Exploring the effect of sulfate level on the properties of limestone calcined clay cement (LC3): Mechanical performance, hydration kinetics and microstructure development

Limestone calcined clay cement (LC3) is attracting significant interest for its carbon mitigation potential. Optimizing sulfate level is critical for strength improvement of LC3, however, this remains challenging owing to competitive reactions among Al 3+ /SO 4 2- /CO 3 2- that govern hydration pathways. This study investigated the effect of sulfate on hydration kinetics, strength development, phase assemblage and microstructure evolution of LC3 systems. Results demonstrated that sulfate suppresses nucleation kinetics but accelerates interfacial reactions. Crucially, the optimal sulfate dosage maximized the strength by balancing the precipitation of ettringite and carbonaluminates, reducing porosity by 19.4% compared to the reference group. Excess sulfate promoted delayed ettringite formation, increasing pores (>200 nm) by 28% and inducing microcracking. Thermodynamic modeling further confirmed the competitive mechanism of phase formation. The findings demonstrated that precise sulfate dosage is a critical parameter in LC3 mix proportion design, enabling the synergistic enhancement of mechanical performance and environmental sustainability, which is essential for its reliable large-scale application.