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Lookup NU author(s): Dr Enrico Masoero
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0).
Cement paste has a complex distribution of pores and molecular-scale spaces. This distribution controls the hysteresis of water sorption isotherms and associated bulk dimensional changes (shrinkage). We focus on two locations of evaporable water within the fine structure of pastes, each having unique properties, and we present applied physics models that capture the hysteresis by dividing drying and rewetting into two related regimes based on relative humidity (RH). We show that a continuum model, incorporating a pore-blocking mechanism for desorption and equilibrium thermodynamics for adsorption, explains well the sorption hysteresis for a paste that remains above $\sim 20$\% RH. In addition, we show with molecular models and experiments that water in spaces of $\lesssim$1 nm width evaporates below $\sim 20$\% RH, but re-enters throughout the entire RH range. This water is responsible for a drying shrinkage hysteresis similar to that of clays but opposite in direction to typical mesoporous glass. Combining the models of these two regimes allows the entire drying and rewetting hysteresis to be reproduced accurately, and provides parameters to predict the corresponding dimensional changes. The resulting model can improve the engineering predictions of long-term drying shrinkage, accounting also for the history-dependence of strain induced by hysteresis. New strategies for quantitative analyses of the microstructure of cement paste, based on this mesoscale physical model of water content within porous spaces, are discussed.
Author(s): Pinson MB, Masoero E, Bonnaud PA, Manzano H, Ji Q, Yip S, Thomas JJ, Bazant M, VanVliet KJ, Jennings HM
Publication type: Article
Publication status: Published
Journal: Physical Review Applied
Online publication date: 17/06/2015
Acceptance date: 06/05/2015
Date deposited: 09/06/2015
ISSN (electronic): 2331-7019
Publisher: AIP Publishing
Notes: Editor's suggestion
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