Category HIGHWAY ENGINEERING HANDBOOK

Recycled agricultural waste has potential for use in many applications not related to high­ways. Uses of agricultural wastes (with a few notable exceptions) in highways are usu­ally restricted to landscaping applications. It is estimated that more than 2 billion tons (1.8 X 1012 kg) of agricultural waste is produced each year in the United States. This rep­resents about 46 percent of the total waste produced in the United States each year.

Animal Manure. Animal manure is produced at a rate of 1.6 billion tons (1.5 X 1012 kg) annually in the United States. Other than its use as fertilizer or as composting material for landscaping rights-of-way, it has little recycling value for highways.

Crop (Green) Waste. Of the 400 million tons (363 X 109 kg) of crop waste produced annually from harvesting operations and grain processing, the potential to use rice husk ash to increase compressive strength in concrete is the most promising highway use. Research has also been conducted into converting cellulose waste to an oil appropriate as an asphalt extender.

Logging and Wood Waste. It is estimated that about 70 million tons (64 X 109 kg) of lumber waste from logging and milling operations is produced each year. Only about one – third of the wood from logged trees is used as lumber. Much of the remainder is used in other industry applications. Uses in highways include mulching and lightweight fill mate­rial for embankments or to repair slides. Application as lightweight fill material has been well documented and proven to be successful. Life expectancy of such embankments is estimated at 50 years.

Coal Refuse. Coarse coal refuse from mining operations is produced at a rate of 120 million tons (109 X 109 kg) per year. Coarse material is banked, while fine coal refuse is put into a silt-sized slurry mix and placed in impoundments. It is estimated that up to 4 billion tons (3.6 X 1012 kg) of coal mining refuse has accumulated in the United States. Concern about spontaneous combustion and leachate of the material (composed of slate and shale with sandstone and clay mixed in) has impeded in-depth studies of the use of coal waste. It is currently being evaluated for use in embankments and as subbase material, two applications that reportedly have been used in the past.

Quarry Wastes. Fairly consistent wastes consisting of fines from stone washing, crushing, and screening and wet, silty clay from washing of sand and gravel are pro­duced from quarrying operations. Most quarry waste is not reusable or sized within stan­dard specifications, are stockpiled in ponds. Reclamation through dewatering and segregating coarse and fine materials would be necessary to use the 175 million tons (159 X 109 kg) of quarry waste produced each year, or any of the approximately 4 billion tons (3.6 X 1012 kg) that have accumulated in the United States. The mineral properties and characteristics of the waste differ from quarry to quarry, limiting the beneficial end use, but quarry wastes have been used as fill and borrow material, flowable fill, and cement-treated subbase.

Mill Tailings. Mill tailings are the remains left after processing ore to concentrate it. Large amounts of mill tailing are generated from copper, iron, lead, zinc, and uranium ores.

They have been used as fill materials, in base courses, and in asphalt mixtures for years in areas where they are abundant and conventional sources are limited. Because of the metal content in the mill tailings, the stockpiles must be carefully analyzed to characterize leachate properties before use would be is deemed appropriate.

Waste Rock. Surface mining operations and subsurface mining operations produce an estimated 1 billion ton of waste rock annually in the United States. Some have been used as construction aggregate and in embankments; however, transportation costs from remote mines to construction areas often render the use of the rock economically infeasible. Where transportation is reasonable, waste rock can be used as stone fill for embankments or as riprap, or crushed for aggregate. These uses have been shown to be successful. Environmental considerations of leachate, low-level radiation, and sulfuric acid content should be investigated before use is deemed appropriate.

Approximately 150 million tons (136 X 109 kg) of industrial waste of the type that can be potentially reused to some degree in highway projects is produced annually in the United States. Little of this waste can be landfilled. Many kinds of industrial wastes are not suitable for highway use because they are hazardous or because leachate from these mate­rials are a threat to the environment. Through treatment, some industrial wastes otherwise deemed a threat to the environment may be rendered usable. Petroleum-contaminated soils, for instance, once thermally treated, can be used as fill material and have been used in asphalt mixtures as fine aggregates. Petroleum-contaminated soils are not currently being recycled into highway projects but have been used on road and street construction at the local level. The principal recoverable wastes from industrial activities are described below.

