In-place pavement recycling

recycling_web_2016Gaps, barriers and a clear path forward

Various forms of in-place pavement recycling have been utilized to rehabilitate and maintain pavements in the United States since the 1930s. The oil embargo of the 1970s and its economic ramifications stimulated the use and the development of in-place recycling.

New binder materials, construction equipment, construction operations, mixture design, quality control/quality assurance techniques and specifications were rapidly developed in the 1970s and early 1980s that improved in-place recycling techniques. Additionally, the equipment manufacturers also concurrently improved their equipment to upgrade and include new technologies in the process.

Since the 2000s, significant improvements have been made with in-place recycling technology with improved emulsions, construction equipment and mix designs that better represent predictability of material performance. However, the use of in-place recycling alternatives for rehabilitation and maintenance of our highway and road systems has not increased substantially. In specific public agencies, in-place recycling use has declined.

In-place recycling and reclaiming techniques are used in a number of North America regions. Regional use appears to be associated with the industry’s physical location, marketing and public agency acceptance. As public agency officials and industry change so does the general acceptance of in-place recycling.

In-place technologies

The benefits of the various forms of in-place recycling need to be based on their proven economic, engineering and environmental advantages in the various climate regions of North America. In-place recycling needs to be, and is becoming, more of an engineering science than a construction art form.

Here are some of the methods being used:

1. Cold In-place Recycling or cold in-place recycling-partial depth (CIR) – partial depth pulverization (2 to 5 inches) of the asphalt bound layers in a pavement, addition of a recycling agent, emulsified asphalt or foamed asphalt, mixing of the recycling agent and pulverized/sized material, laydown and compaction.

2. Cold Central Plant Recycling (CCPR) – where existing stockpiles of recycled materials are mixed in a stationary recycling unit or a central plant pugmill, is similar to CIR. The only difference is that the materials are processed off site rather than on the road. CCPR and CIR are often combined and referred to as cold recycling.

3. Full Depth Reclamation (FDR) (cold in-place recycling-full depth) – pulverization of the asphalt bound layers (6 to 12 inches) of the pavement and a portion of the underlying materials, with or without the addition of a stabilizer (Portland cement, lime, emulsified asphalt, foamed asphalt), spreading and compaction.

4. Hot In-Place Recycling (HIR) – Surface Recycling – softening of the asphalt bound surface through heating and scarifying (1 to 2 inches) with tines or a milling head. The scarified material is mixed with a rejuvenating agent (recycling agent), placed with standard hot mix asphalt paver and compacted.

5. Hot In-Place Recycling – Remixing – similar to surface recycling, except the scarified/milled material is mixed in a pugmill or mixing drum with new hot mix asphalt (typically 18 to 25 percent) or aggregate, if needed and placed as one layer.

6. Hot In-Place Recycling – Repaving – similar to surface recycling however a lift of new hot mix asphalt is placed directly on top of the loose surface recycled material and compacted simultaneously as one layer.

Need for a conference

The 2014 International and Western States In-Place Recycling Conference was held in Denver, Colorado. The conference was sponsored by the Federal Highway Administration, Asphalt Recycling & Reclaiming Association, National Center for Pavement Preservation, Colorado Department of Transportation and Texas A&M Transportation Institute.

Industry members associated with in-place recycling sponsored several conference activities including a field trip to view a hot in-place recycling operation as well as a cold central plant recycling operation.

The attendance at this conference included representatives from the public and private sector as well as academia. Over 180 participants attended from 18 states and four foreign countries (Canada, China, Czech Republic and Peru).

The first two days of the conference provided a summary of the present “state-of-the-practice” for in-place recycling. A copy of the 37 presentations and the conference video of the conference are available from the National Center for Pavement Preservation website at

Based on this foundation and the collective knowledge of the participants, a significant portion of the third day of the 2014 conference was devoted to a workshop session to identify gaps in knowledge and barriers associated with the use of in-place pavement recycling. The purpose of the workshop was to develop a path forward that will result in wider acceptance and use of these pavement rehabilitation/maintenance techniques.

Providing a forum

The primary goal was to provide a forum for public agencies (federal, state, local government), industry (equipment manufacturers, material manufacturers, contractors), engineering consultants and academic/research organizations to discuss in-place recycling, to assess the current state-of-the-knowledge and to identify gaps in knowledge or barriers to usage for each form of in-placed recycling.

The complete life of in-place recycling project development was presented and discussed. Topics focused on project selection, Life Cycle Cost Analysis (LCCA), Life Cycle Assessment (LCA), structural design, specifications, mixture design, long-term performance, extent of existing usage and construction experience. Method-specific workshop sessions were conducted at the end of the conference to actively gather attendee input on gaps, barriers, research and other needs going forward. The workshop was aimed at building a focused plan for future efforts to improve and standardize in-place recycling implementation and quality based on the broad perspective of the conference participants.

Lessons learned

State representatives wrapped up the conference by identifying their lessons learned, their needs and their ideas for moving forward with in-place recycling operations in their states.

Topics included: project selection and selection of rehabilitation alternatives, specifications, mixture design, structural design coefficients including inputs to mechanistic empirical design, performance information, life cycle costs, education/workshops/seminars and life cycle assessment. The need for consistent detailed construction plan information on the project location to be recycled was also an item identified as important to future success. It was agreed that a critical number of projects is needed in a geographic region to insure the future viability of these recycling technologies.

Looking ahead

Research projects have been identified and draft proposals written both to encompass all forms of in-place recycling as well as to focus on the individual forms of CIR (cold in-place partial depth), FDR (cold in-place full depth) and hot in-place recycling.

The 2014 workshop was both well received and highly rated by its participants. Significant momentum was generated by the workshop amongst the DOTs in attendance. Workshop participants believe that capitalizing on this momentum will demonstrate the engineering, economical and environmental benefits of pavement recycling technology.

It is further believed that efforts to maintain and even increase this momentum are valuable to the agencies responsible for infrastructure and to the public and their use of these roads.

Dr. Jon Epps (Texas A& M Transportation Institute), Dr. Stephen Cross (Oklahoma State University), Bill Schiebel and Jay Goldbaum (Colorado Department of Transportation), Michael O’Leary and Dr. Everett Crews (Ingevity) Victor “Lee” Gallivan (Consultant), Todd Thomas (Colas) and Asphalt Institute Senior Regional Engineer Dave Johnson contributed to this article.

The second International and Western States In-Place Recycling Conference will be held in Denver on October 19-20, 2016. This event will share the progress on takeaways from the 2014 conference and will focus on giving attendees the tools necessary to either deliver their first in-place recycling project or to further improve their scheduled in-place recycling projects.

The 2016 conference will highlight the progress made since the last conference, including the successful research efforts initiated at the 2014 conference. This year’s agenda will focus on the latest data on in-place recycling performance, structural modeling, recommended mix design methods, life cycle cost and sustainability and implementation assistance. Conference workshops will focus on providing attendees the project implementation tools to begin to use or improve their own in-place recycling projects this year.

More information: