Properties of modified cotton stalk fiber asphalt mortar and its mixture

Objective To promote the application of environmentally, friendly and efficient admixtures in highway construction, this study investigates the influence of modified cotton stalk fiber on properties of asphalt mortar and its mixture, and analyzes its functional patterns. Method First, softening point test, cone penetration test, dynamic shear rheometer test, and bending beam rheometer test were carried out to evaluate the properties of asphalt mortar with different fiber contents. Second, Burgers viscoelastic model was applied to fit bending beam rheometer test data, obtaining four model parameters and viscoelastic indicators variation. Third, the high-temperature stability, low-temperature crack resistance, and water stability of AC-13 asphalt mixture were tested through rutting test, low-temperature bending test, immersion Marshall test, and freeze-thaw splitting test. Finally, long-term durability of modified cotton stalk fiber asphalt mixture was studied by using an intelligent pavement performance monitoring device. Result The asphalt softening point reached its maximum value with 2% fiber content; this fiber content also most effectively reduced the phase angle and increased the rutting factor of asphalt mortar. The relaxation time and retardation time showed increasing and decreasing trends respectively with the increase of fiber content. The negative influence on low-temperature performance was minimized with 2% fiber content. The asphalt mixture with modified cotton stalk fiber exhibited the best overall road performance. Compared with cotton stalk fiber asphalt mixture, its dynamic stability, maximum flexural tensile strain, residual stability, and freeze-thaw splitting strength ratio increased by 11.8%, 12.1%, 5.7%, and 6.5% respectively; compared with lignin fiber asphalt mixture, these values increased by 8.1%, 6.9%, 0.9%, and 4.9% respectively. Additionally, the rut depth of modified cotton stalk fiber mixture was the smallest, showing 53% reduction compared with the fiber-free mixture. Conclusion Modified cotton stalk fiber asphalt mixture demonstrates good road performance. The fiber could be considered a suitable paving fiber for asphalt pavement applications.