Aging during construction and in-service substantially changes the chemical composition and physical properties of bitumen thereof influences the performance of asphalt pavements. The modification of bitumen by crumb rubber modifier (CRM) significantly increases the complexity of the aging mechanism and is expected to improve the aging resistance of bitumen. This study aims to investigate the effects of laboratory short-term and long-term aging on the chemistry and rheology of crumb rubber modified bitumen (CRMB). Neat bitumen and CRMB with four different CRM contents were studied. Fourier transform infrared spectroscopy and dynamic shear rheometer were employed to measure the change in the chemical composition and rheological properties of binders at different aging states. Bitumen hardening, which was rheologically revealed by the frequency sweep and multiple creep recovery test results, was also reflected in the growth of carbonyl and sulfoxide functional groups. In addition, the aliphaticity and aromaticity indices of binders before and after aging were also investigated. CRMB binders showed improved aging resistance compared to neat bitumen as reflected by the decreased carbonyl and sulfoxide indices as well as the lower change in rheological parameters. Higher resistance against aging was achieved when increasing the CRM content. The results also highlight the correlation between chemistry and rheology of bitumen. Among six selected mechanical parameters of binder, the non-recoverable creep compliance and percent recovery show better correlations with the combined chemical aging index (sum of carbonyl and sulfoxide indices) than the parameters derived from the linear viscoelastic region.

In-depth understanding of the synergetic effect between the various incorporating constituents in asphalt binders (e.g., polymers, fillers) is needed to design durable paving materials with desired properties. In this research, the focus was first on the effect of the reactivity of fillers on the evolution of adhesive strength between stone aggregates and epoxy modified asphalt mastics during the epoxy polymerization. Uniaxial tensile tests were performed on different combinations of fillers and binders with and without the epoxy-based polymer, and at different modification levels. Based on the results of the tensile tests, the increase of the adhesive strength of mastic with aggregates was generally lower when reactive filler particles (i.e., hydrated lime) were added than of epoxy binders with non-reactive filler. In other words, the non-reactive fillers did not influence the adhesion process and were thus selected for the next step studies on aging. The chemo-mechanical changes of epoxy modified asphalt mastics were analysed after pressure aging vessel and oven-conditioning after various aging times by means of Fourier transform infrared spectroscopy and dynamic shear rheometer. Less sulfoxides formed and higher modulus levels were measured with increasing the epoxy polymer in mastics over oven- and PAV-aging conditions. Due to the pressure difference, the rate of modulus increases and phase angle decrease was higher when the materials were conditioned in PAV than in oven.

Recently warm mix asphalt (WMA) technologies have been introduced to rubberized asphalt mixtures to decrease the required construction temperatures and to alleviate the hazardous gas emissions. Rubberized asphalt pavements combining with WMA have the potential to improve the long-term pavement performance. This study aims to investigate the fatigue performance of crumb rubber modified bitumen (CRMB) containing warm-mix additives using different characterization methods. The effects of crumb rubber modifier (CRM) content (5%, 10%, 15% and 22% by weight of base bitumen) and warm-mix additives on the binder fatigue performance were investigated. Various laboratory tests, including frequency sweep tests, time sweep (TS) tests and linear amplitude sweep (LAS) tests, were conducted on the long-term aged binders to obtain indicators of fatigue performance. Results show that there is a good correlation between the measured fatigue life determined by TS tests using the dissipated energy concept and the predicted fatigue life determined by LAS tests using the simplified viscoelastic continuum damage (S-VECD) theory. However, the traditional Superpave fatigue parameter and the G-R parameter cannot characterize accurate enough the fatigue performance of modified binders. CRMB binders exhibit superior fatigue performance compared to the neat bitumen. The effects of warm-mix additives on the fatigue performance are different for neat bitumen compared to CRMB binder. Based on the findings in this study, rubberized asphalt mixture combining with WMA additives is expected to have a promising long-term fatigue performance.

Remarkable variances were observed in permanent deformation curves of a dense asphalt mixture captured in triaxial repeated load permanent deformation (TRLPD) tests. In order to explore the causes of such variances, each permanent deformation curve was characterized firstly by an indicator (B) of the permanent deformation rate at a steady state stage. Meanwhile, a linear relationship was found between the values of indicator B and the resilient moduli of specimens after 1000 load repetitions. Secondly, a profound discussion on the potential relationship between resilient moduli and air voids content was performed. The discussion showed that air voids content appears to have no contributions to the observed variances. Nevertheless, three failure modes, tension failure, shear failure and shear failure with barreling, were observed in the X-ray Computed Tomography (CT) images of failed specimens subjected to triaxial compressive stresses. Furthermore, a significant correlation between failure modes and the resilient moduli was found by means of one-way analysis of variance (ANOVA). Moreover, it was found that the internal weak zones observed in the CT images of intact specimens dominate the behavior of the permanent deformation of asphalt mixture and the internal structure is the essential cause of such variances in the case of this study. This exploration highlights the influence of the internal structure on the mechanical performance of asphalt materials and thus recommends that considerable attention should be paid on the internal structure other than the volumetric properties when selecting test specimens.

