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5 â¢ Guidance for asphalt mix design practices and proce- dures that include different or a higher percentage of recycled materials. â¢ Understanding how the age and type of asphalt plant equipment impacts the addition of recycled materials during production. â¢ Documented pavement performance (service life) of roadways constructed with asphalt mixtures containing higher percentages of RAP, RAS, or with combinations of the two. The accurate measurement of recycled material properties can be difficult because traditional test methods were devel- oped using virgin aggregates and asphalts. Determining the properties of the individual recycled materials requires separat- ing the materials by removing and recovering the asphalt, as well as collecting the remaining mineral materials. It is impor- tant to make appropriate selections of and modifications to test methods used to characterize recycled material asphalt and aggregate properties. It is important that the selected test meth- ods and any modifications be documented, as well as informa- tion about any additional asphalt testing requirements so that increase testing time and costs can be anticipated. Asphalt mix designs are used to determine the optimum asphalt content and the combinations of aggregate sizes (i.e., gradation) needed to achieve key performance-related mixture properties. When recycled materials are added to the mixture, the calculation or estimation of the contribution of recycled material asphalt to total asphalt content is required. The virgin asphalt grade needs to be selected to offset for changes in the asphalt properties owing to the inclusion of the recycled material asphalt. It is important that the existence of standard- ized laboratory practices and procedures, and performance- related laboratory tests and criteria to estimate pavement performance be identified. Asphalt plant type, age, and characteristics influence the uniformity of asphalt mixtures with different or higher percent- ages of recycled materials. Useful processing and stockpiling practices for recycled materials, additional testing for qual- ity control (QC) recycled material property variability, and any asphalt plant modifications that can be made to increase the percentage and/or type of recycled materials needs to be identified. Any documented pavement performance of asphalt mix- tures with high RAP, RAS, or a combination thereof is also necessary. According to FHWA, there are approximately 2.8 million miles of paved public roadways in the United States, which have used approximately 18 billion tons of asphalt mixtures. These mixtures are typically comprised of approximately 95% quarried rock products and/or sand and gravel pit extracted materials, and 5% asphalt obtained from the processing of crude oil. Preserving, maintaining, and expanding the high- way infrastructure requires a continual supply of the natural resources that are used in pavements. In recent years, roofing shingle byproducts from the manufacturing process and from construction and demolition projects have been identified as an additional source of asphalt and aggregate materials that can have economic and environmental advantages when used as a partial replacement for asphalt mixture material components. Although approximately 99% of asphalt pavement material that is removed from any roadway is recycled back into infrastructure-related materials and products, there are a number of factors that limit the most economically and envi- ronmentally beneficial uses of the reclaimed asphalt pave- ment (RAP) materials. Barriers to increased RAP use in higher quality asphalt mixtures include higher RAP variabil- ity because of different RAP sources, demolition and milling processes, and aged asphalt with significantly different prop- erties than required for fresh asphalt mixtures. Major barriers to the acceptance and/or increased use of recycled asphalt shingles (RAS) in asphalt mixtures are the result of significantly different asphalt properties of roof- ing shingle asphalt compared with the properties of paving grade asphalts needed for acceptable pavement service life. Additional barriers to the use of RAS include contaminates from the waste recovery processes (e.g., non-RAS materials from construction and demolition waste), potentially hazard- ous materials in older products (e.g., asbestos and coal tar), and uniform processing practices that provide materials that can be handled with current asphalt plant technology. Information needed to increase the use of RAP or encour- age the general acceptance of RAS by state agencies includes McGraw et al. 2010; Scholz 2010; Copeland 2011; and Willis et al. 2012: â¢ Measuring the recycled material properties and material variability. chapter one INTRODUCTION
6 Information related to these topics was collected through a literature review and two agency surveys. The state materials engineers were surveyed to collect information about determining recycled material properties, procedures, and practices for preparing mix design samples, volumetric and performance testing, and their perceptions of the impact of different types and percentages of recycled materials on performance. State construction engineers were surveyed to collect information about processing and stockpiling recycled materials, asphalt mixture production, transport, and placement of asphalt mixtures with recycled materials. Responses were received from 45 of the 51 agencies (50 states and the District of Columbia), which is an 88% response rate (Figure 1). This synthesis is organized by the follows topics: â¢ Chapter twoâLiterature Review â¢ Chapter threeâState Material Engineer Survey â Topics covered in this survey included recycled material properties, mix design practices and proce- dures, and volumetric and performance testing. â¢ Chapter fourâState Construction Engineer Survey â Topics covered in this survey included producing and placing high RAP, RAS, and combination RAP and RAS mixtures. â¢ Chapter fiveâCase Examples â Topics include revising state specifications to encour- age routine high RAP usage (state agency and con- tractor perspectives), locating and using nonstate agency databases for evaluating pavement perfor- mance, contractorâs perspective for using RAS, and recent research studies to evaluate transfer of recycle material asphalt to virgin aggregate. â¢ Chapter sixâConclusions â¢ Abbreviations and Acronyms â¢ References â¢ Appendix AâState Materials Engineer Survey â¢ Appendix BâState Construction Engineer Survey â¢ Appendix CâResponding Agencies FIGURE 1 Agencies participating in surveys (shaded states are responding agencies). (Source: Stroup-Gardiner.)