Abstract
This study explores the possibility of producing sustainable structural lightweight concrete (LWC) based on limestone calcined clay cement (LC³) using waste from construction and demolition. The main innovation is the dual substitution of waste-derived materials for traditional LC³ constituents: crushed brick powder (CBP) was used in place of metakaolin (MK), and recycled concrete powder (RCP) was used in place of limestone powder (LSP). To achieve lower densities, nine concrete mixtures were created using crushed brick as both fine and coarse aggregates in addition to an air-entraining agent. Flowability, dry density, ultrasonic pulse velocity, compressive strength, resistance to magnesium sulfate attack and high temperatures (200 and 400 degrees Celsius), water absorption, and porosity were all assessed through an extensive experimental program. With only a small drop in 28-day compressive strength (5–8%) and a slight increase in water absorption (10–12%), the results showed that CBP is a very promising substitute for MK. All mixtures met the structural LWC requirements of DIN EN 1045-1 (dry density of 1650–1850 kg/m³ and strength > 24 MPa), but substituting RCP for LSP resulted in a more noticeable decrease in 28-day compressive strength (15–20%) and an increase in water absorption (13–18%). Additionally, after 180 days of sulfate exposure, all LC³ systems showed very little mass loss (< 0.7%) and maintained over 80% of their residual strength at 400 °C. According to the study, CBP and RCP can effectively and sustainably replace MK and LSP in LC³-based LWC, allowing for a 60% reduction in clinker while preserving structural integrity and promoting waste valorization.