Abstract
Three-dimensional (3D) characterisation and modelling of cracking in concrete have been always of great importance and interest in civil engineering. In this study, an in situ microscale X-ray computed tomography (XCT) test was carried out to characterise the 3D microscale structure and cracking behaviour under progressive uniaxial compressive loading. The 3D cracking and fracture behaviour including internal crack opening, closing, and bridging were observed through both 2D tomography slices and 3D CT images. Spatial distributions of voids and cracks were obtained to understand the overall cracking process within the specimen. Furthermore, the XCT images of the original configuration of the specimen were processed and used to build microscale realistic 3D finite element (FE) models. Cohesive interface elements were inserted into the FE mesh to capture complicated discrete crack initiation and propagation. An FE simulation of uniaxial compression was conducted and validated by the in situ XCT compression test results, followed by a tension simulation using the same image-based model to investigate the cracking behaviour. The quantitative agreement between the FE simulation and experiment demonstrates that it is a very promising and effective technique to investigate the internal damage and fracture behaviour in multiphasic composites by combining the in situ micro XCT experiment and image-based FE modelling.
Highlights
Multiscale experiments and modelling of quasi-brittle multiphase materials, such as concrete, bones, and various composite materials, have received increasing interests in order to gain a better understanding of their failure mechanisms [1]
Little difference was found between the two images at 2 kN and 3 kN
This paper presents an application of micro X-ray computed tomography (XCT) to microstructure characterisation of concrete and its cracking process using in situ compression tests
Summary
Multiscale experiments and modelling of quasi-brittle multiphase materials, such as concrete, bones, and various composite materials, have received increasing interests in order to gain a better understanding of their failure mechanisms [1]. An improved understanding of 3D cracking in concrete can be achieved by multiscale experiments and numerical modelling based on realistic microstructures, for the development of materials with higher strength, durability, and fracture resistance. In comparison with numerical models using idealised microscale morphologies [14,15,16] or assumed stochastically random field properties [17], the image-based models faithfully reproduce the intrinsic heterogeneity of the material, such as shape, size, and distribution of inclusions and pores [18]. As an extension to the authors’ previous in situ XCT tests [19], this follow-up study used the simpler uniaxial compression loading condition rather than the Brazilianlike concentrated splitting, and the size of the concrete cube was halved to obtain imaging results of 3D microscale structure and cracking process with higher voxel resolution. The XCT image-based FE models were simulated under uniaxial tension to investigate complicated fracture process
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