Search Content

Cold In-place Recycling (CIR) is pulverizing and rebinding existing Hot Mix Asphalt (HMA) pavements with bituminous and/or chemical additives without heating to produce a restored pavement layer. This process has become a desired rehabilitation alternative for cost, environmental, and performance advantages compared to standard practices. The process utilizes a train of equipment with either volumetric or weight control. It also utilizes various stabilization materials including emulsion, cement, combinations of emulsion/cement, and foamed asphalt. Performance-based laboratory tests to capture fracture energy of materials have shown they can correlate to field performance quite well. These tests offer an excellent opportunity to differentiate between processes and materials used in CIR for characterization and development of a performance-based specification. In this study, the performance of CIR using four different stabilization (rebinding) materials of Engineering Emulsion, High Float Emulsion (HFMS-2s), Commodity Emulsion (CSS-1) with Cement, and Foamed asphalt are compared using a newly developed testing method called Fracture Index Value for Energy (FIVE). This test is performed on notched Semi-Circular Bending (SCB) specimens by controlling the crack mouth opening displacement (CMOD) rate. The FIVE test is found to be a practical easy to perform test that is able to compare CIR material low temperature characteristics. In this study, the FIVE test first was verified against Disc-shaped Compact Tension (DCT) test results and then was applied on the four study mixtures. Furthermore, the FIVE test results went through a validation process with inter-lab comparisons by three different testing labs of Braun Intertec, American Testing Engineering, and the Minnesota Department of Transportation (MnDOT).

In this study, to evaluate the effect of emulsion reduction during the CIR process in the field, three laboratory CIR mix designs were performed using the same RAP material and emulsion at three different mixing temperatures. The mix design results showed that as the mixing temperature increased; the optimum emulsion content decreased significantly. Also increasing the mixing temperature improved the mixture compaction. Both the dry and retained stabilities were also higher for the high-temperature mixtures. The critical low temperatures of high-temperature mixtures were higher than the room-temperature mixture (indicative of a worse performance) but still lower than -20°C. From the results of this study, it appears that reducing the emulsion content of the CIR mixtures during the heat of the day does not necessarily deteriorate the mixture properties. This could result in substantial savings for agencies that use this process without sacrificing long-term performance.

Significant improvements have been made in base stabilization practice that include design specifications and methodology, experience with the selection of stabilizing additives, and equipment for distribution and uniform blending of additives. For the rehabilitation of existing pavements the stabilization of base material has delivered performance as good as or better than reconstruction at a reduced cost. Many additive products exist to stabilize base materials for roadway construction, but it is not always clear which additive is the right one to use. This guidebook intends to focus on stabilization for new construction and Stabilized Full Depth Reclamation (SFDR) and to help with the selection of suitable nonproprietary stabilization additives for individual specific project(s).

Base stabilization entails mixing a stabilizing additive into an acceptable base aggregate material, imported with or without recycled material or from reclaimed hot-mix asphalt (HMA), creating a new bound pavement layer. The fundamental value of stabilizing base materials is achieving similar pavement structures more economically. Stabilizing base aggregates can allow pavement designers to develop stronger, deeper pavement structures with reduced subcut depths and thinner surfacing lifts of HMA.