A combined SPM/NI/EDS method to quantify properties of inner and outer C-S-H in OPC and slag-blended cement pastes

To identify the distinct microstructural features and to provide insight into the mechanism by which the phases in hardened paste possess, this study adopts the coupled techniques of quantitative modulus mapping in the form of Scanning Probe Microscopy (SPM) images, nanoindentation (NI), and energy-dispersive X-ray spectroscopy (EDS) for comprehensive investigation on the chemical-mechanical-morphological properties of C-S-H gel in both ordinary Portland cement (OPC) and slag-blended cement pastes. The thickness of the inner C-S-H (IP) layer is precisely measured for the first time by modulus mapping, it varies with the types of unreacted cores as well as the addition of the supplementary cementitious materials. An interface transition zone (ITZ) is found between the unreacted C3S grain and the surrounding inner C-S-H layer. The mechanical properties of the five types of C-S-H in OPC and the slag-blended pastes are not significantly affected by their chemical compositions. A good correlation between the storage modulus and the indentation modulus of the individual phases is found. The results indicate the significance of SPM-based modulus mapping technique as a powerful tool to characterize the phase in cementitious materials with more attractive features of higher spatial resolution.