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This presentation will review and provide examples of challenges faced by a concrete producer from perspective "low carbon" specifications, and contrasting projects where these issues have been avoided, while still providing significant carbon reduction to the project.

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The presentation demonstrates the acceleration of carbonation kinetics rate in nanostructured interfaces of cementitious systems, crucial for CO2 mineralization in concrete, using 2D carbon-based nanomaterials. Highly exfoliated/nearly monolayered graphene nanoplatelets (GNPs) with 3-5x higher specific surface area than the surface area of cement grains were used. NanoIR mapping on sub-10 nm nanomaterial/C-S-H interfaces of carbonated specimens shown the formation of active sites that generate large quantities of Ca(OH)2 and CaO essential for CO2 mineralization, i.e., CaCO3 formation. A 50-80% higher nanoscale modulus of elasticity and elastic strain energy absorption capability of the carbonated nanostructured interfaces over the material without the GNP reinforcement was demonstrated through quantitative nanomechanical property mapping. Such enhancements in the carbonation kinetics and nanomechanical properties indicate improved CO2 mitigation potential and increased strengthening and toughening/resiliency of carbonated engineered concrete, important performance factors for the material’s serviceability.

With low-carbon concrete requirements gaining momentum worldwide, the construction industry needs to take sustainability education to the next level. In view of the fact that concrete's climate change impact and its solutions vary across regions, education should be provided uniformly and in a large-scale manner based on local conditions. The ACI 130 Committee has developed and organized the Eco Concrete Competition since 2017. This competition aims to promote the idea of environmental performance in concrete mix designs and to think critically about low-impact solutions while considering their performance. This presentation will discuss the structure and experiences of organizing three versions of the competition. The importance of life cycle accounting, the context-specificity of solutions, and concrete performance accounting in educating the upcoming generation of civil engineers will be elaborated. The streamlined life cycle assessment (LCA) tool developed for this competition will be showcased as a possible educational tool for civil engineering students. Finally, lessons learned by and from student participants will be provided to clarify the points that should be emphasized in the LCA education of concrete.

This study investigated a new approach to dispersion of carbon nanofibers (CNFs) in cement paste by coating rice husk ash (RHA) particles using a natural polymer binder. Light Chitosan with low molecular weight was used to provide bonding between CNFs and SiO2 from the RHA substrate. Mechanical properties namely, compressive strength and flexural properties of paste specimens were assessed to evaluate the efficiency of the applied method. Microstructural analysis was carried out using FTIR, XRD, TGA, and SEM to investigate the effects of the coating process on the hydration products and to explain the mechanical properties of specimens with the modified RHA. The results showed that 15% and 5% modified RHA increased the compressive strength and flexural strength of paste specimens at 28 days by 53% and 187%, respectively. Microstructural analysis showed that the coating process delayed the hydration, however, the physical crosslinking effect of carbon nanofibers enhanced the mechanical properties at all ages.

Two approached to reducing the carbon footprint of concrete are to, 1. Reduce the clinker content of the cementitious binder and, 2. Reduce the total binder content. For the first, combinations of supplementary cementitious materials can be combined with Type IL cements while still attaining early-age strength development with at least a 40% reduction in clinker content. For the second, optimizing aggregate gradations with at least three components can result in savings of up to 15% of the required cementitious materials content while also reducing concrete permeability and shrinkage. The methodologies for combining both of these approaches will be discussed.