Recycled Materials and Byproducts in Highway Applications—Summary Report, Volume 1 (2013)

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11 Waste recycling in the early 1990s began to focus on high- volume discarded materials with potential recyclable value (Collins and Ciesielski 1994). Over the last two decades, a num- ber of streams previously considered as waste have become valuable byproducts in highway applications. Increasing pub- lic awareness of green house gas generation, diminishing non- renewable natural resources, and the need for environmentally responsible and resource-efficient (sustainable) construction is focusing more attention on increasing the use of recycled mate- rials. Local, state, and federal programs are encouraging the use of current waste streams as value-added byproducts. At the same time, agencies and legislative bodies are restricting byproduct use with often conflicting environmental regulations, lack of standards for byproducts in specific high- way applications, and arbitrary legislative efforts. Highway applications are perceived by the public as useful means of disposal for a wide range of waste streams because of the large volume of materials used for these projects. However, agencies need to consider any addition to a highway application as a construction material, which should enhance the performance and/or lower the cost of the final application. In some cases, such as the use of fly ash in PCC, both of these goals are met. Hence, there are a number of agencies using this former waste stream as an additive to improve concrete durability and as an economical replacement for portland cement. Some agencies differ significantly in their experiences with the use of other byproducts in highway applications. Differ- ences in cost savings, availability, reported byproduct proper- ties, environmental issues, constructability, and performance are common. Increased use of byproducts is complicated by the range of final applications that can use one or more of these byproducts. Information is needed that can determine the rea- sons for the differences and more consistently assess the viabil- ity of using a given byproduct in a specific application. Although there is a growing body of experience show- ing that these materials can work well in specific highway applications, the related information and experience is not synthesized in a coherent body. Objectives The objectives of this synthesis of highway applications using byproducts were to: • Develop a comprehensive list of current candidate materials and uses in a matrix format. • Identify and review available test procedures for assess- ing physical and chemical characterization, compaction, geomechanical properties, and long-term durability, and environmental performance, including suitability and risks. • Summarize best material preparation and quality con- trol techniques (including stockpiling). • Review possible modifications to transform marginal materials into suitable materials. • Address material handling issues associated with the use of recycled materials. • Explain design adaptations that may be required for successful use. • Identify site construction practices that have proven effective. • Identify failures, causes, and lessons learned. • Identify the major scientific, contractual, and perceptual barriers to the adoption of suitable alternative materials by states and steps used to overcome these barriers. • Identify cost savings from the use of recycling, includ- ing energy and materials. • Assess gaps in knowledge. • Suggest a research roadmap to address these findings. scOpe and synthesis apprOach The objectives of this synthesis were met by collecting infor- mation from an on-line survey of state engineers, telephone interviews of agency staff with experience using byproducts, and a literature review. The agency survey was developed with one group of questions for each major byproduct cate- gory. The full survey can be found in Appendix A. The first question in each group was designed to capture the range of individual types of byproducts used in various highway appli- cations (e.g., concrete and geotechnical) using a matrix that limited the respondent’s options to predetermined choices. The matrix was followed by three open-ended questions to capture the respondent’s experiences with performance, barriers, and identification of contacts with information of projects that demonstrated performance (good or bad). This request yielded contacts for 85 separate telephone interviews that collected information on cost savings, design changes, chapter two intrOductiOn

12 synthesis OrganizatiOn Volume one provides a stand-alone document that summarizes: • Byproduct background information. • Highlights of information collected from the extensive literature reviews for each byproduct category. • Agency survey results on current use of byproducts in highway applications from the 45 states that responded to the survey. • Performance comments submitted to the on-line agency survey. • Advantages and disadvantages to using byproducts in highway applications collected during 85 telephone interviews. • Information that addresses the major synthesis objectives and is generally applicable to all of the byproducts. • Recommendations for future research programs to increase the use of recycled materials in highway applications. Volumes 2–8 are available on the web only at http://www. trb.org/Publications/NCHRPSyn435.aspx. Chapter two is the introduction. Chapters three through nine contain reported data on byproduct properties (physical and chemical), environmentally related properties, and the production and use of the byprod- ucts. Each chapter also contains annotated bibliographies for research and state agency documents that document the use of the byproducts in highway applications. Key information and reported data is included. The agency survey information is repeated in each chapter to provide a single complete docu- ment for each byproduct. • Chapter three—Coal combustion byproducts • Chapter four—Non-coal combustion byproducts • Chapter five—Mineral and quarry byproducts • Chapter six—Slags • Chapter seven—Asphalt concrete pavements • Chapter eight—Scrap tire byproducts • Chapter nine—Manufacturing and construction by- products • Chapter ten—Summary of performance comments on survey • Chapter eleven—Agency interviews • Chapter twelve—Conclusions and recommendations Chapter nine includes information for CKD, roofing materi- als, paper manufacturing waste, foundry sand, waste glass, and sulfate waste byproducts. material testing, construction adjustments, environmental benefits, and application performance. A 90% return rate on the survey was obtained. Categories of byproducts included in the agency survey and the literature review included: • Coal combustion products • Non-coal combustion byproducts • Mineral and quarry byproducts • Slag byproducts • Reclaimed asphalt pavement (RAP) • Recycled concrete aggregate (RCA) • Construction and demolition waste (CDW) • Scrap tire byproducts • Cement kiln dust (CKD) • Roofing materials (shingles, built-up roofing) • Sulfur and sulfates • Foundry sands • Glass byproducts. Highway applications included in the survey and litera- ture review were: • Bound applications – Asphalt binder and HMA – Portland cement and PCC – Surface treatments – Flowable fill. • Unbound applications – Embankments – Granular base – Stabilized base. Although stabilized bases are technically a bound material, they are discussed in the unbound section based on their primary use as base material and the low chance of binding byproduct compounds and metals owing to the low binding material content. The literature review collected additional information for materials characterizations, byproduct preparation, by- product control, material handling guidance, design adap- tations, construction, transformation of marginal materials, failures (causes, lessons learned), barriers, costs, and gaps in the information. Academic, industry, and state agency papers, presentations, and reports were used to document work com- pleted from about 2000 through 2008; information before 1999 has been reported in other documents (Collins and Ciesielski 1994; RMRC 2008).