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Mots-clés : Retrait endogène, volumique, linéique, ressuage, pâte de ciment, granulats, jeune âge, isotherme, métrologie, expérimental, modélisation multi-échelles. Page IV
Abstract The cementitious materials used in the design of civil engineering structures undergo, since their making, volume variations of physico-chemical, mechanical, thermal and/or hydrous origins. The setting and the hardening of these materials are accompanied by shrinkage due to the hydration of the cement paste components. In constant temperature conditions and without water exchange with the outside, the consequence of this phenomenon is called autogenous shrinkage. Autogenous shrinkage is due, on the one hand, to the difference in density between the hydration products and the reactants (Le Chatelier’s contraction), and, on the other hand, to the self-desiccation of the cementitious matrix. In addition, these deformations are locally prevented by the presence of granular inclusions and this can result in the development of microcracks in the hydrated phase of the cement paste. The first part of this research work has consisted in developing devices for the measurement of deformations, especially adapted to the complex behaviour of very early-age cementitious matrices. In particular, a device, enabling the continuous rotation of the sample during the test, has been developed in order to avoid bleeding and segregation of the material. The second part of this work is devoted to the analysis of the results of a multi-variable experimental study carried out to evaluate the relative influence of the mix-parameters, particularly the properties of the aggregates, on the evolution of the very early-age autogenous shrinkage of mortars and cement pastes prepared with various cement types and water-to- cement ratios. The results obtained show that before the setting, the presence of the aggregates causes an increase in Le Chatelier’s contraction. After the setting, the effect of the aggregates on autogenous strain is reversed: the shrinkage of the mortars expressed in mm 3 per gram of cement is lower than the shrinkage of the corresponding cement paste. SEM observations show the existence, at early age, of a microcrack network around the aggregates, which has been attributed to the phenomenon of restrained shrinkage and the development of internal tensile stresses. These microcracks can induce an internal stress relaxation and explain, to some extent, the autogenous shrinkage decrease in the presence of granular inclusions. The third part is dedicated to a micromechanical multi-scale model for the prediction of the early-age autogenous shrinkage evolution of the cementitious matrices with or without granular inclusions. The experimental and numerical results are compared and the differences are analyzed. Page V
Page 1: Université de Nantes ECOLE DOCTORA
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Partie II. Programme expérimental
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Partie III. Analyses expérimentale
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V.2. Caractérisation physico-chimi
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Bibliographie Bibliographie Acker P
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Chen B. et Liu J., “Experimental
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Justnes H., Van Gemert A., Verboven
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Parrott L.J., Geiker M., Gutteridge
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Wittmann F. H. “Surface tension s
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Résumé Les matériaux cimentaires
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