Poly (vinyl alcohol) fiber reinforced concrete: investigation of strain rate dependent interphase behavior with single fiber pullout test under quasi-static and high rate loading

A new single fiber pullout device was used to investigate interfacial debonding in the poly (vinyl alcohol) (PVA) fiber-cementitious matrix system under impact loading. For comparison, PVA fibers with two different surface states were used - as-received and after fiber finish removal by extraction in solvents. The indirect method was employed to determine the interfacial strength parameters, namely, the local interfacial shear strength, , and the critical energy release rate, G(ic), from the peak load values reached in the pullout test. For both fiber surface states, the and G(ic) values for high loading rates appeared to be considerably greater than the corresponding parameters determined by means of a quasi-static pullout test. This can be explained using a model based on Zhurkov's kinetic (thermal fluctuation) theory of the strength of solids, which also enabled to estimate the apparent activation energy for interfacial debonding. Its values (1.3eV for both as-received and treated fibers) evidenced formation of strong bonds between PVA fiber and the concrete matrix and the identity of debonding mechanisms for both fiber types. Finish removal decreased interfacial adhesion due to smoothing the fiber surface and reducing interfacial mechanical bonding.