Evaluation of hybrid steel fiber reinforcement in high performance geopolymer composites

In this paper, cement free high performance alkali activated slag-fly ash composites are designed by applying the modified Andreasen and Andersen particle packing model, and steel fibers of two lengths are applied for strength reinforcement and shrinkage compensation. The influence of the fiber length, dosage and hybrid on the fresh behavior, compressive strength, stress–stain behavior under flexural load, porosity and drying shrinkage are evaluated, and the gel structure of this blended alkali system is also identified. The results show that by applying the hybrid fiber together with the particle packing design approach, a compressive strength of around 100 MPa can be achieved with a w/p ratio of 0.4. The addition of steel fiber slightly decreases the slump flow and increases the porosity, but effectively inhibits the drying shrinkage and improves the stress–stain behavior. The hybrid usage of long and short fiber shows a synergetic effect and leads to the optimum strength. The steel fiber reinforcement is beneficial for the application of alkali activated materials.