The effects of asphalt binder and granular material characteristics on foamed asphalt mix strength

This paper systematically studies the effects of asphalt foam characteristics and pulverized asphalt pavement (PAP) material attributes on foamed asphalt mix strength. A fracture face image analysis procedure was employed to quantify asphalt dispersion, which was key to establishing the relationships between material microstructural features and measured strengths. Foamability of asphalts was found to be one of the primary factors determining foamed asphalt mix quality. Foams with higher expansion ratios and longer half-life have better dispersion through granular materials, resulting in greater strength improvement. High fines contents in the PAP materials negatively affect mix strength by producing a continuous and weak unbonded mineral filler phase. The microstructural analysis found that typically unquantified physical, chemical and/or mineralogical characteristics of the PAP materials significantly affect asphalt dispersion quality and mastic strength. Therefore, the suitability of PAP materials and available binders for foamed asphalt stabilization should be evaluated for each individual project.