Asphalt Binder Laboratory Short-Term Aging - Phase II

This study examined the effectiveness of laboratory short-term aging processes for warm mix asphalt (WMA) binders using response surface methodology (RSM) with various combinations of aging parameters: time, temperature, airflow, and binder weight. The research aimed to enhance understanding of aging parameter efficacy and propose a modified laboratory short-term aging protocol that accurately simulates plant short-term aging in WMA binders. Additionally, the study explored the potential of thermal simulation techniques to model the heat transfer within asphalt mixtures during the compaction procedure. To achieve these goals, three WMA mixtures produced at 135 ºC were collected from plants, and their asphalt binders were extracted and recovered. Virgin binders from the same projects were also obtained and two of them aged in a rolling thin film oven at different combinations of aging parameters, designed by RSM. High-temperature performance grade and carbonyl index were used as model responses to quantify laboratory aging levels. These parameters were also assessed in the plant extracted binders to establish target values. The statistical analysis revealed significant effects of time, temperature, and weight, as well as their interactions, on key rheological and chemical properties of binders, while the airflow rate effect within the studied range was found to be insignificant. Two distinct modified protocols for laboratory short-term aging of WMA binders produced at 135 and 165 ºC were developed, showing consistency with plant short-term aged binder results. The models were successfully validated using chemical and rheological assessments of a third binder aged with the proposed protocols. Thermal simulation results indicated that the average allowable time window for compaction increased slightly with the use of finer aggregates and thicker asphalt binder films around the aggregates. Using the available critical window of time for effective compaction ensures the compaction procedure is conducted within the optimal temperature range, leading to more durable pavement layers.