ALDOT Chooses RCC with PLC for Interstate Improvement Project
The Alabama Dept. of Transportation’s (ALDOT) I-59 highway reconstruction project near Trussville included many components: bridge rail retrofits, ramp improvements, concrete rehabilitation, and shoulder reconstruction. Throughout the project, ALDOT required that highway traffic be kept moving. By specifying concrete for the shoulders, ALDOT was able to speed construction as compared to more conventional asphalt methods.
Because it can handle heavy loads, roller compacted concrete (RCC) is most commonly used in industrial applications, but is proving to be a good fit for paving projects due to advancements in quality and smoothness over the last decade. RCC is an economical and fast way to construct new and rehab old pavements, even on streets and highways. ALDOT already had experience with RCC for travel lanes. In 2018, a contractor used RCC to pave 9,727 sq yd of 10 in. thick pavement. For I-59, the same paving contractor sensed an opportunity to use RCC again, and they suggested pairing it with a more environmentally friendly concrete mix.
The contractor selected an AASHTO M 240/ASTM C595 Type IL portland-limestone cement, which contains up to 10% more limestone than ordinary portland cement (OPC) and provides equivalent performance. Following extensive testing alongside traditional Type I/II cement, ALDOT labs found very little difference in durability, strength, and quality of finish with the PLC concrete. Using PLC reduced the carbon footprint of the concrete by about 10%, or about 550 tons. The particular PLC selected is also appropriate for moderate sulfate exposure.
RCC is especially effective in limited workspaces because equipment does not extend beyond a lane. And without the need for forming and finishing, RCC is less expensive than traditional concrete construction. No formwork also proved helpful for the I-59 shoulder rehabilitation project, which was a little more complex due to pavement edge drains installed about 6 in. below the surface. Each segment had to be done in one operation per ALDOT’s requirement that the interstate lanes could re-open for travel during high traffic periods. To accomplish this, the planer cut the existing shoulder down 5 in. with the RCC equipment following right behind it. In one pass, old shoulder was removed and new material was placed, so no drop-off was ever exposed. The contractor placed more than 128,000 sq yd of 5 in. thick RCC on shoulders ranging from 5 ft to 10 ft wide along nearly eight miles of I-59.
Like all concrete, RCC doesn’t rut, shove, or produce potholes, is resistant to hydraulic fluid and oil spills, and will not soften under high temperatures. ALDOT has found that it is durable and seems to be performing so well that following completion of this project in early fall 2021, they planned to start another project for 7 more miles of shoulder work on the same highway, using the same RCC design and the same PLC mixtures. RCC with PLC concrete is advancing roadway rehabilitation and construction thanks to its speed, durability, and now, improved sustainability.