Mitigation of premature failure of FRP bonded to concrete using mechanical substrate strengthening and FRP spike anchors

Fiber reinforced polymers (FRPs) are being increasingly used to strengthen and repair existing reinforced concrete (RC) structures and possess many advantages with respect to other strengthening methods, such as externally bonded (EB) steel plates. It is presently understood that the strength of the concrete substrate is a key factor affecting the debonding failure mode and the overall bond strength of FRP materials. Although researchers have investigated the application of FRP anchorage systems to delay the critical debonding failure mode, increasing the strength of the concrete substrate to achieve the same goals has been little investigated to date. The present study investigates substrate strengthening techniques in an experimental program where 30-40 mm wide × 20 mm deep concrete chases within the concrete cover zone are introduced in both transverse and longitudinal orientations in order to strengthen the substrate to which the FRP is bonded. In addition, the concept of using two FRP spike anchor dowels with one end drilled into the concrete and the other end bonded to the FRP laminate is evaluated. All of the enhancement techniques tested demonstrated significant enhancements in bond strength.