An experimental investigation on cemented sand particles using different loading paths: Failure modes and fabric quantifications

Abstract

Cemented sands are not only widely found in nature, but also artificially made broadly for various engineering applications. We experimentally studied underlying breakage behaviour of artificially cemented sands under different loading paths at particle scale. Two types of sands (Leighton Buzzard sand and crushed limestone particles) and two types of bond materials (gypsum plaster and Portland cement) were used to prepare artificially cemented particles. Three typical loading paths, resulting in different breakage modes of specimens, including (1) uniaxial compression, (2) combined compression-pure shear (shorted by ‘pure shear’) and (3) combined compression-shear-bending (shorted by ‘bending’) were applied. It was found that when catastrophic failure occurred, cracks propagated roughly parallel to the loading axis in both particles and their bridging cementation in uniaxial compression tests. While under pure shear loads, the macroscopic fracture initiated at and evolved along particle-bond interfaces. By contrast, bending moment induced shear bands of which crack planes only occurred in cementation and were nearly parallel to each other in bending tests. For the intact samples before compression tests as well as fragmentations after breakage, Scanning Electron Microscope (SEM) images were taken for samples prepared by four kinds of materials, and multiscale rotational Haar Wavelet Transformation (HWT) was implemented to quantify their fabric including fabric value and direction. It is concluded that fracture surfaces of particle materials had more distinct fabric than intact particle surface. Meanwhile, due to sliding shear-dominant longitudinal bond fracture surfaces had more evident fabric than their corresponding tensile-dominant horizontal fracture surfaces. Consequently, our developed apparatus combined with the fabric quantification method sheds new light on cemented granular materials at the particle scale.