The concern about the large amount of weathered bottom ash (WBA) produced in waste-to-energy plants (WtE) has caused an increased search for alternatives to reduce their environmental impact. The present study aims to provide an added value through the WBA valorization from municipal solid waste incineration (MSWI) for its use as a sole precursor for developing alkali-activated binders (AABs). Alkali-activated weathered bottom ash binders (AA-WBA) were formulated with a liquid-to-solid ratio of 1.0 and using sodium silicate (80 wt.%) and NaOH (20 wt.%) at different concentrations (2, 4, 6, and 8M) as alkali-activator solutions. AA-WBA were cured at room temperature to extend their applicability. The effect of the alkali-activator solution molarity on the final properties of the AA-WBA was evaluated. The physicochemical characterization by XRD, FTIR, and SEM evidenced the presence of the typical phases (calcium silicate hydrate and gehlenite) of C-(A)-S-H gel. Leaching concentrations of As, Cu, and Mo exceed the acceptance in landfills for inert waste, while the leaching concentration of Sb exceeds the one for non-hazardous waste. The structure of the binders depends on the alkalinity of the activator, obtaining better results using NaOH 6M in terms of microstructure and compressive strength (6.7 MPa). The present study revealed that AA-WBA for non-structural purposes can be obtained. The AA-WBA formulation contributes to the WBA valorization and development of low-carbon cements; therefore, it is an encouraged alternative to ordinary Portland cement (OPC). Considering the amounts and costs of the WBA, sodium silicate, NaOH, and water, the total cost of the developed formulations is comprised in a range between 137.6 and 153.9 €/Tn.
During the glass selection process by optical sorting equipment, a rejection material called CSP (ceramic, stone, and porcelain) is generated, which is lower than 2 wt % of the glass cullet collected in Catalonia (Spain). Although this process should only separate non-glass impurities from the glass cullet, around 84 wt % of glass is found in the CSP. The CSP characterization reveals that CSP is mainly compound by SiO2, Al2O3, alkali metals, and CaO, which are key components for the alkali-activated cement (AAC) development. Consequently, this study is focused on the potential of CSP as a precursor to synthesize AAC. The concentration of the alkali activator (NaOH: 1 M, 4 M, and 8 M) and the liquid-to-solid (L/S) ratio were tested in the formulation of the AAC. The AAC specimens at 28 days cured were evaluated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FIR), scanning electron microscopy (SEM), apparent density (ρapp), and compressive strength (σs). The results obtained showed that the L/S of 0.5 and 4.0 M for NaOH concentration are the best conditions, due to the mechanical properties (ρapp = 1.75 g·cm−3; σs = 52.8 MPa), cohesion (SEM), and formed phases (XRD and FT-IR). Therefore, CSP can be a precursor for developing new, sustainable binders.
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