Correlation of Ca/Si and micromechanical properties in leached grey and white cement pastes

Grey and white Portland cement pastes were prepared and hydrated for 28 days and then partially calcium leached in a 6M ammonium nitrate solution. The samples were then subjected to micromechanical and compositional analysis. Polished surfaces were interrogated using nanoindentation for Young’s Modulus and Hardness. Indents and hydration structures were then imaged in a FESEM, and EDS applied for elemental analysis across a traverse from the exterior to interior of the samples to ascertain the degree of change to Ca/Si in non-degraded and degraded portions of samples. A good agreement is seen between Ca/Si and mechanical properties. The microstructure of the degraded parts shows evidence of increased porosity and alteration to unhydrated binder components. Adequate sample preparation was a critical factor for nanoindentation, to ensure high flatness of the sample surface prior to testing. This results also in an improvement in SEM imaging, and phase discrimination.