Effect of Cross Sectional Shape of Polypropylene Fibers on Flexural Toughness of Composites and Fiber-to-Cement Matrix Adhesion

Abstract

Cement based material are weak in flexure in comparison to compression. Fibers have been used for 100 years ago in an industrial process (i.e. Hatschek machine) to improve flexural and tensile strength of cement based materials. Many researches have been performed to define the best fiber condition such as fiber type, length, and diameter. A few investigations have been done on the effects of fiber cross section on fiber-cement bonding and flexural strength. In this research, polypropylene (PP) fibers which have diversity in cross section were selected and used as reinforcement in cementitious composites. Fibers characterized for cross sectional shape and average surface area. Flexural strength of the specimens at different fiber volume contents was evaluated. Also, the adhesion of the fibers (with different cross sections such as hollow, delta and circular) was measured using the pull-out test. Results showed that the cross section has an important effect on bonding of the fibers to cement matrix and flexural toughness of the specimens. It was observed that the hollow fiber that has the biggest lateral surface showed the highest pull-out load, and the delta fiber showed best flexural behavior.