Development of self-compacting low-carbon concretes for precast industry

To reduce the carbon emissions of concrete, one solution is to use supplementary cementitious materials (SCMs) such as ground granulated blast-furnace slag (GGBS) or metakaolin (MK). However, replacing OPC with a high dosage of SCMs has a major disadvantage for prefabrication with insufficient compressive strengths at the young age of concrete. According to the specification provided by a precast manufacturer, this study aims to obtain self-compacting C45/55 concretes (mean 28-day compressive strength of concrete of 63 MPa on cubes) with carbon emissions of less than 106 kg.eqCO 2 /m 3 and a 24-hour mean strength of at least 25 MPa on cubes. The following three types of binder were tested: slag-cement binary binders (OPC/GGBS), supersulfated cement (SSC) and LC3 binders (clinker/calcined clay/limestone/gypsum) alone or combined with GGBS. The results show that these binders could provide alternative solutions to OPC concretes for prefabrication. SSC-based concretes are the best solution among those tested for reducing carbon emissions, but the mechanical criteria are more difficult to achieve than for those with slag-cement binary or LC3 binders. Nevertheless, performance levers such as the use of finer binders or thermal activation are necessary to achieve the desired strengths, especially at 24 hours. On the other hand, thermal activation has a negative effect on 28-day strengths. To counter this blockage, a combination of these performance levers makes it possible to reduce the curing temperature while maintaining strengths at 24 hours, and without penalizing their 28-day strengths. • Slag-cement, supersulfated and LC3 concretes could replace OPC in precast industry. • Carbon emissions reduction was obtained, while maintaining the compressive strength. • Using performance levers is mandatory to maintain the strengths, mainly after 24 hours.