Analysis of the Crack Behaviour of a GFRP Reinforced Concrete Beam using Computed Tomography

The structural behaviour of glass fibre-reinforced polymer (GFRP) reinforcement in concrete elements differs from that of conventional steel reinforcement. The main distinction is that GFRP reinforcement is linearly elastic until failure, while steel reinforcement exhibits yielding under stress. Furthermore, disparities also extend to the failure mechanisms of reinforced concrete elements and their crack morphology. A comprehensive way to examine the mentioned behaviour and the interaction between FRP reinforcement and the surrounding concrete matrix is to thoroughly inspect the interior of the concrete component. This can be achieved using computed tomography (CT), a technology within non-destructive testing (NDT). CT images reveal complex crack geometry and changes in internal structures, including internal damage that would otherwise go undetected. This paper presents selected results of an in-situ CT bending test performed on small concrete beam specimens containing GFRP reinforcement. The objective is to analyse the behaviour of the beams with FRP reinforcement under load. The in-situ test is performed using an innovative test setup designed to enable CT observations under sustained loading conditions. The image analysis methodology is shown with a focus on emphasizing the observation of crack propagation across different load stages. In addition, existing analytical models were employed to gain an understanding of the cracking phenomena in the experimentally tested concrete elements. The experimental results are compared with these numerical analysis to highlight the differences in crack patterns. Finally, proposals and further test concepts for computed tomography are also outlined.