Properties of coal gangue-Portland cement mixture with carbonation

To promote the recycling of self-ignited coal gangue (CG) as a partial substitute for Portland cement (PC) and reduce carbon footprint of fossil fuel, carbonation curing was applied to PC-CG blend pastes as a novel strength enhancement method. Compressive strength, drying shrinkage and chloride ion permeability of PC-CG mixtures with or without carbonation curing were investigated and related mechanisms were demonstrated by X-ray diffraction (XRD), ²⁹Si solid-state nuclear magnetic resonance spectroscopy (NMR), thermogravimetry-differential thermal analysis (TG-DTA), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and back scattered electron imaging (BSE) measurements. Results showed that carbonation curing behaves a better improvement effect on compressive strength of PC-CG pastes with the higher incorporation of CG. The accelerated carbonation curing can improve drying shrinkage and chloride ion penetration resistance of cement paste specimen due to the refinement of pore structure. The captured CO₂ content reached around 10% of PC-CG blend by weight with this carbonation curing. On the other hand, up to 20% CG can be recycled to replace PC without sacrifice of strength. Therefore, this technology presents a great potential in both sequestration of carbon dioxide and recycling of coal gangue.