Cracking resistance of fiber reinforced asphalt concrete at −20 °C

The reinforcing effect of steel fibers in asphalt concrete is investigated through indirect tension tests conducted at −20 °C. Control specimens with no fibers, and test series with carbon and polyvinyl alcohol fibers are also carried out for comparison. Cracking resistance, indirect tensile strength, fracture energy, and post-cracking energy are obtained from the tests. The effects of fiber diameter, length, deformed shape, and content of steel fibers are investigated in order to provide fundamental understanding of the reinforcing mechanisms mobilized during fiber pull out and select proper reinforcing fibers. The test results demonstrate that the low temperature cracking resistance of asphalt concrete can be significantly improved by adding the proper type and amount of steel fibers, but that the improvements in mechanical properties are sensitive to fiber length and diameter. The indirect tensile strength and toughness of fiber reinforced asphalt concrete increase with an increase in fiber length within the 0.2-0.4 mm diameter range. Mechanical deformations of the fibers, e.g. presence of a hook or twisting, can induce further improvements in post-cracking energy absorption. Compared to unreinforced specimens, fiber reinforced specimens show up to 62.5% increase in indirect tensile strength, and up to 370% and 895% improvements in fracture energy and toughness, respectively. A hypothesis that explains the fiber reinforcing mechanism in asphalt concrete is proposed and critiqued based on the test data.