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Cape Seal: An Economical Pavement Maintenance Solution

Mon January 14, 2008 - National Edition
Construction Equipment Guide

When one thinks of pavement maintenance, chip seal, slurry seal, micro surfacing or asphalt overlay generally come to mind.

All of these methods have their advantages and disadvantages. However, by combining chip seal and slurry seal, you get another alternative — cape seal. Cape seal provides a finish that is similar to an asphalt overlay, but at a lower cost.

A-1 Chipseal, a contractor serving several cities and counties along the Rocky Mountains’ Front Range in Colorado, has performed preventive maintenance construction for 10 years. The company began doing cape seal five years ago and has been introducing it to its customers as a better alternative to chip seal, slurry seal and thin asphalt overlays ever since.

“Chip seal does a good job of sealing the road, but the texture is not always the most desirable because it can be hard and rough,” said Ben Vagher, president of A-1 Chipseal. “With cape seal you get the durability and strength of the chip seal with a smooth slurry seal finish that is more customer-friendly.”

Cape Seal Process

Cape seal combines the processes of chip seal and slurry seal to form a single, more durable surface.

Here is how it works:

Step 1: Road Preparation — this includes sealing cracks, patching potholes, leveling the surface and removing weeds and other particles from the edge of the road. It is important to ensure the pavement is clean before starting the next step.

Step 2: Emulsion — spray a thick layer of polymerized oil on the pavement using a distributor truck — preferably one with computerized shot rates to give a consistent application of oil.

Step 3: Dispense Aggregate — use a chip spreader to disperse the aggregate on top of the oil evenly. The aggregate itself needs to be cubicle in shape, with little or no flat and elongated pieces, and all the same size, for a consistent finish. Haul trucks will be needed to transfer the aggregate to the chip spreader and should be compatible with the chip spreader for a smooth transition.

Step 4: Roll — use a pneumatic-tire roller, generally 5 to 10 tons, to press the aggregate into the oil. The first pass must happen immediately after the aggregate has been laid, and each section of the road should be rolled at least twice. This seals off the existing asphalt and gives it a wearing surface.

Step 5: Remove Extra Aggregate — the next day, broom up any loose aggregate that didn’t stick. Many different brooms exist, including kick brooms and side-delivery brooms which push the extra aggregate into a windrow, or vacuum brooms that suck up the excess material.

Step 6: Slurry Seal — use a slurry seal paver to place a layer of slurry on top of the chip seal. This provides added durability and reduces chip loss and traffic noise. The result is a black surface with a smooth texture. Microsurfacing can be used instead of slurry seal, but is not as common because of higher costs.

Cape Seal Applications

Cape seal works for residential and collector streets because they require a durable, yet smooth finish for safety.

Cape seal works best when the pavement does not have significant structural issues. If the road has many large potholes or major structural problems, an asphalt overlay is needed. Cape seal lasts as long as or longer than chip seal, as well as some asphalt overlays — extending the life of the pavement by up to 10 to 15 years.

A-1 Chipseal’s season starts in May and usually ends in September. The defining factor is the temperature outside — with 50 degrees being a typical measuring point. If the temperature is above 50 degrees — or will be as the process sets — then the job can be done without worry.

In locations where freezing occurs, cape seal should be placed only after a long period of dry weather — to prevent water from being trapped in the pavement. This also holds true for wet-climate areas. It is important that the surface is dry so the water doesn’t damage the new surface.

A quality cape seal pavement has a smooth texture, no loose aggregate and excellent skid resistance. It holds up well against weather conditions with a life span of 10 years or more. Cape seal reduces future cracking better than chip seal or slurry seal alone and can be done in two days or less, according to Bergkamp Pavement Preservation Solutions.

“We have heard the theory that it takes 3 to 5 days to successfully complete a cape seal and we find that inaccurate,” said Vagher. “This process seals the surface, keeping air and water out, and provides an economical way to stretch your maintenance dollars without holding up the area for more than two days.”

Highly Economical Solution

One of the main attractions of cape seal is its price, although it varies somewhat by region or state. According to A-1 Chipseal, while providing a smoother and potentially longer-lasting finish, cape seal costs only approximately $1 more per square yard than chip seal or slurry seal alone.

Aggregate size and the amount of slurry needed can fluctuate and determine the price for each job. Depending on the pavement and its condition, A-1 Chipseal uses anywhere from 0.25-in. to 0.5-in. aggregate for chip seals, and 20 to 30 lbs. of slurry per sq. yd.

In Colorado, cape seal generally costs approximately $2.50 to $2.75 per sq. yd. — a tremendous difference from the $6.40 per sq. yd. cost of a milling, utility adjustment and asphalt overlay.

Ron Martinez, street superintendent for the town of Parker, Colo., has cape seal in his 5-year plan for area cul-de-sacs and minor collector streets.

“It is not feasible to treat each road with an asphalt overlay,” said Martinez. “Cape seal is a cost-effective way to get more life out of our city roads, allowing us to take care of our residential areas quickly with a product that raises the value of the street. In the past, we have had chip seal projects peel up from residential trash trucks, whereas the cape seal does not. Cape seal comes the closest to matching the surface texture of an asphalt overlay.”

Gaining Popularity

Although cape seal is said to have originated in South Africa in the 1950s, its use is not very common in the United States. It is gaining popularity, but is more common on small residential and collector streets.

It is still unknown whether cape seal can handle the consistent weight of heavy vehicles, or stand up to high traffic volumes. This is something that will need more research before it is expanded onto more commercial roads.

Many conditions can affect the cape seal’s efficiency, including traffic volume; strength and quality of emulsion; pavement condition; aggregate gradation; snowplow traffic; turning, starting and stopping of traffic; and elevation.

One potential reason to use cape seal on high-volume roads is its durability against snowplow blades. Most cities and counties use carbide blades on their snowplows, which can break apart chip seal with down pressure. Unlike other preventive maintenance methods, cape seal protects well against these sharp carbide blades and does not deteriorate nearly as quickly.

“We see a huge potential for this process on area streets,” said Vagher. “There is a strong need for it in Colorado and across the country. It provides our customers with a good return on their investment. Once people try this, it is an easy sell and makes sense.”

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