By Brian Hall
Well, summer is here. I know, it’s not technically summer, but it really feels like we went from pushing snow to laying blacktop in a matter of days, completely bypassing spring. During my travels, it is really great to see the smiling faces on the crew as they are getting back to consistent work as the fresh smell of asphalt is in the air. Hitting the ground running is always a great way to gauge how the season will go.
This month, going a little outside the box and talk more asphalt maintenance and preservation, more specifically, chip sealing. My father told me a story about how in the 1950’s, my grandfather convinced the county road department that it was time that our little dirt road became a “tar and chip” road. Chip sealing was mainstream in rural America during the mid-20th century. Remember the gas crisis of the ‘70’s? Chip sealing was a cost effective way to satisfy the traveling needs of the American public. As the cost of asphalt fell, so did the popularity of chip sealing.
But chip sealing is back with a vengeance, not only with municipalities, but contractors as well. I recently talked with a contractor who told me that during the recent slowdown in business, he promoted chip sealing as an alternative to paving to his driveway customers. The cost to the customer was close to half, but his profit margins were almost as high as if he had paved the driveway. I also work with many large highway contractors who use chip seal as their base layer instead of, say, a 19mm base course asphalt. Chip sealing can be done from the ground up to build a new road or as a rejuvenation of an old asphalt or previously chip sealed road. Let’s look at the chip sealing process.
After the area to be worked has been cleaned and free of any residual dirt, rocks or dust, we must put a layer of asphalt emulsion, typically the same design you use for tack but at a higher application rate. If we are using our distributor truck for tack, we are probably applying at a rate of .05 gallons per square yard, but for chip sealing, we will apply at closer to .3 gallons per square yard. This means at 8 feet wide, we will use over 1,400 gallons of emulsion per lane mile. If you are working the spreader at 150 feet per minute, you’ll complete a lane mile in well under an hour if you have your trucks lined up. If your goal is high production, you will certainly run your distributor out of emulsion rather quickly, so it’s a good idea to have a tanker on standby.
Next is the application of aggregate, or “chips”. The old style chip spreaders were manual units that required you to gauge the application rate manually. If you were too light or heavy, you just pulled the lever back a little. Today’s units are computer controlled and will lay a metered layer of aggregate that is measured in pounds per square yard. This amount is usually calculated by an engineer depending on the size of aggregate used and needs to be a washed, graded aggregate. Similar to asphalt paving, larger aggregate is used as a base layer and smaller aggregate is used for surface. The finished result allows you to see a little bit of the emulsion between the aggregate so the wearing surface is a layer on top of the emulsion. For road rejuvenation, only one lift is required. For new road building, 2 or even 3 lifts will be performed.
Finally, the finished product must be rolled with a pneumatic roller. Unlike asphalt paving, you are not trying to achieve density, only “setting” the material in place. That’s why a pneumatic roller is most desired. Since you are not rolling a flexible surface, a steel drum roller will only fracture the rock and create an undesirable finished product. Like asphalt, however, the entire surface must be rolled to ensure the aggregate properly bonds with the emulsion. Optionally you can broom the surface after the emulsion has cured, usually the next day. Some contractors or municipalities will top the finished surface with sand to further fill the voids. All is just a matter of technique.
A quick internet search will give you a lot of information not described here such as videos and photos. Chip sealing has certainly made a comeback in the last 10 years and doesn’t seem to be slowing.
Brian Hall, LeeBoy Territory Manager. He can be reached via email at firstname.lastname@example.org