Enhancing Bond Strength and Impact Resistance in Ultra-High Performance Geopolymer Concrete Using Copper Slag and Steel Fibres

Ultra-High Performance Geopolymer Concrete (UHPGC) is receiving considerable interest as a sustainable substitute for conventional cementitious composites, owing to its exceptional mechanical properties and diminished environmental impact. This study examines the effect of copper slag (CS), a by-product of the copper manufacturing industry, and steel fibres (SF) on the bond strength and impact resistance of UHPGC. Copper slag was utilised as a partial substitute for fine aggregates up to 100%, while steel fibres were introduced at varied volume fractions (1% and 2%) to assess their impact on matrix-reinforcement interaction and energy absorption under dynamic loading conditions. The geopolymer binder system predominantly comprised ground granulated blast furnace slag (GGBS) and silica fume, activated by an alkaline solution, tailored for exceptional performance under ambient curing conditions. A series of pull- out tests was performed to evaluate the bond strength between rebar and the surrounding matrix, while drop-weight impact tests were utilised to quantify the impact resistance of the composites. The microstructural features were analysed via Scanning Electron Microscopy (SEM) to assess the fibre-matrix interfacial bonding and the distribution of copper slag particles. The findings demonstrate that including copper slag up to 80% markedly enhances packing density and facilitates matrix densification, thus improving bond strength. The use of steel fibres significantly enhances the impact resistance and post-cracking toughness of the UHPGC. This research elucidates the formulation of high-performance, sustainable geopolymer concretes utilising industrial by-products and fibre reinforcement, presenting advantageous applications in impact-sensitive and structurally rigorous settings.