Cold In-place Recycling (CIR) and Full Depth Reclamation (FDR) are two economically and environmentally friendly methods of rehabilitating asphalt pavements. While there is a brief mention of FDR in FAA AC 150/5370-10H and AC 150/5320-6F, it is quite limited and there is no mention of CIR, therefore, this project looks to provide comprehensive guidance as to when CIR and FDR can be used, the materials that can be used, the structural design, and the construction of CIR and FDR for airfield pavements.
The ACRP Web Document 40 (Airport Design and Construction Research Roadmap) clearly identifies need for resilient and sustainable infrastructure management as an urgent need for airports. The current FAA advisory circulars on pavement design and evaluation (AC 150/5320-6F), pavement construction (AC 150/5320-10H), pavement maintenance (AC 150/5320-6C), and pavement management (AC 150/5320-7B) provide none to minimal information to airport managers and engineering professionals to adopt in-place asphalt recycling for rehabilitation. Airports in United States (for example, Runway 16/34 at McKinnon St. Simons Island Airport and Spruce Creek Airport in Florida) and elsewhere (for example Frankfurt, Treviso Italy and Penticton Canada) have successfully utilized in-place recycling techniques, such as CIR and FDR, for rehabilitation of airfield pavements in cost-effective and environmentally friendly manner. However, due to lack of national standards to effectively specify materials and to incorporate in-place recycled layers in structural design of rehabilitated pavements, the use of CIR and FDR in United States remains limited.
The proposed study will develop necessary materials for FAA to consider adding to various pavement related advisory circulars to expand the option of asphalt in-place recycling for use by various airports in United States. Specifically, following topics will be developed: (1) decision tool to select appropriate in-place recycling treatments (as function of current pavement condition, pavement structure, aircraft mix etc.); (2) material and construction specifications, including necessary QA process attributes; and, (3) guidance on incorporation of the in-place recycled pavement layer within pavement structural analysis. While plethora of such resources exist for highway pavements and several are currently under development through NCHRP studies, the fundamental differences in design and management of airfield pavements from highway pavements necessitate that material and construction specifications as well as pavement analysis tools for in-place recycling of airfield pavements be developed.
The objective of this project will be to provide draft modifications to the following advisory circulars to provide a comprehensive guidance in terms of materials, structural design, construction, and usage of CIR and FDR in flexible airfield pavement rehabilitation:
• Pavement design and evaluation (AC 150/5320-6F)
• Pavement construction (AC 150/5370-10H)
• Pavement maintenance (AC 150/5380-6C)
• Pavement management (AC 150/5380-7B)
The following sections, at a minimum, of the salient advisory circulars should be reviewed to include discussion on CIR and FDR.
Pavement design and evaluation (AC 150/5320-6F):
While there is a small amount of text on FDR in 5320-6F, significantly more information could be provided so that airports would have a better understanding of FDR. For example, a more robust background on FDR, including when the treatment is most appropriate compared to other standard rehabilitation or replacement techniques, would help airports make more informed decisions if considering FDR. In addition, flexible overlays have almost ten pages of discussion, including examples using FAARFIELD and surface preparation; similar details applicable to FDR would help airports better understand how to use FDR as a potential treatment for their flexible pavements.
In addition, it clearly states that there is no FAA standard specification for FDR, so this would be an area that would need to be explored. While 5320-6F indicates that research is being done on FDR moving in that direction, many items within the standard specification could be completed before the final data is assembled.
As mentioned, there is no discussion on CIR in 5320-6F, therefore, a similar exercise to what is proposed with FDR would be executed with CIR, but all of the content would need to be generated.
Pavement construction (AC 150/5370-10H):
Item P-207 provides a cursory overview of the materials necessary for FDR. However, many of the components need significant work. For example, there are multiple gradations that can be used for FDR, and it is more often a function of the in-place material and reclaiming machine versus what gradation is optimal. In addition, there is no discussion of asphalt emulsion under the stabilization section, and there is only one mix design available for recycling. All of these requirements could use significant expansion and discussion to ensure that FDR is not only used correctly, but also it is designed optimally. There are also significant improvements that could be made in the grading and compacting section, along with the proof rolling. There has been significant research in the field of highway pavements that could be incorporated into this section.
