Transforming landfilled coal ash in ultralow clinker binders

Le résumé fourni par la source

Abstract The gradual shortage of fly ash caused by the closure of coal‐fired power plants in some areas has stimulated increased research into novel pozzolanic supplementary cementitious materials (SCMs), with a particular focus on landfilled coal ash (LA). A novel hybrid alkaline cement (HAC) was developed using 70% LA and 30% ordinary Portland cement (OPC), together with small amounts of sodium sulfate and sodium citrate as sustainable hydration activators. The reaction kinetics, mineralogical composition, and microstructure of HACs were thoroughly investigated using conduction calorimetry analysis, strength testing, X‐ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT‐IR), scanning electron microscopy–energy‐dispersive spectroscopy (SEM‐EDS), and magic angle spinning–nuclear magnetic resonance (MAS–NMR). The effects of sodium citrate and sodium sulfate on the reaction process and product formation in the OPC–LA system were clearly identified. The retarding effect of citrate‐Ca and accelerating effect of sulfate‐Ca led to a modification of wavenumbers in the C–(A)–S–H gel IR bands, and consequently respectively played different roles on activating the LA. Results show that the strength performance of HACs (CA37SuCi group) even without ratio optimization achieve the level of P.O. 32.5. The cost and CO 2 emission during laboratory level production of CA37SuCi group are 56.2% and 57.38% less than those of P.O. 42.5, respectively. An evaluation of technical, economic, and environmental aspects suggests that LA‐based HACs can contribute significantly to energy conservation and emission reduction in the cement industry, while also offering potential solutions to the regional shortage of fly coal ash.

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