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

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Recycled materials and industrial byproducts are being used in highway applications with increasing frequency. Although there is a growing body of experience showing that these materials work well in a number of highway applications, the related information and expe- rience are not synthesized in a coherent body. This study gathered the recent experiences of state agencies, both foreign and domestic, in determining the relevant properties of recy- cled materials and industrial byproducts and the beneficial use for highway applications. It includes strengths and weaknesses of material applications. The synthesis serves as a guide to states revising the provisions of their materials specifications to incorporate the use of recycled materials and industrial byproducts and can assist producers and users in “leveling the playing field” for a wide range of dissimilar materials. This report is presented in eight volumes, the first of which, Recycled Materials and Byproducts in Highway Applications—Summary Report is available in hard copy and on the Internet. Volumes 2–8 are available on the Internet only and present comprehensive informa- tion on the following: (Volume 2: Coal Combustion Byproducts; Volume 3: Non-Coal Com- bustion Byproducts; Volume 4: Mineral and Quarry Byproducts; Volume 5: Slag Byproducts; Volume 6: Reclaimed Asphalt Pavement, Recycled Concrete Aggregate, and Construction Demolition Waste; Volume 7: Scrap Tire Byproducts; and Volume 8: Manufacturing and Construction Byproducts). Volumes 2–8 can be accessed at http://www.trb.org/Publications/ NCHRPSyn435.aspx. The original 1994 survey by Collins and Ciesielski focused on identifying research on waste products in a limited number of highway applications. In fewer than 20 years, a number of these waste products are now considered recycled materials and byproducts that are routinely used in a range of highway applications. In 1994, waste products were gener- ally classified by the main source of the waste stream. The byproducts, identified as waste products in the 1994 survey, were used to prepare a second agency survey, which was administered in the summer of 2009. The results from the agency survey and the literature review of each of the byproducts were used to meet the objectives outlined in the original synthesis scope of work: • Byproducts: Develop a comprehensive list of current candidate materials and uses in a matrix format. • Test methods: Identify and review available test procedures for assessing physical and chemical characterization, compaction, geomechanical properties, long-term durabil- ity, and environmental performance, including suitability and risks. • Material preparation: Summarize best material preparation and quality control techniques (including stockpiling). • Transformation: Review possible modifications to transform marginal materials into suitable materials. This includes mechanical, chemical, or environmental strategies. • Handling: Address material handling issues associated with the use of recycled materials. • Design: Explain design adaptations that may be required for successful use. • Construction: Identify site construction practices that have proven effective. • Lessons learned: Identify failures, causes, and lessons learned. summary recycled materials and Byproducts in HigHway applications—summary report

2 • Barriers: Identify the major scientific, contractual, and perceptual barriers to adoption of suitable alternative materials by states and steps used to overcome these barriers. • Costs: Identify cost savings from use of recycling, including energy and materials. • Gaps: Summarize gaps in knowledge. • Roadmap: Develop a research roadmap to address these findings. Highway applications included in the survey and literature review included hot mix asphalt (HMA) pavement (asphalt binder and HMA mix), portland cement concrete (PCC) pavement (cement manufacture, mortar, mix), drainage, embankment, granular base, stabilized base, flowable fill, and surface treatments. Each application category has a wide range of varia- tions that may or may not be suitable for a particular type of byproduct. Each byproduct section starts with a summary of the types of byproducts and a descrip- tion of the process that produces each type. Historically reported physical, chemical, and environmentally related properties, uses, production quantities, and cost representative data are assembled for research and projects reported prior to about 1998. The literature review focused on information contained in research and documentation published from about 1998 through 2009. Byproducts Currently, a number of the waste streams reviewed in 1994 have been redefined and some- what separated into individual types of byproducts, each with its own advantages and dis- advantages, when used in a given application. The main waste streams and currently identified types of byproducts in each category included in this synthesis are: • Coal combustion byproducts: coal boiler ash, coal bottom ash, fly ash (Types C and F), flue gas desulfurization (FGD), and fluidized bed combustion (FBC). • Non-coal combustion byproducts: municipal solid waste (MSW) bottom ash, MSW combined ash (bottom ash and exhaust fines), and sewage sludge ash. • Slags: – Iron blast furnace slags: blast furnace slag (BFS), air-cooled BFS, granulated ground BFS, expanded BFS, and vitrified pelletized BFS. – Steel slags: basic oxygen furnace (BOF), electric arc furnace (EAF), open hearth (OH) furnace, and ladle slag. – Non-ferrous slags: copper, nickel, lead, zinc, and phosphorous. • Mineral and quarry byproducts: baghouse fines, coal refuse, mill tailings, spent oil shale, pond fines, screenings, and waste rock. • Reclaimed asphalt pavements (RAP): baghouse fines (asphalt concrete mixture), unused plant mix, unmilled RAP [pavement removal where flexible pavement layer remains in large sizes (i.e. chunks)], as-milled RAP, and