Evaluation of Optimum Fiber Length in Fiber-Reinforced Asphalt Concrete

Cracking is one of the most common distresses in asphalt pavement. Because asphalt concrete is relatively weak in tension, synthetic fibers have shown to increase its tensile strength and, therefore, reduce the chance of cracking. An approach was used in this study with the aim of evaluating the interaction between fibers and asphalt mastic and the fiber distribution in asphalt concrete. Three types of aramid fibers and two types of nylon fibers were used. A pullout test was used to determine the typical shear bond strength between fibers and the asphalt mastic. The bond strength obtained from the pullout test was then used to calculate the minimum fiber embedded length on each side of the crack in order for the fiber to reach its full capacity before being pulled out. Of course, increasing fiber length increases the chance of bridging cracks considering the random distribution of fibers in fiber-reinforced asphalt concrete (FRAC) and the random orientation of fibers relative to cracks. On the other hand, increasing fiber length may result in uneven distribution of fibers in the FRAC. Fiber extraction and recovery tests were then used to determine the dispersion of aramid fibers in the FRAC with different fiber lengths. The study showed that aramid fibers in the order of 20 mm would provide a good bond with the asphalt mastic and result in reasonable dispersion in the FRAC. The uniaxial fatigue test and flow number test were also performed on FRAC with different aramid fiber lengths. The 19-mm fibers also showed better performance test results than the 10- and 38-mm fibers. A similar length is recommended for the Nylon 1 fibers based on the bond properties only. Longer Nylon 2 fibers are recommended, but caution needs to be taken to avoid uneven fiber dispersion in the FRAC.