Early Hydration and Mechanical Performance of CO ₂ ‐Assisted Mixed Cementitious Mortars and Pastes

Abstract

CO ₂ ‐assisted mixing was investigated as a process‐integrated approach to modify early hydration and early‐age performance of cementitious mortars. The study focuses on the dosage‐dependent balance between carbonate‐related acceleration and fresh‐state‐induced microstructural drawbacks. At low CO ₂ dosage, 24 h compressive strength increased by approximately 20%, attributed to the in‐situ formation of finely distributed carbonate‐containing phases. At higher dosages, both heat release and compressive strength declined, indicating that excessive CO ₂ injection reduces hydration intensity while simultaneously impairing compaction quality through workability loss. A complementary series with stoichiometrically comparable limestone substitution showed that externally added limestone and injected CO ₂ do not affect hydration kinetics identically. Calorimetric comparison reveals two competing mechanisms: in‐situ carbonate precipitation enhances C‐S‐H nucleation during the acceleration period, while CO ₂ dissolution introduces pore solution modifications that delay the onset of the acceleration period. CO ₂ ‐assisted mixing therefore cannot be described as simple carbonate addition but represents a mechanistically distinct in‐situ process requiring dosage‐optimized application.