The chemical irreversible hardening of epoxy modified bitumen is affected by various physical factors and the successful application of this technology is directly linked with full understanding of chemo-rheological material characteristics. This study proposes a model to describe the material viscosity evolution during hardening of epoxy modified bitumen. The findings from numerical analyses performed to assess the mechanical response of epoxy modified bituminous binders are presented. Information of the chemical interaction of epoxy within a bituminous matrix was collected and all the influential factors have been determined. The proposed chemo-rheological model accounting for the polymerization of the epoxy in the bitumen was formulated and the sensitivity of material parameters, such as activation energy, reaction order and extent of hardening reaction until the gel point of epoxy modified binders, was demonstrated. Results of the analyses suggest that lower levels of activation energy increase the degree of hardening and the rate of viscosity development. By decreasing the hardening reaction until the gel point the achieved viscosity of epoxy modified bitumen was increased showing the importance of gel reaction extent on material viscosity evolution. The numerical studies have shown also that the polymerization rate in the epoxy modified bitumen is highly dependent on the temperature under various (non-) isothermal conditions. Also, the polymerization rate should be considered through all the material curing processes to avoid unwanted variations in the mechanical properties.

Induction heating technique is an innovative asphalt pavement maintenance method that is applied to inductive asphalt concrete mixes in order to prevent the formation of macro-cracks by increasing locally the temperature of asphalt. The development of asphalt mixes with improved electrical and thermal properties is crucial in terms of producing induction healed mixes. This paper studies the induction healing capacity of asphalt mixes without aggregates as the part of asphalt concrete where inductive particles are dispersed notably contributing to the final response of asphalt pavements. Special attention was given to the characterization of inductive asphalt mixes using experimental techniques and numerical methods. The research reported in this paper is divided into two parts. In the first part, the impact of iron powder as filler-sized inductive particle on the rheological performance of asphalt-filler systems was studied. The mechanical response, the induction heating and healing capacity of asphalt mortar by adding iron powder and steel fibers was evaluated as well. In the second part, the utilization of advanced finite-element analyses for the assessment of the induction heating potential of inductive asphalt mortar with steel fibers are presented. The influential factors of induction mechanism in asphalt mixes are also described. The experimental and numerical findings of this research provided an optimization method for the design of induction healed asphalt concrete mixes and the development of necessary equipment that will enable the implementation of induction technology for healing of asphalt concrete mixes.

Porous asphalt concrete is widely used as a surfacing layer on highways in the Netherlands because of its benefit that it is effective in reducing traffic noise. However, the service life of porous asphalt wearing courses is limited due to the fact that it is vulnerable to raveling. A preventive maintenance strategy using surface treatment material is being considered as a cost-effective and environmentally sustainable option to extend the service life of existing porous asphalt wearing courses. In this paper, the effect of a surface treatment to porous asphalt wearing courses is discussed. A surface treatment material was sprayed on the porous asphalt pavement surfaces in two field trials. Computed Tomography (CT) scans were performed on the porous asphalt concrete cores from the field trials to measure their volumetric properties. The rotating surface abrasion tests were used to determine the raveling resistance of the porous asphalt concrete samples. Finite element models with a realistic structure of the porous asphalt concrete were created for analyzing the stresses and strains as a result of traffic loads in the pavement surface with the surface treatment material. It is found that the effect of the surface treatment is positive.

A preventive maintenance strategy of spraying rejuvenators on asphalt pavement surfaces is being considered as a cost-effective and environmentally sustainable option to extend the service life of existing asphalt concrete pavements. Rejuvenators might penetrate into the asphalt concrete and soften (rejuvenate) the bituminous binder. In this paper, the rejuvenation effectiveness of two rejuvenators on an artificially aged mortar is assessed. Cylindrical mortar specimens were prepared from the artificially aged mortar and then treated by the rejuvenators. The rheological and shear fatigue properties of the reference and treated mortar specimens were measured using dynamic shear tests. Meantime, a three-dimensional column model was created to investigate the dynamic shear test's capability of detecting the rheological properties of a composite column with a soft material in its outer part and a stiff material in its inner part. From finite-element modeling, it is found that the shear modulus of the composite column is higher than that of the soft material and lower than that of the stiff material. However, the results of the dynamic shear tests show that the two rejuvenators did not decrease the complex shear modulus of the artificially aged mortar. In addition, the two rejuvenators did not change the shear fatigue life of the artificially aged mortar.