Reducing the carbon footprint of lightweight aggregate concrete

Lightweight aggregate concrete (LWAC) is a special concrete type with density of no more than 2200 kg/m³. Lower densities than normal weight concrete (2400-2500 kg/m³) are achieved using lightweight aggregates, which may originate from by-products of industrial manufacture such as fly ash, for example Lytag. Currently there is an increasing demand for LWAC for the construction of lightweight composite flooring systems, particularly in commercial buildings. Despite the well-recognized issues and challenges associated with the carbon dioxide (CO²) emissions from cement production, LWAC still contains high quantities of Portland cement (Type I or CEM I) as well as high quantities of total cementitious materials content. This has been primarily utilized to attain a certain workability and pumpability, as well as to not compromise the strength development. As such, the carbon footprint of LWAC is generally higher than that of normal weight concrete, owing also to the carbon intensive lightweight aggregates. In this work, several alternative lightweight aggregate mixes were optimized to maximize Portland cement replacement and reduce the total cementitious materials content without compromising the strength, workability and pumpability of a standard, to Eurocode 2, LC 30/33. The developed mixes contained up to 60% of ground granulated blast-furnace slag, as well as limestone powder, which resulted in a reduced carbon footprint compared to the conventional LWAC mixes. It was possible to reduce the Portland cement content by approximately 40%, the total cementitious materials content by 22% and embodied carbon (life cycle stages A1-3) by 12% compared to the initial, conventional LWAC mixes.