The influence of alkaline activation on coal gasification slag–MSWI FA based binder and its associated hydration mechanism

Solid waste binders have been accepted for their eco-friendliness and good mechanical properties. The effect of alkaline activators on binder hydration process is currently a hot research topic in this field. However, there is a lack of systematic summary and analysis on how to utilize the synergistic cooperation among various ions to promote the hydration reaction. This paper designs a scientific system using the chemical composition from gypsum, municipal solid waste incineration fly ash and steel slag, highlighting the differences of alkaline activations on low-hydration coal gasification slag. Results show that replacing 40 % of blast furnace slag with coal gasification slag increases 28-day strength to 34.86 MPa and 31.00 MPa with 5 % Ca(OH)₂ and 15 % steel slag, respectively, representing gains of 51.4 % and 34.7 %. Conversely, NaOH addition results in a 28-day strength of less than 10.00 MPa, with a 60.9 % decrease at 90 days. The reasons for the heavy weakening (57 %) and enhancement (51 %) of strength are then discussed, summarising the notable differences in alkali cations, hydration mechanism and heavy metal curing mechanism. Finally, a sodium-rich C–N–S–H gel model was constructed with considering the microstructure, hydration products, and temperature. It is expected that this paper can provide a reference for the prospective study of alkaline activation.