Development of sustainable structural lightweight concrete with fine recycled aggregates

• A sustainable structural lightweight concrete (LWC) containing recycled fine aggregate (RFA) was produced • A hooked-end steel fibres were utilised to enhance the performance of the LWC • 13 different concrete mixtures of LWC utilising different replacement ratios were produced and studied • In addition to regular tests, non-destructive testing methods were also used to evaluate the produced LWC. • Light-weight tiles were also produced and tested using the developed LWC This study aims to develop a sustainable structural lightweight concrete (LWC) incorporating recycled fine aggregate (RFA) derived from concrete waste. Lightweight expanded clay aggregate (LECA), in both high-density and low-density forms, was used to replace the natural coarse aggregate, while the natural fine aggregate was partially or fully replaced with RFA at 50% and 100% levels. Steel fibres (with 0.75% volume fraction) were added to enhance performance. A total of 13 mixes—12 LWC and one normal-weight concrete—were produced and tested for fresh properties and mechanical performance, including compressive, splitting tensile, and flexural strengths, as well as density. Non-destructive tests (Schmidt rebound hammer (RH) and ultrasonic pulse velocity (UPV)) were also conducted. The study additionally involved producing sustainable precast LWC tiles with varying RFA contents and LECA types. The results illustrated that the incorporation of recycled fine aggregate (RFA) in lightweight concrete (LWC) caused an average reduction in the compressive, splitting tensile, and flexural strengths, with greater decreases observed at 100% RFA replacement, namely; 14.5%, 16.5% and 15%, respectively. Adding 0.75% steel fibres effectively mitigated these losses, particularly improving tensile performance. Except for mixes using low-density LECA with RFA, all the precast LWC tiles met the relevant standard requirements by achieving a fracture load of greater than 8.3 kN. Non-destructive test values (RH and UPV) also declined as RFA content increased, but improved consistently when steel fibres were included, reaching a UPV speed of 4.5 km/s, and hence can be categorised within the good concrete category.