Book Description

Abstract : Foamed asphalt (water-foamed asphalt in this study) is formed by combining hot asphalt with a small amount of cold water, while emulsified asphalt is simply a suspension of small asphalt cement globules in water, which is assisted by an emulsifying agent (or surfactant). The foaming and emulsifying processes are the water-based physical and chemical processes in decreasing the apparent viscosity of asphalt, respectively. Both foamed and emulsified asphalt materials containing some free water, and have been widely used in the cold, half-warm, and warm mix asphalt productions. Also, the pavement surface treatments and maintenances are involved in these asphalt materials. However, it is limited to a profound understanding of mechanical performance and corresponding physicochemical properties. The objectives of this study are 1) to characterize the rheological properties of foamed and emulsified asphalt materials, 2) and to evaluate the mechanical properties of its mixtures in the applications of pavement construction, surface treatments, and pavement maintenances. The rheological behavior of foamed asphalt was measured at various temperatures and with different water content can provide the apparent viscosity and agitation torque of the foamed asphalt. Besides, according to the dynamic foaming processes of the foamed asphalt, this study successfully applied the dynamic movement of water vapor or bubble in foamed asphalt to disperse the nano hydrated lime (NHL) particles in the suspensions into the asphalt. The dispersion condition and the microstructure of the nanoparticles in the asphalt were evaluated via scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. A surfactant of sodium dodecylbenzene sulfonate was added to the water to form suspensions before inserted into the hot asphalt. Also, the study characterized the impacts of the foaming condition and the multiple freeze-thaw cycles on the laboratory tensile strength tests via Materials Testing System (MTS) of the foamed asphalt mixtures. Then, the nondestructive ultrasonic direct test was applied to assess the foamed asphalt mixture damage level after the multiple freeze-thaw cycles. Meanwhile, for another kind of asphalt material containing free water (emulsified asphalt), the interactions of asphalt and water in the emulsified asphalt were characterized first. The moisture (or water) retention of emulsified asphalts during the oven heating was applied to assess the emulsification stability at different acidic and alkaline levels. The dynamic shear rheometer (DSR) experiments characterized the apparent viscosity and rutting indicator as to the parameters for expressing the rheological properties of both emulsified asphalts and the individual residues. The Fourier-transform infrared spectroscopy (FT/IR) analyzed the interactions of asphalt and water in emulsified asphalt from the perspective of molecular chemistry. After that, the application of emulsified asphalt on pavement maintenance; the example of chip-seal was involved. These studies tested the adhesion, interface bond strength, and shear bond strength for the pavement underlying chip-seal. Two innovative laboratory chip-seal tests, Michigan Tech's interface bond test (IBT) and Michigan Tech's shear bond test (SBT), were developed in this study. The testing results concluded that the new developed chip-seal tests are useful in evaluating the bonding performance between the chip-seal and pavements.