Investigation of CFRP-concrete bond performance using 3D image correlation photogrammetry

Carbon fiber reinforced polymers 'CFRP' in the form of laminates and fabrics are increasingly being used in retrofitting of civil infrastructure such as bridges, buildings and pipelines. An essential characteristic of the system is the bond behaviour between the CFRP and the structural element. To measure such behaviour, the most commonly utilised technique is the use of electrical strain gauges. A very large number of such gauges would be required to obtain a realistic assessment of the deformations and strains. In this investigation, a novel non-contact measurement method was used based on the technique of photogrammery. Photogrammetry is a three-dimensional image correlation method that utilises digital cameras and computers to measure deformations and strains. It can be described as digitally photographing the target area through successive load steps to trace the movement of surface features. The three dimensional stereoscopic images taken of the surface consist of millions of 'Pixels'. Each pair of pixels (left and right) represents a point on the surface. A specific matrix arrangement of Pixels called 'Facet' is related to distinct area on the body. The absolute and relative movements of these Facets under load increments are converted mathematically to deformations and strains. This is done with the aid of reference points to account for rigid body motion. The results are successive images 'movie' showing three dimensional strain fields changing on the specimen’s surface due to load increments. Strain results at points, sections and smaller area of special interest can be isolated for detailed analysis. These results were used to analyze the behavior of CFRP-concrete joints during single-lap shear test