Deterioration of bonding capacity of plasma-treated polymer fiber reinforcement

Bonding between reinforcing fibers and a brittle cementitious matrix is the key ingredient for a ductile concrete production. Oxygen plasma treatment proved to be a promising technique for increasing the fiber surface adhesion to liquids, but a question about the stability of activated bonding when exposed to atmospheric conditions arises. We present a comprehensive study on deterioration of such treatment in time for different fibers commonly used as dispersed reinforcement. A microscopy investigation allowed to observe changes in the fiber surface morphology, while the changes in chemical bonds were detected by XPS analysis. To quantify the impact of plasma treatment and its deterioration, water contact angle measurements and pull-out tests were carried out. The results indicate that the exposure to atmospheric conditions has a negligible impact on fiber bonding, because surface roughening plays a major role. Therefore, fibers need not be incorporated into a concrete mix immediately after their treatment.