Aging behaviors of bitumen degraded by the microbial consortium on bituminous pavement

Abstract

As bituminous pavement is under the shady, humid or polluted environments, the bitumen undergoes the microbial degradation by different microorganisms to cause the aging. To understand the microbial aging of bitumen degraded by multiple microorganisms, the typical bacillus licheniformis (BL), bacillus subtilis (BS) and pseudomonas aeruginosa (PA) were selected to compound three microbial consortia in different proportions, and cultured in three culture mediums. A more suitable culture medium for the three microbial consortia is selected. The changes in microscopic morphology, components, molecular weight distributions, functional groups and micromechanical properties of aged bitumen were discussed. Results indicate that the peptone content change of culture medium obviously affects the propagation of microbial consortia. The prepared culture medium II meets the propagation requirements of the three microorganisms, improving their degradation ability. Additionally, the microbial consortia preferentially degrade bituminous light components as their nutrient sources, and show weak degradation ability to macromolecular components, producing potholes with layer structures on bituminous surface. Moreover, the smaller molecules are decreased, but the macromolecules are increased in aged bitumen. The molecular weight distribution of aged bitumen is narrowed. BS, BL and PA in the microbial consortium of S2 show better synergistic effect to efficiently degrade bitumen than those of S1 and S3. Finally, the carbonyl and sulfoxide contents are not changed obviously, but the methylene content is decreased to reflect the aging results of bitumen. The maximum adhesive force of aged bitumen is lowered to cause the decrease in adhesion work, reflecting the decrease in bituminous viscidity. The elastic modulus of bitumen shows an increasing trend as the aging duration is prolonged. The elastic modulus of aged bitumen by the microbial consortium of S2 is higher than those by S1 and S3. This study provides an insight into the microbial aging mechanism of bitumen by multiple microorganisms.