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Hysteresis from Multiscale Porosity: Modeling Water Sorption and Shrinkage in Cement Paste

Lookup NU author(s): Dr Enrico Masoero

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This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0).


Abstract

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.


Publication metadata

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

Year: 2015

Volume: 3

Issue: 6

Online publication date: 17/06/2015

Acceptance date: 06/05/2015

Date deposited: 09/06/2015

ISSN (electronic): 2331-7019

Publisher: AIP Publishing

URL: http://dx.doi.org/10.1103/PhysRevApplied.3.064009

DOI: 10.1103/PhysRevApplied.3.064009

Notes: Editor's suggestion


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