Relating the nano-mechanical response and qualitative chemical maps of multi-component ultra-high performance cementitious binders

Ultra-high performance (UHP) cement pastes with 30–50% of cement (by mass) replaced by multiple cement replacement materials are evaluated in this study through concise nanomechanical investigations and qualitative chemical intensity mapping. Nanomechanical clustering identifies high density (HD) C-S-H and an ultra-high stiffness (UHS) phase as the major reaction products in very low w/b UHP pastes. Chemical mapping revealed HD C-S-H and UHS phases to have similar mean Ca and Si intensities. The indentation modulus (M) - hardness (H) relationships for the C-S-H phases in the UHP pastes are similar irrespective of their starting compositions. The mean Ca/(Si + Al) intensity ratio is found to be lower for the UHS phase, and the Al incorporation is noted to be higher. The Al incorporation in the C-A-S-H gel is seen to depend more on the Ca/Si ratio of the gel rather than on the amount of Al in the starting materials. The normalized chemical intensities and ratios of Ca, Si, and Al species, along with the mechanical property description provided by nanoindentation, allows for further insights into the microstructure of complex, heterogeneous systems such as UHPC pastes.