An experimental study on fatigue properties of emulsion and foam cold recycled mixes

Asphalt emulsion and foam asphalt cold recycling techniques are widely used in asphalt pavement rehabilitation in China. However, after a review of literature, no comparisons of fatigue properties for cold recycled mixes were found. The objective of this study was to determine the fatigue properties of asphalt emulsion and foam asphalt cold recycled mixes using the Nottingham Asphalt Tester (NAT) (Cooper NU-14 tester). In this research, foam and emulsion cold recycled mixes were evaluated for indirect tensile strength, stiffness modulus at three temperatures and four stress levels, and fatigue life at 15 °C and four stress levels. In addition, the law of displacement (deformation) and crack development were also analyzed during the fatigue testing. The results indicated that stiffness modulus decreased with increasing temperatures and stress levels. Through indirect tensile fatigue testing at different stress levels, foam mixes displayed a higher fatigue life at low stress levels, while emulsion mixes displayed a higher fatigue life at higher stress levels. According to the law of vertical displacement (deformation) and crack development, emulsion mixes included three states of displacement development, while foam mixes included two stages of displacement development. Qualitative analysis indicated that emulsion cold recycled mixes showed a plastic fatigue failure, due to its visco-elastic characteristics, while fatigue damage of foam asphalt cold recycled mixes showed a brittle fracture.