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Polyethylene-based modification for asphalt is more and more widely used in paving engineering to deal with growing rutting distress on road pavement. The internal structure of polyethylene (PE) and the resulting asphalt are of interest due to their great influences on performance of pavement. This study investigated the correlation between polyethylene structure and asphalt performance. The polyethylene considered in this paper incorporates high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE). The influence of various PEs on rheological properties of asphalt was investigated by SHRP (Strategic Highway Research Program) method. Compatibility was also evaluated by rheological criterion and microscopic characterisation. The results indicated that modulus, G*/sinδ and viscosity of MDPE modified asphalt are largest among studied samples and it is a good choice for asphalt modification from the perspective of rutting resistance. LLDPE modified asphalt showed the preferable low temperature performance and LDPE is most compatible with asphalt. Higher branched degree of PE improves the low temperature performance of asphalt, but it reduces high temperature performance. A reduction in MFI (melt flow index) facilitates improvement of rutting resistance performance. Unfortunately, low MFI makes PE difficult to be dispersed and leads to poor compatibility with asphalt. [ABSTRACT FROM AUTHOR]

This study involves the development of a full-scale physical model test apparatus to investigate the dynamic performance of the slab track system of a high-speed railway. A portion of a railway ballastless track with embankment and underlying soil strata was built inside a steel box (15 m long, 5 m wide and 6 m high). A sequential-load-generating system consisting of eight high-performance actuators was developed to apply a load that was equivalent to that generated by a train moving at speeds up to 360 km/h. Two loading conditions can be implemented in the tests, a stationary cyclic loading (using one actuator) or a simulated moving train loading (using all eight actuators). Three test cases were performed to demonstrate the capacity of the proposed test facility. The first case was to test the load-sharing ratio of fasteners beneath the rails to determine the load distribution on the track slab. A formula, based on the test results, was proposed to determine the transfer process of the loads between the train wheel and the rail fasteners. The second case was a stationary cyclic loading test, which applied loads with varying frequencies to the rails using a single actuator. The resonance frequency of the track/embankment/soil system was determined in these tests to be about 16 Hz, which coincided with theoretically computed results and field measurements. The final case was to simulate the dynamic excitation resulting from the passage of a train on the track at various speeds (up to 360 km/h). The test results on track vibrations in the physical model test showed reasonably good agreement with field measurements. These three test cases fully demonstrate the ability of the newly developed full-scale test facility to simulate dynamic excitation from trains and its ability to explore the dynamic performance of railway structures under train loadings. [ABSTRACT FROM AUTHOR]