Abstract
Geopolymers are mineral binders obtained by alkaline activation of aluminosilicate materials. They represent today a possible alternative to the Portland cement. Indeed, these materials have physico-chemical properties similar or even superior to those of ordinary cements. In addition, they are more environmentally friendly and develop good durability. However, it is difficult to determine the final material properties in their current state because of the great variability of the source materials (metakaolin, fly ash, blast furnace slag, etc.). Therefore, each studied system requires specific analysis and recommendations depending on the used aluminosilicate source materials. The aim of this work is to develop geopolymers based on recycled glass powder and calcined clay (metakaolin) for application in the construction field. Thus, mortars activated with 5 mol/L sodium hydroxide are developed. The effect of metakaolin content (0; 5; 15 and 30 wt%) on both fresh and hardened state properties including workability, microstructure and compressive strength are evaluated. Isothermal calorimetry study is also performed on paste mixtures. Results show that increasing the metakaolin content up to 30 wt% in the system improves the mortar microstructure and thus, increases their compressive strength. We have been able to elaborate mortars incorporating 30 wt% metakaolin with compressive strength of 29, 37 and 41 MPa after 7, 28 and 91 days, respectively. The gel responsible for this good cohesion is the sodium aluminosilicate hydrate gel (NASH). Furthermore, according to the isothermal calorimetry study, geopolymerization occurs within the first two hours. Increasing metakaolin content induces the reduction of the heat flow and enables a progressive geopolymerization process. However, durability studies including, for example, acid and sulphate resistance should be undertaken to evaluate the durability aspect of such a studied system.
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