Upcycling carbon dioxide to improve mechanical strength of Portland cement

To reduce environmental pollution induced by the production of Portland cement and sequestrate greenhouse gas, a novel approach was developed to manufacture nano-calcium carbonate (nano-CaCO3) suspension by upcycling carbon dioxide. The influence of this nano-CaCO3 suspension on basic performances of Portland cement paste was experimentally evaluated and related mechanisms were demonstrated by isothermal heat conduction calorimeter (TAM Air), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry-differential thermal analysis (TG-DTA), mercury intrusion porosimeter (MIP), scanning electron microscope (SEM) and transmission electron microscope (TEM) measurements. Experimental results showed that the manufactured CaCO3 presented spherical and cubic shapes with size of 20-50 nm. This CO2 upcycling method can improve compressive strength of cement paste by 5.8-9.9% at ages of 3-56 days and significantly reduce the initial and final setting times. The introduction of CO2 in form of nano-CaCO3 accelerated the early age hydration of Portland cement and refined the pore structure. Around 0.4-2.4 kg of CO2 can be recycled by every ton of Portland cement while the usage efficiency of cement was evidently improved. Therefore, both capture and solidification of carbon dioxide and carbon footprint reduction of cement industry can be simultaneously achieved by this technology.