Reducing Uncertainties in Nanoindentation Experiments for Cementitious Materials

Abstract

Limited research is available to guide the intelligent selection of test parameters such as load level, grid size, grid spacing, and sample surface roughness to design nanoindentation experiments on cementitious materials. A cohort of nanoindentation experiments on four different cement pastes utilizing varying indentation depth, load level, grid spacing, grid size, and surface roughness were performed. Results from this study indicate that a “critical indentation depth” exists for each sample such that individual indentations shallower than the critical depth demonstrate greater variability for all measured properties than deeper indentations. Most commercial nanoindentation equipment is load controlled, so careful load selection is important to ensure that the critical indentation depth is achieved. Elastic indentation properties appear to show dependence on grid spacing and grid size. Surface roughness and the polishing method profoundly influence measured properties. The study demonstrates that the choice of test parameters is influenced by the microstructural details (phases) under consideration, as well as the porosity of the sample and therefore cannot be generalized.