Time-dependent rheological behavior of cementitious pastes incorporating carbonated steel slag as a supplementary cementitious material under controlled shear mixing

Cement production contributes around 8% of global anthropogenic CO 2 emissions, underscoring the need for alternative low-carbon binders. Carbonated steel slag addresses this challenge by both sequestering CO 2 and enhancing its reactivity as a supplementary cementitious material (SCM). However, its influence on fresh-state rheology under continuous shear, critical for processing and placement, remains largely unexplored. This study investigated the time-dependent rheological behavior of cement pastes incorporating 20 wt% steel slag powder subjected to different carbonation durations (3 h, 1 d, 28 d). Flow curves, thixotropy, yield stress, viscosity, and rheological index ( c / μ ) were evaluated and linked to hydration heat release. Results show that fresh-state rheology was governed by reversible flocculation at early ages, giving rise to high thixotropy and strong shear-thinning, and by irreversible hydration-induced structuration at later times, increasing yield stress while reducing thixotropy. Carbonation altered slag mineralogy by consuming reactive Ca-bearing phases and forming stable carbonates, particularly fibrous aragonite, which increased interparticle friction and altered hydration kinetics. Short-term carbonation enhanced reactivity and sustained higher thixotropy, whereas prolonged carbonation reduced hydration peaks and weakened shear-thinning. Appropriate carbonation durations can therefore tailor workability, shear sensitivity, and processing robustness for ready-mix transport, pumping, extrusion, and cast-in-place applications. • Study investigated time-dependent rheological behavior of pastes with 20% steel slag under carbonation. • Fresh-state rheology initially governed by reversible flocculation, with high thixotropy, shear-thinning. • Later, irreversible hydration-induced structuration governed, increasing yield stress, reducing thixotropy. • Short-term carbonation enhanced reactivity, thixotropy; prolonged carbonation weakened hydration peaks, shear-thinning. • Adjusting carbonation duration can tailor workability, shear sensitivity, and processing robustness.