A Texas First: TxDOT’s Roller Compacted Concrete Highway in Leakey, Texas, USA
Roller-compacted concrete (RCC) pavement generally has been only for lower-speed roads or industrial applications. But, in November, 2016 the Texas Department of Transportation (TxDOT) completed its first mainline, high-speed RCC federal highway in Leakey, Texas, 100 miles West of San Antonio.
Leakey, in the heart of the Texas Hill Country, is a hub for tourists seeking summer water activities, fall leaf-watching, motorcycle rides and year-round camping. However, this portion of U.S. 83 is also a heavy truck route servicing nearby aggregate quarries and oil/gas activities. TxDOT needed a heavy-duty, low-maintenance pavement that could improve safety and accommodate this busy mix of leisure and heavy-hauling traffic, without major disruption.
RCC + FDR provided a fast, heavy-duty solution. Looking for solutions to road damage in energy sector corridors, TxDOT designed U.S. 83 as an 8-inch RCC section on 8-inches of full-depth reclaimed (FDR), cement stabilized subbase (recycled in place; TxDOT item 275). This also included a short stretch of RM 337 and its intersection with US-83 in downtown Leakey. RM 337 was designed with 7 ½ inches of RCC pavement on the same 8-inch subbase.
Recycling the old pavement in place with 4% cement created a quickly constructed, durable platform that served as a temporary surface for traffic and a stiff, non-erodible subbase layer on which the RCC was placed within days. The prime contractor stabilized the recycled subbase using GPS-guided motor graders, establishing an accurate final grade on which the RCC pavement would then be placed and compacted. The FDR subbase also saved time and money by eliminating the need for new base material, excavation of the old, and associated trucking for over 30,000 tons of material.
The highway needed to remain open day and night during paving because the highway serves as a key truck route for aggregate quarries to the south, and for energy sector traffic known for its devastating impact on rural highways. The 50,500 sy of RCC pavement (TxDOT ss3253) was placed in a 3-week period averaging nearly ½-lane mile per day. This impressive production rate was achieved while keeping the adjacent lanes open to traffic. The fast construction and uninterrupted traffic flow, in an off-peak time of year, minimized losses for the many small business in Leakey. The resilience of the cement-stabilized FDR subbase provided a high-performance temporary surface for traffic. The RCC, placed with high-density asphalt-style pavers in a single lift, was normally opened to traffic within days of paving. RCC’s density and low-water content contributed to its high early strength, which allowed several critical RCC sections to resume full traffic within 24 hours of placement.
The contract also specified diamond grinding if necessary, to meet TxDOT’s tight-surface tolerance specification. However, the RCC subcontractor achieved specified ride quality, even in the 55-mph sections, without grinding. Key to accomplishing this were quality materials, an optimized 3-part aggregate blend, and an ideal mix design, as well as the use of a high-volume pug mill with high-density asphalt-style pavers.
Roller-compacted concrete is currently built under a TxDOT “special specification”, allowing it to evolve from one project to the next in any TxDOT District. The specification used for this contract was TxDOT ss3253. TxDOT continues to roll out more RCC pavement.
For more information about this project, RCC paving, or FDR with cement, contact:
Matthew Singel: Phone: 817-709-4313 | E-mail: msingel@cementx.org
To read the entire Cement Council of Texas’ article, please go to:
http://www.cementx.org/projects/rcc-txdot-us83.