Cold In-Place Recycling a Success in the Badlands
For the Federal Highway Administration's (FHWA) Central Federal Lands
office, cold in-place recycling (CIR) of asphalt pavements has proven
to be a viable method of rehabilitating roads that both minimizes
user delay and is more environmentally sustainable. In June 2001,
a group of engineers from the North Dakota Department of Transportation
(DOT) and FHWA visited a CIR project in the Badlands National Park
in South Dakota to learn more about the methods Central Federal Lands
uses to select, design, and construct CIR projects. The site visit
was designed to help the North Dakota DOT engineers determine if CIR
could be a cost-effective method of rehabilitating some of North Dakota's
low volume roads.
CIR is performed by milling, screening, and crushing existing asphalt
pavement. An asphalt rejuvenator, usually in the form of an emulsion,
is then blended with the asphalt and the material is laid back down
to form a new pavement structure. A new surface consisting of hot-mix
asphalt (HMA) or a seal coat is also usually applied.
The road to be rehabilitated in the Badlands consisted of two 3.6-m
(12-ft) lanes with no shoulders and 7.6 cm (3-in) of asphalt pavement
with a 25-cm (10-in) aggregate base. As part of the reconstruction,
the road was being widened by 1.2 m (4-ft) to provide .6-m (2-ft)
shoulders on each side of the roadway. The plan called for 7.6 cm
(3-in) of new hot bituminous pavement to be placed on top of the recycled
roadway.
To determine if CIR is a viable rehabilitation strategy, Central
Federal Lands assesses the physical condition of the pavement, traffic
volume at the site, and material characteristics of the existing soils,
base, and aged HMA. CIR does not improve the underlying soils, so
if the pavement is rutting because of problems in the subgrade, CIR
is not a viable rehabilitation option. CIR is also usually not performed
on projects that are less than 4.8 km (3 mi) in length because of
the mobilization costs. And generally, Central Federal Lands does
not perform CIR on projects with traffic volumes higher than an annual
average daily traffic of 3000.
On the first day of the project, the contractor began by milling
the full 7.6 cm (3 in) of HMA. However, the remaining soil and base
structure was unable to support the weight of the equipment, so the
contractor decided to perform CIR on 6.35 cm (2.5 in) of the remaining
portion of the project to eliminate the problem. After milling, the
asphalt was screened and crushed. The material was then mixed with
emulsion. For this project, High Float Emulsion HFMS-2s was used as
the recycling agent. Field adjustments were then made to the recycling
agent to achieve adequate mixture properties.
During the CIR process, the paving machine had to stay far enough
behind the recycling train to allow for some of the moisture in the
mix to evaporate prior to being laid down by the paving machine. The
amount of water in the recycled asphalt pavement is critical to achieving
adequate density.
The compaction was performed by a 30-ton pneumatic roller, followed
by a double-drum steel wheel roller. Traffic was allowed back on the
roadway about 2 hours later.
"I thought the demonstration was very useful," says Ron
Tessier of North Dakota DOT. "There were a lot of questions I
had about cold in-place recycling and those were answered. I think
that we have a project that it could be used on."
"CIR appears to be working well for Central Federal Lands,"
says Carl Ramos of FHWA. The major advantages of this rehabilitation
method are retardation of reflective cracking, reduction in the use
of virgin aggregates, and less disruption of traffic due to the quick
progression of work. Use of the method can also add years to the expected
service life of the pavement and lower life-cycle costs. Local agencies
in Iowa and the Iowa DOT, which uses CIR on about a dozen projects
a year, have found that it adds 2-4 years of life to the pavement
by retarding or eliminating reflective cracking.
After 10 years of experience with the method, says Ramos, "we
have found that the keys to success are appropriate project selection,
adequate design, and quality construction by both the contracting
agency and the contractor."
For more information, contact Carl Ramos at the Central Federal Lands
office, 701-250-4345 (email: carl.ramos@fhwa.dot.gov).
 |
 |
 |
 |
| Two
3.6-m (12-ft) lanes were rehabilitated in the Badlands National
Park using cold in-place recycling. |
Other articles in this issue:
From Arizona to Alaska: Maintaining
access and mobility on federal lands highways
Cold in-place recycling a success in the badlands
New data collection tools get a tryout
in Denali
Combatting pavement roughness with ROSAN
How well do you know your asphalt
mix design?
The ABCs of heat-straightening repair
for steel bridges
