Soyez le premier à aimer ceci
Volcanic ashes are raw materials with variable chemical and mineralogical compositions from one deposit to another. When combined with suitable alkali activators they can be converted to geopolymer cements at ambient temperature. In this study we investigate the possibility of use bauxite and calcined oyster shell powders as mineral additives to volcanic ashes in other to enhance the properties of the resulted geopolymers. Different methods of analyses such as Fourier Transform Infrared Spectroscopy, X- Ray Diffractometry and Scanning Electron Microscopy were used to assess the variations of setting time, linear shrinkage and 28 days compressive strength of geopolymer pastes. Also, chemical and mineralogical compositions of bauxite and calcined oyster shell were determined. It appeared that bauxite and calcined oyster shell are respectively sources of Al2O3 and CaO and can compensate the deficiency of these oxides in volcanic ashes. These mineral additives are weakly dissolved in alkaline medium due to their high crystalline phase content. Addition of about 20 % of bauxite or 10 % calcined oyster shell lead to the decreasing of the setting time respectively from 415 to 275 min (bauxite) and 195 min (calcined oyster shell). Addition of any percentage of these minerals lead to the decrease of linear shrinkage and 10 % of bauxite is enough to prevent efflorescence. The increasing of the 28 days compressive strength of the geopolymers synthesized is trivial up to 10 to 20% addition of bauxite and calcined oyster shell respectively. More than these percentages additives have deleterious effect on the compressive strength.