Pull-off characterization of FRCM/Concrete interface

Fabric-reinforced cementitious matrix (FRCM) composites are usually surface-applied for strengthening reinforced concrete (RC) structures. The efficacy of the FRCM strengthening systems is dependent on the FRCM/concrete bond performance. This paper reports on the experimental results of FRCM/concrete bond characterization through pull-off tests. Six FRCM-strengthened RC slabs (500 mm x 500 mm x 100 mm) were prepared and enabled conducting 72 FRCM/concrete pull-off tests. The parameters investigated included: (a) FRCM material (carbon or polyparaphenylene benzobisoxazole (PBO)); (b) level of substrate roughness (no/low/high roughening); and (c) specimen's test age (7, 28, 56, and 84 days). All FRCM systems were single-plied. The study revealed a significance of the surface preparation and test age of specimens on the FRCM/concrete pull-off strength. High-roughness specimens showed an average of 74% pull-off strength increase compared to those without roughening. Also, specimens tested at Day 84 showed 54% strength increase compared to those tested at Day 7, on average. PBO-FRCM system showed slightly higher pull-off strength than that of the carbon counterpart. The specimens showed two distinctive failure types at the (i) fabric/mortar interface and (ii) concrete/matrix interface: the latter was more prominent in carbon-FRCM. Nonetheless, the failure mode was most dependent on the fabric geometry and the substrate roughness. Based on a statistical analysis of the tested specimens, prediction models were proposed for the FRCM/concrete pull-off strength and failure mode.