Long-term performance of flexible pavements with cold-recycled asphalt base layer

Abstract

Cold recycling with emulsified or foamed asphalt has been widely used in China to convert the existing asphalt surface layer to an asphalt base layer. A new asphalt surface layer between 12 and 18 cm is then paved. Since these semi-rigid pavements were originally built with cement treated base, this reconstruction practice has resulted in a special pavement structure: cement treated subbase + cold recycled asphalt base + new asphalt surface. This paper reports the long-term performance of such pavement structure on two expressways located in Jiangxi, China. In-situ distress survey and coring were conducted, as well as data collection of traffic and load spectra. Laboratory testing was then carried out on materials collected from the site. Numerical modelling was also conducted to investigate the possible influence from different materials and design options. Results from this study indicated that the main reason of premature failure of this type of pavement structure was the weakening and fatigue of the cold-recycled asphalt base layer. Poor quality control during construction might be the cause since the air voids of the cold-recycled base layer was found to be much higher than the limit. Structural analysis showed that increasing the new asphalt surface layer from 14 cm to 16 cm on top of a 12 cm cold-recycled asphalt base layer could increase the fatigue life and traffic endurance (in terms of equivalent single axle load) 1.6-3.2 times. Therefore, it was concluded that increasing the thickness of the new asphalt surface layer could significantly improve the long-term performance of flexible pavements with cold-recycled asphalt base layer.