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, Oregon, 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 1980s 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, Colorado, 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 tank trail. A total of approximately 70,000 cubic yards 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-inches thick RCC placed on 10 inches) of granular base. Design flexural strength for all the RCC applications was 550 pounds per square inch (psi) at 28 days. To minimize random cracking, joints were sawed at 60-by-60-feet spacing.
The mix design per cubic yard consisted of:
Cement (Type I/II) 383 lbs
Coarse Aggregate (ASTM C33; No. 7) 1,565 lbs.
Mid-Size Aggregate Crusher Fines 522 lbs.
Fine Aggregate (ASTM C33) 1,391 lbs.
Water 220 lbs
The original mix design included 25 percent of the total cementitious material to be Class F fly ash 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.
Roller-Compacted Concrete Construction
Interstate Highway Construction, Inc. (IHC) of Englewood, Colorado, began roller-compacted concrete (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/hour, although the actual production during construction varied from 200 to 250 tons/hour 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.
Placing RCC with High Density Paver
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 percent of the specified required minimum compacted density of 98 percent of the modified Proctor density in accordance with ASTM D1557.
Initial and final compaction of RCC Tank Headstands
Placing adjacent lane of RCC
Final compaction was achieved using a 10-ton dual drum vibratory roller, followed by a combination pneumatic roller and a 4-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-by-60-feet 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.
Saw-Cut Joints on Completed RCC Tank Hardstands
Completed RCC Tank Hardstands
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 pounds per cubic foot and the optimum moisture content was 5.7 percent. Testing results indicated that the specific minimum density of 98 percent of the modified Proctor test was easily achieved. RCC strength results from beams cast in the field met or exceeded the 550 psi 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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