Shear Capacity of RC Beams Strengthened with Flax Fiber Sheets Grafted with Nano-TiO2

Abstract

Flax fiber sheets provide the advantages of high specific strength, a short growth cycle, environmental friendliness, wide availability, and low cost. Therefore, in this study, the shear capacities of reinforced concrete (RC) beams strengthened with ordinary flax fiber sheets, flax fiber sheets grafted with nano-TiO 2 , and unidirectional basalt fiber sheets were compared. The bearing characteristics and failure modes of RC beams strengthened with flax fiber sheets were investigated. The results showed that after reinforcement with flax fiber sheets, the bearing capacity and mid-span deflection of the RC beams are considerably improved, and the reinforcing effect of flax fiber sheets grafted with nano-TiO 2 is greater than that of unmodified flax fiber sheets. After reinforcement with flax fiber sheets grafted with nano-TiO 2 , the shear capacity of the RC beams is considerably improved to 653 kN, which is 72.8% higher than that of the unreinforced RC beams. Meanwhile, the mid-range deflection of the beam reached 14.6 mm, which is 75.9% higher than that of the unreinforced RC beams.surface morphology of the flax fiber sheets, but it can also transform the hydrophilic surface into a lipophilic surface, which improves the compatibility of the flax fiber monofilament with epoxy resin [15,16]. After grafting, a nanoparticle layer structure is produced on the surface of the flax fiber. This can create new covalent bonds, such as -Ti-O-Si-and -Si-O-C-. The degree of defects on the surface of the flax fiber sheets is reduced, and a nano-reinforced epoxy resin composite layer is formed between the flax fiber sheets and the epoxy resin, which fully exerts the reinforcing effect of the nano-TiO 2 [15,17].In this study, the shear capacity, bearing characteristics, and failure modes of reinforced concrete (RC) beams and RC beams strengthened with ordinary flax fiber sheets, unidirectional basalt fiber sheets, and flax fiber sheets grafted with nano-TiO 2 were analyzed and compared. An equation for the shear bearing capacity of RC beams strengthened with flax fiber sheets was also proposed. Materials and Methods Materials and ReagentsThe RC beam was cast with commercial concrete. The concrete grade was C30, water-cement ratio was 0.42, and ratio of cement:water:sand:gravel was 360:151:632:1282 by weight. The cement was Swan brand P.O grade 42.5 ordinary Portland cement, produced by the Harbin Cement Factory of the Jilin Yatai Group, China. The maximum particle size of the coarse aggregate was approximately 25 mm. The measured concrete slump was 43 mm [18]. After pouring was completed, the RC beam was continuously watered at room temperature for 7 days, after which it was removed from the mold and rinsed until 28 days. According to the requirements in the standards for the test of mechanical properties of ordinary concrete (GB/T 50081-2011) [18], the compressive strength of the concrete cube (100 mm × 100 mm) was measured to be 38.2 ± 0.3 MPa.The vertical, structural, and erecting steel rebars were HRB400 grade ordinary hot ro...

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