An assessment of the fracture parameters of ultra-high-performance fiber-reinforced geopolymer concrete (UHPFRGC): The application of work of fracture and size effect methods

Abstract

This research aimed to study the effects of a certain volume of fiber on the fracture characteristics of ultra-high-performance geopolymer concrete (UHPGC) based on the ground granulated blast furnace slag and silica fume. To this end, seven mixtures were selected and three different volume fractions were used in them. Three mixtures were used to study the effect of steel fiber (SF) volume fraction and the other three mixtures were used to assess the effect of replacing 0.25% of the SF volume fraction with polypropylene fiber (PPF). Fracture parameters, including total fracture energy (GF), initial fracture energy (Gf), characteristic length (Lch), the effective size of process zone (Cf), brittleness number (β), fracture toughness (KIC), and critical effective crack-tip-opening displacement (δc) were calculated by the work of fracture (WF) method and size effect (SE) method, and the results were compared. Furthermore, the relationship between the fiber’s volume fraction with GF, Gf, Lch, Cf, and KIC was individually obtained in the form of polynomial functions. For this purpose, 84 notched beams were tested by three-point bending. The results show that increasing SF volume fraction significantly increased the fracture properties of UHPGC and increased fracture energy and ductility. On the other hand, partial replacement of SF with PPF slightly affected fracture characteristics adversely versus the specimens containing only SF. Finally, the GF/Gf ratio, which is an important parameter in fracture mechanics, was calculated. This ratio was increased with increasing fiber fraction so that it reached from 2.84 for UHPGC to 13.64 for UHPFRGC.