17 Décembre – Thesis defense - Nathalie Kouta

14 h Full videoconferencing

Mechanical behavior and characterization-durability of new materials based on clay.

Nowadays, the use of ecological and sustainable materials has become a necessity. This is due to the depletion of natural resources and to the large amounts of CO2 emissions generated by the construction sector. Raw earth, composed essentially of fine particles like clay, has been used as a building material for thousands of years in various forms. The low cost and the high availability of this material, in addition to its ecological and hygrothermal properties, have been the reasons for its usage in the construction industry.
During the last years, several studies have been realized to develop more common and easy methods to apply in the construction field, which has led to the designation of earth concrete. This concrete is constituted of clay soil treated with small quantities of one or more hydraulic binders and can be poured like ordinary concrete. However, the diversity presented in these materials makes them very complex and difficult to use. In addition, the presence of fine particles makes them very sensitive to plastic shrinkage and consequently increases the risk of cracking due to the low resistance of this concrete at early age. In this study, the mechanical behavior and durability of an earth concrete composed of an artificial soil stabilized with cement and lime have been evaluated. In order to overcome the cracking sensitivity, flax fibers have been added and the effect of different percentages and lengths of fibers has been studied.
First, the behavior of earth concrete at early age was studied. Plastic shrinkage was measured in parallel with the weight loss, the capillary pressure and the temperature. In addition, the effect of flax fibers on cracking at early age was studied using the digital image correlation technique. A reduction in plastic shrinkage and a better resistance to cracking were observed with the addition of fibers due to different transfer mechanisms and stress redistribution.
Secondly, the effect of flax fibers on the mechanical behavior of soil concrete was studied. Compression and flexural tests have been realized at different curing ages and monitored simultaneously with the digital image correlation and the acoustic emission techniques. These tests allowed to monitor and better understand the damage evolution. An increase in the acoustic emission activity was observed with the addition of fibers indicating additional damage mechanisms and an improved ductility.
Finally, the durability of earth concrete was evaluated. An experimental investigation of damage evolution during drying was realized with a continuous monitoring using the acoustic emission technique. The effect of curing conditions and wetting/drying cycles on the mechanical properties of earth concrete was also evaluated. The results showed visible cracks on the surface of the specimens with a clear degradation of the mechanical properties.

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