Influence of fiber type and fiber orientation on cracking and permeability of reinforced concrete under tensile loading

During the service life of structure, cracks developed due to various internal or external stresses. These cracks offer a preferential path for the ingress of water, gas and aggressive ions through the concrete. This increase of concrete's permeability promotes the structure deterioration. A good understanding of structure permeability is thus required to design durable structures. An innovative permeability device was used to measure the impact of fiber orientation and fiber type on the water permeability of high performance fiber reinforced concrete (HPFRC) tie-specimens submitted simultaneously to a uniaxial tensile loading. Specific casting techniques provided tie-specimens with three fiber orientations (favorable, average and unfavorable) that can be found in fiber reinforced concrete (FRC) structural elements. Experimental results showed average fibers angles relative to the loading direction of tie-specimens of about 39°, 42° and 54° respectively for the favorable, average and unfavorable orientations. As fiber orientation become less favorable (from 39° to 54°), the tensile strength (ft) of characterization specimens reduced up to 33%, while the increase in permeability (Kw) tie-specimens achieved 1990% at fixed load and 600% at fixed stress in the rebar. For HPFRC casted with the same procedure, synthetic fibers provided a lower efficiency to control cracking at material and structural scales, and to limit water permeability in comparison to steel fibers. The impact of fiber orientation is clearly more significant on water permeability of HPFRC than on their mechanical behavior. These results provides insights of the impact of fiber orientation on durability of reinforced FRC structures.