Experimentally informed micromechanical modelling of cement paste: An approach coupling X-ray computed tomography and statistical nanoindentation

Abstract

This work proposes a method for numerically investigating the fracture mechanism of cement paste at the microscale based on X-ray computed tomography and nanoindentation. For this purpose, greyscale level based digital microstructure was generated by X-ray microcomputed tomography with a resolution of 2 μm/voxel length. In addition, statistics based micromechanical properties (i.e. Young's modulus and hardness) were derived from the grid nanoindentation test which was set to have an interaction volume the same as the resolution of the digital microstructure. A linear relationship between the two probability density functions of greyscale level and local Young's modulus was assumed and verified by the two-sample Kolmogorov-Smirnov (KeS) statistic. Based on this assumption, the fracture and deformation of a digital cubic volume with a dimension of 100 μm under uniaxial tension was simulated using a lattice fracture model. In addition, the influence of heterogeneity on fracture response was studied. Furthermore, the proposed method was compared with the results obtained from a traditional approach used previously by the authors in which discrete phases (capillary pore, anhydrous cement clinker, outer and inner hydration products) were considered. The two methods show similar crack patterns and stress-strain responses. The proposed method is regarded more promising as it captures also the gradient of material properties (within the discrete phases) in the cement paste.

Combined experimental and numerical study of uniaxial compression failure of hardened cement paste at micrometre length scale

“…Heterogeneity of the observed system is considered by introducing spatial distributions of the mechanical properties of local elements. This can be achieved by using either a statistical distribution [33] or a specific material structure (i.e., a voxel based material structure [34]).…”

Experimentally informed fracture modelling of interfacial transition zone at micro-scale

“…To consider the heterogeneity of HCP at the micro-scale, both the continuous greyscale level based material structure [46] and multiphase based material structure [42] can be used. Herein, a global thresholding approach that developed in the authors' previous work was adopted to segment the HCP part into a 4-phase material consisting of capillary pore (CP), inner hydration product (IHP), outer hydration product (OHP) and anhydrous cement particle (ACP).…”

Assessing Hydrated Cement Paste Properties Using Experimentally Informed Discrete Models

“…These issues could be resolved by correlating the grayscale value from the X-ray tomography directly with the cement paste mechanical and transport properties, which would then not require phase segmentation but would include the influence of gel pores. This approach is currently being developed for determining the mechanical properties of cement paste (Zhang et al 2019). And third, in simulating chloride diffusivity, steady-state conditions were assumed and chloride binding was not considered.…”