Micromechanical Response of Crystalline Phases in Alternate Cementitious Materials using 3-Dimensional X-ray Techniques

Abstract

Cementitious materials are complex composites that exhibit significant spatial heterogeneity in their chemical composition and micromechanical response. Modern 3-dimensional characterization techniques using X-rays from synchrotron light sources, such as micro-computed tomography (μCT) and far-field high-energy diffraction microscopy (ff-HEDM), are now capable of probing this micromechanical heterogeneity. In this work, the above mentioned techniques are used to understand the varying micromechanical response of crystalline phases (cubic iron oxide and α-quartz) inherently present within an alkali-activated fly ash (AAF) during in-situ confined compression. A subset of the crystals probed using ff-HEDM are registered with the tomographic reconstructions and tracked through the applied loads, highlighting the combination of μCT and ff-HEDM as a means to examine both elastic strain in the crystalline particles (and by extension local stress response) and plastic strain in the matrix. In this study, significant differences in the load carrying behaviors of the crystalline phases were observed wherein the cubic iron oxide crystals laterally expanded during the confined compression test, while the α-quartz particles laterally contracted and at the final load step, shed load likely due to failure in the surrounding matrix. Finally, the two characterization techniques are discussed in terms of both advantages and associated challenges for analysis of multi-phase cementitious materials.

Small-Scale Mechanical Testing

“…In the system described by Vonk et al (97), deformations and interlayer damage development can be tracked under controlled conditions of humidity in a cardboard. Using a combination of micro-computed tomography and far-field high-energy diffraction, Nair et al (98) track stress partitioning in individual grains of a cement-quartz mixture, demonstrating that the loss of a diffraction peak from a grain can signal the onset of fracture in these granular materials. Synchrotron measurements used to track recovery in nanocrystalline Ni-0020 (99) showed that, while thermal recovery due to initial point defects is homogeneous, the recovery aided by mechanical deformation (which is different during compression and tension) arises from and perhaps contributes to internal stresses driven by load partitioning between easy and hard grains.…”