Geopolymer artificial aggregate from industrial by-products as a substitute for brick aggregate in concrete: strength, durability and carbon footprint

Clay-burnt brick coarse aggregates (BCA) are predominantly used where natural stone scarcity is acute, but their production is associated with significant environmental issues. In this study, Geopolymer artificial coarse aggregate (ACA) produced from alkali-activated sewage sludge ash, coal fly ash, and incinerated medical ash was used as a replacement for BCA in concrete. The fresh, mechanical, fire resistance, and durability of artificial aggregate concrete (AAC) were evaluated, alongside a cost and CO2 footprint analysis. Adding ACA reduced the fresh concrete slump up to 36.4%, yet a high degree of workability could be maintained. Compressive strength, splitting tensile strength, and flexural strength decreased at higher ACA content. However, by limiting the ACA to 50%, a reasonably high-strength concrete (strength>40 MPa) could be produced with a marginal reduction in splitting tensile and flexural strengths (8.7% and 9.2%, respectively). At elevated temperatures, AAC demonstrated good fire resistance. The density of concrete complied with the ACI 213 requirements for lightweight concrete. Furthermore, AAC offered better strength-to-CO2 ratios than control specimens (100% BCA). Therefore, partial replacement of BCA with ACA derived from waste by-products can be a significant step towards sustainable concrete production in countries that lack natural resources.

Authors: Md. Rafiqul Islam, Md. Shahjalal, Mohammed Russedul Islam, K. M. Ariful Islam, Syed Ishtiaq Ahmad, Abdullah Al Noman, Tanvir Ahmed