X-ray Computed Tomography (XCT) is a powerful technology that can accurately image the internal structures of composite and heterogeneous materials in three-dimensions (3D).We report in this study three in-situ micro XCT tests of concrete, fibre reinforced polymers, and ultra high performance fibre reinforced concrete under progressive loading,which are carried out to obtain a better understanding of 3D fracture and failure mechanisms in these materials.