Tracking spatiotemporal evolution of cementitious carbonation via Raman imaging

AbstractCarbonation of cementitious systems is an important phenomenon from both durability (rebar corrosion) and greenhouse emissions (CO2 sequestration) perspectives. Several analytical techniques are well‐established for measuring the kinetics of this dynamic phenomenon, ranging from measuring the pH change to quantifying the calcite content over time. However, the majority of these methods (with the exception of electron imaging) rely on bulk measurements which may miss the fine, microstructural changes that occur during carbonation. In this study, we investigate and evaluate the potential of Raman imaging to follow the spatiotemporal evolution of carbonation in cementitious pastes. By analysing mm‐scale maps (1 mm × 1 mm) at the micron‐scale resolution, we find that nearly ~40% of the sample surface was covered with calcite at the end of a 2‐week carbonation exposure. Simultaneously, the portlandite content declined from ~15% to 5% in the same period, suggesting portlandite consumption for the sake of calcite growth. Finally, the difference between the calcite growth rate and portlandite consumption rate strongly suggests simultaneous carbonation of CSH and ettringite—a finding that is in agreement with recent experimental investigations of carbonation kinetics. Overall, these new results on the spatiotemporal evolution of cementitious microstructure pave the way for utilizing Raman imaging for understanding dynamic phenomena in complex systems.