Effect of Microbial Activity on the Rheological Behavior of Asphalt Under Thin-Film Inoculation

Microorganisms present in asphalt pavement service environments can alter the composition of asphalt through metabolic activities, thereby affecting its rheological properties. To investigate this influence and compare performance variations across asphalt types, two asphalt-degrading bacterial strains were isolated from in-service pavements. Following 16S rRNA gene sequencing and phylogenetic analysis, the strains were identified as Pseudomonas putida and a putative novel species within the Citrobacter genus. Using a custom-designed thin-film inoculation system, the performance evolution of base asphalt and styrene-butadiene-styrene (SBS) modified asphalt was systematically evaluated after microbial activity periods of 5, 10, and 15 days. Conventional property tests and multi-temperature rheological analyses (temperature sweep, multiple stress creep recovery test, linear amplitude sweep, 4 mm DSR) were conducted. Results demonstrated that microbial action reduced penetration, elevated softening point, and decreased ductility in both asphalt types, with more pronounced changes observed in base asphalt. High-temperature rheological parameters (G*/sinδ), recovery rate, and non-recoverable creep compliance indicated compromised resistance to permanent deformation. SBS-modified asphalt substantially mitigated these detrimental effects. Fatigue life of base asphalt decreased overall with periodic fluctuations, whereas SBS-modified asphalt exhibited superior fatigue stability: after an initial decline at 5 days, performance recovered and stabilized between 10 and 15 days. Low-temperature performance showed slight improvement in base asphalt, while SBS-modified asphalt demonstrated significant enhancement during later activity stages.