Tailoring Cementitious Materials Towards Value-Added Use of Large CO2 Volumes

The massive quantities of concrete used worldwide (estimated at 30 billion tons/yr), and the susceptibility of concrete to carbonation provide opportunities for chemical binding of significant quantities of carbon dioxide. The resulting carbonates can enhance the material properties of concrete by supplementing the binding effects of cement hydrates. Carbonation of concrete without tailoring its chemistry, however, lowers the pore solution alkalinity, and thus the long-term stability of cement hydrates and the oxide layer protecting reinforcing steel against corrosion. Beneficial CO2 sequestration in concrete also requires development of economical means of delivering carbon dioxide to induce timely and homogeneous carbonation reactions across the concrete volume. The main thrust of this project is to develop robust and commercially viable methods for chemical binding of large CO2 volumes in concrete while realizing balanced gains in material properties. These methods are compatible with the manufacturing process of cementitious materials and the prevalent concrete production and construction practices. They suit existing concrete chemistries, and can also stimulate longer-term transition to more sustainable chemistries. The project employs the inherent affinity of cementitious materials for carbonation to make direct use of flue gas, thus eliminating the need for costly CO2 separation. The Phase I project developed economical and scalable methods for delivering carbon dioxide to concrete in the form of carbonate anions incorporated into cementitious particles. This approach induces timely and homogeneous carbonation reactions which supplement hydration of cementitious materials for enhancing the structure and properties of concrete. Additives with complementary mechanisms of action were identified for enhancing the CO2 uptake, the beneficial carbonation reactions, and the long-term stability of cement hydrates and steel reinforcement in concrete. The compatibility of the technology with the conventional chemistry of concrete was demonstrated, and its enabling role towards transition to more sustainable chemistries was verified. Initial and life-cycle analyses validated the significant merits of the technology as a commercially viable approach to high-impact CO2 sequestration, and as an effective means of addressing critical needs relevant to the concrete-based infrastructure. The proposed Phase II project will: (i) adapt the technology for use with broader selections of raw materials and additives; (ii) devise refined chemistries for selective sorption of carbon dioxide from flue gas; (iii) thoroughly characterize the structure and properties of cementitious materials embodying carbonate anions, and concrete materials with integrated hydrate and carbonate binders; (iv) scale-up the process in an industrial manufacturing plant where cement and slag processing is accompanied with flue gas emission; (v) demonstrate the compatibility of cementitious materials embodying carbonate anions with industrial-scale concrete production and field construction; (vi) elaborate and model the mechanisms of CO2 sorption and the subsequent beneficial carbonation; and (vii) conduct refined initial and life-cycle analyses to further verify and quantify the benefits of the technology in terms of CO2 sequestration and emission control, energy and cost savings, and enhancing the longevity, efficiency and life-cycle economy of the concrete- based infrastructure. Cement and concrete industries have made commitments towards pilot-scale implementation and field evaluation of the technology.