Using fine sand shape metrics determined from X-ray microcomputed tomography to illustrate the influence of particle shape on the properties of dispersed mortars

Abstract

This study follows a first paper written on some three-dimensional geometrical quantities of a selection of sand particles from the United Arab Emirates (UAE), determined using a combination of X-ray microcomputed tomography (μCT) and spherical harmonic analysis, and their correlation to the properties of mortars made with these sands, with no added dispersant. This paper studies other shape metrics of these same sands, the degree of convexity and the Hofman shape entropy, and the influence of particle shape, as judged from these shape parameters, on the water demand and other properties of dispersed mortars. Five sands from different sources were sampled, wet sieved, and classified into six sieve size classes: 20 μm–75 μm, 75 μm–150 μm, 150 μm–300 μm, 300 μm–600 μm, 600 μm to 1.18 mm and 1.18 mm–2.36 mm. The paper discusses the methods of sample preparation, μCT scanning, and the classification of particles based on their shape. The mortars used a dispersant agent enabling experiments to be conducted at low levels of water to cement mass ratios. A cause and effect relation was established between sand particle shape, in the presence of a dispersant, and properties of mortars such as the wet packing density, the workability in the form of slump-flow, and the water demand. A relationship between plastic density, after the peak of packing, the volumetric water to cement mass ratio (vw/c), and workability, as measured by slump-flow, was developed.