Microscopic characterization to study the mechanism of beneficial CO2 utilization in ready mixed concrete production

A beneficial carbon dioxide utilization technology has been developed for ready mixed concrete production. Industrial installations have shown that carbon dioxide can be injected into concrete, while it is being batched and mixed, and a strength benefit, circa 10%, can arise. The performance is sensitive to the dose but the CO2 is typically acting on the order of about 0.05% by weight of cement. A series of questions developed - how could such a small addition create a large performance change? Mechanistic understanding would require knowing what the reaction products look like, how they formed and what they were composed of. Microscopic investigations have started to uncover the physiochemical process at work and build evidence for describing the mechanism. SEM was used to examine a model C3S system and show that the action of the CO2 is almost instantaneous - dissolution pits are visible on particle surfaces within 30 seconds of the dose. Reaction products consistent with amorphous calcium carbonate were examined though FIB sectioning and low energy EDS analysis of the chemical composition. Atom Probe Tomography was used to examine the atomic composition of a reaction product in three dimensions.