Factors influencing pull-off tests on concrete

The pull-off technique has grown in popularity for testing the surface zone strength of concrete, and when used in conjunction with partial coring is particularly suitable for the bond testing of repairs. Theoretical and laboratory experimental studies have been undertaken to examine a number of important practical factors which influence the results obtained during surface and partially cored pull-off tests. Finite-element methods were used to analyse failure zone stress distributions. Disc material and proportions were shown to be particularly significant in both types of test, and in some circumstances the results are also affected by the elastic modulus of the concrete. These factors may influence correlations with compressive strength, demonstrating the importance of standardization of disc characteristics to permit direct comparisons of results. This will also be an important consideration when comparing measured test results with specified values. A very wide range of loading rates is provided by currently available test equipment, and this feature merits further study, together with other factors relating to partially cored tests as applied to repairs.