Modelling macroscopic shrinkage of hardened cement paste considering C-S-H densification

Abstract

Shrinkage of hardened cement paste is a direct result of its desorption isotherm. The relationship between the desorption isotherm and the relative humidity in a hydrating cement paste is mainly controlled by the pore size distribution (nanopores to micropores). There are several hydration models to describe the microstructure of cement paste, but the desorption isotherm and self-desiccation are not direct outputs from those models as they are usually given as constitutive inputs. In this study an attempt was made to fill this gap by predicting the sorption isotherm, the drying shrinkage and the self-desiccation of cement paste directly from the evolution of its microstructure. A simple hydration model was developed to predict the microstructure of Portland cement pastes, as well as the nanostructure of calcium silicate hydrate (C-S-H), considering its densification during cement hydration. Predictions from the model were compared with some recent experimental findings from studies in the literature where the influence of the water-to-cement ratio was evaluated. The main contribution of this work is the integration of nanoscale and microscale material models towards determining the macroscopic properties of cement paste.