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Early age volume changes in metakaolin geopolymers: Insights from molecular simulations and experiments

Lolli, F., Thomas, J.J., Kurtis, K.E., Cucinotta, F. and Masoero, E. 2021. Early age volume changes in metakaolin geopolymers: Insights from molecular simulations and experiments. Cement and Concrete Research 144 , 106428. 10.1016/j.cemconres.2021.106428

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The early age volume changes occurring during the geopolymerisation reaction are not sufficiently understood yet, due to shortage of experimental data and theoretical models. This work presents new results on chemical and autogenous deformation of sodium-activated geopolymers from metakaolin, focussing on the first 72 h of reaction. The results show that the geopolymers undergo early-age chemical expansion, not shrinkage. A model is proposed to explain the experimental result, leveraging recent advances from molecular simulations. The model predicts how the extent of chemical expansion is controlled by confined water in the molecular structure of the geopolymer. However, despite this underlying chemical expansion, geopolymer samples undergo autogenous shrinkage at the macroscale, which excludes self-desiccation as the origin of autogenous deformation. A better insight is gained by monitoring the kinetics of geopolymerisation using isothermal and differential calorimetry. Two kinetic regimes are identified, with apparent activation energies of approximately 90 kJ/mol and 70 kJ/mol. This suggests that two microscopic mechanisms concur to determine the early-age volume changes of geopolymer pastes.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Engineering
Publisher: Elsevier
ISSN: 0008-8846
Date of First Compliant Deposit: 4 October 2021
Date of Acceptance: 7 March 2021
Last Modified: 07 Nov 2023 00:25

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