Cold In-Place Recycled Expanded Asphalt Mix

Cold in-place recycling (CIR) is a environmentally friendly pavement rehabilitation method that grinds up an existing asphalt pavement, sizes it, mixes in a small amount of asphalt cement, and lays it back down without any off-site hauling and processing. The added asphalt cement is typically emulsified asphalt, a blend of asphalt cement and water droplets. The material is then profiled and compacted. A new surface of hot mix asphalt (HMA) is placed after the emulsion has set and moisture and compaction requirements have been met, which can take from 14 to 30 days. Application of CIR is usually limited to the warmer, drier months due to the use of emulsified asphalt.

A recent innovation in the CIR technology is Cold In-place Recycled Expanded Asphalt Mix (CIREAM). In this new process, hot asphalt cement is pumped through an expansion chamber on the cold recycling unit, where a small amount (1%) of cold water is injected and immediately vaporizes. This creates thousands of tiny bubbles within the hot asphalt cement causing it to rapidly expand (foam). Next, the expanded asphalt is mixed with the reclaimed asphalt pavement. As with conventional CIR, the material is then profiled and compacted. The major advantage of CIREAM over conventional CIR is that a new HMA surface layer can be applied following as short as a 2-day curing period, rather than the minimum of 14 days required for CIR. The process is also less dependent on warm, dry weather for placement.

CIR has been found to be an effective pavement rehabilitation treatment, mitigating reflective cracking and extending pavement life. By reusing existing aggregates and asphalt cement (a zero waste approach), CIR/CIREAM is both environmentally sustainable and cost-effective. Other benefits of using CIR/CIREAM can be illustrated by looking at Greenhouse Gas (GHG) emissions and aggregate conservation. When compared to a traditional roadway rehabilitation technique of milling and 130 mm HMA overlay, the CIR/CIREAM process can decrease GHG emissions by 50 to 60% and aggregate use by more than 60%.

Since 1990, the ministry has successfully carried out over 40 CIR contracts and more recently, three CIREAM contracts. As a result, the ministry has reduced carbon dioxide emissions by 54,000 tones, nitric oxide/nitrogen dioxide by 440 tones, sulphur dioxide by 9,400 tones and conserved over 740,000 tones of aggregate.

CIR/CIREAM technology is a sustainable alternative to conventional methods of pavement rehabilitation and allows the ministry to reduce GHG emissions in support of the Kyoto Protocol while addressing the triple-bottom-line: the Social, Economic, and Environmental (SEE) impacts of our decisions.