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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]

Warm mix asphalt (WMA) is an emerging clean production technology that alleviates the energy and environmental concerns of asphalt pavement industry. It is particularly suitable for asphalt rubber (AR) pavement, which provides longer service life and lower road-tyre noise but requires higher production temperature. Evotherm-DAT, a common liquid warm-mix asphalt (WMA) additive, can effectively improve the workability of AR binder, thus reducing the construction temperature of AR pavement. However, the properties of the Evotherm-DAT modified AR binders (Evo-AR) might be affected by the procedure of incorporating the WMA additive into AR, which unfortunately has not been fully studied yet. This study aims to address this issue by characterizing the rheological properties and chemical compositions of the Evo-ARs prepared by the following three procedures: 1) preparing AR first and then blending it with Evotherm-DAT (AR-E), the conventional approach; 2) mixing Evotherm-DAT and rubber first and then incorporating them to asphalt (ER-A); and 3) adding Evotherm-DAT during the mixing process of AR (REA). It was found that AR-E and REA had similar rheological properties. Besides, the workability of ER-A was slightly worse than those of AR-E and REA, but still much superior to that of AR without WMA additive. The anti-rutting performance of ER-A is better than those of AR-E and REA while no obvious difference was observed in the fatigue and low temperature cracking resistance among three types of Evo-ARs. Chemical characterization indicated that the preparation procedures affected the amount of epoxy groups in Evo-ARs, which possibly contributed to the difference in their rheological properties. Overall, it was concluded that incorporating Evotherm-DAT at an early stage has insignificant negative effect on the rheological properties of warm AR binder, but allows for more energy saving and emission reduction during the warm AR binder production process. [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]