Measuring and modifying interface properties of PVA fibers in ECC matrix

A single fiber pullout test was used in this study to measure the bond properties of polyvinyl alcohol fibers that are available at various diameters in a mortar matrix. Despite short fiber embedment lengths, the small diameter fibers ruptured during the pullout tests. However, it is shown that even if full fiber pullout is not achieved, it is still possible to determine a chemical debonding energy, G(d), and an initial interfacial frictional bond strength, tau (o). Despite high G(d) values, the fibers did not rupture during the fiber chemical debonding process, but during fiber pull-out, a strong slip-hardening effect, characterized by the high values of the slip-hardening coefficient, beta, induced severe abrasion damage visible under scanning electron microscope on the fiber surface. As a consequence, when the fiber apparent tensile strength was exceeded, fibers ruptured by delamination. Finally, an attempt was made to lower the values of the bond properties to minimize fiber rupture during pullout. This goal was partially achieved by applying an oil coating on the hydrophilic polyvinyl alcohol fiber surface to reduce any strong fiber/mortar interaction.