Effect of synthetic fiber surface treatment on the post-crack residual strength and toughness of fiber reinforced concrete

This research involves an experimental investigation into the improvement of bonding characteristics between a mixture of polyethylene/polypropylene fibers and concrete comparing various chemical and physical surface treatments and their effect on the mechanical properties of the fiber reinforced concrete (FRC). For the chemical surface treatment, several techniques of chemical etching of the fiber's surface were used, such as two types of chromic acid solutions, potassium permanganate, and hydrogen peroxide solutions. For the physical surface treatment, UV treatment and a combination of UV and Ozone treatment were used. Non-treated and treated fibers were added at 0.32% by volume and 0.50% for the best treatment method. Compressive, flexural strength and contact angle were measured to quantify bond improvement. Among the chemical treatment techniques, chromic acid solution type B was found to be the most efficient technique versus potassium permanganate which had negative effect on the bonding strength between fibers and concrete. Investigations of physical treatment techniques showed using UV does not have a significant change on the bonding strength, but 10 minute exposure of fibers to the UV lamp in presence of ozone gave the best result in bonding of fibers. As a cumulative result, using the chemical treatment was found to be a more efficient technique rather than the physical treatment in surface modification of fibers. The contact angle was found to have no correlation to the toughness. The higher volume of fibers gave better properties than the surface treatment techniques indicating surface treatment may not be an economical alternative