Repair Composite Adhesion Strength: A Comparison of Testing Methods

The adhesive strength of repair composites to concrete substrates was assessed through both Ukrainian and European standard test methods. The types of adhesion loss observed included adhesive failure along the contact layer (AF-S), and cohesion failure along the substrate (CF-S). The Ukrainian method showed adhesive bond loss in 90.5% of samples (181 out of 200), while the European method showed loss in 76% (152 out of 200). However, under identical conditions, the EU standard showed greater consistency (standard deviation 0.25) than the Ukrainian standard (standard deviation 0.42 and 0.32). The effect of pull-off techniques on failure models varied depending on the epoxy thickness and the mechanical testing performed. Repair composites meeting the highest Ukrainian structural class criteria (PM1) were classified as R3 materials according to the European standard. This research highlights that statistical analysis shows a significant improvement in reliability with an increased number of pull-off tests.