Compressive strength development and microstructure evolution of mortars prepared using reactivated cementitious materials under carbonation curing

The effect of carbonation curing on depth-wise carbonation gradient and compressive strength development of RCM was evaluated. The RCM mortars were carbonated for seven curing periods, complemented by a thorough investigation of carbonation degree, phase assemblage, and microstructural at varying depths. Results showed a significant increase in compressive strength, from 3.3 MPa on the first day to 51.7 MPa after seven days and 63.5 MPa after 28 days of carbonation curing. A notable gradient in CaCO₃ concentration was observed, decreasing from 41.4% at the surface to 16.8% at 25 mm depths. Additionally, the formation of CaCO₃ polymorphs and Ca-modified silica gel in the surface layers was found to enhance microstructural density and impede CO₂ penetration, while a higher prevalence of micropores was noted in the inner regions. These findings highlight the potential of optimizing the carbonation regime or employing internal carbonation methods to achieve a more homogeneous microstructure.