Corn straw fiber-modified asphalt for high-RAP recycled PAC-13 mixtures: preparation, rheology, and pavement performance

Introduction Open burning of corn stalks causes environmental pollution, while recycled asphalt mixtures with high reclaimed asphalt pavement (RAP) content require adequate binder performance to maintain pavement durability. This study evaluated corn stalk fibers as bio-based modifiers for high-RAP recycled PAC-13 mixtures. Methods Corn stalk fibers were prepared using physical-mechanical and chemical alkali treatments, and treatment conditions were evaluated using Fourier-transform infrared spectroscopy and thermogravimetric analysis. Asphalt binders containing 0.4%–2.0% fiber were tested using a dynamic shear rheometer and a bending beam rheometer. The selected binder was used to prepare recycled PAC-13 mixtures containing 20%–60% RAP, and their pavement performance was assessed. Results Chemical alkali treatment with 3% NaOH for 50 min produced fibers with superior thermal stability and oil absorption capacity. The optimal fiber content was 1.2%, improving the binder’s high-temperature shear resistance and low-temperature stress relaxation. As RAP content increased, optimum binder content, Marshall stability, dynamic stability, moisture resistance, and low-temperature crack resistance declined, while air void content increased. At approximately 40% RAP, all key performance indicators met the relevant technical specifications. Discussion Under the materials and experimental conditions investigated, approximately 40% RAP is the recommended upper limit for corn stalk fiber-modified recycled PAC-13 mixtures.