Microscale Testing and Modelling of Cement Paste as Basis for Multi-Scale Modelling

Abstract

This work aims to provide a method for numerically and experimentally investigating the fracture mechanism of cement paste at the microscale. For this purpose, a new procedure was proposed to prepare micro cement paste cubes (100 × 100 × 100 µm3) and beams with a square cross section of 400 × 400 µm2. By loading the cubes to failure with a Berkovich indenter, the global mechanical properties of cement paste were obtained with the aid of a nano-indenter. Simultaneously the 3D images of cement paste with a resolution of 2 µm3/voxel were generated by applying X-ray microcomputed tomography to a micro beam. After image segmentation, a cubic volume with the same size as the experimental tested specimen was extracted from the segmented images and used as input in the lattice model to simulate the fracture process of this heterogeneous microstructure under indenter loading. The input parameters for lattice elements are local mechanical properties of different phases. These properties were calibrated from experimental measured load displacement diagrams and failure modes in which the same boundary condition as in simulation were applied. Finally, the modified lattice model was applied to predict the global performance of this microcube under uniaxial tension. The simulated Young’s modulus agrees well with the experimental data. With the method presented in this paper the framework for fitting and validation of the modelling at microscale was created, which forms a basis for multi-scale analysis of concrete.

Towards understanding stochastic fracture performance of cement paste at micro length scale based on numerical simulation

“…Based on the same principles, peak-force tapping atomic force microscopy (AFM) can be applied as an alternative tool to quantify the local elastic properties [7]. These techniques provide a meaningful experimental input for analytical and numerical models used to calculate the global micromechanical properties of cement paste [8][9][10][11][12][13] which can be further used as input within a multi-scale framework to simulate the macroscopic mechanical performance of concrete [14][15][16].…”

“…Therefore, it is hard to correlate the fracture properties with its microstructure for quantitative assessment at the micro scale. Instead, application of a microstructure-informed numerical model [12,13,19,20] offers an opportunity to achieve this. Such a model requires a detailed microstructure and micromechanical properties of individual components in the material.…”

Use of X-ray computed tomography as input for fracture modelling of cement paste-aggregate interface

“…At the micro metre level, a multi-phase material structure of cement paste should be considered to model the fracture behaviour. Herein, a global thresholding approach that developed in the authors' previous work [3] was adopted to segment the cement paste part into a 4phase material consisting of pore (P), inner hydration product (IHP), outer hydration product (OHP) and anhydrous cement particle (ACP). This method determines the threshold value of greyscale value using both cumulative and histogram of the greyscale level in the ROI.…”

“…A discrete lattice fracture model, as described in [3], was used to model the mechanical performance of the generated specimens. In total, 9 types of elements as listed in Table 1 were considered.…”

“…In total, 9 types of elements as listed in Table 1 were considered. For the elements that exist in the cement matrix, their mechanical properties have been calibrated and validated in the authors' previous works [3][4][5]. With respect to the element within the aggregate, its elastic modulus is taken from [6].…”