Microstructural effect of a new combined thermal and CO2 curing protocol for low-carbon cementitious materials

Enhancing the early-age mechanical performance of low-carbon cementitious materials is essential for their wider adoption. While thermal curing is widely used in precast and prestressed concrete, and carbonation curing has recently emerged for strength improvement and CO₂ sequestration, their combined effect remains unexplored. This study introduces a novel curing regime that combines thermal and carbonation curing to assess its impact on strength development and CO₂ capture. Four curing conditions (humid, thermal, carbonation, and combined thermal and carbonation) were applied to cement pastes with only CEM I then with 60 % clinker replacement using binary and ternary blends of blast-furnace slag and calcined clay. Results show that carbonation curing achieved the highest CO₂ uptake (up to 14 % of slag binder mass), while thermal curing significantly enhanced early compressive strength. Notably, the combined thermal-carbonation curing led to the highest 48 h strength gain, particularly for the ternary binder, and improved micromechanical properties, as evidenced by higher indentation and creep modulus. These findings highlight the potential of this innovative curing approach to optimize both mechanical performance and carbon sequestration in sustainable cementitious materials.