Development of ultra-high performance geopolymer concrete (UHPGC): Influence of steel fiber on mechanical properties

This study reports the development of ultra-high performance geopolymer concrete (UHPGC) and overcoming the brittleness feature of geopolymer matrix by using different steel fibers. Four straight steel fibers with different aspect ratios and two different deformed steel fibers were investigated. Flowability, compressive strength and flexural behavior including strengths and deflection, and energy absorption capacity of UHPGC, were systematically evaluated. A deformation ratio of steel fiber was introduced to quantitatively correlate the steel fiber shape and the mechanical performance. The flowability of fresh UHPGC mixtures decreased when the fiber content and length increased, as expected, and was inconspicuously influenced by fiber shape. The increase in fiber content and the decrease of fiber diameter contributed to the improvement of the mechanical strengths of UHPGC. The flexural behaviors of UHPGC improved as the fiber volume and length increased, while the compressive and first crack strengths were affected by both curing conditions and fiber dosages as well. Different from Portland cement-based composites, the corrugated fibers with a higher deformation ratio added in UHPGC, had an inferior strengthening and toughening efficiency, while for straight fibers, those longer and smaller in diameter were more preferred. Finally, based on the previous research, a new one with adjustment and simplification was proposed for that of newly-developed UHPGC, and the fitted results had higher correlation coefficients (r²).