Contribution a l'etude du comportement au jeune age des materiaux cimentaires en conditions de deformations libre et restreinte (French text)

This thesis is devoted to the study of the early-age behavior of hydrating cement systems in free and restrained conditions. The main motivation at the basis of this project is the recurring appearance of the early-age cracking of high performance concrete in major construction structures (footing slabs, bridge decks, etc.). This document is divided in three sections.; The first part of the document presents a review of the literature. External shrinkage and basic creep phenomena are first briefly discussed. The apparatus and empirical models used to estimate and describe shrinkage and creep at early-age are also presented.; Afterwards, a study of the early-age behavior of concrete in various field projects is detailed in the second section. The data bank, established on bridge decks construction projects, clearly emphases the importance to apply adequate curing conditions to concrete in the first days of its hydration. This precaution helps to prevent early-age cracking.; The last part of the document concerns the study of the behavior of concrete in laboratory. The volumetric shrinkage and restrained shrinkage apparatus used during this project are briefly described. The first apparatus has demonstrated that the reduction of the binder content contributes to increase chemical and external shrinkages. Besides, the addition of silica fume increases the self-desiccation of materials. Tendencies observed with the second apparatus clearly illustrate the intricate influence of temperature on the free and restrained shrinkages of concrete. Complementary measurements of calorimetry and self-desiccation are also presented to illustrate this phenomenon. Finally, a comparison between the linear and volumetric measurements of external shrinkage was completed by using simultaneously both apparatus. A few hypotheses are proposed to explain the discrepancies between the results of the different procedures.