The Effect of Combinations of Treated Polypropylene Fibers on the Energy Absorption of Fiber-Reinforced Shotcrete

Abstract

The dosage of fiber reinforcement in shotcrete increases the toughness and tensile stress and depends on the fibers’ aspect ratio, toughness and energy absorption. Polypropylene (PP) fiber is hydrophobic, causing weak bonds to the cement matrix. One of the causes of the aforementioned is the “saturated hydrocarbon” classification of PP fibers. Their chemical structure is such that it is deprived of forming acid–base reactions needed at the interface of fiber–cement matrices. When surface treatment is applied, the bond can be increased, thus improving the load transfer mechanism. This increases the composite matrix’s flexural, tensile strength and energy absorption characteristics. This research project compared the residual loads and energy absorption characteristics of two types of individual treated PP fibers (3000D and 450FT) to those yielded when combining the two fiber types, as described in the European Federation of National Associations Representing for Concrete (EFNARC) document. The fibers tested were surface treated by a process called Crypsination. The results indicate that the performance of the weaker single fiber was increased, when the PP treated fibers are combined. The combination of treated fibers yielded sufficient energy absorption to satisfy the toughness classification of EFNARC.