Development of one-part high-strength ultra-high-toughness geopolymer composites (HS-UHTGC) against low-velocity impact loading

One-part geopolymers offer high mechanical efficiency, environmental sustainability, and convenient field application. To enhance their applicability in impact-resistant structures, this study aims to develop one-part high-strength ultra-high-toughness geopolymer composites (HS-UHTGC) reinforced with hybrid steel and polyethylene (PE) fibers. Five mixtures with a total fiber content of 2 vol% were prepared and tested under 10 J, 20 J, and 30 J low-velocity drop-weight impacts. Results show that the hybrid mixture (S3, 1.0 vol% steel + 1.0 vol% PE) achieved the most balanced performance, exhibiting 94.2 MPa compressive strength, 22.0 MPa flexural strength, 35–60 % smaller crack widths, and the highest energy dissipation coefficient (0.99 at 30 J). Steel-only composites provided high strength but limited ductility, whereas PE-only composites offered good deformability but rapid strength degradation under repeated impacts. A comprehensive evaluation confirmed that S3 outperformed all other mixtures in both static and dynamic responses. The synergistic mechanisms of stiffness enhancement, crack control, and post-cracking energy absorption were also clarified. The developed HS-UHTGC provides a sustainable and high-performance material solution for impact-resistant engineering applications. • Hybrid 1 % steel + 1 % PE fibers produced optimal strength–ductility performance. • S3 showed the smallest crack width and most stable damage under impact loading. • Hybrid fibers improved repeated-impact resistance and maintained high residual strength. • A combined stiffness-bridging mechanism clarified the multiscale toughening behaviour.