What's the Favorite Topping?

Denver comparing asphalt and concrete overlays

Concrete Roads Article July 17, 2003
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The Colorado Department of Transportation (CDOT) Region 6
chose whitetopping to address rutting and continual maintenance on a
high-traffic asphalt highway in Denver. Interstate Highway Construction (IHC)
completed the 3.5-mile project ahead of schedule, producing a smooth-riding,
long-lasting pavement. 

Stopping the fight

According to Kevin Sullivan, CDOT project engineer,
Wadsworth Boulevard was widened to four lanes in the late 1970s and since has
received several asphalt overlays. It was showing minor rutting and cracking.
"Maintenance had been fighting the road for the past few years,"
Sullivan said.

CDOT designers chose to cover the 6 in. of asphalt with a
like amount of concrete.

Roy Guevara, CDOT design engineer, viewed the Wadsworth
Boulevard overlay as a pilot project for the district. "The 6-in.
thickness is the most unique feature," he said.

CDOT also decided to vary pavement thickness and joint
spacing on a 400-ft test section. They used 4-in.-thick concrete with 4-sq-ft
and 6-sq-ft panels. They also varied the joint spacing on part of the
6-in.-thick pavement to 6 x 9 ft and 6 x 6 ft.

Guevara said CDOT also built an asphalt overlay section on
the north side of the road to provide a means of evaluating the two systems.
"We will compare concrete and asphalt performance visually during yearly
visits," he said. "We'll see what works best and develop a standard
based on our observations."

The contractor milled the existing asphalt less than 1 in.
to enhance the bond, and then paved the road in 38-ft widths. IHC received
incentives for ride, thickness and strength. The ride averaged 8.1 in./mile on
a 1/10 blanking band. IHC received an incentive of $12,000 for completing the
job three days ahead of the 70-calendar-day limit.

Wadsworth Boulevard sees an average daily traffic of 33,000
vehicles. The traffic maintenance plan minimized inconvenience to motorists by
moving traffic to one side of the divided highway, head-to-head with one lane
in each direction. 

Traffic control was greatly assisted by the emphasis on
public relations, according to Sullivan. "There was a public relations
spec in the contract and a large amount of communication with the public and
local businesses. This encouraged a lot of people to use alternate
routes," he said.

Minimal interruption

The project included three major intersections. According to
Sullivan, the contract called for weekend closures of these intersections.
"The contractor proposed closing each of them for a 24-hour period during
the week," said Sullivan. "It worked out really well. People were
impressed that we'd close the intersection in the morning and open it by noon
the next day."

"Getting through the intersections in the minimum
amount of time was critical to getting the whole job done on time," said
Sullivan. "Scheduling was very important." Several subcontractors had
to get their jobs done in sequence within the 24-hour closures.

Guevara was impressed with the fast-track paving. "It
sure goes quicker than it used to," he said.

The 71/2-sack mix achieved 2,500 psi in 20 hours. The
straight cement (no fly ash) mix design included 3 lb per cu yd of fiber.

"We received a lot of positive comments," Scott
said. "The big one was that we got in and out so fast. Even our concrete
paving competitors called the office and complimented us." He attributed
the success of the project to the teamwork between the contractor, highway
department and "all our great subcontractors." style="mso-spacerun: yes"> 

Sullivan agreed the project was a success. "We got an
excellent product," he said. "We got in and out fast. The paving crew
did a very good job. It all worked the way we wanted it to, and we're confident
it will perform the way we want it to."

"The benefit of whitetopping is it's maintenance-free
and thus won't disturb traffic for repairs to the road," said Guevara.

Scott added that speed of construction is the key. style="mso-spacerun: yes">  "If we can put concrete down as
fast as asphalt, and minimize the impact to the public, we can make concrete
more competitive," he said.

About the author: 
Information provided by the American Concrete Pavement Association, Skokie, Ill.
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