Effect of carbon nanotubes on strengthening of RC beams retrofitted with carbon fiber/epoxy composites

The effect of carbon nanotubes (CNTs) in improving the strengthening efficiency of carbon fiber/epoxy composites retrofitted reinforced concrete (RC) beams was investigated. A total of sixteen simply supported RC beams were prepared and tested under four-point loading. The incorporation of CNTs within the systems was done by modifying the epoxy resin using CNTs and/or coating the carbon fiber sheets with CNT enriched sizing agent. The effects of epoxy modification with CNTs, incorporation of CNT enriched sizing agent, anchorage length, and number of retrofitting layers were investigated through crack patterns, failure modes, load-deflection curves, and scanning electron microscopy (SEM) micrographs of fractured surfaces. Experimental results showed that using CNT modified epoxy resin enhanced the ultimate load and stiffness of retrofitted beams. The enhancement efficiency highly depends on the level of dispersion of CNT, anchorage length, and number of retrofitting layers. SEM characterization showed that CNTs could improve the adhesion at the concrete/epoxy interface and carbon fiber/epoxy interface leading to improvement in the load transfer and ultimate load of the strengthened beams. (C) 2015 Elsevier Ltd. All rights reserved.