Carbon capture in ultra-high performance concrete using pressurized CO2 curing

•Carbon capture in ultra-high performance concrete (UHPC) using fresh state carbon curing.•Cement replaced with ground granulated blast furnace slag (GGBS) at 30, 50 and 70% by wt.•Up to 80 kg CO2 per cum of UHPC can be captured with only 16 h of CO2 curing at 3 bar pressure.•Replacing 30% by wt. cement with GGBS found to give the highest carbon sequestration. This study demonstrates a novel means of carbon capture and storage (CCS) in ultra-high performance concrete (UHPC) to reduce its carbon footprint. A two-pronged approach of developing eco-friendly UHPC was employed by 1) replacing cement in the mix with ground granulated blast furnace slag (GGBS) and 2) capturing CO2 in fresh UHPC mixes. The replacement levels of cement with GGBS were 30, 50 and 70% by weight. Samples were cured in fresh state inside a pressurized chamber using high purity CO2 for the first 16 h. The curing pressure in the chamber was maintained constant at 3 bars for the entire duration of curing. A replicate batch was allowed to cure at room temperature under ambient conditions. The ambient and carbonated samples were investigated for compressive strength, phase composition using thermo-gravimetric analysis (TGA) and X-ray diffraction (XRD). Hydration kinetics under normal conditions were monitored using isothermal calorimetry (ITC). The CO2 uptake by the samples was determined from TGA results. Carbon curing resulted in a slight decrease in the compressive strength of the UHPC mixes but substantially improved the degree of carbonation (DOC) of the mixes. Replacement of cement with GGBS further increase the DOC values. Carbon uptake was highest (80 kg CO2 per m3 of UHPC) when using 30% by wt. GGBS, but decreased with higher GGBS content. The findings of this study are envisaged to provide a new approach towards CCS and generate further interests in developing ‘greener’ version of UHPCs.