Durability of recycled aggregate concrete derived from railway sleepers with Graphene Quantum Dots (GQDs) under harsh environmental exposure for circular practices

This study evaluates the durability of recycled aggregate concrete (RAC) derived from wasted railway sleepers and modified with liquid graphene quantum dots (GQDs) under sulphate, acid, and marine exposures. Concrete mixes with 50% and 100% recycled aggregates were tested at a GQDs dosage of 0.3% by binder weight. At full replacement, compressive strength remained within 2% of that of natural aggregate concrete (NAC). In RAC50, the incorporation of GQDs resulted in increases of approximately 9% in compressive strength and 3% in flexural strength. Durability assessments indicated that unmodified RAC experienced strength losses under acid and marine exposure, whereas mixes modified with GQDs showed improved resistance. QRAC50 exhibited a 4% reduction in chloride penetration relative to RAC50. Under marine exposure, QRAC50 limited the compressive strength loss to 25% after 60 days when compared with unexposed QRAC50, whereas NAC exposed to the same conditions exhibited a 37% reduction in strength compared with unexposed NAC. Under acid exposure, QRAC100 retained 31% higher compressive strength than RAC100. Sulphate exposure caused a 20% compressive strength reduction in QRAC50 compared with RAC50. These results demonstrate the potential of sleeper‑derived RAC with GQDs for sustainable infrastructure, provided exposure to severe sulphate and acidic environments is carefully managed.