Flexural performance of recycled concrete beam reinforced with modified basalt fiber and nano-silica

To increase the surface roughness of basalt fiber (BF) and enhance the bonding properties with the concrete matrix, three modified solutions were prepared to treat the BF surface. The BF surface was modified by the best mixture-ratio solution after SEM and AFM tests. Modified basalt fiber (MBF) and nano-silica (NS) were used as reinforcing materials to improve the RC. The MBF and NS contents were used as the mix ratio control parameter. Ten recycled concrete beams were designed. Through a four-point flexural test, the destruction characteristics, deflection, cracking load, maximum bearing capacity, and strain of RC beams were obtained. The effects of replacement rate, MBF content, and NS content on the flexural properties of the RC beams were obtained. The results showed that in comparison to modification by other solutions, the surface roughness of BF was greater with modification by 2.91% KH550 and 5% NS mixed solution. The failure characteristics were similar for natural aggregate concrete beams and RC beams reinforced with MBF and NS; all underwent four stages of ordinary concrete damage. The natural aggregate concrete beams had greater flexural strength and flexural resistance than RC beams. However, the MBF and NS, added separately or together, improved the dehiscence load, peak load, ductility, and tensile strain of the RC beams. The current standards can be used to calculate the cracking moment and ultimate bearing capacity of MBF and NS reinforced RC beams; their effect was significant.