Effect of the inherent eccentricity in single-lap direct-shear tests of PBO FRCM-concrete joints

Investigation of the bond between fiber reinforced composites and the substrates onto which they are applied is of critical importance to understand their failure mechanisms. The bond behavior can be studied using different experimental test set-ups; the most commonly used are the single-lap and double-lap direct-shear tests. Although single-lap shear tests are simpler to carry out than double-lap shear tests, the presence of an eccentricity between the pulling and restraining forces leads to a mixed mode fracture process at the interface, which may influence the results. This study investigates the eccentricity effect on the bond behavior of fiber reinforced cementitious matrix (FRCM) composite-concrete joints. FRCM composite strips with the same bonded length were applied to concrete blocks of different lengths and tested using the single-lap shear test. The use of digital image correlation (DIC) allowed for studying the strain field on the surface of the bonded composite. Results were compared with those from double-lap shear tests of the same composite. The results obtained confirm that the eccentricity effect is negligible for bonded lengths longer than the effective bond length.