Hybrid glass-steel fiber reinforcement in geopolymer concrete: synergistic durability enhancement against sulfuric acid attack through optimized fiber architecture and matrix stabilization

This study presents a novel hybrid fibre-reinforced geopolymer concrete system optimised for superior durability under aggressive acidic environments. While prior research has focused on single-fibre reinforcement or neutral conditions, this work demonstrates that a balanced combination of 0.25% alkali-resistant glass fibres and 0.75% steel fibres, integrated with a silica-fume-modified geopolymer binder, achieves unprecedented synergistic performance. The key innovation lies in a dual protective mechanism: glass fibres act as a sacrificial barrier, shielding steel fibres from sulphuric acid attack, while steel fibres provide tensile strength and crack-bridging capacity. Specimens with this optimised hybrid formulation retained 75% of their original compressive strength after 90 days in pH 1 sulphuric acid, significantly outperforming both single-fibre and other hybrid combinations. Notably, this high durability was achieved without compromising mechanical properties, as the system exhibited the highest 28-day compressive strength (99 ± 3.9 MPa) and splitting tensile strength (6.59 ± 0.33 MPa). A strong inverse correlation between ultrasonic pulse velocity (UPV) and acid-induced degradation validates UPV as a reliable non-destructive durability indicator. This optimised hybrid geopolymer concrete offers a sustainable, high-performance solution for infrastructure in corrosive environments.