Toughening alkali-activated construction materials using nanocarbon composites from red mud-catalyzed plastic waste upcycling

Plastic waste accumulation and cement industry decarbonization demand cross-sectoral solutions, with disposal-challenged red mud (RM) offering an opportunity. We couple plastic pyrolysis with RM catalysis to co-produce H2 and binder-compatible carbon nanotubes (CNTs)/RM composites, which serve as nano-toughening additives in alkali-activated materials (AAMs). We explore effects of RM-to-plastic ratio, feedstock and RM type on H2 production, CNT yield and structure. At an optimal RM-to-PE ratio of 1:4, 21.0 mmol/gplastic H2 and 262 mg/gplastic CNTs are obtained. At 1 wt% CNT dosage, CNTs/RM composite enhances AAM compressive and flexural strengths by 33.1% and 54.3%, respectively, increasing the flexural-to-compressive strength ratio by 16.4%. This improvement arises from fiber-bridging, pore-filling and nucleation effects of CNTs, and depends on CNT structural parameters. Here, we show that this scalable route converts wastes into low-carbon, cost-effective toughening additives, reducing carbon emissions, energy demand, and cost by 65.8%, 71.1%, and 13.6%, respectively, compared with conventional CNTs production. This study converts red mud and plastic waste into nanocarbon composites that strengthen and toughen alkali-activated materials, offering a route to upcycle two major waste streams into low carbon construction materials.