From the Regional Administrator
Welcome to our February 2015 newsletter. This month we talk about highway resurfacing. Plus, it’s still winter so please drive carefully and always be prepared.
Please drive carefully and always be prepared for winter driving. Also, on these foggy days, it’s a good idea to drive with your headlines on. It helps you and the other drivers, see each other.
As always, if you have any questions on items in this newsletter, or other transportation issues, please let me know. Give me a call at (509) 324-6010 or drop me an e-mail at: firstname.lastname@example.org .
WSDOT Eastern Region
Most of the asphalt pavement resurfacing needs are solved with either a two-inch grind out and inlay or a two-inch overlay. However, there are some conditions where cracking and pavement distress have migrated deeper into the asphalt and something more extensive needs to be done. If there are isolated areas of distress, we have the contractor dig those areas out and replace with new layers of asphalt. On two of our paving projects in 2015 the pavement has deteriorated to the point that the cracking has migrated down through the top two layers of pavement (approximately four inches). To repair this we could either grind out two layers of asphalt and replace with new asphalt or complete a “Cold-in-Place Recycle” (CIPR) for the base layer. We chose the CIPR for the following reasons:
It saves money. On the upcoming US 195 resurfacing project we expect to save about $200,000 by using CIPR. On this summer’s SR 290 project in the Spokane Valley, our savings will be over $500,000.
CIPR is an eco-friendly pavement rehabilitation process performed without the use of heat. The first step is to reclaim the top three or four inches of the existing asphalt pavement using a milling machine. The reclaimed material is then run through a screener/crusher for proper sizing. The sized aggregate material is then mixed with asphalt oil emulsion and lime then placed using a paver.
The newly placed material is then compacted with a combination of steel drum and rubber tire pneumatic rollers.
This entire process is done in one operation by using a combination of machinery referred to as a "train.” The pieces of equipment used in CIPR are an emulsion tanker, a water tanker, a milling machine, a crusher, and the paver.
The Cold-in-Place Recycle layer needs to have a layer of new asphalt over the top of it. This is the reason we don’t use CIPR on highway sections that just need a two inch layer. This isn’t a fix-all, cure-all process but under the right circumstances this is the most cost effective way to fix a road.
Recycling and reusing the existing pavement layer does away with the need for purchasing and transporting fresh aggregate. Not only do we save on the product that is used, but we also save money on transportation costs. Cold-in-Place Recycle is good on the taxpayer’s wallet and the planet.
What is a “chip-seal?”
In nearly every construction year, we have a "chip seal" construction project. This is a pavement surfacing that we use on most lesser-traveled, rural highways. Here's a nice explanation of the process first published by our co-workers from the North Central Region office in Wenatchee:
"Chip Seal" is the slang term for Bituminous Surface Treatment (BST). In simplest terms, a tanker truck sprays asphalt oil onto the roadway followed by a spreader pulling a dump truck full of gravel (known as "chips"). The chips are "spread" and stick to the asphalt oil. Next, it's compacted with a rubber-tired roller and allowed to “cure.” After it has cured, any loose gravel is swept off, the temporary speed signs come down, and a crew will come back and install new stripes, arrows, stop bars and rumble strips.
Why do we chip seal instead of paving with asphalt or concrete?
Cost is a significant factor - A BST lasts an average of six to eight years at a cost of about $40,000 per mile, while Hot Mix Asphalt (HMA) lasts about 10-13 years but costs $260,000 per mile. To convert an asphalt roadway to Portland Cement Concrete (PCC) pavement can cost five times more than that. Both HMA and PCC are stronger and handle higher traffic volumes, but BST is the better cost effective choice for many lower volume rural highways. A chip seal layer is more flexible than asphalt or concrete and more resistant to cracking when temperatures range from below zero to over 100 degrees from winter to summer. BST seals cracks and fills areas where some of the gravel aggregate may have broken away on the old pavement. It also keeps water from penetrating down into the load bearing road structure and provides a highly skid-resistant surface, particularly when wet.
A chip seal project requires a series of phases, often performed a few days apart up to several weeks later. The crack-seal and/or pavement repair crew will be scheduled first. The chip seal operation is next, followed by curing, then sweeping. After that, a few days or weeks later, “fog seal oil” is applied. Lastly, the paint striping is applied.
Very importantly, every phase of a chip seal project requires dry weather. Unfortunately, that makes it somewhat difficult to pinpoint the working schedule.
From the time the gravel goes down to when the excess is swept away, the speed limit is reduced to 35 mph. At that speed, there is less of an issue with flying rocks. Vehicles at higher speeds create dust, limiting visibility and break gravel loose from a fresh chip seal creating flying rock. Those rocks then crack windshields and chip paint. More seriously, flying rock could injure pedestrians, bicycle riders or motorcyclists. So drive the posted speed, and hope others do as well.
Please be patient. Traveling at the posted speed limit in construction zones ensures your safety and that of highway workers. It's also the law. Traffic fines are doubled in construction zones. Obeying warning signs and flagging personnel instructions benefits all of us.
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Chip seal operation photos
Chip seal equipment train getting ready to start
Spraying the oil emulsion on the roadway.
Spreading the chips. You can see the loaded gravel trucks in the background waiting their turn. The spreader is coming toward the camera with the dump truck behind in reverse.
A close-up view of the spreader.
A side view of the spreader.
The rubber-tired rollers pressing the gravel "chips" into the oil.