1H-NMR Relaxation and Application Study of Evaporatable Water in Foamed Asphalt

The use of foam-based warm mix asphalt (WMA) technology decreases the viscosity of asphalt and makes it more workable during the construction. Conventional hot mix asphalt (HMA) is typically produced at temperatures from 140 degrees C similar to 160 degrees C, while WMA is produced at 100 degrees C similar to 140 degrees C. However, after the construction, the viscosity increases rapidly as the foam disappears and the temperature drops. During the process of foam dissipation, the moisture may be trapped inside the mixture, causing detrimental failures by breaking the adhesive bond between the aggregates and asphalt binder (because of diffusion and freeze/thaw cycles). Therefore, it is crucial to know how the moisture escapes from the asphalt mixture as the specimen cools down and the foam disappears. In this research, the dissipation of moisture from foamed asphalt binders is directly measured and quantified by using 1H nuclear magnetic resonance (1H NMR) system. The results show that as the curing time increases, the viscosity of asphalt decreases and the curing temperature increases. Moreover, this paper demonstrates that 1H NMR is a practicable and valuable test method, which also is simple, rapid and nondestructive. In conclusion, curing time, viscosity of asphalt and curing temperature are the key factors that impact the water content in asphalt.