Comprehensive microstructural characterizations of 1-D consolidated kaolinite samples with fabric tensors and pore elongation factors

Abstract

In this paper, through micromechanical analyses, the microstructural responses of kaolinite samples subjected to 1-D consolidation were quantitatively analyzed. Using a tailor-made, 3D-printed oedometer in preparing samples subjected to different loading levels, the applied loading was maintained during the freezing process of the sample in order to preserve the fabric associations for the subsequent characterizations using Mercury Intrusion Porosimetry (MIP) and Scanning Electron Microscopy (SEM). At least 3000 particles were identified in each sample to provide representative data for the micromechanical analyses. Besides, the voids and solids (particles and aggregates) were separated using proper binary images; the voids of the irregular shapes were further described using an equivalent ellipse. With the boundary established between the intra- and inter-aggregate pores based on the MIP results, the quantitative SEM analyses further revealed that the inter-aggregate pores exhibit a significantly large area fraction and therefore dominate the deformation responses. Fabric tensors were used to further quantify the directional behavior of the voids and particles. In addition, to provide complementary information and to further understand the associated deformation mechanism, the shape evolution of the inter-aggregate pores was examined, also based on the SEM images. All the findings further describe the compression process of the inter-aggregate pores during the collapse of the card-house structure formed by the aggregates. As the vertical stress increases, the card-house structure is gradually compressed; hence, the enclosed inter-aggregate pores that are initially elongated vertically are compressed into a rounder shape. For those pores which are initially aligned horizontally, they are further compressed and become more elongated in the horizontal direction. Ultimately, the inter-aggregate pores gradually align in the horizontal direction, and the associated pore shape becomes flattened. The particles that form the aggregates also unavoidably follow the same trend, to also align in the horizontal direction.