Performance-Related Tests of Recycled Aggregates for Use in Unbound Pavement Layers (2008)

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2Project Background When used appropriately, recycled materials provide good- quality, cost-effective road construction materials that benefit the environment and lessen the use of raw materials. In most cases, the use of recycled materials offers economic benefits, because recycled materials often cost less than virgin aggregate materials, particularly when used in reclamation jobs, and may also save transportation and disposal-related costs. The societal benefits of using recycled materials include saving available natural resources and extending the life of available landfill space. Although much research has been conducted on using recycled materials, especially reclaimed asphalt pave- ment (RAP) and reclaimed concrete pavement (RCP), in bound pavement layers, limited research has been reported on the use of RAP and RCP in unbound pavement layers. Research Objective The objective of this research was to recommend proce- dures for performance-related testing and selection of re- cycled hot-mix asphalt (HMA) and portland cement concrete (PCC) materials for use as aggregates in unbound pavement layers, singularly or in combination with other materials. The research included evaluating existing aggregate tests known to predict pavement performance for their applica- bility to RAP and RCP and to develop new tests or modify existing tests. Scope of Study The research consisted of nine tasks as described below. Task 1. Review NCHRP Report 453, and collect and review other relevant domestic and foreign literature, research find- ings, performance data, current practices, and other infor- mation relative to the use, testing, and evaluation of recycled HMA and PCC materials in unbound pavement layers. Task 2. Identify the performance parameters of pavements that may be affected by the properties of recycled aggregates used in unbound layers, including consideration of the layer’s structural behavior, constructability, and related environ- mental concerns. Task 3. Identify and discuss the recycled aggregate properties that influence the performance parameters identified in Task 2. Chemical, mechanical, mineralogical, and physical properties shall be considered. Task 4. Identify and evaluate—with consideration of perfor- mance predictability, precision, accuracy, practicality, cost, and other pertinent factors—those test procedures currently used for measuring the performance-related properties iden- tified in Task 3. Task 5. Identify—with consideration of practicability, accu- racy, and other relevant factors—potential new procedures or modifications of current test procedures for measuring those performance-related properties for which no suitable test method has been identified in Task 4 and recommend proce- dures for further evaluation. Task 6. Prepare a detailed work plan for an experimental in- vestigation to evaluate and validate the most promising pro- cedures for measuring recycled aggregate properties that relate to pavement performance. Task 7. Execute the work plan and, based on the results of this work, recommend sets of tests for evaluating recycled aggre- gates used in unbound pavement layers and provide criteria for interpreting test results and assessing recycled aggregate acceptability for use in unbound pavement layers. Task 8. Develop protocols for the tests recommended in Task 7 for which standards are not currently available, in a format suitable for consideration and adoption by AASHTO. Task 9. Submit a final report that documents the entire re- search effort. C H A P T E R 1 Background and Research Approach

3Research Approach The research approach included a literature search and phone interviews with individuals representing state highway agencies and relevant industry groups. NCHRP Report 453 (1) served as the initial guide for the literature search. The tele- phone interviews provided information on agencies’ practices regarding recycling of RAP and RCP as unbound aggregate in base/subbase layers. The approach also included the selection of pavement performance parameters that may be influenced by the properties of recycled aggregate in unbound pavement layers, the identification and evaluation of recycled aggregate properties that affect pavement performance parameters, and identification and evaluation of current aggregate test proce- dures and potential techniques that can be used to measure relevant recycled aggregate properties. Report Organization Chapter 2 of this report discusses pavement perfor- mance and recycled aggregate properties that affect pave- ment performance. Chapter 3 describes the methodology used to select candidate test methods and candidate recycled ma- terials. Chapter 4 presents the laboratory test data. Data analy- sis is presented in Chapter 5. Chapter 6 provides research con- clusions, recommendations, and a validation plan. Appendix A provides details of the literature search and the telephone interviews with state DOTs. Testing protocols for the recommended test methods are presented in Appen- dix B. Appendix C presents the results of surface dielectric measurements. Appendixes A through C are not published herein but are available as NCHRP Web-Only Document 119 on the TRB website.