Investigation of the mechanical and physical properties of bio-modified cold asphalt emulsion mixtures by microbial carbonate precipitation

Abstract

The effects of Microbial Carbonate Precipitation (MCP) on physical and mechanical properties of Cold Asphalt Emulsion Mixtures (CAEMs) have been investigated. MCP method was performed on CAEMs by two scenarios: (I) Bio-deposition treatment of aggregates and, (II) using a medium culture containing bacteria and urea-CaCl2 nutrient solution as a replacement for optimum water content. Additionally, in the second scenario, the effect of different curing durations (7, 14, 28 and 56 days) on the mixtures’ properties has been examined. X-Ray Diffraction, Fourier-Transform Infrared Spectroscopy, Atomic Force Microscopy and FE-SEM technique tests were employed to evaluate the formation of CaCO3 precipitation, micro-roughness of aggregates’ surface and the structure of bio-modified CAEMs. The physical properties, and mechanical properties including ultrasonic pulse velocity, dynamic modulus, indirect tensile strength, fracture energy and resistance to crack propagation (semi-circular bending test) were measured. Results indicated the formation of CaCO3 precipitations and increase of roughness on the surface of treated aggregates. Significant improvements (p-value < 0.05) were observed in the mechanical properties of CAEMs of first and second scenarios, however, these improvements are higher in the CAEMs of first scenario (p-value < 0.05). Findings revealed that MCP method can significantly improve the mechanical properties of CAEMs. But, it doesn’t significantly affect their physical properties.