Recycling of geopolymer waste: Influence on geopolymer formation and mechanical properties

Abstract Geopolymers are new binders resulting from the activation of an aluminosilicate source by an alkaline solution. These binders are economically and environmentally profitable since they have the advantage of reusing recycled waste and industrial by-products as aluminosilicate sources. In this context, this paper focuses on the geopolymer wastes incorporation in different formulations and their effect on geopolymer formation and the properties of the final materials. For this purpose, the geopolymer wastes were at first characterized. Three compositions differing in the used alkaline solution and the amount of metakaolin added were investigated. A feasibility study allowed retaining 20% as the waste percentage added or substituted to the metakaolin to still obtain geopolymer materials. Moreover, it was shown that the incorporation of the geopolymer waste may disturb the polycondensation rate which was proven to strongly depend on the solid to liquid ratio and the Si/K ratio of the alkaline solution. Finally, relationships were demonstrated between the compressive strengths and the chemical compositions of the different samples. The low reactivity of geopolymer waste can be compensated with the use of highly reactive alkaline solution or the increase of the amount of metakaolin in the mixture.