Carbon nanotubes (CNT) hold the potential to enhance the performance of construction materials such as asphalt binders and mixtures. With the goal of designing long-life asphalt pavements, this research report investigates the laboratory performance of CNT-modified asphalt. Mixing combination conditions including shearing time and shearing rate are studied in the first step. Then modified asphalts with different CNT contents are evaluated by penetration, softening point, and ductility indexes. Storage stability of modified asphalt is accessed using the separation test. After that, aged asphalts are obtained by using the thin film oven test (TFOT). Samples of base and CNT-modified asphalts before and after ageing are characterised by running the rotational viscosity (RV) test, dynamic shear rheometer (DSR) test, and bending beam rheometer (BBR) test. Furthermore, Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) are employed to characterise the functional groups and microstructures of base and modified asphalt binders before and after ageing. It is shown that shearing rate and shearing rate*shearing time interaction have a profound influence on the property of modified asphalt whereas shearing time does not. Conventional test results indicate that increasing CNT content would decrease penetration and ductility while increasing the softening point. The separation test shows that CNT may settle down during the storage process. Rheological test results show that the addition of CNT can improve the high temperature performance and ageing resistance while decreasing the low temperature performance. The functional groups in base and modified asphalt are found to be similar which indicates that there are no chemical reactions during modification. It demonstrates that CNT-modified asphalt has better anti-ageing property with a lower increase in sulphoxide index after ageing. AFM characterisation provides details of the CNT modification mechanism. This research provides useful guidance and potential problems on the use of CNT as a high performance modifier.

Four kinds of polymer modifier widely used in China are selected to modify the performance of asphalt mixture: styrene butadiene styrene (China), PR PLAST.S (France), Domix (Germany), and Rad Spunrie (China). The main objective of this paper is to evaluate the influence of these polymer modifiers on the performance of asphalt mixture with the dynamic modulus | E∗ | indicator through simple performance test. Dynamic modulus is adopted as the primary material property of hot mix asphalt mixtures in the M-E Pavement Design Guide 2002. In this study, the influences of temperature, frequency, and confining pressure on the dynamic characteristic of asphalt mixture are analyzed, and the master curves of dynamic modulus are developed and interpreted. The Witczak | E∗ | predictive model, which is used in the M-E Pavement Design Guide, is also applied to predict the dynamic modulus, and the predicted values are compared with the examined results. Results show that all these polymer modifiers, especially Domix, can ...

Pyrolytic carbon black (CB_p) from scrap tire pyrolysis is a potential modifier for the bitumen industry. Binders containing different contents of CB_p were prepared and experimentally investigated to examine the effects of CB_p on the electrical and thermal conductivity, conventional physical properties, rheological properties, high-temperature antirutting performance, aging resistance, and storage stability. Laboratory test results indicated that the incorporation of CB_p effectively improves the electrothermal properties, rheological properties, high-temperature rutting resistance, and aging resistance. It also increases the viscosity and decreases the storage stability of bitumen. The study confirms that CB_p-modified bitumen with proper selection of content can be a multifunctional paving material.

Freeze-thaw damage is a typical distress incurred in road and railway engineering in cold regions. Concrete waterproofing layer is commonly used in high-speed railway tracks to prevent the penetration of surface water, however, it cracks easily under thermal stress, especially in cold regions. Recently solutions have been proposed to increase the waterproofing layer’s cracking resistance by using asphalt layers. Nonetheless, the use of emulsified asphalt as well as dense-graded asphalt mixture were not effective enough. To improve the effectiveness, in this study, mastic asphalt was designed for application as the waterproofing layer on the subgrade surface of high-speed railway tracks in cold regions. The overall performance of mastic asphalt was preliminarily evaluated by laboratory tests, then a 200-m test section was constructed for field validation in northeastern China as part of a new high-speed railway line, and water content sensors were placed inside the subgrade to monitor the performance of the mastic asphalt waterproofing layer (MAWL). The subsequent field investigation and monitoring data during the two years operation showed that MAWL dramatically outperformed the conventional concrete waterproofing layer in terms of waterproof performance. Plenty of serious cracks were found in the conventional concrete waterproofing layer, but only a limited number of local cracks were observed in MAWL. As a result, MAWL keeps the water content of subgrade at a stable level. In addition, MAWL showed relatively high stability during the two years investigation period, and no obvious deterioration was observed in the test section.