Experimental study on bond behavior between FRP and concrete Jianzhuang Xiao * , Jie Li, Quanfan Zha Department of Building Engineering, Tongji University, Shanghai 200092, PR China Received 30 March 2002; received in revised form 13 April 2004; accepted 14 April 2004 Available online 22 July 2004 Abstract In this paper, two kinds of tests were designed to investigate and study the bond behavior between fiber-reinforced-plastic (FRP) and concrete. By newly designed double-shear test setup, the strain development and distribution in FRP plate was acquired. At the same time, the direct shear bond distribution was given and the effective bond length was suggested. Through a bending test on simply supported beam with an extended end, the strain and stress distribution of FRP plate in the negative moment zone were studied. Based on the test results, conclusions including the maximum effective bond length, the mean bond stress and the devel- opment length for flexural bond in the negative moment zone were presented. The effective bond length is about 100 mm and the mean bond stress is about 1.287 MPa. The development length for flexural bond in the negative moment zone is about 300 mm. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Bond behavior; Fiber-reinforced-plastic; Concrete 1. Introduction Fiber-reinforced-plastic (FRP) plates are being suc- cessfully applied worldwide for strengthening existing reinforced concrete structures [1]. The bond of FRP reinforcement to the concrete substrate is of critical importance for the effectiveness of the technique, be- cause it is the means to develop composite action by the stress transfer between concrete and FRP. Any factors that cause the failure of the bond area may lead to brittle failure of strengthened structures, so the expected strengthening effect cannot be achieved. Even the final bond failure of the interface does not occur, the strength, stiffness and the deformation capacity of the structure after repairing will also be obviously influ- enced by both the occurrence and the development of the cracks on the bond interface. Generally, the an- chorage failure between FRP and concrete interface are due to: (1) poor distribution or lacking of bond agent; (2) existing of wider flexural cracks or shearing cracks in concrete; (3) coarse concrete surface; (4) fatigue loading. Although the stiffness, ductility and the bearing capacity of the structure can be greatly improved by wrapping FRP, the widely application of FRP will be restricted due to the interface anchorage failure. Therefore, further research on the bond behavior of FRP to concrete in- terface is needed. Chajes et al. [2] studied the bond and force transfer mechanism in FRP plates bonded to concrete by using a single-lap shear test. The test setup is shown in Fig. 1. The first set of tests was performed to investigate the effect of surface preparation, type of adhesive, and concrete strength on the average bond strength. The second set of tests, in which the bonded length was varied, was performed to study the force transfer from the composite plates to the concrete. Test results showed that: (1) surface preparation of the concrete can influ- ence the bond strength; (2) if the failure mode of the joint is governed by shearing in the concrete, the ulti- mate bond strength will be proportional to the square root of the concrete compressive strength; (3) there is an effective bond length for a joint beyond which no further increase in failure load can be achieved. Brosens and Van [3] performed direct shear tests on two concrete prisms connected with three plies of carbon-fiber-rein- forced-plastic (CFRP) on two opposite sides. They * Corresponding author. Tel.: +86-21-65983422; fax: +86-21- 65986345. E-mail address: jzx@mail.tongji.edu.cn (J. Xiao). 0950-0618/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2004.04.026 Construction and Building Materials 18 (2004) 745–752 Construction and Building MATERIALS www.elsevier.com/locate/conbuildmat