Synergistic Upcycling MSWI Ash and Class F Fly Ash to Prepare a Sustainable Ternary Cementitious Composite

Abstract

Class F fly ash (FA) is often limited in its application in the cement industry due to its low hydration reactivity. This study explores the synergistic utilization of municipal solid waste incineration fly ash (MSWIA) and FA to valorize these two industrial waste streams for application in the concrete industry, aimed to reduce the carbon footprint associated with extensive cement use. The study proposes replacing part of the cement with MSWIA and Class F FA, with a baseline mix ratio of MSWIA: FA: Cement = 40%:40%:20%. In addition, silica fume (SF), nano-montmorillonite (nMMT), and calcium oxide (CaO) were added to the system to modify and activate the binder, with the goal of meeting practical engineering requirements. Experimental results indicate that the optimal dosages are 15% SF/(FA+MSWIA), 0.3% nMMT/(FA+MSWIA), and 3% CaO/(FA+MSWIA), achieving a 28-day compressive strength of 21.12 MPa, which represents an increase of 186.2% compared to the baseline. Furthermore, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and deconvoluted Fourier transform infrared spectroscopy (FTIR) were used to investigate the effects of various variables on the microstructural morphology, hydration process, and hydration products of the samples. The results demonstrate that the addition of SF, nMMT, and CaO not only promotes the formation of highly polymerized hydration products, refines the pore structure, and improves the microstructural compactness but also significantly enhances the overall mechanical properties and durability of the cementitious system.