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Enrichment treatments  adding fresh asphalt to an aged surface and lengthen the pavement surface life.


Fog Seal

Fog seals are a method of adding asphalt to an existing pavement surface to improve sealing or waterproofing, prevent further stone loss by holding aggregate in place, or simply improve the surface appearance.


Fog Seal Features

Function of a Fog Seal

A fog seal is designed to coat, protect, and/or rejuvenate the existing asphalt binder. The addition of asphalt will also improve the waterproofing of the surface and reduce its aging susceptibility by lowering permeability to water and air. To achieve this, the fog seal material (emulsion) must fill the voids in the surface of the pavement. Therefore, during its application it must have sufficiently low viscosity so as to not break before it penetrates the surface voids of the pavement. This is accomplished by using a slow setting emulsion that is diluted with water. Emulsions that are not adequately diluted with water may not properly penetrate the surface voids resulting in excess asphalt on the surface of the pavement after the emulsion breaks, which can result in a slippery surface. Figure 1 conceptually shows a fog seal application.

Fog Seal Project Selection

Fog seals are used as a method of enrichment of a pavement surface and as a method of holding stone in place. Thus, they are suitable to treat raveled and aged pavements. There is, at the present time, no simple way of quantifying the degree of aging in a pavement other than by visual inspection. Different asphalts will age at different rates and the experience of individual districts is key to determination of treatment timing. Some modified asphalts such as asphalt rubber and polymer modified asphalts will age at a slower rate than conventional binders. Fog seals will not correct distresses such as cracking, base failures, excessive stone already lost, or any other severe pavement defects.

On the traveled way, fog seals should only be used where surface penetration of the emulsion can be expected; that is, aged and raveled hot mix surfaces, chip-sealed surfaces, and open graded asphalt surfaces. On shoulders, gores, or dikes, penetration is desirable, but it is not essential. Fog seals darken the pavement surface and create distinct demarcation in these regions. In general, traffic level is not a determining factor except in job set up. For situations requiring that the sealed pavement be opened to traffic shortly after the application of the seal, a blotter coat of sand may be used to prevent pick-up.

Fog Seal Performance - Benefits and Limititations

Fog seals are an inexpensive way of arresting raveling and adding binder back into aged surfaces. They can also hold chips in place in fresh chip seals, (or older chip seals beginning to loose rock) reducing the potential for vehicle damage.

Fog seals are not useful as seal coats on tight surfaces without the addition of aggregates as they will reduce surface texture and may create a slippery surface. Fog seals should not be used on Rubberized Asphalt Concrete (RAC) or polymer modified mixes unless the pavements are over five years old as these binders age at a different rate.

The application of fog seals is also limited by weather. A cut off date in the fall (e.g. September 1st) will ensure that rain will not be a factor and that the emulsion will fully cure before freezing conditions are encountered. In addition, seal coats applied in the winter have less time to penetrate the pavement and are more prone to cause slick surface conditions.

Site Conditions

To be effective, fog seals need to break quickly (revert to solid asphalt) and cure completely (lose water to form a cohesive film). This should be at a rate that allows traffic to be accommodated without the binder being picked up by vehicle tires. To achieve this behavior, the film forming properties of the binder must be adequate (i.e., the binder must be able to coalesce into a continuous film prior to allowing traffic on the new seal). Asphalt films do not form well at low temperatures in the absence of low viscosity diluents. Thus, warm conditions with little to no chance of rain are necessary to ensure successful applications. Fog seals should not to be applied when the atmospheric temperature is below 10°C (50°F), and pavement temperature below 15°C (59°F).

If unexpected rain occurs, prior to the emulsion breaking, the emulsion may wash out of the pores of the pavement and break on the surface of the pavement creating a slippery surface.

Surface Preperation

Immediately before applying a fog seal, the pavement surface must be cleaned with a road sweeper, power broom, or flushed with a water pump-unit to remove dust, dirt, and debris. The pavement surface must be clean and dry before applying the fog seal. If flushing is required, it should be completed 24 hours prior to the application of the fog seal to allow for adequate drying.

Materials Preperation

Asphalt emulsions (original emulsions) contain up to 43% water, but must be diluted further before use. This additional dilution reduces viscosity and allows the application of small amounts of residual binder to be adequately controlled. Generally, the supplier will dilute the original emulsion, in the field or at the plant. A dilution rate of 50% (1:1) (equal parts water to equal parts emulsion) is recommended. Dilution water must be potable and free from detectable solids or incompatible soluble salts (hard water).


Fog Seal Benefits

Fog seals are an inexpensive way of arresting raveling and adding binder back into aged surfaces. They can also hold chips in place in fresh chip seals, (or older chip seals beginning to loose rock) reducing the potential for vehicle damage.


Fog seals are an inexpensive way of arresting raveling and adding binder back into aged surfaces.

Reduced Damage

Fog seals hold chips in place in fresh chip seals,  reducing the potential for vehicle damage.


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At Asdaş Asfalt, we are designing solutions to solve your most demanding problems and reducing costs while saving time & energy. Our team of experts can help you choose the right emulsifier, learn about sustainable hot mix asphalt or improve recycling.

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