This doctoral thesis deals with the volume changes of structural concrete caused by its shrinkage. Great importance is given to the evaluation of concrete resistance against shrinkage cracking, too. A lot of physical and numerical experiments were carried out before results and conclusion of observed phenomena was publicized. The amount of physical tests and utilization rate of the experiments can be enlarged and intensified due to the usage of materials made of micro-concrete. Consequently, the design of concrete mixtures with the ordinary size of aggregate particle reflected the large knowledge obtained by micro-concrete. In this work, the effect of different fibres and its different amount was also researched. Finally, the optimized fibre concrete mixture was designed. During the testing, the unique method referred to as “Complex experiment” was developed. Obtained data from the Complex experiment allows predicting when the shrinkage cracks may occur. The final comparison between all tested materials made of concrete was performed by means of unique parameter referred to as “Critical degree of restraint”. It was proofed that the resistance of optimized fibre concrete against to shrinkage cracking is twice of ordinary concrete. Moreover, the shrinkage cracks did not occur in the developed fibre concrete during the observed period. Based on the obtained results the new scaling factors for the rheological model B4 were derived. Due to the new scaling factors, the model B4 describes the real behavior of special composite materials very well.

Cette recherche porte sur les fils multifilamentaires de verre utilisés pour renforcer les matériaux à base de ciment. Elle est focalisée sur les interactions mécaniques de ce type de fils, constitués d'un assemblage de milliers de filaments micrométriques, avec un micro-béton et sur le rôle spécifique de l'imprégnation du fil par cette matrice cimentaire. Trois pré-conditionnements des fils ont été employés lors de la fabrication des éprouvettes afin de moduler les conditions d'imprégnation par la matrice cimentaire. L'imprégnation de 5 fils multi-filamentaires par la matrice cimentaire a été caractérisée et les paramètres d'imprégnation ont été définis en s'appuyant sur des observations MEB, ainsi que des essais de porosimétrie au mercure et des essais spécifiques d'écoulement le long du fil enrobé. Des essais classiques d'arrachement de type pull-out ont été utilisés pour la caractérisation mécanique. L'analyse des liens entre les propriétés mécaniques et les paramètres d'imprégnation ont permis de mieux comprendre les micro-mécanismes d'interaction filaments / matrice cimentaire et d'expliquer le comportement macroscopique à l'arrachement. / This research deals with multi-filaments glass yarns used as reinforcement of cement based materials. It focuses on the mechanical interactions of these yarns, made of thousands of micrometric filaments, with a micro-concrete and on the specific part of the impregnation of the yarn by the cementitious matrix. Modulated impregnation conditions of the yarns were obtained by using three different manufacturing processes for the samples preparation. The impregnation of 5 multi-filament yarns by the cementitious matrix has been characterized and physical parameters of impregnation were determined using SEM investigations, mercury intrusion porosity measurements and specific tests of flow all along the embedded yarn. Classical pull-out tests have been used for the mechanical characterisation. The study of the links between the mechanical properties and the physical parameters of impregnation allowed accessing a better understanding of the filaments / cementitious matrix interaction micro-mechanisms, and explaining the macroscopic pull-out behaviour.