Carbonation Potential for Concrete Using Thermodynamic Modeling for Concrete Sustainability Calculations

Abstract

The design of concrete is transitioning from mixtures that are predominately clinker based to mixtures that have less clinker with a substantial replacement with fillers and supplementary cementitious materials (SCMs). There is a growing interest in accounting for the CO₂ sequestered by concrete mixtures via carbonation. This paper discusses some nuances of how material composition and mixture design are affected as industry drives toward zero carbon emission goals. This paper begins by discussing the current life-cycle assessment (LCA) approaches and outlines the complexity of determining at which step in the LCA process carbonation should be considered, a particularly important point as current environmental product declarations focus on the A1 to A3 (cradle to gate) stages and therefore “favor” forced carbonation approaches. Specifically, it highlights how upfront minimization of CO₂ is generally preferable to forced or natural carbonation. It also discusses the need for clarification on carbonation in the LCA process. The paper uses thermodynamic modeling to determine similar paste performance and indicates that the potential CO₂ sequestered varies from mixture to mixture. From a carbon emissions perspective, calculations show that moderately reactive SCMs might be preferable to highly reactive ones as the former allow higher clinker replacements while maintaining required concrete performance. The work illustrates how this would be affected by the paste volume of the concrete—higher paste volumes should be avoided. Carbonation potential of structures with large and exposed surfaces, such as pavements, might help reduce the global warming potential of concrete.