Phase volumes of ultra high performance concrete containing nanoscale pozzolan

Abstract

Grid nanoindentation and quantitative X-ray diffraction are employed to provide quantitative information on phase constituents of nanoscale pozzolan-containing ultra-high-performance concrete (UHPC). Three UHPC samples containing nanoscale pozzolan and cured with and without microwave energy are investigated. The volume fraction of each phase constituent is independently evaluated using both techniques: nanoindentation (NI) and quantitative X-ray diffraction (QXRD). For the NI, the volumes have been evaluated by taking into account the thresholds characterising the phase constituents. The NI could assess phase mixtures or composites rather than single phases. The microwave-cured samples (CMW and CPMW) contain in total more hydration products that the sample that was not cured with microwave energy (C000). In all three samples, a nanocomposite (C–S–H/CHnm) consisting of high-density (HD) calcium silicate hydrate (C–S–H) and nanoscale portlandite (CH) is included, and its amount is more than double for the pressure-compacted and microwave-cured sample (CPMW). The heat curing by microwave energy together with the very low amount of water and restriction of the available space for hydration products, favour the formation of the nanocomposite (C–S–H/CHnm) in the CPMW sample.