Laboratory Characterization of Stone Mastic Asphalt Mixtures using Simple Performance Test Protocols

Abstract

Rutting and fatigue in flexible pavements are one of the common distresses manifested on national highways of Pakistan. Various factors are associated with these distresses including but not limited to overloading, high temperatures and empirical design approach used for structural design. Stone mastic asphalt (SMA) using cellulose fiber is considered effective solution in heavily trafficked areas because of the larger single size aggregate that can be used with the increased bitumen thus controlling rutting susceptibility. This study investigated the dynamic response and rutting behavior of three SMA mixtures selected on basis of nominal maximum aggregate size (NMAS): 25 mm, 19 mm, and 12.5 mm using cellulose fiber 0.3% of the total SMA mixtures aggregate. Superpave gyratory specimens were fabricated and subjected to dynamic modulus |E*| and Flow tests (Flow Number, FN and Flow Time, FT) using asphalt mixture performance tester (AMPT). The |E*| test results were employed to develop stress dependent master curves for each mix which indicated that SMA mixture of NMAS of 19 mm is relatively stiffer than other tested mixtures. Also, fatigue parameter derived from dynamic response and phase angle was evaluated and results revealed that 25 mm mix has better resistance to fatigue than other tested mixtures. Non-linear regression model specifications were used to predict strain as function of loading cycles. The models of flow number and flow time test result values showed that the predicted and observed outputs of 25 mm SMA mixture were found appropriate and exhibited excellent strength against rutting characteristics. The study results help in understanding the performance and behavior of SMA mixtures under varying simulated temperature and stress level variations.