relaxation behavior, which is indicated by high phase angle, is important at low temperatures [39]。 Changes of dynamic rheological parameters over a wide range of temperature or frequency also give information for the chemical composition of polymer modified bitumen。 Effect of aging, segregation of modifier and the con- sistency of good quality can be well distinguished。 The creep tests and relaxation tests done by DSR can be applied for ranking binder performance purpose。 The rates of creep and stress relaxation could be good indicators related to binder performance。

Mogawer used Superpave classification test to determine the performance grade of APJ binders [33]。 Two tested binders showed performance grades of PG88-22 and PG94-22 respectively。 Compared to a PG64-28 neat (unmodified) bin- der that is considered for local asphalt pavements, it can be seen that the high-tem- perature performance grade had been increased significantly。 However the low- temperature performance grade did not meet a minimum of —28 °C。 It was sug- gested that the APJ binder should have the same or lower performance grade at the minimum temperature to reduce the risk of thermal cracking and fatigue。

Fatigue and age embrittlement of the binder is believed to be important for joint performance。 Field measurement and numerical simulations indicated the joint material was subjected to cycled high stress/strain due to temperature fluctuations that results in fatigue damage。 Aging resistance, including short-term aging due to the installation process and long-term aging for field use should be evaluated since the asphalt binder will lose some of its ductility after aging。 The loss of ductility accelerates fatigue fractures that will likely produce tensile failures through the joint material over time。 The extensibility test at low temperatures is one of the most important tests for assessing the durability of joint binders。 Researches done by Hean indicated that the decomposition of SBS polymers in the binder can be as high as 26–63% at installation temperatures of 185–195 °C [27,28]。 Pre-aging pro- cess at the installation temperature should be carried out to investigate the change of binder properties before and after aging。 Traditional rolling thin film oven test (RTFOT) was found to fail to reflect the installation thermal aging process because strong air supply resulted in serious oxidation aging [27,28]。 Long term field mon- itoring of APJs was conducted using a high frequency rheometer [14]。 The damping and elastic constants were determined as indicators for the long-term influence of climate and aging on the material。 Measurement data showed that stiffening of joint materials occurred over years。 The elastic constant at 20 °C was increased about half within 3 years。

Table 4

Requirements on aggregate properties。

It is indicated that the temperature and time dependence of joint binder can be

well investigated by means of dynamic shear rheolometer。 The construction of mas- ter curves of complex modulus and phase angle can provide more information on the rheological properties of polymer modified binder。 The desired binder after modification should have the following response: at the range of low frequencies (high temperatures), the modulus should increase with  decreasing  phase  angle。 This  will  result  in  relatively  stiff  and  more  elastic  bitumen  for  rutting resistance。

On the contrary, bitumen after modification showing lower stiffness and higher

phase angle is needed at the range of high frequencies (low temperatures)。 Ample

110 L。 Mo et al。 / Construction and Building Materials 45 (2013)  106–114