separated and stockpiled RAP. • Recycled concrete aggregate (RCA): concrete plant end of day waste and water; recy- cled concrete material (RCM); hardened, crushed, and washed RCM; and returned fresh concrete in a new batch. • Construction demolition waste recycled concrete aggregate (CDW RCA): recycled concrete aggregate from general construction demolition projects. • Scrap tire rubber: whole tires, slit tires, ground tires, shredded or chipped tires, ground rubber, crumb rubber aggregate (dry process), crumb rubber modifier (wet process), and tire buffing. • Kiln dusts: cement and a combination of cement and lime kiln dust. • Roofing shingles: paper backed, fiberglass backed, tear-offs, and built-up roofing. • Paper manufacturing: pulp and lime mud, manufacture, and post-consumer. • Spent foundry sand: green sands and core sands. • Sulfur and sulfates: sulfur, fluorogypsum, and phosphogypsum. • Waste glass: processed glass aggregate (amber, green, flint colors), and powdered glass.

3 test metHods In some cases, standard test methods may need to adjust certain handling and mixing meth- ods such as how long to dry a material to a constant weight or when and how to add the byproduct during mixing. Highly water-absorptive byproducts may need further adjustments to laboratory drying times so that an accurate measure of moisture at the time of construction can be obtained. Byproducts that can be degraded by handling may need to have specific requirements for sampling and handling of samples taken for quality control. material preparation Optimum byproduct preparation and quality control considers the differences between each type of byproduct and the byproduct variability when developing stockpiling, quality control, and quality assurance programs. Although each category and type of byproduct has a range of best practices for handling, production, and placement, a general list of information needed to identify the most economical and beneficial practices has been assembled. The best material post-processing and stockpiling practices are typically the most eco- nomical as well. A regional recycling facility can provide the best means of controlling byproduct separation, any required post-processing, and quality control. Post-processing of industry byproducts may be needed to broaden the acceptance of a byproduct to meet the required application specifications. A highway application that uses a particular byproduct needs to be identified so that the waste materials can be post-processed based on the specified application properties for improved usage. As technological changes are made to the industry producing the byproducts, the physical and chemical properties of the byproducts can change. This may require altering the disposal practices of the industry producing the byproduct. When industries producing various types of a given category of byproduct provide separate disposal sites or stockpiles, improved consistency of the byproduct properties can be achieved. Improvements in key properties of each byproduct should be periodically determined and documented. If the byproduct is post-processed at the plant site, environmental and noise regulations are addressed by the contractor. In the case of on-site crushers, regulations for fugitive dust and the noise from crushing in an urban environment are considered. Handling Optimum storage of byproducts to be used in highway application provides proper drainage to minimize runoff and fugitive dust for fine, dry byproducts. Good locations for stockpiles are within the environmentally permitted area with good drainage. In some cases, byproduct proper- ties can be enhanced with weathering, whereas others can solidify when in contact with water so that dry storage may be needed, depending on the byproduct. Finer ash byproducts are added by using a separate storage silo at ready-mix plants and metering technology for adding mineral filler during HMA production. Consideration by plant managers of size differences between the byproduct and virgin materials can improve the efficiency of the plant particulate emis- sions removal system. Byproducts, as with all other construction materials, require proper on-site storage facilities, material stockpiling best practices, potential handling degradation owing to possible environmental impacts, and worker safety. designs The majority of the agencies interviewed for their experience with byproducts in highway applications reported that simple changes are needed, such as adjustments to mix volumet- rics and pavement thickness. Changes to volumetric mix designs for either HMA or PCC

4 applications consider differences in specific gravities and moisture absorption. PCC applica- tions are adjusted for specific gravities, inclusion of cementitious materials (i.e., pozzolans), and the water demand for the mix. In the case of HMA applications, volumetric adjustments are used to obtain the desired in-place air voids, voids in mineral aggregate, and voids filled with asphalt cement. The in-place HMA mat thickness is commonly specified in units of pounds per square yard and byproducts that will be influenced by the changes in specific gravities. High specific gravities result in thinner mat thicknesses if the unit weights for the project are not adjusted. When byproducts are used in unbound applications, in-place density and ground water contamination are considerations for optimal performance. Density is commonly determined using the sand cone method or a nuclear density gauge. In some cases, adjustments to the test method procedures can be made to conventional procedures to provide more accurate mea- surements; for example, byproducts with high hydrogen contents resulted in higher nuclear density measurements compared with laboratory density testing. Correlations between gauge and lab results for each project can be used to overcome these differences. Byproducts with the potential for ground water contamination are located above the water table, both for the project and for the production