The analysis of the bond strength between natural fiber reinforced polymer (NFRP) sheets and concrete

This study was conducted to develop an empirical model for predicting the bond strength between Natural Fiber Reinforced Polymer (NFRP) sheets and concrete. This was achieved through the production of 22 concrete block specimens with a size of 100 mm x 100 mm x 300 mm, having a single longitudinal reinforcing bar with a diameter of 10 mm in the center of its cross-section and a pre-existing crack in the middle of its length on 2 opposite sides. NFRP composites with a size of 50 mm x 240 mm were subsequently applied to both sides containing a crack. It is important to note that the NFRP was produced from fabric using 4 different types of fibers including jute, silk, pineapple, as well as dense and non-dense abaca fibers. Moreover, three different types of bonding adhesives were applied to bond the NFRP composite produced from abaca fiber to the concrete surface, and these include the standard epoxy resin, polyester resin, and thixotropic epoxy resin. Meanwhile, those produced using other types of fibers only required the standard epoxy resin. The NFRP was also made with different numbers of fabric layers ranging from 1 to 3, thereby, resulting in different thicknesses for the sheets. A tensile load was later applied through both ends of the reinforcing bar to rupture the NFRP sheets. It is pertinent to state that the bond strength model was proposed as a function of NFRP sheet thickness with due consideration for the influence of fiber density, fiber type, and bonding adhesive type. It was discovered that the bond strength calculated using the proposed model was very similar to the value obtained from the experiment. This study also determined the load-strain relationship and strain distribution along NFRP sheets. Moreover, the use of 2 and 3 layers of fabrics enhanced the bond strength by 118-350% and 312-400% respectively depending on the fiber and bonding adhesive types.