Mechanical characterization of thermally treated calcite-cemented sandstone using nanoindentation, scanning electron microscopy and automated mineralogy

In this study, we proposed a series of experimental and imaging techniques to investigate variations in the mechanical properties (reduced modulus, Er and hardness, H) of minerals and mineral-to-mineral contacts at a nanoscale in calcite-cemented sandstone subjected to high temperature treatment (500 °C) in a furnace. Automated mineralogy combined with environmental scanning electron microscope (ESEM) was used to determine minerals and mineral-to-mineral contacts in oven-dried and furnace-heated calcite-cemented sandstone. The crack density in oven-dried and furnace-heated calcite-cemented sandstone samples was measured using a MATLAB code written for ESEM image processing. The results showed significantly increased microcrack densities in furnace-heated samples compared with oven-dried samples. Additionally, nanoindentation tests were performed to determine the Er and H of the minerals and mineral-to-mineral contacts subjected to high temperature treatment. The Er and H of the minerals and mineral-to-mineral contacts significantly decreased in furnace-heated samples compared to oven-dried samples. Finally, an effort was made to understand the relationship between nanoscale mechanical properties and mesoscale properties of calcite-cemented sandstone. The decreased Er and H of the different minerals and mineral-to-mineral contacts due to high temperature treatment were likely to be caused by the decreased mesoscale mechanical properties of calcite-cemented sandstone.