Experimental bond tests on concrete members strengthened with NSM FRP systems: Influence of groove dimensions and surface treatment

This paper deals with the results of an experimental program to investigate on the bonding behavior of different Fiber Reinforced Polymer (FRP) bars applied with the near surface mounted (NSM) technique for strengthening of reinforced concrete (RC) members. The experimental program consisted of 12 single shear tests (SST) on concrete specimens strengthened with carbon (3 tests) and basalt (9 tests) bars. These tests have been carried out in addition to 24 bond tests previously performed on concrete specimens strengthened with carbon, basalt and glass bars (18 tests) and carbon strips (6 tests). The twelve additional experimental tests herein presented aimed at investigating the influence of surface treatment and grooves dimensions on the bond of NSM strengthening system. The tests were performed on concrete prisms casted in the same batch with a concrete characterized by a low compressive strength to investigate the bonding behavior of existing reinforced concrete (RC) structures. The experimental outcomes of 12 tests are herein presented and discussed in terms of failure mode, debonding load, and load-slip relationship. The comparison with the results of previous 24 tests is also reported to point out the influence of bars' surface treatment as well as of different groove dimensions.