Repair of heat-damaged RC columns using carbon nanotubes modified CFRP

This paper reports on the influence of carbon nanotubes (CNT) on the axial load capacity of heat-damaged RC columns repaired with carbon fiber reinforced (CFRP) composites. The nanotubes were incorporated in the composites by using CNT-modified epoxy and/or coating the carbon fiber sheet with sizing agent enriched with CNT. Twenty-two reinforced concrete columns were casted, heated at 500 and 600 degrees C, repaired with FRP or nano-modified FRP composite, and then tested. The mode of failure, ultimate load, initial stiffness, and toughness were analyzed. Scanning electron microscopy (SEM) characterization was performed to explore the morphology of the tested specimens. The results revealed that the load capacity and the toughness of the repaired columns were enhanced when CNT-modified resin and/or CNT-enriched sizing agent were incorporated in the composite. Compared with the unmodified FRP sheets, SEM micrographs showed more debris were attached to the FRP sheets in the cases where CNT were incorporated in the composite reflecting an enhancement in the adhesion at the epoxy/fiber interface thus the load transfer process.