Sustainable ultra-high-performance basalt fiber-reinforced geopolymer concrete incorporating carbon nanotubes and treated recycled aggregates

In this study, the performance characteristics of ultra-high-performance geopolymer concrete (UHPGC) incorporating basalt fibers and carbon nanotubes (CNTs) synthesized from waste polypropylene using kaolin as a catalyst were investigated. Recycled aggregates treated with calcium silicate hydrate (CSH) were also considered. The experimental program focused on the workability, mechanical properties, and durability of basalt fiber- and CSH-based geopolymer concrete with CNT dosages of 0.05%, 0.1%, and 0.15%. Furthermore, the performance of untreated and treated recycled aggregates was analyzed. The CNTs significantly improved compressive strength specially at 0.05% CNT dosage achieving the best performance. The combined effects of CNTs, basalt fibers, and CSH treatment improved the mechanical properties and durability of UHPGC. The treated recycled aggregates improved the interfacial transition zone, internal curing, and compressive strength of UHPGC. The sulfate resistance of UHPGC was tested at varying concentrations and durations. The best performance was achieved for the 0.05% CNT mix, particularly when combined with treated aggregates. The high-temperature resistance of UHPGC was evaluated at 200, 400, 600, 800, and 1000 °C. Silicate treatment improved the strength and thermal stability of UHPGC. Microstructural analysis supported these results, showing that the UHPGC matrix was more densely packed with the incorporated CNTs and basalt fibers. This study demonstrates the potential of using waste-derived CNTs, basalt fibers, and treated recycled aggregates to produce UHPGC suitable for the construction and infrastructure industries.