Cold Mix Asphalt (CMA) is highly susceptible to moisture damage, manifesting itself in stripping, raveling, rutting, and cracking faults. This study aimed to tackle this concern with bio-treatment. In doing so, this effort investigates the efficacy of microbial calcium carbonate precipitation in (i) the post-biostrengthening (PBS) of mechanical properties and (ii) bio-remediation (BR) of moisture damage in cold-mix asphalt emulsion mixtures. To study the post-bio-strengthening potential, a set of cold-mix asphalt specimens was sprayed and injected with bacterial culture medium and nutrient solution to induce calcium carbonate precipitation for the purpose of post-strengthening. Then, the effect of curing times of 7, 14, 28, and 56 days on the fixation of precipitates in the mixtures was examined. To study the bio-remediation potential, another set of cold-mix asphalt specimens was subjected to a freeze-thaw cycle (modified Lottman test) intended to cause moisture damage and bacterial culture medium and nutrient solution were injected, afterward. For these specimens, the appropriate curing time of the fixation process for the bio-remediation was determined. All specimens were subjected to the destructive and non-destructive tests of mechanical properties, semi-circular bending (SCB), moisture susceptibility and also Cantabro test to assess indirect tensile strength (ITS), Tensile strength ratio, Indirect tensile fracture energy ratio, percent of toughness loss, crack propagation by SCB fracture energy, ultrasonic pulse velocity ratio, electrical resistivity, as well as the abrasion resistance. The Analysis of Variance (ANOVA) of the results was performed at 95% confidence level. A Field Emission Scanning Electron Microscope (FESEM) examination was also performed to study the microstructure and precipitates formed in the mixtures. The results showed that the post-bio-strengthened specimens had significantly better mechanical and resistance to moisture damage properties than those of control. The moisture-damaged specimens that underwent the bio-remediation also showed significant improvements in mechanical properties, and in some cases were similar to the undamaged control specimens. The results indicate that microbial calcium carbonate precipitation (MCP) can serve as an effective and sustainable method for both post-strengthening and remediation of cold mix asphalt mixtures.

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