storage areas. It is important that unusual factors such as the fire potential of shredded tires be considered when defining the layer heights of the byproduct in an embankment or fill design. construction The most successful PCC construction processes factor in changes in set times and slump (workability) in the work schedule and the time at which finishing can be started or forms stripped. In the case of HMA applications, the contractor assesses the need to establish a nonstandard rolling pattern or equipment sequencing to achieve optimum density and ride quality. As with conventional materials used in embankments, fills, and stabilized bases, testing and monitoring of the optimum moisture and density are needed. Some production quality control programs increase the numbers of samples tested to account for increased application product variability. Agencies routinely using a given byproduct in highway application(s) reported no or only limited changes in construction processes. costs From the financial point of view, it is beneficial for byproducts to be located close to the project location to provide a cost savings. Suggested distances were fewer than 30 to 50 miles from the project. Alternatively, a regional recycling facility can be used to economically pro- duce a post-processed byproduct that can be packaged, bagged, or shipped longer distances. Byproduct generators without their own captive landfills have a higher economic incentive to find markets for byproducts; for example, typical power plant landfill costs range from $3 to $15/ton for plants with their own landfills, which increases to $10 to $35/ton for those with- out landfills. The lower the market value of the byproduct, the less likely a plant owner will be to spend money on improving the quality and consistency of its byproduct. Transportation costs may limit the use of byproducts to local projects. Agencies routinely using byproducts in highway applications almost always reported cost savings as one of the primary reasons for using recycled materials. However, finan- cial costs can increase for agencies and contractors because of the increased efforts needed for additional post-processing, increased requirements for quality control/quality assurance (QC/QA) testing, and additional environmental monitoring over time. The variability in the byproducts may require additional preconstruction and construction quality control testing

5 to design and monitor the uniformity of the project. Additional testing can increase both the design and construction costs. Monitoring wells for tracking changes in water quality may be needed when byproducts are used in unbound or semi-bound applications. Some byproducts with high specific gravities can make it more costly to haul, because tonnage is needed for the same volume. Higher absorbed water percentages in the byproducts can result in increased drying costs during production of the highway application products. These high liquid absorption capacities will increase the binder demand, and therefore the cost, because binders (portland cement or asphalt cement) are the most expensive component in the mixes. Highway applications routinely monitor and pay on units of mass and/or volume. Some byproducts require plant adjustments to account for different specific gravities (e.g., fly ash vs. cement-specific gravities) or to account for higher unit weights when calculating haul costs for the same volume of materials (e.g., steel slag in HMA). lessons learned Regardless of byproduct type or application, agencies routinely using a specific byproduct identified improved performance as a benefit compared with traditional materials. However, these respondents also noted that data and proper documentation is still needed to confirm the perceived improvement in performance with the use of recycled materials and byproducts. Training for the field and laboratory staff is needed to achieve the optimum benefits and performance improvements resulting from the sometimes steep learning curve for possible production and construction process changes. Agencies generally noted that byproduct vari- ability increased the need to monitor QC/QA testing and/or increase the testing frequency. The availability of storage and/or stockpiling space for the byproduct at the plant can influence whether or not the contractor uses the byproduct. Environmental and noise regula- tions may limit additional post-processing such as crushing at the plant. A total of 85 telephone interviews revealed that very few agencies had poor perfor- mance with the byproducts and applications commonly used in their state. However, there were some differences between agencies using the same byproduct in similar applications. For exam- ple, agency experience with roofing shingles in HMA applications ranged from good to poor. The reasons for the difference in experiences need to be more rigorously defined so that best practices guidelines can be developed for specific types of byproducts in specific applications. gaps environmentally related gaps First and foremost, communications between environmental and materials engineers need to be improved. Each group of agency engineers must appreciate the needs, regulations, and requirements that another group is required to meet. Improved communication is required to help streamline the best use for each byproduct type in each application. Education and com- munication is essential between byproduct suppliers and users so that each group of stakeholders understands the importance of byproduct properties, availability, and quantities on application uses. Education and communication is also needed to help identify and minimize differing and/ or conflicting federal, state, and local regulations. Regulations may have different impacts on different stakeholders. Consistent environmental guidelines are needed before increased use of byproducts can be achieved. Estimates of the recyclability at the end of the service life of the application (i.e., sustainability) are also needed.

