Multi-physical properties of a structural concrete incorporating short flax fibers

An experimental investigation was undertaken on the physical characterization of a flax fiber-reinforced concrete (FFRC) in both fresh and hardened state. The objective of this study is to provide guidance for the mix-design of these FFRC. The study was conducted from two points of views: improving the workability of the concrete in a fresh state and improving the flexural strength in the hardened state. Several parameters have been studied independently as fiber length, fiber content, or the paste content. The characterization of flax fibers highlighted a high water absorption capacity which must be taken into account for the concrete mix-design. In addition, the flax fibers significantly impact the compactness of granular skeleton. For the characterization of concrete, testing in the fresh state showed a significant decrease of the workability of concrete with the addition of flax fibers. However, the use of shorter fibers, allows to reduce this damaging influence on the fresh concrete workability. Moreover, increasing the paste content allows compensating this fluidity loss. In the hardened state, the increase of the fiber content enhances the flexural strength, but a decrease of the compressive strength is observed. A greater porosity of the concrete was also observed with the incorporation of flax fibers. An increase in porosity was also observed when increasing the paste content.