Sustainable concrete formulations to mitigate Alkali-Silica reaction in recycled concrete aggregates (RCA) for concrete infrastructure

The Alkali-Silica Reaction (ASR) is a Portland Cement Concrete (PCC) distress of greater relevance worldwide, and several authors have successfully mitigated ASR with improved concrete mixture formulations. These con-crete mixtures are mainly associated with incorporating Supplementary Cementitious Materials (SCM), which usually involve recycled materials or co-products from other processes, thus contributing to concrete production sustainability. Due to global warming and irreversible impacts on the planet, the circular economy and sus-tainability concepts are now of particular concern in the cement and concrete industry. Different ways to reduce the environmental impacts of Portland cement concrete include using SCM and Recycled Concrete Aggregates (RCA) to replace natural aggregates. Despite there are no concrete structures made with RCA that have been reported showing signs of ASR, it is essential to check the potential reactivity of RCA to take the necessary corrections to use them safely. This paper includes a laboratory investigation on mitigating the ASR of RCA in PCC production by using several SCM (fly ash, slag, and silica fume) to achieve a more sustainable material, reducing the production cost and the environmental load associated. Results indicate that replacement levels of fly ash (FA, 20%), slag (SL, 40%), and silica fume (SF, 10%) were able to mitigate the alkali-silica reaction of one source of RCA successfully. The optimum dosage of RCA is suggested to be between 25 and 50% (by weight of total coarse aggregate) for mixes containing fly ash and 50-100% for silica fume and slag mixes, respectively. The work also involves a life cycle assessment (LCA) to quantify the environmental benefits depending on the SCM used and the aggregate portion replaced by RCA on PCC mixtures. SCM and RCA in concrete mixtures significantly reduced greenhouse gas (GHG) emissions and energy demand due to lower Portland cement contents.

Automated summary

The study focuses on mitigating ASR in concrete with RCA by using SCM, reducing production costs and environmental impact. Optimal RCA dosages and replacement levels with SCM were determined to successfully mitigate ASR, leading to reduced GHG emissions and energy demand in concrete production.