Reactivation of alkali-activated materials made up of fly ashes from a coal power plant

•Reactivation of fly ash is used to contribute to the sustainable construction.•Successive activations of fly ash were carried out to determine waste circularity.•A second activation leads to a material with low porosity and adequate strength.•Loss of mechanical properties is observed with the successive alkaline activations.•Lower reactive alumina content of the reactivated fly ash is noticed. Fly ash, generated during the combustion of coal for producing energy, is an industrial by-product that is suitable as starting material for the synthesis of alkali-activated materials due to its amorphous aluminosilicate content that is a mandatory requirement for obtaining materials with improved mechanical properties. According to the circular economy concept and taking into account some specific issues such as waste circularity, that provides environmental and societal benefits, this work proposes the successive alkaline activation processes of already alkali-activated materials with the purpose of being recovered several times, contributing to the sustainability of the construction materials. In this work, alkali-activated materials have been prepared using fly ash as starting waste material during successive activations, maintaining constant the alkaline activator and modifying the liquid/solid ratio according to the workability of the mixtures. The materials obtained have been fully characterised. A mineralogical and microstructural study of these materials was conducted by FTIR, XRD, and ESEM-EDX. Moreover, it has been determined their bulk density, strength resistance, open porosity and efflorescence formation, confirming their suitability for being used in a second activation.