A preliminary assessment of microstructural and compositional characteristics of two variants of precarbonated and postcarbonated concrete mixes

摘要

> The hydration, precarbonation, and postcarbonation microstructural and compositional attributes of 2 variants of concrete were studied using scanning electron microscope, energy dispersive spectroscopy, and X‐ray diffraction techniques. Results obtained showed presence of large number of diffraction peaks indicative of SiO ₂ as major phase. Higher pH, alkalinity, and absence of effects of carbonation were suggested from the presence of portlandite peaks. Evidence of effect of carbonation was studied through the analysis of the experimental diffraction peaks obtained postexposure to accelerated carbonation in a controlled environment. Presence of all the 3 polymorphs of calcium carbonate (CaCO ₃ ) such as aragonite, vaterite, and calcite depending upon the moisture content and the material constituting the concrete sample were envisaged signifying carbonation. Precipitation of these CaCO ₃ crystals was responsible for depletion of CH as well as calcium–silicate–hydrate, ettringite with the progress of carbonation as suggested by their absence in the X‐ray diffraction diffractograms of the carbonated samples. The crystal structure of the newly formed minerals in both the variants of concrete sample was highly controlled by the stages of carbonation, with development of amorphous CaCO ₃ (amalgamated with that of calcium hydrates) in early stages of carbonation as well as fully developed rhombohedral CaCO ₃ crystals in later stages.