Surface treatments such as fog seal, double chip seal, micro surfacing, thin hot-mix asphalt overlays, and seal coat, help pavement last longer. All surface treatments seal existing surfaces with asphalt. If more friction is necessary, an aggregate is applied on top. The asphalt can be a cutback or emulsion; emulsions are typically recommended because they offer reduced environmental impact and provide increased safety.
The most common forms of surface treatments are fairly similar and tend to vary based upon the type and amount of aggregate placed on top of the asphalt emulsion in order to seal the pavement. Knowing the exact type of surface treatment roadways require is key to a job well done.
The following types of popular surface treatments are all beneficial investments in order to increase lifespan of roadways.
1. Fog Seal
A fog seal is a rather inexpensive diluted asphalt emulsion that does not include a cover aggregate. It is used to seal and enhance surfaces as well as to fix minor cracks, reduce risks for raveling and deliver shoulder delineation.
Fog seals are commonly used on high-volume roads as well as low-traffic roads. When used in high-traffic locations the main purpose is to prevent raveling of open-graded friction courses, as well as to define the mainline from the shoulder.
Fog seals are required more or less frequently depending on the original thickness of existing asphalt mixture.
As with most sealants, this method is best applied during warmer weather, as cooler temperatures will require longer curing times and therefore roads must remain closed for longer. No traffic should enter the area until the emulsion has completely cured. Traffic speeds should be reduced until some of the asphalt has a chance to wear off the surface.
2. Seal Coat
A seal coat includes a coat of asphalt followed by an aggregate cover. Seal coats are used to waterproof surfaces, seal minor cracks and rehabilitate surface friction.
Pavement may be sealed with this type of treatment at any time of its life, but this method is especially beneficial for dry and raveled pavements. Even if roads are in good condition, this is a great way to revitalize and reduce need for maintenance down the road.
No vehicles can drive over roadways until the rolling is completed and bituminous materials set, otherwise materials will transfer to tires.
A seal coat should last between 3-6 years, depending on levels of traffic a road gets.
3. Double Chip Seal
A double chip seal is similar to a seal coat, but it includes two single seal coats as opposed to one. The second coat is applied directly following the first coat, with 60% of the total asphalt binder applied first with larger aggregate. The second coat includes 40% total asphalt binder with aggregates half as large as the first layer.
Generally, this type of sealant is applied to older asphalt, following previous applications of seal coat and fog seal. Prior to applying a double chip seal, all cracks and chips must be fixed and pavement cleaned.
In order for the best results, this type of sealant must be applied during daylight and when the pavement and air temperature are at least 60° F, and the humidity no higher than 75%.
All materials must completely set before traffic is allowed back on the roadway. If loose chips are not properly integrated with the asphalt membrane they could come loose and damage vehicle windshields.
4. Slurry Seal
A slurry seal contains a precise combination of aggregate, asphalt emulsion, mineral filler (most commonly Portland cement) and water. This type of sealant is commonly used to seal pavement, reduce surface raveling, seal minor cracks and enhance surface friction.
Slurry seals are comparable to double chip seals, as they both rely on heat from the sun and pavement to set. Generally, this sealant takes between 2 and 8 hours to set, based upon the heat and humidity that day.
If the main problem is oxidation and hardening of surfaces, a slurry seal is a great option. If pavement is covered in lots of cracks, this type of sealant is not going to take as well. All repairs should be conducted prior to applying slurry seal.
Microsurfacing is a rut-filling material used to treat surfacing and rut filling on roads that get moderate to heavy levels of traffic. This preventative maintenance technique is skid-resistant and helps reduce water penetration.
Microsurfacing differs from polymer-modified slurry seal because of the curing process, which is chemically controlled as opposed to undergoing a thermal process.
Microsurfacing takes less time to cure than slurry seals, and roads may be reopened to traffic in as little as one hour. This type of surface treatment is necessary about once every 7 or so years, depending upon traffic flow as well as the condition of pavement when treatment is applied.
6. Thin Hot-Mix Overlays
This form of sealant is made from aggregate and asphalt cement. This type of surface treatment is used to enhance functional conditions of pavement, with thickness ranging between ¾ to 1-1/2 inches. Mixes are often combined with polymers in order to accommodate the need for higher performance. This treatment is recommended before signs of fatigue-related pavement distress sets in.
Thin hot-mix overlays can be used on all types of roads, and remain especially popular for high-traffic roads in residential areas where longevity and decreased surface noises are important.