National Concrete Pavement Technology Center

Project description

Cement production is the third largest producer of carbon dioxide worldwide, with each cubic yard of concrete responsible for an estimated 400 lb of CO2. The industry has taken many steps to mitigate this impact, ranging from the increasing use of SCMs to a shift to Type IL portland cement. While these approaches focus on reducing the demand for portland cement, one more recent development involves collecting carbon dioxide from industrial application and sequestering it in concrete. CarbonCure has developed a technology that injects carbon dioxide into concrete during the mixing process, claiming that up to 25 lb/yd3 of CO2 can be permanently mineralized in the concrete. CarbonCure also claims this process increases the compressive strength of concrete; however, the effect of this sequestration on the long-term durability of concrete has not been established. Concrete will slowly absorb CO2 from the atmosphere over time in a process known as carbonation. In the process of carbonation, CO2 reacts with calcium hydroxide (Ca(OH)2), a component of hydrated portland cement, to produce calcium carbonate and water: CO2 + Ca(OH)2 → CaCO3 + H2O. While the process of carbonation does not significantly impact the strength of concrete, it does lower the pH. Newly cast concrete typically has a pH of around 13.5. Steel reinforcement will corrode in concrete if the pH drops below 11.5, even in the absence of chlorides. Furthermore, the resistance of reinforcement to chloride-induced corrosion decreases as the pH decreases. As a result, carbonation can reduce durability of reinforced concrete even at moderate reductions in pH. Given the impact that atmospheric carbonation can have on the durability of reinforced concrete, it is critical to establish what impact, if any, the addition of CO2 to plastic concrete has on the corrosion resistance of reinforced concrete structures. This research proposal aims to: (1) establish the effect of CarbonCure technology on early and long-term pH of concrete; and (2) determine the corrosion resistance of reinforced concrete with CarbonCure relative to conventional reinforced concrete.