C-S-H gel densification: the impact of the nanoscale on self desiccation and sorption isotherms

TL;DR

This paper demonstrates that incorporating nanoscale densification of C-S-H gel into hydration models improves predictions of self-desiccation and sorption behavior in cement pastes, linking microstructure evolution to macroscopic properties.

Contribution

It introduces a combined nanoscale simulation and hydration model approach to predict C-S-H densification effects on cement microstructure and sorption isotherms.

Findings

C-S-H densification is essential to explain self-desiccation.

Water-to-cement ratio influences microstructural evolution.

Curing temperature affects C-S-H gel densification.

Abstract

The relationship between humidity and water content in a hydrating cement paste is largely controlled by the nanostructure of the C-S-H gel. Current hydration models do not describe this nanostructure, thus sorption isotherms and self-desiccation are given as constitutive inputs instead of being predicted from microstructural evolution. To address this limitation, this work combines a C-S-H gel description from nanoscale simulations with evolving capillary pore size distributions from a simple hydration model. Results show that a progressive densification of the C-S-H gel must be considered in order to explain the self-desiccation of low-alkali pastes. The impact of C-S-H densification on the evolution of microstructure and sorption isotherms is then discussed, including the effect of water-to-cement ratio, cement powder fineness, and curing temperature. Overall, this work identifies an area where nanoscale simulations can integrate larger-scale models of cement hydration and poromechanics.