Tracking spatiotemporal evolution of cementitious carbonation via Raman imaging

Abstract

Carbonation 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.

Elucidating the Size and Shape of Individual Clinker Phases via Raman Imaging: Impact on Cement Hydration

“…The scattered light is analyzed by a spectrometer to obtain a Raman spectrum that shows the intensity of scattered light vs the shift of wavelength away from the excitation wavelength of the incident laser (Raman shift) . Previous studies have found Raman spectroscopy to be instrumental in studying cement clinker, mortars, the main hydration products, , alkali–silica reaction gels, , as well as cementitious pastes containing SCMs. − Recently, Raman imaging has been successfully used to study and quantify phases in static systems such as anhydrous cements and aggregates, and dynamic systems such as cements undergoing hydration , and carbonation. − In this study, the spectra obtained on a grid of points on a 5 mm × 5 mm area (spatial resolution: 1.25–10 μm) is analyzed and split into corresponding components and ultimately converted into binary phase images, where white denotes the presence and black denotes the absence of a mineral. We then obtained the PSDs from both the individual phase images (phase-specific PSD) and the composite phase images (overall PSD) using the procedure outlined in the Materials and Methods section.…”