A fog seal consists of a slow setting asphalt emulsion (e.g., SS-1, SS-1h, CSS-1 and CSS-1h) diluted with one to four equal parts of water and applied at rates between 0.06 – 0.13 gal/yd2 on an existing pavement surface without a cover aggregate. It is intended to penetrate into the surface pores of the pavement to seal very small cracks and surface voids as well as coat surface aggregate particles. Pavement surfaces with high void contents are more susceptible to oxidative aging due to greater exposure of the binder to air and higher temperatures. The asphalt binder becomes stiffer, and consequently, more brittle through oxidation, leading todeterioration.
Rejuvenators can be added to fog seals to treat raveled and aged pavements by improving penetration into the pavement and improve flexibility of the aged binder.
Rejuvenators are petroleum or bio-based oils with chemical and physical characteristics selected to restore properties of the aged asphalt binder in the surface
layer. Adding a rejuvenator to a fog seal reduces the likelihood of cohesive failure within the asphalt binder film and can slow the rate of aging caused by oxidation. For optimal restoration of the aged asphalt binder, consideration should be given to the chemical composition of the rejuvenator rather than just its capacity to reduce the viscosity of the aged binder. Furthermore, the degree of diffusion of the rejuvenator into the aged binder is of utmost importance since it allows chemical changes to take place that affect the physical properties.
Although rejuvenators can be categorized based on the material source or manufacturing process (i.e., aromatic oils, naphthenic oils, paraffinic oils, tall oils and fatty acids), it is also important to differentiate among products based on their chemical fractions. The composition of an asphalt binder is often defined by its so-called SARA fractions: saturates (S), aromatics (A), resins (R), and asphaltenes (A), which have increasing molecular polarity (saturates have the lowest and asphaltenes the highest). Often, asphalt is described as a colloid that consists of dispersion of asphaltenes in an oily matrix constituted by saturates, aromatics, and resins. Asphaltenes are stabilized in crude oils by natural resins, which are surfactant-like agents.
• Rejuvenators that are most compatible with the aromatics of the asphalt binder will reduce the viscosity and modulus of the asphalt binder through lowering the
viscosity of the continuous solvent phase.
• Rejuvenators that have affinity for various fractions of the asphalt binder will reduce the viscosity of the binder through restoration of the original binder asphaltenes to maltenes ratio (i.e., the asphalt chemical fractions).
• Rejuvenators that exhibit low compatibility with the aromatics, asphaltenes and resins fractions of the asphalt binder, due to the presence of paraffinic and saturated materials with high crystalline fractions, will reduce the modulus of the binder. However, with aging, these components can increase the colloidal instability of the asphalt binder resulting in the precipitation of the asphaltenes.