Structural repair and strengthening have long been dynamic and challenging activities in construction work. One of the most commonly used methods for such repairs is the application of Fiber Reinforced Polymer (FRP) sheets to strengthen reinforced concrete or even steel structural members. A major issue of concern in flexural strengthening of reinforced concrete beams with FRP laminates is their debonding off the concrete substrate, which leads to premature failure of the structural member thus strengthened. One reason for this premature rupture may be lack of proper preparation of the concrete surface in contact with the FRP sheet. Surface preparation is typically associated with such constraints as adverse environmental impacts, economic losses due to stoppage of activities, repair costs, or even inaccessibility of the member(s) to be strengthened. This study aims to investigate surface preparation for application of FRP sheets in an attempt to develop substitute methods for conventional surface preparation methods.

   The experimental specimens used in this study included 120 prism specimens of dimensions 100×100×500 mm subjected to 4-point flexural loading. The specimens were divided into the two control and experimental groups. The control group lacked FRP sheets while the experimental one had FRP sheets tested for their ultimate failure strength. Conventional surface preparation as well as transverse, longitudinal, and diagonal grooves as alternative techniques were applied on concrete surface. The results indicated that surface preparation prior to bonding of FRP sheets increased ultimate rupture strength. However, It was found that the substitute preparation methods greatly compensated for the lack of conventional surface preparation such that they changed, in some cases, the ultimate failure behavior of the strengthened specimens from debonding to rupture failure of FRP.