Three-dimensional mortar models using real-shaped sand particles and uniform thickness interfacial transition zones: Artifacts seen in 2D slices

Abstract

All scanning electron microscopic (SEM) examinations of mortars are based on 2D slices through the true 3D microstructure. There are many artifacts that can be seen in such 2D slices that are different from 3D reality, even if the sand were perfectly monosize and spherical. A mortar containing a size distribution of randomly-shaped sand grains, surrounded by interfacial transition zones (ITZs), is more complicated, so that the 2D artifacts are expected to be even more complex. Using the Anm model, we for the first time generate mortar models with measured sand particle size/shape distributions and realistic sand volume fractions, surrounded by rigorously uniform (in 3D) thickness ITZs, and then examine 2D slices and discuss the multiple types of artifacts that are generated. The Anm model shows the considerable variety of artifacts that can be observed in the 2D slices, including a wide thickness distribution of ITZ widths, isolated ITZ regions, apparently unconnected to any sand grain, and overlapping ITZ regions, which can be mistaken for real 3D features. It is shown that some, but probably not all, of the porous patches seen in SEM images are due to these apparently isolated (in 2D) ITZ regions.