Characterization and synergistic hydration mechanism of a low-carbon binder from MSWI fly ash and chlor-alkali salt...

In this paper, based on the physicochemical properties of chlor-alkali industrial solid waste salt mud (SM) and municipal solid waste incineration fly ash (MSWI fly ash), and utilizing the principle of alkali activation, a calcined salt mud and MSWI fly ash co-activated slag binder (CMS) was developed. The properties and hydration mechanism of CMS were investigated through compressive strength, soundness, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), ¹H low-field nuclear magnetic resonance (¹H LF-NMR), and inductively coupled plasma mass spectrometry (ICP-MS) tests. The results showed that in the alkaline environment established by calcined salt mud (CSM) and MSWI fly ash, CSM primarily provided OH^- and Ca²⁺, while MSWI fly ash mainly contributed Cl^-, SO₄^2-, and Ca²⁺. Based on this, the two components synergistically activated ground granulated blast-furnace slag (GGBS), generating ettringite (AFt), Friedel's salt (C₄ACl₂H₁₀), and C-(A)-S-H. Recommended mix ratio was CSM:MSWI fly ash:GGBS = 5:25:70. With this ratio, the 28 days compressive strength reached 51.9 MPa, while its soundness and heavy metal leaching concentration remained within standard limits. Analysis of cost and carbon emissions demonstrated the low-cost and low-carbon characteristics of the binder. In general, the low-carbon binder developed in this research offers a new approach for disposing of SM and MSWI fly ash, while facilitating the synergistic valorization of solid wastes.