Recycling carbon dioxide into concrete: a feasibility study

The feasibility of recycling carbon dioxide into concretes through their curing processes was investigated. The CO2 uptake capacities of four commonly used concrete building products: masonry block, paving stone, cement board and fiberboard, were evaluated. It was found that, based on the cement content used in the product, the uptake capacities of the four products ranged from 9.8% to 18.9% when recovered CO2 was used in a static system and from 6.3% to 8.1% when as-captured cement kiln flue gas was used in a quasi-dynamic system. In the United States and Canada, annual cement consumption by these four products is approximately 14 million tonnes (300 billion lb). If all of these products were carbonation treated, the net annual sequestration of CO2 in concrete could reach 1.8 million tonnes (4 billion lb) using recovered CO2 (at a net efficiency of 87.1%) and 0.98 million tonnes (2.1 billion lb) using flue gas (at a net efficiency of 84.0%). The proposed process offers a feasible method of safe and permanent sequestration of carbon dioxide in manufactured concrete products. Either recovered carbon dioxide or flue gas could be used, though the direct use of flue gas would save considerable energy and offset the costs associated with the CO2 recovery process. Reaction efficiency is nevertheless lower since there is a smaller fraction of carbon dioxide available for reaction at a given pressure. The direct use of flue gas as a carbonation curing agent is thus only appropriate for situations in which curing is performed adjacent to a CO2 point source. On the other hand, recovered CO2 is expected to become available at low cost in the near future and could be shipped to concrete plants as a curing agent to replace steam in precast concrete production.