Microstructure and Phase Assemblage of Low-Clinker Cements during Early Stages of Carbonation

Increasing and widespread use of Supplementary Cementitious Materials (SCMs) in the cement industry has become common practice. However, such systems hydrate more gradually than pure Portland Cement (PC) systems, and though concrete standards include recommended modified curing lengths for more slowly hydrating systems, the premature removal of formwork risks exposing an underdeveloped microstructure that is vulnerable to ingress and attack from aggressive species. Design models established for Portland Cement systems are acceptable when low levels of replacement are used, but may be unsuitable if higher levels of replacement are used. In such systems an understanding of the complex relationship between composite cement hydration, drying of the sample surface and phase carbonation kinetics is imperative. The main objective of this project will be to develop an understanding of the changes and development of the early-stage morphology and phase assemblage of composite systems as a result of carbonation. Evolution of the morphology will be investigated using SEM and TEM, while changes in the phase assemblage will be analysed through XRD, NMR and TGA. Further complementary analysis using Raman and FTIR Spectroscopy will also be performed. It will be key to establish how the systems evolve over time in these very early stages as a result of slower hydration, desiccation and phase carbonation.