Evaluation of the Minnesota Asphalt Mixtures Based on Balanced Mix-Design Approach

Abstract

The State Department of Transportation have started to put into practice performance tests as a part of the volumetric mix design process to evaluate asphalt mixtures performance, including the use of a balanced mix design (BMD) approach. This approach aims to improve asphalt mixture durability and stability and to better relate asphalt mix design requirements to field performance, as compared to only using the volumetric mix design approach. A BMD approach relates to field performance because it depends on standardized performance tests that have been correlated to distresses such as rutting, fatigue, and thermal cracking. In this study, the BMD approach was applied to four different asphalt mixtures designed by the Minnesota DOT (MnDOT) based on the volumetric mix design approach. The volumetric asphalt binder content (ACV) was determined for all mixtures. Asphalt mixtures 1 and 3 were designed with carbonate aggregate, while noncarbonate aggregate was used for asphalt mixtures 2 and 4. The nominal maximum aggregate size (NMAS) of Mixtures 1 and 2 was 12.5 mm, while 9.5 mm was used for Mixtures 3 and 4. The four asphalt mixtures were tested at three different asphalt binder contents each: ACV,ACV+0.5%, and ACV−0.5%. Three different cracking tests and one rutting test were performed for evaluation and determination of the allowable tolerance of asphalt binder content (AC) in each asphalt mixture. The cracking tests were the Illinois flexibility index test (I-FIT), indirect tension asphalt cracking test (IDEAL-CT), and disk-shaped compact tension (DCT) test were performed. The Hamburg wheel tracking (HWT) test was selected for rutting evaluation. For each asphalt mixture and based on each test, the balanced asphalt binder content (ACB) was determined and compared with ACV. The results showed the impact of AC on cracking and rutting resistance. For mixtures with a noncarbonate aggregate, the ACB was constant through all cracking and rutting tests and slightly different from ACV. In contrast, the ACB of mixtures with a carbonate aggregate had a higher deviation from ACV. Mixtures 1 and 2 were more resistant to rutting comparing to Mixtures 3 and 4.