Circular economy, data analytics, and low carbon concreting: A case for managing recycled powder from end-of-life concrete

Reuse and recycling are vital practices in the circular economy. Despite progress in recycling aggregates from end-of-life concrete, the potential for reusing recycled concrete powder (RCP) as supplementary cementitious material (SCM) is now attracting research and commercial interest. Herein, a meta-analysis of concrete in which RCP was used as an SCM was conducted, and a multivariate regression model was developed for predicting strength from mix composition. The carbon footprint of alternative beneficiation strategies, including milling only, milling plus thermal treatment and milling plus CO2 injection, were quantified and used with the regression model to investigate RCP-containing concrete's embodied carbon (eCO2). The comparison was made with conventional SCMs and end-of-life scenarios of concrete from different cement types. The meta-analysis and regression model showed that 15% cement replacement by the non-beneficiated RCP caused a 40% reduction in 28-day compressive strength, and at 50% replacement, the strength reduction was 70%. Above 30% cement replacement, the RCP beneficiated through CO2 injection reduced the concrete's eCO2 per unit strength by 10–25%, while the thermally treated RCP had greater eCO2 than conventional SCMs. Thus, circularising end-of-life concrete does not guarantee low carbon concrete production. Instead, treating RCP with waste CO2 leads to a carbon-negative SCM, presenting the most promising route for low-carbon concrete in the circular economy.