The old adage, “Cheap, Fast, Good: Pick Any Two,” applies to most things. Defying this commonly held belief, rehabilitating a roadway with cold-in-place recycling (CIR) can actually be faster and cheaper than traditional methods and still yield outstanding results.
CIR is a single operation. An existing deteriorated hot-mix asphalt (HMA) layer is recycled and treated, typically with an asphalt emulsion. The layer is re-compacted to form a newly stabilized base layer. A new HMA surface layer is then placed on top. Four-to-eight inches of asphalt are usually recycled in a single pass.
Texas A&M Transportation Institute (TTI) Senior Research Engineer Tom Scullion and Research Scientist Stephen Sebesta have kept an eye on two CIR test sections that were placed by the Texas Department of Transportation’s (TxDOT’s) Amarillo District. The first CIR section was constructed in Ochiltree County in fall 2010, the second in Hemphill County in fall 2013. Recent visual evaluations show both sections are performing well.
CIR isn’t appropriate for every rehabilitation project. The base layer below the HMA layer must be structurally sound. As Scullion says, “If there are old, deteriorated stripped-out asphalt layers, which may be four-to-five inches down, you end up with four-to-five inches of good asphalt material on top of a bunch of ball bearings. No matter what you do to the upper layers, the deteriorated layer will cause the top layer to fail rapidly.”
That’s where TTI’s unique forensic pavement capabilities come into play. Using ground penetrating radar, falling weight deflectometers and pavement core samples, TTI can determine if and where deteriorated asphalt layers exist, and if the underlying base is sound.
“We gather the material, bring it into the lab and design a mix to see if we can make a good base out of it,” Scullion says, describing the TTI-developed procedures. “If you have the technology and the lab procedures to make this work, it’s a no-brainer.”
If the proposed section is a good candidate, the CIR process can accelerate the construction process. “I think of a more holistic viewpoint of planning processes, pavement designs, materials selection and traffic-handling strategies that all come together as a package to accelerate the construction timeline,” Sebesta says. “CIR can be part of a broader accelerated construction package.”
Besides saving time, CIR has a number of environmental advantages over milling the old surface and replacing it with new material. Reusing materials saves the cost of purchasing new materials, of course, but also the cost of transporting it to the site. From an environmental perspective, the energy required to produce and transport new materials is also saved.