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Projects > Fort Carson, Colo. Tank Hardstands
Tough Duty for RCC
The U.S. Army Corps of Engineers (USACE) have been specifying roller-compacted
concrete (RCC) for both dams and paving applications for more than
25 years. USACE designed the first RCC dam in the United States—Willow
Creek Dam in Heppner, Ore. which was completed in 1982. The USACE
has also pioneered the use of RCC for heavy-duty paving applications
at military bases throughout the U.S. Successful long-term performance
of projects at Ft. Gordon, Ft. Lewis and Ft. Hood in the early ‘80s
set the stage for additional work at Fort Bliss, Toole Army Depot,
Fort Benning, Fort Campbell, Fort Drum, Fort Bragg and others.
Fort Carson, the army’s mountain post located outside Colorado
Springs, Colo. is the latest military facility to utilize RCC pavements
at its facilities. As part of an expansion program at the post,
RCC is being used to pave the tank hardstands of several new maintenance
facilities, as well as a 1.6 mile (2.6 km) tank trail. A total of
approximately 70,000 cy (53,500 m3) of RCC will be placed at the
facility.
Design Details
The pavement design for both the hardstand pavements and the tank
trail consists of 10 in. (250 mm) thick RCC placed on 10 in. (250
mm) of granular base. Design flexural strength for all the RCC applications
was 550 psi (3.8 MPa) at 28 days. To minimize random cracking, joints
were sawed at 60 ft x 60 ft (18.3 m x 18.3 m) spacing.
The mix
design per cubic yard (cubic meter) consisted of:
| Cement (Type I/II) |
383 lb (173.7 kg) |
Coarse Aggregate
|
|
|
(ASTM C33; No. 7) |
1565 lb (709.9 kg) |
Mid-Size Aggregate
|
|
Crusher Fines |
|
522 lb (236.8 kg) |
Fine Aggregate
|
|
|
(ASTM C33) |
1391 lb (631.0 kg) |
| Water |
220 lb (99.8 kg) |
The original mix design included 25 percent of the total cementitious
material to be Class F flyash for use as a mineral filler and to
increase the minus No. 200 sieve size aggregate proportion of the
mix. However, unfavorable early strength results as well as spalled
joints during relief sawing operations caused the contractor to
abandon its use on the project.
RCC Construction
Interstate Highway Construction, Inc. (IHC) of Englewood, Colo.
began RCC placement in April 2008. The RCC was produced in a Rapidmix
400 pugmill set-up on site. Capacity of the plant was 400 tons/hr
(363 metric tons/hr), although the actual production during construction
varied from 200 to 250 tons/hr (181 to 227 metric tons/hr) due to
work area availability, access and obstructions. Separate storage
stockpiles were created for the three aggregate sizes. A front end
loader transferred the aggregates from the stockpiles to a three
bin cold feed blender where it was blended according to the mix
design before being transferred by conveyor into the pugmill’s
aggregate bin. The mixed RCC was hauled to the placing location
using rear dump trucks.
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| Pugmill Producing RCC at Fort Carson |
Placing RCC with High Density Paver at Fort Carson |
At the placement site the trucks discharged the RCC into a Gomaco
RTP transfer device which then was used to maintain a constant feed
of material into the Ingersoll Rand Titan 8820 ABG paver. The high
density paver was able achieve up to 92% of the specified required
minimum compacted density of 98% of the modified Proctor density
in accordance with ASTM D1557.
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| Initial and Final Compaction of RCC Tank Hardstands at Fort
Carson |
Placing Adjacent Lane of RCC at Fort Carson
|
Final compaction was achieved using a 10-ton (9.1-metric ton) dual
drum vibratory roller, followed by a combination pneumatic roller
and a 4 -ton (3.6 -metric ton) dual drum roller for surface sealing.
Immediately following final compaction a concrete curing compound
was applied to the surface to prevent premature surface drying.
To minimize the development of random cracking, joints were cut
and sealed on a 60 ft x 60 ft (18.3 m x 18.3 m) joint pattern. The
relief sawing was accomplished with a Soff-Cut early entry saw,
allowing the cutting to be performed soon after final surface rolling.
The sawed joints were then cleaned of any loose debris and filled
with a silicone sealant.
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| Saw-Cut Joints on Completed RCC Tank Hardstands
at Fort Carson |
Completed RCC Tank Hardstands at Fort Carson |
Quality control testing consisted of in-place density tests using
a nuclear moisture-density gauge. The maximum density and optimum
moisture content were determined using the modified Proctor test
method. The determined maximum dry density was 143 pcf (2290 kg/m3)
and the optimum moisture content was 5.7 %. Testing results indicated
that the specific minimum density of 98% of the modified Proctor
test was easily achieved. RCC strength results from beams cast in
the field met or exceeded the 550 psi (3.8 MPa) at 28-days strength
requirement.
Credits:
Owner: U.S. Army Corps of Engineers
Designer: U.S. Army Corps of Engineers
General Contractor: Bryan Construction
RCC Contractor: Interstate Highway Construction, Inc. (IHC)
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