Influence of surface roughness on the bond of FRP laminates to concrete

The potential of Fiber Reinforced Polymer FRP in the reinforcement of concrete structures has been shown in many studies and practical applications. However, few works have been focused systematically on the development of quantitative criteria to measure surface roughness and relate this parameter to the debonding stress. Roughness has a direct influence on the FRP performance in terms of bond to concrete, which is important to ensure the effectiveness of the external FRP reinforcement. Currently, there is not much evidence about the parameters related to surface state of concrete structures nor many guidelines about assessing the optimal conditions of concrete surface for the application of the FRP. To respond to these needs, the presented study deals with the effects of the surface characteristics of concrete on debonding strength of the FRP; this objective has been pursued by means of experimental tests on concrete specimens characterized by different levels of roughness of the concrete surface. The paper describes the experimental campaign outlining the analyzed surface preparation procedures (i.e., sandblast, bush-ammering, grinding, brushing) and the subsequent tests performed on the installed FRP by means of two different test methods. The former is a laboratory method which performs shear tests to evaluate the debonding shear strength of the FRP reinforcement; the latter is pull-out test which is a typical method used for in situ check of quality of the FRP application. The results of these experimental tests are discussed in the paper with emphasis on the correlation between the roughness of the surface and the outcomes of both shear and pull-out tests; this information can be used in design in order to prescribe the minimum roughness level necessary to attain the expected debonding strength of the reinforcement.