What are the best practices for cold in-place recycling of asphalt pavements?

1 Evaluate pavement condition

Before choosing CIR as a rehabilitation option, you need to evaluate the condition of the existing pavement. CIR is suitable for pavements that have moderate to severe distresses, such as cracking, raveling, rutting, and potholes, but not for pavements that have severe base or subgrade problems, such as frost heave, swelling, or softening. You also need to consider the traffic volume, climate, and drainage conditions of the pavement. You can use visual inspection, deflection testing, coring, and laboratory testing to assess the pavement condition and determine the feasibility of CIR.

2 Select recycling agent and mix design

The recycling agent is a binder that helps restore the viscosity and cohesion of the aged asphalt. The type and amount of recycling agent depend on the characteristics of the existing asphalt, such as penetration, viscosity, and binder content. The most common recycling agents are emulsified asphalt, foamed asphalt, and chemical additives. You can use laboratory tests, such as Superpave performance grading, to select the appropriate recycling agent and dosage. The mix design also involves determining the optimum moisture content, compaction level, and gradation of the recycled material.

3 Prepare equipment and materials

CIR requires specialized equipment and materials to perform the milling, mixing, and paving operations. The equipment includes a milling machine, a recycling train, a paving machine, and a compaction roller. The milling machine removes the existing pavement to a specified depth and width, and transfers it to the recycling train. The recycling train consists of a crusher, a screening unit, a pugmill, and a tank for the recycling agent and water. The pugmill mixes the milled material with the recycling agent and water, and produces a homogeneous recycled mix. The paving machine places the recycled mix on the road as a new base layer. The compaction roller compacts the recycled mix to the desired density and smoothness.

4 Control quality and performance

Quality and performance control is essential for ensuring the success of CIR. You need to monitor and adjust the equipment settings, the material properties, and the environmental conditions during the CIR process. You also need to conduct field tests, such as density, moisture, and strength tests, to verify the quality of the recycled mix and the finished pavement. Additionally, you need to apply a surface treatment, such as a chip seal or a thin overlay, to protect the CIR layer from moisture and traffic damage. You can also evaluate the long-term performance of the CIR pavement by measuring its structural and functional indicators, such as deflection, roughness, and friction.

5 Follow best practices guidelines

CIR is a complex and dynamic process that requires careful planning, design, and execution. To help you achieve the best results, you can follow some of the best practices guidelines that have been developed by various agencies and organizations. For example, you can refer to the FHWA's Cold In-Place Recycling Best Practices Manual, which provides comprehensive information and recommendations on CIR. You can also consult the AASHTO's Guide for Design of Pavement Structures, which provides methods and criteria for designing CIR pavements. By following these guidelines, you can optimize the benefits and outcomes of CIR.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?