Process
Fog sealing is primarily used to seal small cracks, restore flexibility to the pavement surface, and protect from oxidation and aging. A single light application of emulsified asphalt is sprayed on an existing asphalt surface. Typically, a slow-setting and low-viscosity grade of emulsified asphalt is used to allow the emulsion flow easily into cracks and surface voids. This also enables the emulsion to coat aggregate particles on the surface and further improves the waterproofing of the surface.
When fog sealing pavement, there are a few critical steps in the process:
1. Surface Preparation: Before fog sealing can begin, the pavement surface must be clean and dry. Achieving this typically involves sweeping or blowing the surface to remove loose debris, dust, and dirt.
2. Asphalt Emulsion Application: The diluted asphalt emulsion is sprayed onto the pavement surface using a distributor truck. The application rate is critical to the success of the fog seal and depends on the condition of the existing pavement and the type of emulsion used.
3. Curing Time: After the emulsion is applied, it needs time to cure and break (the water in the emulsion evaporates, leaving the asphalt behind). During this time, traffic should be kept off the surface to allow for proper curing.
4. Quality Control: For a successful fog seal, the uniformity of the application and the cure rate are essential. Properly controlling these factors ensures the effectiveness and longevity of the treatment.
Variations
Equipment Variations
1. Emulsion Distributor: A calibrated emulsion distributor is used to apply emulsion evenly across the pavement surface. Proper calibration ensures that the application rate is consistent and accurate, which is critical for the success of fog sealing.
2. Calibration Standards: ASTM D-2995 is a standard method used to estimate the application rate of emulsions and their residual application rate. This standard helps determine the appropriate amount of emulsion needed for effective fog sealing.
ASTM D-2995 can be used to estimate the emulsion application rate and residual application rate.
Material Variations
Slow-setting types of emulsion are normally used for fog sealing. These include SS-1, SS-1h, CSS-1, and CSS-1h, often diluted with water to reduce viscosity for spraying. The dilutions can vary, with up to 1 part emulsion to 5 parts water, although a one-to-one dilution is commonly used. Slow-setting emulsions are designed to seal small cracks effectively and have a slower curing time, allowing for better penetration and sealing.
Some agencies may accept the use of other emulsions such as quick- (QS/CQS), medium- (MS/CMS), or rapid-setting (RS/CRS) grades. While effective in properly formulated systems, care must be taken to ensure these emulsions remain stable during dilution. Dilution friendliness decreases with increasing set speed.
- Dilution may be improved by pre-warming the dilution liquid to 25 to 90° C (77 to 194° F).
- Never add emulsion to water; always add water or other diluent to emulsion.
- Due to their limited shelf life, diluted emulsions are not normally stored unless bad weather necessitates temporary storage.
- Water for dilution should be clean, potable water, free from detectable solids or incompatible soluble salts.
- Test for dilution incompatibility, whenever in doubt, by diluting the emulsion in the severest conditions anticipated (e.g., high dilution, cold water, hard water, high shear pumps).
Common Combinations
Fog seals can be effectively combined with other pavement treatments to enhance their performance and longevity. Some of the most common combinations include:
- FOG SEAL + CHIP SEAL: Fog seals can be combined with chip seal applications to hold chips in place and prevent vehicle damage from flying chips. After the chip seal application, where aggregate chips are spread on a layer of asphalt emulsion, a fog seal is applied over the chips.
- FOG SEAL + FULL-DEPTH RECLAMATION (FDR) / COLD IN-PLACE RECYCLING (CIR): Fog seals can be combined with FDR and CIR applications to hold surface fines in place and prevent raveling from early traffic application. After FDR or CIR treatment, where existing pavement is recycled in place to create a new base layer, a fog seal is applied to the surface.
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