Effects of microbial degradation on morphology, chemical compositions and microstructures of bitumen

Bitumen is usually suffered from microbial degradation when bituminous pavement is under the shady, humid or polluted environments, leading to the microbial aging of bitumen. To further understand the microbial aging of bitumen, such typical microorganisms on bituminous pavement as bacillus licheniformis (BL), bacillus subtilis (BS) and pseudomonas aeruginosa (PA) were selected to degrade bitumen. Then effects of microbial degradation on morphology, chemical compositions and microstructures of bitumen were discussed. Results indicate that the microorganisms preferentially regard light components in bitumen as nutrient source to propagate on bituminous surface, forming some potholes. Microorganisms further penetrate into the interior of bitumen, resulting in the microbial aging of bitumen. Further, BS and BL have a stronger degradation ability to light components, while PA can degrade more complicated structural components in bitumen. The molecular weight distribution of aged bitumen becomes more concentrated. However, the microbial aging of bitumen does not promote the conversion of unsaturated bond to C=O group, and also does not increase the content of S=O group. Finally, the microbial aging damages the continuity of bituminous surface elevation, and the whole roughness of aged bituminous surface is lowered. The three microorganisms show the faster aging rates to light components, and are difficult to degrade resins and asphaltenes. BS has a higher prophase activity and a faster aging rate to bitumen than BL at the early stage. The propagating rate of PA is between those of BS and BL, and its prophase activity and aging rate are relatively stable. This study provides an insight into the microbial aging mechanism of bitumen. (C) 2020 Elsevier Ltd. All rights reserved.