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To explore the effect of waterborne polyurethane (WPU) on the performance of styrene-butadiene rubber (SBR) emulsified asphalt and broaden the application range of polymer-modified emulsified asphalt, WPU-SBR-modified emulsified asphalt with 0%, 3%, 6%, 9%, and 12% WPU was prepared. The penetration, softening point, ductility, and storage stability tests were used to explore the effect of different contents of WPU on composite-modified emulsified asphalt. Meanwhile, the rheological properties of five modified emulsified asphalts were analyzed by temperature scanning test, multiple stress creep recovery test, and low-temperature bending creep test. The results show that the addition of WPU improved the performance of SBR emulsified asphalt, and the improvement effect varied with the addition amount. With the increase of WPU content, the penetration and unrecoverable creep compliance Jnr of WPU-SBR-modified emulsified asphalt gradually decreased, and the softening point, rutting factor G*/sinδ , and creep recovery rate R gradually increased, indicating that the high-temperature stability of modified emulsified asphalt was enhanced, and when the WPU content was 9%, the best improvement effect was obtained. However, excessive content of WPU will deteriorate the low-temperature performance of WPU-SBR-modified emulsified asphalt, and thus the content of WPU should be appropriately selected in practical engineering applications. [ABSTRACT FROM AUTHOR]

Bitumen materials will occur a physical hardening effect when stored isothermally in a low-temperature environment, and ignoring the physical hardening factor has become one of the important reasons for premature cracking of asphalt pavement during the service period. This paper investigates the response of bitumen binder and bitumen mastic to physical hardening effects at different storage temperatures and times using the bending beam rheometer and dynamic shear rheometer. The response of the material to physical hardening effects is analyzed through temperature index system changes, mathematical model fitting, and stiffness master curve fitting. Results indicate that the response of the material to physical hardening effects can be classified into two stages: the rapid growth and the gradual stabilization periods. The response time of these two stages is related to factors such as aging degree and storage temperature. The physical hardening effect will cause the temperature loss of the material at low temperature, and its influence law on T S 60 = 300 MPa and T m 60 = 0.300 is different. It is recommended to extend the isothermal storage time specified in the test from 1 h to 9 h, considering the time cost and the change in temperature index. Moreover, the stiffness master curve study revealed the occurrence of the "tail drift" phenomenon. • Physical hardening effects cause temperature loss in bitumen, even over a grade. • Recommend extending BBR test storage to 9 h for better scientific validity. • "Tail drift" occurs during the fitting of the stiffness master curve. • The Logistic model can well fit the S and m values in the physical hardening process. [ABSTRACT FROM AUTHOR]

In this study, the rheological properties and adhesion characteristics of foamed CRA binder were studied. Firstly, the optimum foaming conditions of foamed CRA binder with different crumb rubber powder (CRP) content and foaming agent were studied. Secondly, stress creep recovery (MSCR) test, temperature scanning and frequency scanning tests were carried out by using dynamic shear rheometer (DSR), and the high temperature performance, temperature sensitivity and viscoelastic characteristics of each asphalt binder sample before and after aging were studied. Finally, the surface free energy theory was used to evaluate the adhesion characteristics of each sample. The results showed that the commonly used foaming agent cetyl trimethyl ammonium bromide has no effect on the foaming of CRA binder. With the increase of CRP content, the foaming temperature became higher, and it was difficult to foam successfully when the rubber powder content was higher than 15%. Increasing the content of CRP in a certain range can improve the high temperature performance and adhesion of foamed CRA binder and reduce its temperature sensitivity. With the aging process of the sample, the high temperature performance of foamed CRA binder increased, and the temperature sensitivity and adhesion characteristics decreased. The surface free energy of foamed CRA binder is mainly composed of dispersion component, and the polarity component is relatively small. The surface free energy of foamed CRA binder increased with the increase of CRP content. In addition, foaming agent B (water-in-oil emulsifier) would reduce the temperature sensitivity and high-temperature performance of foamed CRA binder, but it had no obvious effect on adhesion. • Optimal foaming conditions for rubber asphalt are discussed and the commonly used cetyltrimethylammonium bromide does not enhance its foaming effect. • The amount of crumb rubber powder used has an effect on the rheological properties of the foamed crumb rubber asphalt binder. • Aging reduces the surface free energy of the foamed rubber asphalt binder and reduces its adhesion properties. • The amount of crumb rubber powder mixed affects the surface free energy of the foamed crumb rubber asphalt binder. [ABSTRACT FROM AUTHOR]