Abstract
This chapter aims to highlight the effect of clay mixture mineral composition and alkali concentration of potassium alkaline solutions on the thermal behavior of geopolymer materials. For this, three mixtures composed of kaolin (pure, impure kaolin or mixture of both), calcium carbonate, sand and potassium feldspar and three potassium alkaline silicate solutions with different concentrations were used (5, 6 and 7 mol.L−1). At first, the effect of rotary calcination parameters at 750°C such as the dwell time (30, 60, 120 and 180 min) and weight powder (100, 400 and 500 g) was investigated. It was demonstrated that the kaolin dehydroxylation is quasi complete (> 90%) and do not significantly depend on the dwell time and powder weight. Whereas the carbonate decomposition degree increases with the increase of dwell time and the decrease of powder weight but still not complete (<80%). These differences influence the feasibility of consolidated materials. Indeed, a flash setting occurs for samples based mixtures with high calcium carbonate decomposition degree (> 50%) and low wettability values (500 μL/g) for the three used alkaline solutions. The thermal behavior at 1000°C depends on the chemical composition of the aluminosilicate source and the concentration of alkaline solution. A conservation of the compressive strength at 43 MPa after thermal treatment at 1000°C of geopolymers based on mixture of pure and impure kaolin and a low potassium concentration solution (5 mol.L−1) was evidenced.
Highlights
The term geopolymer was introduced by Davidovits [2] to design amorphous three-dimensional materials resulting from the activation of an aluminosilicate source by an alkaline solution [3].They are generally synthesized from metakaolin [4, 5] or other more abundant and low-cost clays or industrial coproducts [6, 7]
After thermal treatment, the compressive strength depend on the chemical composition of the aluminosilicate source
The objective of this study is to evaluate the thermal behavior of geopolymer materials based on different clay mixtures and potassium alkaline solution with different concentrations
Summary
Thermal resistance is an essential property for different applications. Inorganic refractory materials are generally used. Dupuy et al [10], Clay and Clay Minerals have shown that geopolymers based on argillite (mainly composed of interlayered illite/smectite and 22% of calcite) exhibit a good thermal resistance that depends on the argillite calcination process. Rashad and Zeedan [12] found that for fly ash based materials, the concentration of the activator had a significant effect on and residual strength after heating. San Nicolas et al [17] have undertaken a comparative study between rotary and flash calcinations of kaolin and have shown that the method of thermal treatment influences the physical properties of resulting metakaolins and and their reactivity for geopolymer synthesis. The objective of this study is to exacerbate the effect of rotary furnace on the physical and chemical properties of clay mixtures and on the thermal behavior at 1000°C of the resulting geopolymers
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