Performance characterization of hot in-place recycled asphalt mixtures

Despite the widespread use of in-place recycling, limited information is available in the literature on in situ and laboratory properties of materials placed through in-place recycling. The main objectives of present study were to investigate the in situ recycled material characteristic that includes the potential of asphalt mixtures for permanent deformation, fatigue cracking, and low-temperature cracking, and the effect of a special technique of hot in-place recycling and rejuvenation on asphalt binder rheological properties. To accomplish these objectives, a two-phase experimental program was designed to determine the performance-related parameters of 100% in-place recycled mixtures using one of the in-place recycling techniques in which overlay is not needed. The experimental program included the measurement of mixtures' mechanical properties and binder rheological properties. The present study revealed that the stiffness of the asphalt mixtures after recycling had increased compared to that before recycling. In general, specimens exhibited a low permanent deformation potential of 2-3 mm after 20,000 loading cycles by using the Hamburg wheel-track test. Stable crack propagation could not be obtained in the fracture tests at -12°C, which indicates the asphalt mixtures' brittleness at that temperature. Asphalt binder and aggregates, extracted from the samples as collected at various stages of construction, were characterized to assess the effect of the recycling process on mixtures' properties. Results obtained from the asphalt binder frequency sweep test indicate an increase in the modulus value, which was primarily caused by a heating process at surface layer. This increase in the modulus value of asphalt binder was efficiently compensated by an addition of a rejuvenator. Alternative additives or rejuvenators may also be considered to improve blending and compatibility between the old and new binder, and to reduce the mixture's stiffness to avoid any possible premature deterioration. The selected rejuvenator should achieve several goals, including complete blending with existing binder and reducing the combined binder performance grade below the binder performance grade of existing mixes.