Strength and creep behavior of geomaterials for building with tannin addition
Résumé
A clay mined in Djénné (Mali) was used to elaborate geomaterials, with tannins addition from Parkia biglobosa pods (Néré). The compressed blocks of clay-sand mixtures show a composite microstructure. The clay contains significant quantities of kaolinite, illite, pyrophyllite, quartz and iron minerals as goethite and ferrihydrite. Quantitative mineralogical composition was assessed by X-ray diffraction and DTA/TG analyses. When tannin extract is added, the formation of a chemical complex with clay-iron hydroxides is evidenced by IR spectroscopy, which reveals specific bands. The compressive strength and creep behavior under 0.2 MPa during 20 days evidence different behaviors depending on humidity and tannin contents. Creep curves exhibit successive stages which can be described by the Granger model. The multi stage creep is explained by the visco-plastic behavior of clay constrained between large sand grains, where local and delayed deformation may occur with micro-cracking. Tannin addition has proved to increase the macroscopic strength, and reduce micro-cracking.