Recycling and Reclamation of Asphalt Pavements Using In-Place Methods (2011)

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44 CHAPTER SIX CONCLUSIONS, GAPS, AND RESEARCH NEEDS CONCLUSIONS The following conclusions can be drawn from the informa- tion presented in this synthesis. Project selection: • The type, severity, and extent of distresses are used to identify the most useful in-place recycling method. • Both the distresses and recycling process will help define the depth of the milling to be used. State agen- cies and contractors use the Asphalt Recycling and Reclaiming Association (ARRA)-recommended range of full-depth reclamation (FDR) recycling depths greater than 6 in. The actual depth of recycling is proj- ect specific. • Agencies appear to underutilize FDR on thinner pave- ments (2 to 4 in.). • Roadway geometry and features need to be considered during project selection. • Climate conditions need to be considered during proj- ect selection. Structural design: • Structural design parameters need to be assessed before construction so that the final product meets or exceeds the desired performance. Preconstruction testing: • The availability or collection of in-place material prop- erties information needs to be considered when devel- oping the project design, specifications, and agency estimates of project costs. • Preconstruction testing is key to designing recycling mixes and identifying areas that may need an alterna- tive design. The time needed for this testing as well as the costs to the project need to be considered in devel- oping cost estimates and project timelines. Materials for in-place recycling projects: • Emulsions historically used in the same environmental conditions may have base asphalts with a wide range of performance-graded asphalt properties, which will likely influence the success or failure of recycling projects. • Additives and stabilizers need to be selected on the basis of their ability to improve key material and mix properties or facilitate construction processes. Quality management program: • Contractor quality control programs include field tech- nician training; validation of mix design properties, material properties, and density; and documentation of application rates. • Quality control/quality assurance programs include measurements of density, moisture content, recycling layer depth, verification of material properties, and performance-related mix testing. Specifications: • Method specifications are commonly used by agencies for in-place recycling projects. However, agencies also routinely require the contractor to select additives and provide mix designs for in-place recycling projects, which suggests that end result or short-term perfor- mance specifications may be more appropriate types of specifications. • There is no consistent use of in-place recycling terms or specification content. Benefits and barriers: • Contractor project records can be used to provide quantifiable environmental and cost benefits from in- place recycling. • Cost savings can be realized when using in-place recy- cling processes. • The magnitude of the savings will be directly related to the appropriate choice of the surface treatment. • Limited guidance is available for use in life-cycle cost analyses or for the life expectancy of the recycled roadway. • Both agencies and contractors identified the common most frequently encountered barriers as – Unsuccessful experiences, – Competing industries, and – Lack of specifications.

45 • Barriers more frequently cited by agencies than con- tractors are a lack of – Mix design methods, – Experienced contractors, and – Agency experience. • The only barrier cited more often by contractors than agencies is a lack of project selection criteria. GAPS The following information is lacking: • Well-defined terms for in-place recycling processes and materials [e.g., differences between the ARRA definition of “integral overlay” and the use of the same term by agencies as it applies to cold in-place recycling (CIR) and FDR], • Weather condition guidance for successful construc- tion of in-place recycling projects, • Climate considerations for each recycling project’s long-term performance, • Quantifiable performance characteristics, • Education and information on how various roadway geometry and other features are handled during in- place recycling processes, • Consistent curing procedures for laboratory prepara- tion of CIR and FDR mix samples, • Consistent compaction procedures for in-place recy- cling mixes, • Emulsion binder specifications that are performance graded, and • Rapid field tests to determine when CIR mats can be overlaid (e.g., when the moisture content is below 1%). RESEARCH NEEDS Specific research needs include • Reasons for the lack of use of CIR in the Southern and Southeastern states are likely related to weather con- ditions (e.g., humidity, temperature, and rainfall) and should be identified by future research to facilitate the selection of the most appropriate in-place recycling process. • The use of HIR, CIR, and FDR on roadways with annual average daily traffic (AADT) greater than 30,000 may be underused by agencies and overused on facilities with AADT less than 5,000. Subgrade support for equipment needs to be considered. The reasons for the differences in acceptable traffic levels need to be explored. • Research on the maximum FDR recycling depth (i.e., lift thickness) is needed so that the desired layer den- sity can be obtained. • The impact of roadway geometry and features needs further research to identify the reasons for differences between agency and contractor responses. • Specific reasons for contractors’ and agencies’ climate preferences need to be explained in future research efforts. • Using a structural overlay when structural capac- ity improvement may not be needed requires further research to define the criteria for selecting this option. The ability of other surface treatments to provide acceptable surface courses in this circumstance also needs to be explored. • Research is needed to quantify environmental and cost benefits. • A well-designed experimental approach to evaluating the progression of pavement distresses and the overall decline in the pavement condition index for in-place recycling methods is needed to provide reliable life- cycle cost and life expectancy information. • Structural coefficients for CIR and FDR can be better defined and based upon performance testing.