Waste tire rubber has been incorporated into asphalt modification for decades due to its various benefits. There are two main mechanisms during bitumen–rubber interaction: rubber swelling and chemical degradation. This study surveys these two processes from the viewpoint of polymer science. The kinetics of rubber dissolution and thermodynamics of rubber swelling are discussed to provide a fundamental understanding of the interaction process and to demonstrate how optimisation of material selection and processing procedures can lead to the desired binder properties. Factors including the interaction conditions and raw material characteristics are analysed based on the previous theories and compared with experimental results.

As bitumen oxidizes, material stiffening and embrittlement occur, and bitumen eventually cracks. The use of anti-oxidants, such as lignin, could be used to delay oxidative aging and to extend the lifetime of asphalt pavements. In this study, the chemical and rheological effect of lignin on bitumen was evaluated by using a single dosage organsolv lignin (10 wt.% dosage). A pressure aging vessel (PAV) was used to simulate the long-term aging process after performing the standard short-term aging procedure, and the lignin-modified bituminous binders were characterized by an environmental scanning electron microscope (ESEM), Fourier-transform infrared (FTIR) spectroscopy, and a dynamic shear rheometer (DSR). From the ESEM results, the uniform microstructure was observed, indicating that the addition of lignin did not affect the worm structure of bitumen. Based on the FTIR test results, lignin-modified bitumen showed that a lower number of carbonyl and sulfoxide compounds were generated after aging than for neat bitumen. Based on the linear amplitude sweep (LAS) results, the addition of lignin slightly reduced the fatigue life of bitumen. From the frequency sweep results, it showed that lignin in bitumen acts as a modifier since the physical interaction between lignin and bitumen predominantly affects the material rheology. Overall, lignin could be a promising anti-oxidant due to its economic and environmental benefits.

Bitumen ageing has a significant impact on the mechanical performance of asphalt concrete. This study utilises dynamic mechanical tests (frequency sweep, fatigue, and relaxation) to investigate the effect of ageing on the viscoelastic characteristics of bitumen. As ageing progressed, a shift of the Black diagrams curves towards lower phase angles was observed; at the same time the shape of the curves changed to a straight line and the curvature reduced. Interestingly, based on the standard fatigue analysis criteria, ageing appears to have a positive effect on bitumen fatigue life. Consequently, it occurs that studying only the stiffness and fatigue behaviour of bitumen cannot directly characterise ageing-induced degradation. The stress relaxation test was found to be more suitable to characterise ageing of bitumen. Aged bitumen had higher residual stresses and longer relaxation times. Hence, aged bitumen was found to be more susceptible to stress accumulation and thus cracking. A linear relationship was established between the crossover modulus and the stress relaxation ageing indices for the studied bitumen. This relationship suggests that crossover modulus has the potential to be used as a parameter to characterise the bitumen relaxation properties by means of routine tests such as the DSR frequency sweep tests.

Warm mix asphalt (WMA) technology has been increasingly utilised in rubberised asphalt pavements to reduce the production and compaction temperatures and the incidental fumes and odours. This study aims to investigate the high, intermediate and low-temperature performance of crumb rubber modified asphalt binders containing WMA additives. The asphalt-rubber interactions under various mixing combinations of temperature and time were investigated through both microscopic and mechanical methods to obtain the optimum mixing procedure. The effects of WMA additives (wax-based and chemical-based products) on the binder performance were investigated by multiple stress creep and recovery (MSCR) test, linear amplitude sweep (LAS) test and low-temperature frequency sweep test. Results show that rubberised asphalt binders significantly improve the binder performance of base asphalt at different temperature ranges. The effects of WMA additives on binder performance varied with base asphalt and rubberised asphalt binder. In addition, the nonrecoverable compliance difference was found not suitable to characterise the stress sensitivity of rubberised binders and the difference in the nonrecoverable compliance for an incremental change in applied stress was proved to be a more accurate alternative. For the cyclic LAS test, the failure energy was found to have a strong correlation with the predicted fatigue life using simplified viscoelastic continuum damage analysis and therefore can be considered as a simple indicator for binder fatigue performance ranking. Relaxation modulus and rate derived from low-temperature frequency sweep tests produced comparable results for ranking the low-temperature performance of different binders. It is feasible and promising to use a unified DSR test methodology to characterise the binder performance covering the whole service temperature range.

Oxidative aging is responsible for the irreversible asphalt stiffening and embrittlement leading to asphalt pavements of increased susceptibility to fatigue and thermal cracking. In recent years, various flexible binders have been introduced in asphalt industry to produce long-life pavements and the epoxy asphalt binders are among them. Nevertheless, in-depth understanding of the oxidative aging mechanism of epoxy asphalt binders and binding systems is still needed to enable reliable predictions of material degradation through service life. In this research, the compositional and rheological changes of epoxy asphalt, with and without filler, were analysed by means of Fourier Transform Infrared spectroscopy and Dynamic Shear Rheometer. Especially, kinetics (Arrhenius) parameters of epoxy asphalt have been determined by tracking the chemical composition changes. Oxidation of carbon species in epoxy asphalt is compositional dependent, and low values of activation energy accompany in low values of reaction rate are shown by adding epoxy in asphalt. Furthermore, the epoxy asphalt mastics (binders with filler) have been subjected to rheological testing to evaluate the stiffening effect as oxidation proceeds. Increase of modulus over a wide range of frequencies, decrease of frequency dependency of modulus of epoxy asphalt and shifting of phase angle to lower values are some important observations noticed as well. Overall, oxidation in epoxy asphalt materials occurs slowly yielding to oxygen-resistant binders when epoxy compounds are incorporated in asphalt binders.

This study aimed to explore the long-term aging influence on chemo-rheological properties and develop novel consecutive models for the long-term aging reaction kinetics of bitumen. The results revealed that the aging index was significantly dependent on the types of selected parameters. The Zero-order model was suitable to describe the long-term aging reaction kinetics of bitumen based on the oxygen-containing functional groups with the reaction rate constants in 0.7–3.3*10⁻⁴ (mol L⁻¹·h⁻¹). In the SARA-based consecutive reaction model, the most optimum kinetics model for aromatic fraction was the Third-order reaction model and the corresponding reaction kinetics constant (k₁) was 0.02 (mol·L⁻¹)⁻²(h)⁻¹. The Zero-order model could well fit the generation kinetics of asphaltene molecules with the reaction rate constant k₂ of 3.85*10⁻⁴ mol·(L·h)⁻¹. Further, the transformation reaction from the resin to asphaltene molecules was the control step of the whole consecutive reaction model. In this study, when one-unit resin fraction was generated, the consumption amount of aromatic fraction was about 2.82 units. Meanwhile, when one-unit resin fraction was consumed, only 0.58-unit asphaltene could be generated. The developed reaction kinetics models could be beneficial to predict the functional groups distribution and SARA fractions in aged bitumen with different aging degrees.