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Keywords: nanoindentation, cement paste, delayed recovery, micromechanics, microlevel modelling.

Summary

This paper focuses on the nanoindentation of cement pastes and explores suitable constitutive models for the modelling of their behaviour at a microscale in order to be used in the multiscale framework [1]. Hydrated phases of hardened cement paste were experimentally tested in different loading regimes, mainly cyclic. The comparison of several constitutive models such as linear viscoelastic [2], nonlinear viscoelastic and viscoelastoplastic models were shown. It was found that simple linear viscoelastic model cannot capture more general loading path in case of cyclic loading. Plastic yielding needs to be included to match the cyclic experimental data. The qualitatively best suitable model was based on a nonlinear viscoelastic model combined with plasticity. However, the difficulty of using such a model lies in finding its material parameters. Rigorous fitting of material parameters raises significant obstacles that are caused by the impossibility of distinguishing between plastic and viscous deformation from experimental measurement. In this paper, we propose to solve this difficulty by using a special loading path including subsequent scanning of deformations after load removal. At this stage, the increment of plastic strains is negligible and viscous effects dominate. This delayed recovery of the material can be utilized for identification of the viscous part of the model parameters.

References

1: V. Šmilauer, Z. Bittnar, "Microstructure-based micromechanical prediction of elastic properties in hydrating cement paste", Cement and Concrete Research, 36(9): 1708-1718, 2006. doi:10.1016/j.cemconres.2006.05.014
2: M. Vandamme, F.-J. Ulm, "Viscoelastic solutions for conical indentation", International Journal of Solids and Structures, 43(10): 3142-3165, 2006. doi:10.1016/j.ijsolstr.2005.05.043

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 89 PROCEEDINGS OF THE SIXTH INTERNATIONAL CONFERENCE ON ENGINEERING COMPUTATIONAL TECHNOLOGY Edited by: M. Papadrakakis and B.H.V. Topping Paper 141 Modelling Nanoindentation of Cement Pastes J. Nemecek and P. Kabele Department of Mechanics, Faculty of Civil Engineering, Czech Technical University in Prague, Czech Republic doi:10.4203/ccp.89.141 purchase the full-text of this paper Full Bibliographic Reference for this paper J. Nemecek, P. Kabele, "Modelling Nanoindentation of Cement Pastes", in M. Papadrakakis, B.H.V. Topping, (Editors), "Proceedings of the Sixth International Conference on Engineering Computational Technology", Civil-Comp Press, Stirlingshire, UK, Paper 141, 2008. doi:10.4203/ccp.89.141 Keywords: nanoindentation, cement paste, delayed recovery, micromechanics, microlevel modelling. Summary This paper focuses on the nanoindentation of cement pastes and explores suitable constitutive models for the modelling of their behaviour at a microscale in order to be used in the multiscale framework [1]. Hydrated phases of hardened cement paste were experimentally tested in different loading regimes, mainly cyclic. The comparison of several constitutive models such as linear viscoelastic [2], nonlinear viscoelastic and viscoelastoplastic models were shown. It was found that simple linear viscoelastic model cannot capture more general loading path in case of cyclic loading. Plastic yielding needs to be included to match the cyclic experimental data. The qualitatively best suitable model was based on a nonlinear viscoelastic model combined with plasticity. However, the difficulty of using such a model lies in finding its material parameters. Rigorous fitting of material parameters raises significant obstacles that are caused by the impossibility of distinguishing between plastic and viscous deformation from experimental measurement. In this paper, we propose to solve this difficulty by using a special loading path including subsequent scanning of deformations after load removal. At this stage, the increment of plastic strains is negligible and viscous effects dominate. This delayed recovery of the material can be utilized for identification of the viscous part of the model parameters. References 1 V. Šmilauer, Z. Bittnar, "Microstructure-based micromechanical prediction of elastic properties in hydrating cement paste", Cement and Concrete Research, 36(9): 1708-1718, 2006. doi:10.1016/j.cemconres.2006.05.014 2 M. Vandamme, F.-J. Ulm, "Viscoelastic solutions for conical indentation", International Journal of Solids and Structures, 43(10): 3142-3165, 2006. doi:10.1016/j.ijsolstr.2005.05.043 purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £95 +P&P)
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