Effect of surface treatment on the post-peak residual strength and toughness of polypropylene/polyethylene-blended fiber-reinforced concrete

This study involved an experimental investigation into the improvement of mechanical properties of fiber-reinforced concrete (FRC) utilizing chemically treated polypropylene/polyethylene fibers. Four types of chemical surface treatments were examined: two types of chromic acid (Types B and C), potassium permanganate (PP), and hydrogen peroxide solutions. Untreated and treated fibers were added at 0.32% by volume of concrete and also at 0.50% for the best treatment technique. Compressive and flexural strength were measured to quantify improvement. It was found that there were no significant differences in compressive strength. Type B chromic acid solution was found to be the most effective technique in improving the flexural strength of FRC resulting in average increases of 8.9% and 17.6% for peak and residual strengths, respectively, compared to nontreated fibers. While not as effective as plasma treatments, further research may be warranted for chemical treatments. Surface wettability of the treated fibers was measured by contact angle with water. The contact angle was found to have no correlation to the toughness. The higher volume of fibers, both treated and nontreated gave higher residual strength and toughness; however, surface treatment did not significantly enhance mechanical properties.