Relating Laboratory and Natural Aging of Asphalt Mixtures Based on Low-Temperature Performance

Thermal cracking of asphalt pavements is primary distress in cold regions. The Bending Beam Rheometer (BBR) can be used as a thermal cracking prediction tool for asphalt mixtures based on AASHTO TP 125. This study investigates the change in the low-temperature performance after aging asphalt mixtures in both indoors (forced-draft oven in the laboratory) and outdoors (open environment on a roof). The BBR thin-beam specimens aged outdoors were tested for up to 5 years. As the BBR test is nondestructive, the same thin-beam mixture specimen can be tested frequently to obtain its aging information. Therefore, after 5 years of aging, a relationship between laboratory aging and natural aging can be obtained. An Aging Index was proposed in this study to differentiate among mixture characteristics and aging methods. It is a measurement of the mixture-specific sensitivity to the aging of the material. It was found that the laboratory aging methods used in this study would simulate approximately 5 years of aging in the field, which is similar to the AASHTO R30 protocols. Successful application of this idea can connect AASHTO TP125 with the AASHTO R30 aging protocols and make BBR testing applicable as a performance test in the field. (C) 2022 American Society of Civil Engineers.