Fog Seal

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Research & Performance

Quantification of Reduction in Hydraulic Conductivity and Skid Resistance due to Fog Seal in Low Volume Roads
Prepared By: Readul Mohammad Islam, Shams Arafat, and Nazimuddin M. Wasiuddin

Fog seal increases pavement life and postpones major rehabilitation. The reduction of permeability due to fog sealing will reduce moisture induced damage, but this benefit comes with a temporary loss of surface friction. However, quantifying the effectiveness of fog seal by measuring the permeability is a difficult task. While fog seal may be a good low-cost maintenance option for low volume roads, the rate of recovery of the friction may be very slow due to less rubbing action between fog sealed surface and tire. Four low volume parish roads in Caddo parish, LA have been selected for this study. Two emulsions, namely CSS-1H and E-fog, with three different application rates, were used to evaluate the reduction in hydraulic conductivity and to assess the characteristics of friction over time. Results show that fog seal is expected to be fully cured within 2.5 to 3.5 hours for 0.2-0.4 gal/yd2 application rate. The same field-cores were tested before and after fog sealing to exactly quantify the reduction in hydraulic conductivity. It was observed that fog seal has significant potential to reduce the hydraulic conductivity. Considering all four pavements and application rates of 0.1-0.22 gal/yd2, the average reduction in hydraulic conductivity was 38.5%. Reduction in hydraulic conductivity shows very slight sensitivity to the application rate. Irrespective of road type, emulsion and application rate, fog seal causes a sudden drop in the International Friction Index parameter F60 by 20 to 40%. Fog sealed surface does not return to the original level of friction after three months, however, the rate of recovery was the highest for the busiest of the observed Caddo parish roads.