The rheological, chemical and microstructural properties of asphalt binders change with oxidative aging which is accelerated at elevated temperatures. Aging stiffens asphalt binders and increases the embrittlement of asphalt mixtures which would lead to fatigue cracking and eventually pavement failure under repetitive traffic loading. This study explored the feasibility of using antioxidant additives and copolymers with antioxidant agents to retard oxidative aging of asphalt binders. The performance of the additives was evaluated at the binder and mastic levels. The laboratory experiments included two unmodified binders, various antioxidant additives and copolymers, and three aggregate types. The fatigue characteristics of asphalt binders and mastic were determined before and after aging and an aging index was defined to evaluate the effect of the additives on aging. The results demonstrated that certain antioxidants and copolymers such as Redicote AP, Solprene, and Calprene may retard the aging and improve the rheological properties of the asphalt binders. In addition, the results of mastic testing confirmed the favorable effect of certain antioxidants on improving the resistance to fatigue cracking. Furthermore, the type of aggregate was found to influence the rate of aging of asphalt mixtures. Based on the rheological and fracture test results on asphalt binders and mastic, the effect of antioxidants was further investigated and validated at spectroscopic, chemical and microstructural level using Fourier-transform infrared spectroscopy (FTIR), Gel-permeation chromatography (GPC) and Atomic Force Microscopy (AFM), respectively. The spectroscopic analysis with FTIR supported the efficacy of the additives in retarding aging by reducing the carbonyl growth in aged binders. The chemical analysis with GPC confirmed that both Redicote and Solprene were capable of reducing the large molecular size fraction in binders subjected to long-term aging. The image analysis with AFM provided insight on the spatial distribution, surface roughness parameters and micromechanical properties (i.e., adhesion, stiffness) of various phases and the effect of aging on the micro-rheology of antioxidant-modified binders. The last part of this study examined the effect of aging on the viscoelastic response of asphalt mixture using the Prony series representation and a newly developed parameter called aging state variable 'A'. The dynamic modulus test data was used for the analysis. The aging state variable 'A' was found to capture the effect of aging temperature and duration of aging on the viscoelastic properties of asphalt mixtures.

Asphalt binder is a highly heterogeneous organic material; thus, its aging and restoration phenomena are very complex. Since the effects of aging and restoration on behavior of asphaltic materials are considered chemo-physical and mechanical in multiple length scales, a multiscale experimental approach can provide some significant insights to the understanding of the complex phenomenon. This study aims to investigate the laboratory aging protocol and compare it with the field aging process as well as to examine the short and long-term effects of different restorators on the mechanical, rheological, and chemical characteristics of asphaltic materials. To meet the objectives of this study, a multiscale experimental method was proposed and conducted. Three different binders (i.e. two virgin binders and one field aged binder) and restorators, a blend of different source of aggregates, and reclaimed asphalt pavement were selected/used. Test-analysis results showed that the mechanical/rheological properties and chemical analyses of the laboratory aged binders presented good correlations between aging indicators (e.g., carbonyl and colloidal index). It was also found that the long-term laboratory aging process has a limited ability to properly simulate long-term field aging. The kinetic analysis indicated that a mixed control regime, chemical reaction together with diffusion, governs the binder laboratory aging process. Test-analysis results from binders restored due to additives showed that the addition of restorators improve viscoelastic properties and fatigue resistance while they diminish rutting resistance. However, the petroleum-based restorator might contribute to maintaining the performance of the binder after another round of long-term aging. The chemical analysis indicated that the tall oil restorator contained many hydrogen bond-forming functional groups (-OH), which may increase the moisture sensitivity of the mixture. Outcomes from this study are expected to help more sustainable and energy-efficient civil infrastructure engineering due to the better selection/development of mixture components and more engineered blending of those.

Extraction and recovery of asphalt binders is an important procedure, although the rheological properties of the recovered binder may vary from the actual values due to many factors. This study has been conducted to evaluate the effect of different chemical solvents on the rheological properties of the recovered asphalt binder at high, intermediate, and low temperatures excluding the other factors that may affect the results. Five different binders were taken into consideration when this study was conducted, PG 58-28, PG 64-22, PG 64-28, PG 70-22, and PG 76-28, along with three different types of chemical solvents largely used as an industrial solvent, which are Trycoloroethelene (TCE), N-Propyl Bromide (nPB) brand called Entron-AE and Toluene.To catch the effect left by these solvents on the recovered binders, each binder has been dissolved in a specific amount of each of the three chemical solvents individually, the proportions of the solvent to the asphalt binder used was almost equal to the amount of the solvent needed to extract the same amount of binder out of a mixtures using a centrifuge. After leaving it for a while and making sure that the binder is totally dissolved, the binder is then recovered using a normal distillation process called the Abson method. In order to determine whether the age of the binder affects the results obtained from the recovered binders or not, testing has been done on unaged binders, short term aged binders, and long term aged binders, and in order to do that, short term aging has been simulated using the Rolling Thin Film Oven Test (RTFO), and the long term aging has been simulated using the Pressurized Aging Vessel (PAV).Finally, both original and recovered binders were tested at different aging conditions using the Dynamic Shear Rheometer (DSR), and the Bending Beam Rheometer (BBR). Data were used to obtain a full continuous grading of both the original (base) binder and the recovered binder for the five different binders used in this study using the three chemical solvents. Direct Comparisons were also made to compare the results of the original binder to the recovered binders using Trichloroethylene (TCE), Normal Propyl Bromide (nPB), and Toluene. Results showed that TCE will exhibit high softening effect unlike the Toluene which showed reasonable and representative data compared to the base binder, while nPB kept on giving un consistent data without a specific pattern.

This final report, in four volumes, of Strategic Highway Research Program (SHRP) Project A-002A describes intensive investigations of the chemical and physical properties of petroleum asphalts used in the construction of highway pavements. The model and predictive capability constitute the major portion of volume 1.

This paper presents the results of investigations on the rheological properties of modified asphalt binders and their influence on the performance of asphalt mixes. Asphalt mixes with modified binders such as styrene butadiene styrene polymer, crumb rubber, natural rubber, and waste plastics were evaluated for their rheological properties and compared to the properties of asphalt mixes with unmodified VG30 (viscosity grade) asphalt binder. The dynamic modulus values and rutting characteristics of the asphalt mixes were studied with due consideration to different levels of aging and temperature variations. Studies on the rheological properties showed that the energy dissipated by unmodified asphalt (VG30) binder is higher than that of modified asphalt binders. Long-term aged natural rubber and waste plastic modified asphalt binders showed significant increase in the properties compared to unmodified asphalt binder (VG30). Reduced temperature susceptibility of polymer modified asphalt binder showed that only polymer modification can enhance both high temperature rutting resistance and low temperature thermal cracking resistance of asphalt mixes. The transient nature of polymer modified asphalt mix from viscoelastic solid-like to viscoelastic fluid-like condition is significantly shifted to higher temperature compared to that of the mix with unmodified asphalt binder. Aging and rutting indices showed that rubber modified asphalt mixes are highly susceptible to aging. Statistical analysis of test results showed that the process of modification of asphalt binder, aging, and temperature during the test influence the rheological and rutting characteristics of asphalt mixes significantly. Correlation between the asphalt binder properties and its influence on the rutting resistance are found to be statistically significant. The analysis using least significant difference showed that polymer modified asphalt binder significantly improves the aging and rutting resistance of asphalt mixes compared to unmodified asphalt binder.