Transforming industrial by-products into sustainable building materials: A pathway to eco-efficient quaternary binders

The increasing environmental burden of Portland cement production has accelerated the search for low-carbon alternatives using industrial By-products. This study investigates the development of a novel alkali-activated composite binder by synergistically incorporating ground granulated blast furnace slag (GGBFS), ladle furnace slag (LFS), and Class F fly ash (FA) as supplementary cementitious materials (SCMs). Unlike conventional approaches, this research introduces a hybrid binder system in which 40% of the ordinary Portland cement clinker is replaced by GGBFS and LFS in varying proportions, while maintaining fixed levels of 10% for FA and 5% for gypsum. Sodium carbonate was employed as an eco-friendly activator to enhance the reactivity of LFS and promote the formation of hydration products. The mix design was optimised based on mechanical and microstructural performance, with Mix 2 (30% GGBFS and 10% LFS) achieving a peak compressive strength of 64.80 MPa at 56 days. Advanced characterisation techniques, such as XRD, FE-SEM, FTIR, and XRF, confirmed the presence of dense C–S–H and C–A–S–H gels, refined microstructures, and reduced porosity. The novelty of this work lies in the effective valorisation of low-reactivity LFS through mechanical activation and alkali stimulation, enabling its viable use in sustainable binder systems. The findings provide compelling evidence for reducing clinker consumption and CO 2 emissions without compromising strength, thereby contributing to the advancement of greener cement technologies. • Optimised binder mix is clinker (40%), GGBFS (30%), LFS (10%), FA (10%), gypsum (5%), and solid activator (5%). • XRD and microstructural analyses confirmed intense CSH peaks and denser gel, validating enhanced strength development. • FTIR spectra corroborated formation of CSH and CASH, indicative of higher polymerisation and microstructural refinement. • Findings showed superior properties compared to the control despite incorporating a 50% clinker replacement.