Effects of steel fibers and carbon nanotubes on the flexural behavior of hybrid GFRP/steel reinforced concrete beams

Background

Glass fiber-reinforced polymer (GFRP) bars offer a superior alternative to steel bars in concrete reinforcement but are associated with wider cracks and higher deformation rates. This study introduces a novel approach by combining steel fibers (SFs) and carbon nanotubes (CNTs) to address these drawbacks and enhance the performance of GFRP-reinforced concrete beams. The unique contribution of this study lies in the simultaneous use of SFs and CNTs, which has not been extensively investigated, particularly in the context of GFRP-reinforced concrete. The study involved testing three sets of nine specimens with different concrete mixtures and reinforcement forms.

Results

The results showed that adding 0.04% CNTs by cement weight and 0.6% SFs by volume fraction significantly improved the mechanical performance of GFRP and steel reinforced beams. GFRP reinforced beams with CNTs and SFs exhibited a reduction in crack width, a 20% increase in load-carrying capacity, and a 25% reduction in deflection compared to reference specimens. Scanning electron microscope analysis further revealed that CNTs effectively enhanced tensile load transfer, improving flexural behavior of the beams. The finite element analysis using ANSYS confirmed the experimental findings, highlighting the improved stress distribution in the modified concrete mixtures.

Conclusions

Incorporating SFs and CNTs in concrete significantly improves the mechanical performance of GFRP-reinforced beams, making them more durable and resilient. These findings suggest that the proposed approach can enhance the longevity and sustainability of concrete structures, particularly in dynamic load applications such as bridges and high-rise buildings. Further experimental and analytical studies are recommended to assess the practical implications and cost-effectiveness of these materials in large-scale construction projects.