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Featured Application: This work provides reference for selecting appropriate approaches to evaluate the fatigue characteristics of rubberized asphalt specimens containing warm mix asphalt additives or other modifiers. Warm asphalt rubber (WAR) mixture is a sustainable paving material with advantages including waste recycling and noise reducing. A comprehensive understanding of the fatigue performance of WAR specimens is helpful to its wide application. However, research on evaluating the fatigue performance of WAR binder and mixtures is very limited. This paper applies five fatigue analysis approaches to evaluate the fatigue life of WAR samples with three different warm mix asphalt (WMA) additives. The conventional G*sinδ, linear amplitude sweep (LAS), indirect tensile fatigue test (ITFT), and four-point bending beam (4PB) test were conducted based on available standards. In addition, a novel shear fatigue test was performed on WAR mortars. Test results indicated that the incorporation of crumb rubber has a significantly positive effect on fatigue resistance. WAR with chemical and foaming additives exhibited a poorer performance than asphalt rubber (AR), but their fatigue performance was still greatly superior to the non-rubberized samples. Finally, LAS as well as mortar shear fatigue and 4PB tests provided the same prediction of fatigue resistance, while the results of G*sinδ and the ITFT were inconsistent. It is recommended to use LAS, the mortar shear fatigue test, and the 4PB test for the fatigue resistance evaluation of rubberized specimens. The validation of the findings with more materials and field performances is recommended. [ABSTRACT FROM AUTHOR]

Asphalt rubber (AR) is a sustainable paving material with merits including waste tire consumption, low traffic noise, and enhanced mechanical performance. However, the poor workability and storage stability limited its further application. This study attempted to alleviate these two concerns of AR simultaneously by incorporating heavy bio oil (HBO). To achieve this goal, bio-AR binders with three different mixing sequences were prepared. A series of rheological and chemical tests were conducted. Test results prove that the bio-AR binders exhibited superior rutting and fatigue resistance compared to AR binder. The viscosity values of bio-ARs were closed to AR modified with commercial warm mix additive, which indicates enhancement in workability. Due to the relatively high density of HBO, the density difference between the asphalt liquid phase and crumb rubber in the bio-AR system narrowed, which brought improved storage stability. Among bio-ARs prepared with different mixing sequences, the direct mixing one (ARB) had the most satisfied overall performance. The early incorporation of HBO had limited negative influence on binder performance, but allowed for more energy saving during the bio-AR binder production. Future study will be conducted on performance of bio-AR mixtures and quantitative estimation of its energy saving during the blending and compacting process. [ABSTRACT FROM AUTHOR]

Asphalt rubber (AR), which is prepared by blending crumb rubber and bitumen, provides various advantages, including superior rutting resistance, lower road-tire noise and longer service life. However, contractors have expressed concerns regarding its poor storage stability, which in turn limits its wider application. This study aims to address the storage stability concern by incorporating nano-montmorillonite (nanoclay). Three types of nanoclay were dispersed into hot AR binder by high shear blending. The rheological properties of nanoclay-crumb rubber modifier (CRM)-modified bitumen were evaluated through Superpave performance grade (PG) tests and the storage stability was characterized by measuring the difference in softening points or complex moduli at the top and bottom portions of binders after lab-simulated storage. X-ray diffraction (XRD) evaluation was conducted to observe the variation of nanoclay layer gap distance for mechanism investigation. It was found that all selected nanoclays had insignificant effects on workability, rutting and fatigue properties. The layered nanoclay transformed to intercalated or exfoliated structures after interaction with bitumen fractions, providing superior storage stability. Among the three selected nanoclays, pure montmorillonite with Na+ inorganic group, which has an intermediate hydrophilic property and middle layer gap, showed the most obvious effect on enhancing the storage stability of AR. [ABSTRACT FROM AUTHOR]

This study investigated the interaction among different components of asphalt binders collectively modified with crumb rubber and warm mix additives through thermal gravimetric analysis (TGA) and differential scanning calorimeter (DSC) testing. The modified binders were divided into two parts for analysis purpose, namely the extracted crumb rubber modifier (CRM) by removing all asphalt components and the separated binder system by removing insoluble CRM particles. The main findings of this study include that: (1) the interaction between CRM and base asphalt was a component exchange process, i.e., natural rubber and styrene-butadiene rubber were released from CRM and blended with asphalt molecules; (2) wax-based warm mix additives penetrated into CRM during the mixing process; (3) the incorporation of warm mix additives especially the wax-based additives, promoted the component exchange between rubber and asphalt. [ABSTRACT FROM AUTHOR]

This study aims to investigate the rheological and chemical characteristics of asphalt rubber (AR) binders modified with four non-foaming warm mix asphalt (WMA) additives: Evotherm-DAT, Sasobit, conventional paraffin wax, and combined Evotherm-DAT and Sasobit. The main findings of this study include that: (1) all selected WMA additives are effective in enhancing AR’s workability; (2) using combined Evotherm-DAT and Sasobit is not a viable option to reduce the construction temperature of AR mixture; (3) paraffin wax is a potential WMA additive for AR; and (4) WMA additives may affect the dissolution status of crumb rubber in base asphalt. [ABSTRACT FROM AUTHOR]