The crumb rubber modified bitumen (CRMB) has been utilized in pavement industries to mainly reduce the environmental impacts of the wasted tires by turning unwanted scrap tires into new bituminous materials. However, the relatively high viscosity compared to the conventional asphalt is the major drawback of the CRMB. The higher mixing and working temperatures are thus required in order to achieve the desired workability of the CRMB. This results in more asphalt fume emission, higher energy consumption, and more harmful working environments for workers. Warm mix asphalt (WMA) technologies have been intentionally developed to lower the manufacturing and working temperatures of the asphalt by reducing the viscosity of the asphalt binder. Many studies suggested that coupling CRMB with WMA additives can promote better working conditions and minimize environmental issues of the CRMB.
In this study, experimental works were carried out to evaluate rheological and performance-based properties of the CRMB containing WMA additives in order to investigate the effect of the crumb rubber modifier (CRM) content and WMA additives (wax-based and chemical-base WMA additives) by using only one dynamic shear rheometer (DSR). The performance of the studied binder at high, intermediate, and low road service temperatures were investigated by performing Multiple Stress Creep and Recovery test, Linear Amplitude Sweep test, and 4-mm Dynamic shear rheometer test, respectively. Moreover, the Fourier Transform-Infrared Spectroscopy and the storage stability test were also performed to investigate the effects of the CRM dosage and the WMA additives on the aging susceptibility and the high-temperature storage stability of the binders. The results show that the incorporation of crumb rubber modifier can clearly improve the overall performance (rutting, fatigue damage, low-temperature thermal cracking resistances), and aging resistance of the asphalt binder in a bitumen-level. The high-temperature storage stability of the CRMB became more stable at the higher dosage of the CRM. Moreover, it was found that the wax-based WMA additive can only enhance the high-temperature rutting resistance but negatively impacted the fatigue and low-temperature damage resistances of both neat and CRM binders. The effect of the chemical-based additive on the neat and CRM binders are different as it improved the performance over the whole service temperature of the neat but lowered the damage resistances of CRMBs. Additionally, the addition of both WMA additives decreased the high-temperature storage stability of the CRMB.