6 Environmental testing programs along with environmental cost information are needed to assess the environmental costs and benefits of applications that use byproducts. Life-cycle environmental assessments require information on anticipated changes in energy and heat for both the traditional raw materials and byproducts in the application process. There are a number of software programs available to assist with environmental impacts such as leaching or emissions potential. Examples include: • CalTOx: This program is a risk assessment model that calculates emissions of a chemical, the concentration of the chemical in the soil, and the risk of adverse health effects. • IWEM (Industrial Waste Management Evaluation Model): Software is designed to minimize or avoid adverse ground-water impacts by evaluating types of liners, hydro- geological site conditions, and the toxicity and expected leachate concentrations from the recycled material. • PaLATE (Pavement Life-Cycle Assessment Tool for Environmental and Economic Effects): This is an Excel-based program designed to record inputs on design, ini- tial construction, maintenance, equipment, costs, and output cost and environmental results. • STUWMPP (Screening Tool for Using Waste Materials in Paving Projects): Uses dilution-attenuation factors obtained from the seasonal soil compartment (SESOIL) model and relates leaching concentrations from byproducts and soils to concentrations in underlying ground water. • WiscLEACH: This model is based on a three-analytical solution using the advection- dispersion-reaction equation to describe transport in the vadose zone and ground water. The development of the model was calibrated to results from HYDRUS-2D (Lin et al. 2005). There are two other programs that can also be used; however, these are marketed (i.e., purchase required) software programs: • IMPACT™: Provides methods for conducting analyses for the transport and accumu- lation of contaminates, and for calculating the dose or risk to humans. • HYDRUS-2D: This software is a finite-element program for simulating the movement of water, heat, and multiple solutes in variably saturated media. application gaps The most readily identifiable missing information in the literature and agency responses includes a lack of training and education programs for all stakeholders with regard to byproducts, potential uses, and how to evaluate the environmental and financial advantages and disadvantages. There is a consistent lack of understanding of regulations, processes, and specification requirements that must be met by each stakeholder group. For example, byproduct producers are unaware of highway application aggregate properties that influ- ence an application’s performance. The number and variation of byproduct descriptions limit the development of material specifications for byproducts. The lack of specifications for key material properties for each type of byproduct appears to be a factor in an inappropriate selection of a byproduct to be used in a particular application. The lack of specifications makes it difficult for the byproduct suppliers to efficiently post-process and/or stockpile byproducts so that they can be more readily used in highway applications. The identification of spatial location and potential quantities of byproduct sources is needed before an agency engages in a recycling program. Alternatively, the same informa- tion is needed by the byproduct producer for local highway projects before an optimal and economical use for the byproduct can be identified.