As mentioned, there is no discussion on CIR in 5370-10H, therefore, a similar exercise to what is proposed with FDR would be executed with CIR, but all of the content would need to be generated.
Pavement maintenance (AC 150/5380-6C):
Neither CIR nor FDR are maintenance treatments. However, it is recommended that some text be added to 5380-6C that would clearly delineate the concept of maintenance from rehabilitation, and list the potential treatments that would fall under each umbrella. That would allow airports to fully understand all of the options available to them in one place, with clear delineation as to when some treatments are more appropriate than other treatments.
Pavement management (AC 150/5380-7B):
Similar to the discussion on 5380-6C above, there is no mention of specific maintenance or rehabilitation treatments in 5380-7B. It is recommended that text be added to 5380-7B that would clearly delineate the concept of maintenance from rehabilitation, and list the potential treatments that would fall under each umbrella. Historically, the ties between highway pavement management groups and highway maintenance/rehabilitation groups are not strong. Therefore, there are often disconnects when tying specific maintenance and rehabilitation treatments to actual distresses. By providing text on maintenance versus rehabilitation, and what treatments can be used based on the existing condition of the pavement, would help build bridges between the management group and the materials/design/construction groups.
It is estimated that this project would cost $480,000 and would take 36 months. There have been several National Cooperative Highway Research Projects in the past five years that have tackled some of these topics. A typical 6-month project for one treatment and one area costs approximately $60,000 (based on comparable NCHRP and ACRP projects). Therefore, since there are two treatments proposed here (CIR and FDR), and four areas (design/evaluation, construction, maintenance, management), would cost $480,000. Since there would be some overlap between CIR and FDR, it is anticipated that the project could be executed in 75% of the full time (48 months). Therefore, the project should be completed in 36 months.
In preparation of this RNS, the ACRP research roadmaps were carefully reviewed. A continuous research gap with respect to adoption of innovation construction materials, and resilient and sustainable infrastructure management arises in the ACRP roadmap. The proposed research fits within the known research gaps under Roadmap theme areas of: 2) Integrating Advanced and Disruptive Technologies; 5) Sustainability and Resilience of Infrastructure; 6) General Design and Construction.
Use of in-place asphalt pavement recycling as pavement rehabilitation and pavement capacity enhancement technique has been shown by numerous researchers to be cost-efficient and environmentally friendly as compared to commonly adopted airfield pavement rehabilitation techniques of milling and overlay and/or reconstruction. A good example is that of Runway 16/34 rehabilitation at McKinnon St. Simons Island Airport.
There have been several recent and on-going research efforts funded by NCHRP to develop similar products as proposed herein for highway pavement applications (see list below). These efforts on highway pavements to adopt in-place asphalt recycling clearly demonstrate the need for proposed research for development of similar research products to adopt sustainable and innovative pavement rehabilitation methods of in-place asphalt recycling.
NCHRP Synthesis 20-05/Topic 51-08: Practice and Performance of Cold In-Place Recycling and Cold Central Plant Recycling
NCHRP 09-51: Material Properties of Cold In-Place Recycled and Full-Depth Reclamation Asphalt Concrete for Pavement Design
NCHRP 09-62: Rapid Tests and Specifications for Construction of Asphalt-Treated Cold Recycled Pavements
NCHRP 14-43: Construction Guide Specifications for Cold Central Plant Recycling and Cold In-Place Recycling
While specific details on how current research gaps will be addressed is covered in the previous "Approach" section, the proposed study is expected to use collective knowledge of pavement engineering, pavement researchers and airfield operators in developing necessary additions for FAA to consider in current pavement advisory circulars. As a first step, the similarities and dissimilarities in available "ready to implement" information from highway pavements should be assessed. Advisory circular additions that are applicable from highway pavement domain can be ready considered. Where dissimilarities exist (such as, airfield pavement structural design and analysis or impacts of airfield functional features in pavement rehabilitation method selection), it is proposed that researchers rely on combination of subject matter expert surveys and laboratory testing/numerical modelling, to develop the necessary research products.