The nano-mechanical properties of ultra high performance fibre reinforced concrete

Recent progress in nanoscience and technology makes it possible to assess the mechanical properties of cement based materials at the nanoscale and to identify the universal material properties. In this paper, we apply for the first time a novel statistical nanoindentation technique to identify the nano-mechanical properties of a class of ultra high performance concretes. A deconvolution analysis of the data allows to statistically determinate the invariant properties (elastic stiffness and hardness) of each single mechanical phase and the volume proportions of the low and high density calcium silicate hydrates. The results provide strong evidence that the macroscopic performance of UHPC materials is determined, at a nanoscale, by the pre-dominance of HD C-S-H among the cement hydration products ; and at a microscale by the absence of a weak transition zone between the fibers. Those two phenomena are intimately related since the higher density of the C-S-H entails and improved transition zone, which ultimately translates into the macroscopic performance