The recent endeavor toward a bio-based economy in the U. S. leads to more attention to converting organic matters into bio-fuels. Efforts have been made to look for practical applications for bio-char, a carbonaceous by-product from converting plant matters to bio-fuels through pyrolysis. Bio-char is considered to be able to use as an asphalt binder modifier due to its carbon nature and morphology. In this study, bio-char derived from switchgrass through different types of pyrolysis were tested as bio-modifier for asphalt binder. A commercially activated carbon was utilized for comparison. All the carbonaceous additives were incorporated into one commonly used asphalt binder at different concentrations in order to obtain the optimal content. The samples were tested in the laboratory for their rheological characteristics, rutting and fatigue performance and ductility properties. Highest treatment temperature (HTT), pyrolysis method, particle size of bio-modifier and modifier content were investigated to achieve the optimal modification effect. It was found that bio-char was capable of reducing the temperature susceptibility and significantly increasing the rutting resistance of the asphalt binder. The addition of the bio-char showed little effect on the fatigue and cracking resistance, with the best fatigue and cracking resistance found on the bio-char with finer particles (-75 mu m) produced at lower HTT (400 degrees C) and lower heating rate (15 degrees C/min). Based on the testing results, bio-char appears to be a more effective binder modifier than commercially activated carbon within addition of 10 wt.%. (C) 2014 Elsevier Ltd. All rights reserved.