Comportement thermique des g��opolym��res obtenus �� partir d'une argile kaolinite

The aim of this work is to study the thermal behavior of geopolymers derived from kaolinite (clay). The geopolymers were characterized by various technics: Thermal analysis (DTA, TGA and dilatometer), X-ray diffractography (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Certain physical properties of the products were equally determined: linear shrinkage of curing, percentage of water absorption and compressive strength. The results obtained after drying and thermal treatment showed that the products preserved their initial forms, but showed variable colours based on the temperatures they were treated at. The products obtained at 90, 300 and 500 ��C contained hydroxysodalite. The synthesis of geopolymers is not complete at 300 ��C (presence of kaolinite in the material) but the products obtained are quite consolidated. The geopolymers obtained have weak values of linear shrinkage of curing (less than 0.6 %) and the compressive strength increases from room temperature (4.9 Mpa) up to 400 ��C (8.9 MPa) then becomes constant between 400 and 500 ��C. The combination of results demonstrates the efficiency of the temperature parameter during the synthesis of geopolymers based on kaolinite. // L���objet de ce travail est l�����tude du comportement thermique des g��opolym��res �� base d���une argile kaolinite. Les produits obtenus ont ��t�� caract��ris��s au moyen de plusieurs techniques : analyses thermiques (ATD, ATG et dilatom��trie), microscopie ��lectronique �� balayage (MEB), analyse par diffraction de rayons X (DRX), analyse infrarouge par transform��e de Fourier (IRTF). Certaines propri��t��s physiques des produits obtenus ont ��galement ��t�� d��termin��es : retrait lin��aire de cuisson, pourcentage d���absorption d���eau et r��sistance �� la compression. Les r��sultats obtenus montrent qu���apr��s le s��chage et �� la fin du traitement thermique, les ��prouvettes des produits conservent leur forme initiale mais pr��sentent une variation de couleur en fonction de la temp��rature de traitement. Les produits obtenus �� 90, 300 et 500 ��C contiennent de l���hydroxysodalite. La r��action de synth��se g��opolym��re n���est pas encore termin��e au moins �� 300 ��C (pr��sence de kaolinite dans le mat��riau) mais les produits obtenus sont assez consolid��s. Les g��opolym��res obtenus pr��sentent de faibles valeurs de retrait lin��aire de cuisson (inf��rieure �� 0,6 %) et une r��sistance �� la compression qui augmente de la temp��rature ambiante (4,9 MPa) jusqu����� 400 ��C (8,9 MPa) puis devient constante entre 400 et 500 ��C. L���ensemble de ces r��sultats permet de mettre en exergue l���efficacit�� du param��tre �� temp��rature �� au cours de la synth��se des g��opolym��res �� base de kaolinite.

Elaboration et caract��risation de ciments g��opolym��res �� base de scories volcaniques

Two types of volcanic ashes referenced as ZD (volcanic ashes from Djoungo) and ZG (volcanic ashes from Galim) were collected from two Cameroonian localities. They were characterized (chemical and mineralogical compositions, amorphous phase content, particle size distribution and specific surface area) and used as raw materials for the synthesis of geopolymer cements at ambient temperature of laboratory (24 �� 3 ��C). The synthesized products were characterized by determining their setting time, linear shrinkage and compressive strength, X-ray Diffraction, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy. The mineralogical composition, the amorphous phase content, the particle size distribution, the specific surface area of the volcanic ashes as well as the mass ratio of the alkaline solution (sodium silicate / sodium hydroxide) were the main parameters which influenced the synthesis of geopolymers with interesting characteristics at ambient temperature (24 �� 3 ��C). The volcanic ashes (ZD) whose mineralogical composition contained anhydrite, low amorphous phase content and low specific surface area led to long setting times. Moreover, its products swelled and presented cracks due to the formation of ettringite and these resulted in low compressive strengths (7 to 19 MPa). The volcanic ashes (ZG) containing high amounts of amorphous phase and high specific surface area led geopolymers with setting times between 490 and 180 minutes and compressive strength between 7 and 50 MPa at ambient temperature of laboratory. The properties of geopolymers were improved when elaborated with a mixture of volcanic ashes and metakaolin (ZD���MK and ZG���MK). For geopolymers obtained from ZD���MK, the setting time was between 500 and 160 minutes while it was between 220 and 125 minutes for geopolymers obtained from ZG���MK. The compressive strength greatly increased between 23 and 68 MPa and 39 and 64 MPa for geopolymers obtained from ZG ���MK and ZD���MK respectively. A comparative study of the properties of mixtures of metakaolin���alumina and volcanic ash���alumina based geopolymers shows that metakaolin is a good source of Al2O3 and SiO2 and which highly reactive with alkaline solution and produces geopolymers with better characteristics compared to volcanic ash based���geopolymer. The properties of volcanic ash���based geopolymer were also improved when amorphous alumina was incorporated into the volcanic ash. This additive is used to compensate the deficiencies in Al2O3 content in the volcanic ash. Compare to when volcanic ash is used alone 20 to 40 % incorporation of this additive corresponded to increases of the compressive strength by 18.1 % for metakaolin-alumina based-geopolymers and by 32.4 % for volcanic ash-based geopolymers.