7 Mineralogical, chemical, and mechanical properties for each source of byproduct need to be developed so that changes in key properties over time and between sources can be defined; this will help in the development of byproduct specifications for physical and chemical properties. Standard test method adjustments are required to properly evaluate byproduct and high- way application product properties and performance. For example, a correlation between laboratory and nuclear field density test results is needed so that accurate in-place densities can be made when the byproduct contains a significant amount of hydrogen constituents. Mix design test methods define the order of addition of application components during sample preparation so that samples are fabricated that represent construction processes. Precision statements for test methods could be redeveloped or expanded when using byproducts since the original statistics were likely developed using variations in traditional materials. This is important because testing variability must be considered in the development of quality con- trol and specification limits. Best practices guidelines for stockpiling, handling, and placement are essential. These guide- lines may or may not vary by the type of byproduct and application. Contractor and crew training are needed to successfully construct for the best performance the modified application. Post-construction evaluations involving on-site environmental impact assessment should be a part of implementing the use of byproducts in highway applications. This is particularly important when using byproducts in unbound applications without a history of use. Life-cycle cost analyses require additional information about the financial costs asso- ciated with preparing the byproducts. Cost information on additional testing and inspec- tion requirements are needed as well as changes in construction processes so that potential changes in cost can be estimated. Agencies reported that when permitting is based on environmental issues using environmen- tally friendly byproducts processes can result in significant carbon dioxide (CO2) reduction credits. However, more work is required to fully document the environmental benefits. Barriers Byproducts in highway applications need to be economically advantageous when compared with traditional materials and processes. A byproduct with little difference in cost but result- ing in improved performance can overcome the financial barrier. However, there is limited information on either the economic or performance improvement for most byproducts in highway applications. Limited sources or quantities of byproducts in a region of the country prevent a few agencies from using potentially beneficial byproducts. In some cases, there may be a local requirement to use more of a byproduct in highway applications when the supplier has a greater financial incentive for an alternate use. Byproduct variability is a consistent agency concern. However, byproduct suppliers are not always motivated to provide their byproducts in a form that is useful or best for highway applications. Producers may not separate stockpiles of different byproducts from the same process (e.g., power plants). This is possibly a financial or site consideration with available square footage. It is also possible that the byproduct supplier is not aware of the specific needs for each highway application. Suppliers may also resist additional post-processing of the byproduct such as crushing the material to a specific range of sizes or instituting a drying process for byproducts in slurry form. Some byproducts may need time in the stockpile to weather, which may require more storage capacity at the process site. Alternatively, some byproducts would be prepared as-needed to prevent long-term storage deterioration.

8 Key byproduct properties that relate to the application product properties and constructabil- ity must be conveyed to the byproduct supplier. It is important that agencies and contractors understand the original materials and processes that produce the byproduct. Byproduct suppli- ers need to be aware that the size, size distribution, particle shape, specific gravity, absorption capacity (water), toughness, and durability are primary concerns for highway applications. Byproducts that have a high water absorption capacity may generate problems with frost heave in unbound applications in cold, wet climates. Byproducts with primarily one-sized fine particles (e.g., spent foundry sand) have a desirable quality for casting operations but may create gradation problems when used as fine aggregates in PCC or HMA applications. Some byproduct reactions with other components result in destructive expansive reactions or a loss of ultimate application product strengths. In some applications, appearance is also a consid- eration so any influence of the chemistry, color, or texture of the byproduct can be important. Byproduct suppliers, contractors, and agencies must be aware of the chemistry of the byproducts as well as their potential for air and ground-water contamination, and potential chemical interactions with other application materials. Leaching of heavy metals is a major consideration when using nontraditional materials in highway applications. The ultimate recyclability of the application product at the end of life is to be assessed so that agencies can evaluate the long-term environmental impact. This information can be used to evaluate the impact of cradle-to-grave life-cycle costs and environmental assessments. Environmentally related barriers include additional sets of environmental regulations when using byproducts, lack of federal guidance, lack of state environmental guidance, increasingly rigorous air and water quality standards, and difficulty in finding and using environmental software by engineers and contractors. Other barriers include arbitrary limits on material properties (e.g., a maximum specific gravity for aggregates) and maximum or minimum limits on use as a replacement (e.g., fly ash and ground granulated blast furnace slag), inadequate contractor experience, lack of agency experience, lack of test data to support the use in a given application, cost informa- tion, performance history, and needed adjustments to traditional empirical relationships (e.g., PCC compressive strength used to estimate flexural strength). “Stove piping” by byproduct generators and users of the byproducts in highway appli- cations also restrict increased use. Stove piping refers to the lack of generators and users understanding of each other’s needs and limitations. Each stakeholder group is limited to an understanding of the processes of their own industries.