Chip sealing is a technique primarily used to prolong the life of paved roads. The average life span of a road paved with asphalt is approximately 10 to 12 years. The integrity of the asphalt remains solid for the first 6 or 7 years, then begins to diminish more drastically. The ideal time to apply a chip seal to the road is just before this drop-off occurs. A chip seal typically lasts 4 to 8 years depending on how much traffic passes over it. A chip seal can be applied as needed every few years to maintain a road.
In addition to the fact that a chip seal is significantly less expensive that asphalt paving, it is also much less of an inconvenience to the residents who live and work in the area where the road work is taking place. It takes far less time to chip seal a road than to pave it and the road can be driven on about an hour after the final coat of oil is applied. Drivers aren't the only people who benefit from chip sealed surfaces -- horses prefer them as well! The chip rock provides horses with traction not found on surfaces paved only with asphalt, especially important during the rainy season.
Step 1 - Emulsion is sprayed
Step 2 - A truck carrying chip rock backs up to the chip spreader & loads the chip into the machine as it is being towed by the chip spreader
Step 3 - The chipper applies the rock on top of the emulsion at a consistent rate determined by the Project Engineer
Step 4 - The chip is rolled into the emulsion
Step 5 - Any inconsistencies in the chip left by the machines are quickly evened out for a uniform finish
The emulsion truck leads the "procession" with the chip spreader pulling the dump truck and the roller following close behind
There are several different types of chip seals. The simplest type is a single chip seal where a layer of hot emulsion (oil and water) is sprayed on a paved surface, chip rock is applied by the chip spreader at a consistent rate appropriate for the type of traffic the road will see, and finally a roller presses the chips into the emulsion. This process must move quickly and consistently, as the water in the emulsion begins to evaporate as soon as it's sprayed on the surface and the oil begins to set. Depending upon the weather the road will need to cure before a sweeper is run to sweep off any excess chip. Motorists can use the road at reduced speeds during the curing process, which is typically no more than a day or two long.
A multiple layer chip seal is where the process described above takes place two or more times until the road is built up to the desired level. This is a great option for native (dirt or base) roads that have low traffic volume because a multi-layer chip seal is so much less expensive than aspahlt paving.
A fog seal is often applied on top of a fresh chip seal or asphalt pavement in order to seal the surface. A fog seal generally consists of approximately 40-50% water and 50-60% oil and is sprayed on the surface after the excess chip is swept off the road. A fog seal gives the road a smoother and darker appearance, making reflectors and other pavement markings stand out.