Effect of Carbon Nanotube‐Modified Epoxy on the GFRP Confinement Performance of Concrete

ABSTRACT This study investigated the effect of incorporating 0.3 wt.% carbon nanotubes (CNTs) into the epoxy matrix used in glass‐fiber‐reinforced polymer (GFRP) confinement systems for concrete cylinders. Sixteen concrete specimens, divided into low‐ and normal‐strength groups, were cast. Twelve of them were wrapped with GFRP using either plain or CNT‐modified epoxy and tested under monotonic axial compression. The results showed that the addition of CNT enhanced interfacial bonding, as evidenced by fiber shredding and improved mechanical interlocking with concrete. For specimens with insufficient GFRP overlap (10 mm), CNT yielded modest improvements in the hoop rupture strain and compressive strength but reduced the ultimate axial strain. In low‐strength concrete with an adequate overlap (150 mm), CNT modification unexpectedly decreased the confinement efficiency, causing premature rupture. Conversely, normal‐strength concrete specimens with CNT‐modified epoxy exhibited significant improvements in confinement efficiency, strength, and strain enhancement ratios. Existing analytical models underestimate the performance of CNT‐modified systems, particularly for low‐strength concrete, highlighting the need for CNT‐specific design guidelines. The findings demonstrate the potential of CNT‐enhanced GFRP confinement for structural retrofitting, particularly under moderate confinement ratios, and emphasize the necessity for further research on durability, scalability, and cyclic loading effects.