Street Sealcoating Information
Sealcoating is a street maintenance technique which preserves the condition of a street by sealing the surface and small cracks within the existing asphalt pavement. When this type of preventative maintenance is performed on a timely basis, a typical pavement may last 30 years before it needs to be reconstructed. Sealcoating involves applying hot emulsified liquid asphalt to a street surface and covering the street with a graded aggregate to produce a waterproof membrane. There are several steps to seal coating:
- First, the street surface is swept clean of all loose pavement and dust.
- Next, the surface of the asphalt is completely covered with a layer of liquid asphalt using a tank truck called a distributor.
- Afterwards, a layer of gravel is placed over the liquid asphalt with a machine called a chip spreader.
- Trap rock or crushed granite gravel chips are then worked into the asphalt with a rubber tire roller.
- Traffic is allowed back on the street within several minutes of placing and compacting the gravel, as the weight of vehicles helps to work the gravel into the soft asphalt.
- Finally, after a few days of cure time, the streets are swept to pick up any loose gravel.
- Recovered gravel is reused on City streets over the winter mixed with sand and salt.
Why is the Sealcoat Program important?
The City of Cambridge has been using the sealcoat method for several years to keep streets in good condition and prolong their lifetime. The process is extremely effective as well as inexpensive, creating a good efficiency for our tax dollars.
How is the sealcoat program funded?
The sealcoat program is part of the annual Street Department Pavement Management budget. In 2016 we have budgeted $120,000 to go toward street sealcoating.
How long does the sealcoat process take?
Typically, on most streets the work is done very quickly, taking about 30 minutes per block, per lane. Some driveways may be blocked during this 30-minute period. As noted, while the road is reopened to traffic, the first sweeping does not take place for 48 to 72 hours and drivers are encouraged to drive slowly. After sweeping, the surface is still tender for the remainder of the curing process. Tight turns, quick accelerations, or sudden stops and heavy braking may leave permanent marks in the surface in the first few months, especially, on very hot days.
How will I be notified if a sealcoat is applied to my street?
A door hanger card will notify residents and business owners two to three days before any work begins.
Approximately what time will the crews be on my street?
The crews work during daylight hours from 8:00 AM- 6:00 PM. The sealcoat treatment must be applied in warm, dry weather, so the work done between June and September as weather permits. The work may be deferred if rain is in the forecast. If so, that street is rescheduled for the next clear workday.
What type of material is in the sealcoat?
Sealcoat is made up of an asphaltic binder and a uniform-sized aggregate gravel on the surface. An asphaltic binder is a water-based emulsion that does not contain any “coal tar”. Coal tar has been implicated as a contaminant in storm water runoff, which is why it is not used in our process. The sealcoat material protects an aging asphalt surface and seals up most of the small cracks to keep water out of the pavement.
Why is there excess gravel left on my street?
There will be some loose gravel particles that break loose under hard braking or fast acceleration. There may be some spots where the sweepers miss gravel, particularly at intersections or corners. However, all of this typically amounts to less than a gallon of gravel per block, and it does tend to accumulate at low spots, on the outside of curves, and at intersection corners
The street appeared to be in good shape. Why was the sealcoat needed?
Asphalt streets consist of a 2 to 4 inch layer of pavement. This mixture contains sand, rock and asphalt to bind it together. As the asphalt binder in the mix ages, weathers, and oxidizes, it becomes brittle. This causes cracks to form and water to penetrate into the pavement. The asphalt also loses its ability to hold the rock in place and the surface can start to lose rock and wear down. The rock itself starts to polish off and the street can become slicker in wet weather. While the old surface appears smooth, it contains hairline cracks that if not treated would continue to widen and deepen, eventually forming potholes.
Why does my street need to be sealcoated?
At first, the roadway asphalt aging process is slow, but after 9 to 10 years the process accelerates as cracks widen and allow more water to enter at more locations. The street will begin to contain a series of potholes and patches. The sealcoat process is applied to streets before they become badly cracked to stop the oxidation and slow the cracking process. A sealcoat can substantially extend the life of a street as much as 15 years if applied on a stable street surface.
How can the asphalt binder be removed?
If the asphalt emulsion is tracked onto shoes, carpets, or cars, WD-40 will soften the asphalt and allow it to be wiped off (but spot test carpets for color stability). If the material becomes stuck on people or pets, baby oil will dilute the material.
If the material is tracked onto a concrete driveway or sidewalk, do not dilute it, as it will soak into the concrete. If a large area is involved, sand blasting can remove the asphalt, but excessive blasting could damage the concrete finish. For smaller areas, it may be better to let the material wear off with normal traffic.
Sticky spots the size of dinner plates have appeared in the new sealcoat. Why did this happen?
When leaving your driveway, power steering turns can squeeze the gravel particles and roll them over, thus exposing the sticky side. This results in the dinner plate sized areas. Drivers can help limit these areas by slowly turning and using less power on the turns. If traffic hits that area again, the rock is often broken loose and pulled up. This problem is generally limited to specific driveways and becomes less likely as the surface cures, settles, and ages a little. In most cases, the affected areas are limited and will eventually blend in with the rest of the surface.
Is the asphaltic binder harmful to our environment?
No. The asphalt binder is a water-based emulsion that does not contain any "coal tar." Coal tar has been used in some private parking lot resurfacing and was implicated as a contaminant in storm water runoff. The asphalt emulsion Cambridge uses is a completely different material. Once the original emulsification water has evaporated, the asphalt is no longer water-soluble and does not wash away after it is applied. The gravel aggregate is clean, hard gravel that does not leach, crumble, or break down.
The sealcoat surface is too rough. My kids can’t roller blade and my dog can’t walk in the street. What can be done to smooth it out?
The surface will smooth out over the first four to six weeks as the material cures and the gravel particles interlock and embed into a tighter surface. While this process is slow, it is happening. The street will look completely different in six to eight weeks with a darker, tighter, smoother surface. It will never be as slick as the old surface, but it will provide good wet weather traction and preserve the remaining life of the street, sealing most of the cracks. Dogs, cats, and squirrels are usually back on the street within 10 days!
If you have questions, please contact Lucas Milz at 763-552-3279.