Nano-porosity as the governing parameter of creep of calcium-silicate-hydrates

The creep properties and nano-porosities of C-S-H (the nanometer-sized building blocks of concrete) were measured by nanoindentation. Such a measurement was made possible by extending indentation analysis to heterogeneous plastic linear-viscoelastic materials. Cement pastes with various mix proportions and processing conditions were tested. On each sample several hundreds of 3-minute-long indentation creep tests were performed. At the nanoscale all C-S-H phases exhibited a creep that was logarithmic with respect to time. The amplitude of this creep is inversely proportional to a modulus which we named contact creep modulus. The contact creep modulus governing the C-S-H creep rate (∼1/t) scaled uniquely with the nano-porosity of the indented C-S-H, independent on mix proportions and processing conditions.