Exploring High-Volume Cementitious Blends for Carbon Sequestration: Quantifying Carbon Storage and Mineralogical Changes

Abstract

This study investigates the carbon sequestration potential and the ensuing mineralogical and morphological effects in high-volume cementitious blends of fly ash and slags. 10 distinct paste samples with a water-to-binder ratio of 0.5 were prepared by partially replacing OPC with ground granulated blast furnace slag (GGBS) and fly ash (FA) at different proportions (15-65% by weight). Samples underwent 24 hours of pre-hydration followed by carbon curing under ambient temperature and pressure (20% CO2, 1 atm, 25 ± 2 °C). Thermogravimetric analysis (TGA) showed that the degree of carbonation (DOC) in blended samples was significantly higher compared to OPC, attributed to the dilution effect of blending, which facilitated better CO2 diffusion into the microstructure. The carbon uptake of the carbonated mixes blended with GGBS, FA, and GGBS+FA was 60%, 83%, and 50% higher than that of OPC at a replacement level of 45%, 25%, and 50%, respectively. The X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed a higher carbonate peak in blended samples, while peaks of unhydrated alite (C3S) and belite (C2S) diminished due to the carbonation. Post-hydration of samples after carbon curing up to 28 and 56 days enhanced the degree of hydration (DOH), with calcite acting as a nucleation site for C3S/C2S hydration. These mineralogical changes also contributed to pore structure densification and changes in the morphology of carbonates as observed under Scanning Electron Microscopy (SEM). Overall, the findings elucidate the potential of high-volume blended cementitious systems for enhanced carbon sequestration.

Keywords: Carbon curing, SCM, High volume blend, carbonation, Carbon uptake