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RCC Pavement Provides Performance and Economy
at
Denver International Airport
by Jamie Johnson, P.E., Rocky Mountain Cement Council
"Once DIA recognized the product durability and the cost
savings offered by RCC, it became their pavement of choice in this
application." John L. Edwards, Interstate Highway Construction,
Inc.
Project Focus
While fresh fallen snow is desirable for Colorado's ski tourism
industry, for airport operations it can be quite a challenge—especially
at airports like Denver International Airport (DIA) where the annual
snowfall is more than 61 inches (1.5 m). Removing the snow is one
thing, finding a suitable place to store it is another. For the
DIA Concourse C RON Project, 20,862 square yards (17,443 square
meters) of 8-inch (200 mm) roller-compacted concrete (RCC) was selected
for the pavement adjacent to the concourse apron areas. These areas
are where snow removal efforts stockpile excess snow from around
the DIA concourses during heavy snow events.
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| High-density paver placing RCC at DIA. |
The City and County of Denver, the owner of this project, originally
bid the project with an asphalt pavement section. Englewood-based
Interstate Highway Construction, Incorporated (IHC), recommended the
replacement of the asphalt section with a RCC pavement section utilizing
a value engineering change to help meet the owner’s requirements
and financial goals. The owner chose the RCC alternative because it
brought all of the quality characteristics of an industrial concrete
pavement at a price cheaper than both the original asphalt pavement
option and a portland cement concrete (PCC) alternative. DIA had never
previously specified a RCC pavement alternative in any of its previous
pavement applications, so IHC (with support from the Portland Cement
Association (PCA) and the Rocky Mountain Cement Council) drafted and
presented appropriate RCC plans and specifications for the project.
In addition, the consulting firm of DMJM Aviation reviewed and collaborated
in the development of the specifications focusing on the constructability
and logistical impacts for the project.
Project Details
The pavement design consisted of 8-inch (200 mm) RCC pavement placed
directly on top of 6 inches (150 mm) of recycled concrete pavement
base. The base utilized on-site waste concrete as an environmentally
friendly alternative to virgin base materials.
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| RCC paving operations on snow removal storage
area. |
The RCC material was produced with an Excel pugmill set up on the
airport property, with double end dump tractor-trailers feeding
an Ingersoll Rand Titan 8820 ABG paver. Project specifications required
a minimum compacted density of 96% of the modified Proctor density.
Initial in-place density readings taken immediately behind the paver
prior to compaction by the rollers consistently yielded densities
between 90 and 92 percent. Final compaction was achieved using a
10-ton (9.1 metric ton) dual drum vibratory roller, followed by
a combination pneumatic roller and a 2-ton (1.8 metric ton) dual
drum roller for surface sealing.
RCC pavement construction began in late fall in conditions where
the daytime highs were in the 50's and 60's F° (10's C°)
, with overnight temperatures reaching into the low 30's F°
(0's C°). Care was taken to ensure that the subgrade soils and
granular base material were not frozen at the time of RCC placement.
All RCC pavement placed when overnight temperatures were expected
to be below 35 F° (2 C°) were covered with paving blankets
to protect it from freezing. In-pavement Hi-Low temperature sensors
recorded the actual overnight pavement temperatures to ensure compliance
with specifications. To verify acceptable strength gain, 4-inch
(100 mm) diameter pavement cores were taken within 24 hours of RCC
placement and tested for concrete pavement strength. When the unconfined
compressive strength (UCS) of retrieved cores demonstrated strengths
greater than 2,000 psi (13.8 MPa), protective blankets were removed.
Consistently throughout the project, 24-hour UCS test on RCC pavement
cores yielded average strengths of 3,325 psi (22.9 MPa). Unlike
PCC pavements, control joints in RCC pavements are typically not
required for long-term performance and serviceability. However,
the owner chose to incorporate control joints on this project. The
joints were cut and sealed on a 30' x 30' (9.1 m X 9.1 m) joint
pattern. The relief sawing was accomplished with a Soff-Cut early
entry saw, allowing the cutting to be performed immediately upon
final surface rolling. The sawed joints were then cleaned of any
loose debris and filled with a silicone sealant.
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| Compaction of adjoining 8-inch (200 mm) RCC layer. |
Completed RCC layer showing protective blankets. |
Quality Control Testing
In-place density tests were taken at specified intervals behind
the finished pavement section using a nuclear moisture-density gauge
in accordance with ASTM C1040. The maximum density and optimum moisture
content (OMC) were determined using the modified Proctor test method
in accordance with ASTM D1557. The dry density was 147 pcf (2,355
kg/m3) and OMC was established at 5.9%. All tests performed indicated
OMC within specified parameters and all density tests exceeded 96%
of modified Proctor. Aggregates were selected and blended in accordance
with the requirements given in PCA publication Guide
Specification for Construction of Roller-Compacted Concrete Pavements.
Although the project specifications required 4,000 psi (27.6 MPa)
UCS at 28 days, average 28-day UCS on cylinders cast in the field
according to ASTM C1435 yielded breaks of 6,069 psi (41.8 MPa).
Summary
RCC in this application provided a very serviceable concrete pavement
at a significant cost savings to the owner. While the surface characteristics
of this industrial pavement varies slightly in appearance and aesthetics
from that of a conventional concrete pavement, RCC can prove a very
cost-effective alternative to either PCC or asphalt pavements for
similar applications. The RCC pavement application provided the
owner with a pavement that can stand up to heavy snow plowing and
heavy truck traffic during snow events, is strong and durable enough
to resist the shoving and rutting common with asphalt pavements,
and will not deteriorate under the saturated conditions caused by
melting stockpiles of snow.
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