Assessing the Ability of Fog Seals to Seal Pavements, to Rejuvenate in Situ Binder, and to Retard Binder Oxidation (0-5091-3)

This work was conducted for the purpose of assessing the effectiveness of fog seal treatments as an aid to highway maintenance managers in making sound decisions for fog seal treatments. Replicate cores of both treated and untreated highway and general aviation pavement sections were analyzed. Whole cores were assessed by water permeability and by susceptibility to permanent deformation. Replicate cores were sawed into one-quarter inch slices which were individually analyzed for total air voids, binder content, oxidative aging and rheology, and for the presence of fog seal material. The fog seal materials used in this project were emulsions of asphalt materials and coal tar type materials. Results showed that if the fog seal is penetrating into the pavement, it is no doing so to a detectable level, the permeability of the pavement is not significantly reduced, and APA test did not show any softening of the pavements by the treatments. Additionally, 1) differences between untreated and treated pavement slices generally seem more likely due to original binder variability with depth than to the fog seal treatments, although coal-tar treatments appear to harden the top layer; 2) effects of the fog seal treatments on oxidative aging were not observed; 3) previous work, that the aging rates of asphalt binders are decreased by very low accessible air voids is supported. In summary, the effects of fog seals on pavement durability appear to be minimal, with respect to binder rejuvenation or sealing. Cosmetic effects or protecting against shelling or raveling remain as possible benefits, although they were not assessed by this project. In response to this work, engineers should reassess the cost-benefit balance of fog seal treatments.