Development of A Mixing Protocol for Biochar-based Carbon Neutral Binder

Abstract: Incorporating biochar, generated during bio-based energy production, into asphalt pavement reduces the construction industry's carbon footprint by trapping carbon within the infrastructure. Carbon remains stable in biochar structure for long periods of time and enhances environmental sustainability. Generally, biochar is added to the asphalt binder using wet process during the production of asphalt mix. Due to the variation of material properties, there is a possibility of phase separation between asphalt binder and biochar during storage. This study was focused on developing a protocol for mixing asphalt binder and biochar that will provide uniform blending. Also, the rheological properties of the binder blends with biochar were investigated. For this purpose, biochar was produced by converting switchgrass biomass using a pyrolysis oven. Binder blends were prepared by mixing a PG 64-22 binder from a commonly used Oklahoma source with biochar at 0, 2, 4, and 6% (weight % of the total unaged binder) using a high shear mixer. Three different mixing protocols were evaluated in this study by varying the mixing temperature, speed and time. The blending efficiency of different mixing protocols were evaluated by using the Cigar Tube test following the ASTM D7173 test method. The Dynamic Shear Rheometer (DSR) tests were conducted on the bottom, middle and top sections of the Cigar Tube specimens to determine the differences in shear modulus and identify the protocol that produces uniform blending. In addition, the effect of the increase in biochar content on the high- and low-temperature rheological properties of the binder blends were determined.