In a September issue of Construction Canada, Jennifer Wagner and Mark Hagel described the history of concrete and cement, which dates back to the ancient Romans. Since then, concrete production has advanced due to the advent of many new technologies.
The article describes the difference between the two types of carbonation: weathering carbonation and early-age carbonation of concrete. The second form of carbonation–early-age carbonation–involves using carbon dioxide in the production of concrete, typically in the mixing stage. The addition of CO2 results in an immediate carbonation reaction that occurs alongside the heat of hydration reaction of cement. The technology process is described in detail in the article. Carbon dioxide that is incorporated into concrete during mixing is permanently sequestered as solid limestone embedded within the concrete matrix.
The primary benefit of incorporating CO2 into concrete is the carbon sequestration benefit. Other potential benefits that can be achieved vary from plant to plant, but can include reduced shrinkage, decreased defects in the finished block units, reduced energy required to cure the product, and finally higher early strength of concrete. Higher early-strength gains can allow for producers to reduce their cement loading, which further reduces the CO2 footprint.
The article describes how the environmentally friendly product can contribute to points with the Leadership in Energy and Environmental Design (LEED) certification system. Projects that have used these products are also featured.