Use of nanoindentation phase characterization and homogenization to estimate the elastic modulus of heterogeneously decalcified cement pastes

Nanoindentation phase characterization is used with a homogenization method to estimate the macroscopic response of heterogeneous, multiphase materials with large chemically-induced gradients from their measured micromechanical properties. The method was applied to predict the macroscopic response of a non-uniformly degraded cement paste from leaching-induced decalcification by ammonium nitrate under 3-dimensional exposure conditions. Coupled nanoindentation with scanning electron microscopy and energy dispersive x-ray spectroscopy constitutive phase elemental analysis was used to link the mechanical response at each nanoindentation location to chemical composition and relate the mechanical phases identified statistically by Gaussian deconvolution to the chemical phases present in the microstructure. The nanoindentation phase characterization- based micro-macroscale upscaling method provided quantitative characterization of the relationship between microstructure evolution and mechanical properties as a function of chemical changes. The calculated homogenized elastic moduli of the reference and decalcified cement pastes ranged from 24.2-31.2 GPa and 9.2-11.7 GPa, respectively, and were of similar magnitude to the dynamic elastic moduli measured experimentally (31.1 +/- 0.9 GPa and 13.7 +/- 1.7 GPa, respectively). Furthermore, the degradation of the cement paste macroscale elastic modulus was controlled by the decalcification of the calcium-silicate-hydrate phases and the mechanical properties of the most prominent zone of the material. (c) 2018 Elsevier Ltd. All rights reserved.