Development of CO₂-induced SCMs for calcium sulfoaluminate cement : towards enhancing hydration, compressive strength and later stage-ettringite stability

Abstract

Calcium sulfoaluminate cement (CSA) often exhibits limited long-term strength due to the lack of suitable supplementary cementitious materials (SCMs) that can effectively promote secondary hydration. This study introduces a novel approach for preparing CO<inf>2</inf> induced SCMs (CSCMs) derived from CSA, aiming to overcome this limitation and enhance both hydration kinetics and mechanical performance. CSCMs, produced by CO<inf>2</inf> induced CSA for three hours, consist of polycrystalline calcium carbonate phases, specifically, aragonite (7.6 %), vaterite (2.1 %) and calcite (22.4 %), alongside amorphous Al-Si gel. When incorporated into CSA at a dosage of 10 wt%, these CSCMs significantly accelerated hydration, resulting in increased formation of AFt and AH<inf>3</inf>, which boosted early compressive strength by 22.7 % in one day and 14.4 % at three days compared to control samples. Beyond early strength gains, the presence of CSCMs facilitated further reactions among calcium carbonate, Al-Si gel, and C<inf>4</inf>A<inf>3</inf>Š, leading to the generation of Mc and Hc phases. These products stabilized AFt and contributed to improving compressive strength over extended curing periods. After 180 days, samples containing CSCMs exhibited strength increases of 26.1 % (5 % CSCMs), 31.8 % (10 % CSCMs), and 27.2 % (20 % CSCMs), while the control sample experienced a 5.9 % strength reduction and 8.2 % AFt decomposition. The enhanced performance is attributed to the high reactivity and nucleation effects of the calcium carbonate and Al-Si gel components. This study developed low-cost CSCMs for dedicated CSA, while resolving the conflict between CSA strength development and carbon emission reduction.