produce new concrete could reduce the use of natural gravel, and the quantity and area of landfills, which is conducive to natural environmental protection and economic development. How to effectively reduce the hazards of construction waste is an urgent problem to be solved. Recycled aggregate concrete is one of the effective ways to realize the utilization of resources. This paper provides a new method for the resource utilization of construction waste, which is helpful for expanding the range of engineering applications for recycled aggregate concrete. The recycled aggregate concrete was reinforced with basalt fiber and nano-silica, and its mechanical properties, including compressive strength, splitting tensile strength and flexural strength were tested. Meanwhile, the microstructure of the recycled aggregate concrete was analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). It was found that basalt fibers and nano-silica improve the recycled aggregate concrete. Nano-silica is beneficial for enhancing the bonding of the basalt fibers and cement matrix. The appropriate content of nano-silica was conducive to the improvement of the recycled aggregate concrete density and the performance of the interface transition zone, thereby increasing the bridge effect of the fibers. When the nano-silica content was high, the calcium-silicon ratio increased, and the concrete density decreased. In terms of the compressive strength and microstructures, when the recycled aggregate replacement ratio was no more than 50%, the optimum nano-silica content was 6%, and when the recycled aggregate replacement ratio was 100%, the optimum nano-silica content was 8%. The addition of basalt fiber and nano-silica is conducive to expanding the scope of engineering applications for recycled aggregate concrete and improving the natural environment, which is helpful to the sustainability of the construction industry.