Strength and creep behavior of geomaterials for building with tannin addition

International audienceA 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

Strength and creep behavior of geomaterials for building with tannin addition

International audienceA 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

Mechanism of traditional Bogolan dyeing technique with clay on cotton fabric

International audienceBogolan is a traditional dyeing technique, deeply rooted in Mali. It uses local clays from Niger River region and a leave extract from N'galama trees (Anogeissus leiocarpa). The clay contains a significant amount of iron (hydr)oxides, mainly akaganeite. It reacts with N'galama coating onto cotton to form black or brown colors. UV/Vis and IR spectroscopy indicated very similar behavior of N'galama leaves extract and carboxylic aromatic acids, mainly ellagic or gallic acids, which form dark colored complexes with iron. Since iron (hydr)oxides are coated on clay mineral particles, they contribute to the fixation of the clay mineral particles and also cause the dark color. X-ray diffraction of oriented tissue and SEM observations confirmed the presence of clay particles attached on the fiber surface