An Experimental Study on Effect of Concrete Type on Bond Strength of GFRP Bars

One of the common methods to create bond strength in reinforced concrete is providing development length. The bond strength of glass fiber reinforced polymer (GFRP) bar is inherently poor due to its shape, as well as its inadequate mechanical interlocking with concrete. Therefore, providing sufficient development length in this bar is different and more conservative in comparison with steel bars. In this study, three types of concrete are selected, namely normal-weight concrete (NWC), light-weight concrete (LWC), and light-weight fiber reinforced concrete (LFRC). In order to investigate the adequate development length required for GFRP bars and its relation with the concrete type and compressive strength, for Each type of concrete, two different mix designs which have various compressive strengths are considered. 18 cube specimens are fabricated and the direct pull-out test is performed. The results indicate that, in all types of concrete, as the compressive strength increases, the bond strength between concrete and rebar augments. In addition, assessing the bond strength of different types of concrete demonstrates that the use of LWC, due to its inherent weakness of aggregates interlocking, causes pre-mature cracks and loss of the bond strength compared to NWC. Furthermore, LFRC mixtures containing 0.3% and 0.5% macro-synthetic fiber volume fraction reveal that the presence of fibers can be effective in controlling cracks and increases the bond strength between GFRP bars and concrete. As a result, with the increase of the bond strength between the GFRP bar and the concrete, the ultimate capacity of the concrete cross-section augments.