Development of sustainable ultra-high performance concrete recycling aluminum production waste

Ultra-high performance concretes (UHPC) are a promising means to foster sustainable and resilient infrastructures as they allow reducing concrete volume, while enhancing structural durability. However, their applications are often limited by the high cost and the availability of raw materials. This study aims to engineer a novel UHPC mix design at a relatively low cement content by recycling treated spent pot lining (SPL) from aluminum smelters, herein called LCLL-ash. First, the UHPC mixtures with different cement content replacement levels by LCLL-ash powders were designed by means of the Compaction-Interaction Packing Model (CIPM). Then, a multi-technique characterization was carried out for measuring the fresh properties, microstructure images and crystalline phases by SEM and XRD analysis, heat transfer by isothermal calorimetry, autogenous shrinkage, compressive strength and microindentation properties. The presented results show that the addition of LCLL-ash delayed the hydration kinetics, while slightly reducing the workability and compressive strength. On the other hand, replacing 12% of cement with LCLL-ash reduced the early-age autogenous shrinkage by 19%. Finally, the environmental impact and the cost of the developed UHPC were assessed, confirming the potentials for producing sustainable LCLL-UHPC with reduced shrinkage.