Evaluation of Pull-Off Tests as a FRP–Concrete Bond Testing Method in the Laboratory and Field

Abstract

The direct tension pull-off test has gained popularity as a test method used in the laboratory and especially in the field to assess the quality of bond between externally bonded fiber-reinforced polymer (FRP) repair materials and concrete owing to its low cost and simple procedure. However, the small scale and localized nature of the test can lead to high variability in the results. Furthermore, the test does not load the bond in a way that is representative of service conditions. Because of these limitations, satisfactory interpretation of results can be difficult. This paper examines the challenges that may be encountered when analyzing the data obtained during testing, including the high variances. Past research efforts using pull-off tests, and results of recent field and laboratory testing by the authors, are discussed to evaluate the benefits and weaknesses of pull-off tests as a quality control and research tool. The authors conclude that pull-off tests have many drawbacks, and if they are used, great care is needed in their application. It is recommended that if this method is to be used as a quality control procedure in the field, pull-off tests on the concrete alone should be conducted to obtain baseline values, and supplementary tests such as acoustic sounding also be used. For laboratory conditions, it is advised that alternative testing procedures be considered and large sample sizes be used to make statistical validation possible.