Experimental study of failure mechanisms in brittle construction materials by means of X-ray microfocus computed tomography

X-ray microfocus computed tomography (CT) is a powerful tool in the 3D visualization of fracture initiation and propagation in brittle materials, based on the attenuation of X-rays. Aim of this paper is to present the experience obtained at the Building Materials and Building Technology research group in using CT for the experimental study of failure mechanisms in brittle construction materials during three test programs, focusing on following issues: (i) triaxial behaviour of mortar joints, (ii) effect of pore saturation on micro fracture in sandstone and (iii) influence of flow distance on fibre distribution and orientation in fibre reinforced concrete. The resolution limit of the applied system is in the order of micro meters (microCT). Common goal of the presented experimental programs was to analyse the material’s inner structure and fracture propagation at microscale, in support of studying local failure mechanisms and developing numerical models. For each test program, setup optimization and resulting failure modes will be discussed. Several types of in-house-made loading stages were applied for observation of step-wise induced failure mechanisms. As a general conclusion, most test results supported the theoretical framework relevant to the effects of varying conditions (relative stiffness, pore saturation, viscosity) on the observed failure modes. However, sample size / image resolution balance remains an important focus point. Additionally, future research is briefly discussed, in relation to the experience gained in the described test programs.