Mechanical properties and behaviour of high-strength plain and hybrid-fiber reinforced geopolymer composites under dynamic splitting tension

Abstract

Geopolymer materials have been of particular interest to the construction industry due to their environmental benefits. However, their behaviour has rarely been investigated under dynamic loadings, although it is of fundamental concern to assess their vulnerability against higher loading rates. In this study, the dynamic tensile properties of a newly fabricated high-strength ambient cured geopolymer material and fiber reinforced geopolymer composites (FRGC) are presented. Since geopolymers are intrinsically brittle, novel equal-part blend of hooked-end and spiral-shaped steel fibers at two different fiber volume fractions and hybrid steel-polyethylene combination were used to reinforce the geopolymer matrix. The quasi-static splitting tensile tests were performed using a 300 KN displacement controlled Shimadzu test machine, while a modified Ø100-mm split Hopkinson pressure bar (SHPB) apparatus was used to conduct the dynamic splitting-tensile tests. A high-speed camera was used to capture the fracture development processes and crack-opening of different types of FRGC. The test results show that under quasi-static splitting tension, the unreinforced geopolymer exhibited minimal tensile strain capacity. With the addition of steel fibers and hybrid steel-polyethylene fiber reinforcement, the energy absorption capability of FRGC samples was significantly improved. The dynamic tests reveal the strong strain rate dependency and prominent tensile strength enhancements for all composites, although unreinforced geopolymer samples were more sensitive to the strain rate effect within the considered test range. A comparison between the test data and modified CEB guidelines reflect the non-suitability of code formulae to establish the dynamic increase factor (DIFft) relation for geopolymers. Based on the test data, empirical DIFft relationships are proposed for unreinforced and different types of FRGC samples. It is also indicated by image analyses that the excellent bonding of spiral steel fibers with the geopolymer matrix is befittingly complemented by polyethylene fibers to maintain the material integrity.