Geopolymers: An option for the valorization of incinerator bottom ash derived “end of waste”

In the present paper, bottom ashes from urban waste incineration were used as sole source material to develop geopolymers activated with alkali solution. This study intends to gather basic structural data on the synthesized materials at fixed curing times (3 h; 1, 4, 5, 7, 30 days; 20 months) by X-ray (XRD) and Fourier Transform Infrared (FTIR) analysis. Curing time affects both crystalline phase transformation and the geopolymeric gel structure. The XRD results showed the starting of geopolymerization, due to the alkali activation, already within the first 3 h of curing. New phases such as hydrated sodium carbonate and gismondine, confirming the progressive ash reactivity, appeared after 4 h and 1 day of curing respectively. Finally, after approximately 30 days curing at room temperature, the condensation process and, consequently, the formation of a stable 3D gel of aluminosilicate network occurred. FTIR showed a 40 cm−1 displacement of the band at 980 cm−1 during the first hours of the geopolymer formation confirming the formation of the geopolymeric network also from a matrix without metakaolin. Furthermore Scanning Electron Microscopy (SEM–EDS) analyses were performed to assess morphological characteristics and to evaluate the presence of unreacted aluminosilicate particles in the obtained geopolymers.