Influence of silica fume and polypropylene fiber on fracture properties of concrete composite containing fly ash

A parametric experimental study has been conducted to investigate the effect of silica fume and polypropylene fiber on the fracture properties of concrete composite. By means of three-point bending method, the fracture toughness, fracture energy, effective crack length, maximum mid-span deflection, critical crack-opening displacement, and maximum crack-opening displacement of the specimen were measured, respectively, and the relational curves between the vertical load and the mid-span deflection (P_v–δ), crack mouth-opening displacement (P_v–CMOD), and crack tip-opening displacement (P_v–CTOD) were obtained. The results indicate that silica fume and polypropylene fiber both have great effect on the fracture parameters and relational curves of the three-point bending beam specimen. When the content of silica fume increases from 0% to 3%, and the fiber volume fraction increases from 0% to 0.12%, the fracture parameters gradually increase and the fracture relational curves become plumper and plumper with the increase of silica fume content and fiber volume fraction, respectively. However, the fracture parameters begin to decrease and the curves become thinner and thinner after the silica fume content exceeds 3%. It seems that the silica fume contributed well to the improvement of fracture property of concrete composite only when its fume content does not exceed 3%. Furthermore, the capability of polypropylene fiber to resist crack propagation of concrete composite containing fly ash and silica fume appears to become stronger and stronger with the increase of fiber volume fraction with the fiber volume fraction not beyond 0.12%.