Characterization of the effect of foaming water content on the performance of foamed crumb rubber modified asphalt

Crumb rubber modified asphalt (CRMA) is a "green" paving material which provides an effective way to recycle waste tires. However, it also faces the criticism of increased energy consumption and air emissions during construction. Foaming technology allows CRMA to be constructed at lower temperatures, but very limited research has been conducted on the influence of foaming water content on the properties of foamed CRMA binder. In this study, foamed CRMA binders were produced at various foaming water contents (0%, 1%, 2%, 3%, and 4%) in laboratory, and their high-temperature performance, low-temperature performance, temperature sensitivity, and fatigue resistance were characterized and compared through laboratory testing. The test results indicated that foamed CRMA binders provide slightly worse high-temperature performance but better low-temperature performance, temperature stability, and fatigue resistance, compared to regular CRMA binder. With the increase of foaming water content, the high-temperature performance of foamed CRMA binder drops off, the low-temperature performance of foamed CRMA binder first decreases and then increases, and the temperature stability and fatigue resistance of foamed CRMA binder keep increasing.