Analysis of Bitumen-Lignin Blends: A Statistical Exploration of Laboratory Mixing Variables for Bio-Pavements Applications

The use of lignin as a bio-based modifier in bitumen blends offers a sustainable and innovative solution to enhance asphalt pavement performance. While numerous studies have explored lignin-modified bitumen, each employs distinct mixing protocols without systematically analyzing the impact of key variables on material properties. Mixing is a critical step for scaling lignin use in real-world road engineering applications and merits detailed laboratory investigation. This study provides a novel contribution by examining the effects of laboratory mixing parameters—lignin content, mixing temperature, shear rate, and mixing time—on the properties of bitumen-lignin blends for bio-pavement applications. A factorial experimental design comprising 96 scenarios was employed to evaluate these variables. The engineering properties assessed included penetration, softening point, viscosity at 135℃ and 160℃, and penetration index. Rheological behavior was analyzed using a dynamic shear rheometer to measure the complex modulus and phase angle, while Fourier-transform infrared spectroscopy (FTIR) quantified chemical changes, such as carbonyl and sulfoxide group formations. Statistical analyses, including Univariable Analysis of Variance (ANOVA) and Multivariable Analysis of Variance (MANOVA), allowed the evaluation of the influence of the mixing variables, revealing the influence of the mixing variables on material properties. Based on the obtained results, a recommended mixing protocol to preserve lignin's beneficial properties includes using less than 30% lignin, a mixing temperature around 135℃, a shear rate between 4000 and 6000 rpm, and a mixing time of approximately 45 to 60 minutes.