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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.
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