Experimental and statistical dry-fracture assessment of the CFRP-concrete interface bond

A study of the dry CFRP-concrete interface bond is presented. The main objective of this research endeavor is to characterize this bond as a material property, akin to that of Young's modulus or Poisson's ratio, using the novel experimental single contoured-cantilever beam (SCCB) fracture mechanics testing approach. The dry fracture results came from two categories of specimens: pristine as well as representative companion beams, the latter category of which was taken from a larger accelerated cycling study (not presented herein) that accompanied wet-dry as well as freeze-thaw weathered specimens. A statistical scheme was used to appropriately reduce and characterize the Mode I critical strain energy release rates (GIc) of the dry CFRP-concrete interface bonds. Weight and strain changes were also monitored in the specimens to verify negligible effects occurring on the bulk concrete substrate. The measured strains enabled assessments to be made relative to ACI Code provisions using both the tensile and splitting-tensile strengths of concrete as critical parameters, to further validate that there was no appreciable development of strain formed at the CFRP-concrete interface. Based on the conducted experimental study, the ranges of the GIc values are determined for these two categories of dry beams. It is found through the experimental program that the CFRP-concrete interface bond exhibits stable cracking as confirmed, both, by quantitative means, using the brittleness index, as well as through a qualitative observation of the fractured surface displaying a cohesive mode of failure. It is also shown that the experimental tensile strengths of the interface bonds are dramatically well within ACI Code strength predictions.