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4 Cold recycling processes provide agencies with cost-effective and environmentally friendly pavement maintenance and rehabilitation options for aged asphalt pavements. Cost savings are achieved by reducing the need for new materials; requiring fewer haul trucks; lowering fuel consumption; and eliminating the need for adjustments to curb, gutter, and overhead clearances. Environmental benefits include the reduced need for natural resources and lower generation of greenhouse gases by both the construction process and the reduced time vehicles spend in traffic queues. Cold in-place recycling (CIR) is a process in which 3 to 4Â in. (75 to 100Â mm) of the existing asphalt pavement layers are pulverized, mixed with a recycling agent, and repaved in place (Wagner 2018). Cold central plant recycling (CCPR) is similar to CIR, but it can recycle thicker pavement layers and the recycling operation occurs at a nearby, usually mobile, plant location. CCPR can use reclaimed asphalt pavement (RAP) obtained from the roadway under construc- tion, a mixture of RAP from various nearby projects, or previously stockpiled RAP. Neither CIR nor CCPR is used to modify the underlying base and subgrade materials, so roadways need to be structurally sound with good drainage. The objective of this synthesis is to document how projects suitable for CIR and CCPR processes are selected, considered in the pavement design phase, constructed, and evaluated. Three methods were used to accomplish this objective: (1) an online agency survey, (2) a litera- ture review, and (3) interviews to collect agency experiences for case examples. The online state agency survey assessed the size, extent, and experience with CIR and CCPR as well as with newly published AASHTO and Asphalt Recycling and Reclaiming Association (ARRA) standards. A total of 40 agencies responded for a response rate of 80%, although not all respondents answered all questions. The literature review evaluated published CIR and CCPR literature, research reports, and conference proceedings published on agency research websites, in peer-reviewed journals, and by regional user-producer organizations. The literature review documented information about pavement design, mix designs, performance testing, service life, cost savings, and environmental benefits. Presentations by agency staff and researchers at local, regional, state, and national conferences that were posted to websites were also reviewed. Six agency case examples were developed to address individual key topics that were not specifically covered with the survey and the literature review. The topics include (1) project selection criteria based on pavement distresses (Indiana), (2) a first experience with CCPR (Minnesota), (3) a CCPR plant owned and operated by an agency (Maine), (4) innovative mix design and construction control (Utah), (5) smoothness specification applied to cold recycled C H A P T E R 1 Introduction
Introduction 5Â Â mixes (Caltrans), and (6) more than four decades of experience with cold recycling (Federal Lands Highway). This synthesis is organized into the following chapters: â¢ ChapterÂ 2 â Literature Review â¢ ChapterÂ 3 â Agency Survey â¢ ChapterÂ 4 â Case Examples â¢ ChapterÂ 5 â Conclusions