Coal Ash By-Products. NCHRP Synthesis 199 cites an American Coal Ash Association publication, (Coal Combustion By-Product Production and Consumption. 1992) when noting that 66 million tons (60 X 109 kg) of coal ash is produced annually from the 420 coal-burning power plants across the country. Coal is either anthracite, bitu­minous, or lignite (subbituminous); the particular form has a bearing on the characteris­tics of the by-products.

Fly Ash. ASTM divides fly ash into two classes: class F, from anthracite coal; and class C, from lignite coal. Class F fly ash reacts with calcium and water at ordinary tem­peratures to form a cementlike compound. Class C fly ash has a higher lime content than class F fly ash and can be self-setting. To be usable as a cementitious substitute for Portland cement, fly ash must meet quality standards established by ASTM (Standard C-618). Approximately 25 percent of the fly ash produced meets this standard, yet only about half of the viable resource is being used.

Bottom Ash and Boiler Slag. Bottom ash and boiler slag are also by-products of coal burning, amounting to approximately 18 million tons (16 X 109 kg) of waste produced annually. These by-products are being researched for use in embankments, unbound aggre­gate, and asphalt paving and antiskid material.

Blast-Furnace Slag. Slag that is the by-product of producing iron in a blast furnace is nonferrous and consists of silicates and aluminosilicates of lime. Of the three types of slag produced from blast furnaces (expanded, granular, and air cooled), about 90 percent of that recovered for use in construction is air cooled. Air-cooled slag is porous and suitable for use as aggregate in lightweight concrete, in asphalt, in roadway bases, and in fill material. Granulated slag can be finely ground as slag cement, and expanded slag can be used as aggregate in lightweight concrete. The primary barrier to use of slag is that it was not sep­arated into homogeneous piles and it was mixed with steel slag.

Steel Slag. Steel slag is the product of lime flux reacting with products in a steel furnace such as pig iron. Steel slag consists of calcium, iron, unslaked lime, and magnesium. It can be very expansive if not properly “aged” through treatment with water. Because of its characteristics of being very hard, stable, and abrasion-resistant, it is used in paving mate­rial and snow control. It is heavier than most aggregate and has been used as fill material and as railroad ballast. However, some concern has developed recently that the leachate from these two uses clogs drains and can affect receiving waters. About 7.9 million tons (7.2 X 109 kg) of steel slag is sold in the United States annually.

Nonferrous Slag. Slag from smelting operations for other ores such as copper, lead, zinc, nickel, and phosphates is grouped together under a single heading. Each must be evaluated and treated separately because of the varying properties these slags possess. Phosphate slag, copper oxide blasting slag, and zinc slag have been used as aggregate in paving mix­tures. Aluminum slag has been used experimentally for asphalt paving aggregate, but the material proved not to be durable and is no longer used.

Foundry Wastes. It is estimated that 3 million tons (2.7 X 109 kg) of foundry wastes are produced annually in the United States, including furnace dust, arc furnace dust, and sand residue. Foundries are concentrated primarily in the Great Lakes states. Foundry dust is often disposed of as hazardous material because of its high concentration of metals. Foundry sand, however, is not generally hazardous and has been used as fill material, pipe bedding, and fine aggregate in paving mixtures. Tests must be conducted on the material prior to reuse to determine the properties of the leachate and to ensure that it is environmentally safe. Research into the use of foundry sand is being conducted by departments of transportation in five states, and its use has met with limited success. The permanence of foundry sand as pipe bedding in Illinois, however, was not consid­ered acceptable.

Flue Gas Desulfurization Sludge. Flue gas desulfurization sludge (FGD) is the product of wet scrubbing of flue gases at coal-burning plants and consists of calcium sulfate or sulfite slurry. These slurries are generally landfilled. By dewatering FGD (especially the sulfate slurries) and blending it with a reactant such as portland cement, or cement fly ash, the mixture can be used as stabilized base material or as fill material. FGD has also been used as a dust control palliative, and additional uses are being investigated.

Paper Mill Wastes. Inorganic paper mill sludge has been used occasionally for dust con­trol on highway projects. Although research has indicated that spent sulfide liquor from the paper milling process may have application in soil stabilization, it is believed that a higher level of use exists for the material within the paper industry. The ash residue from burning bark at paper mills, when pulverized with coal and burned, has been shown to be as effec­tive a portland cement substitute as class F fly ash and is being considered for use in high­way projects.

Much construction demolition debris consists of wastes with little recycling value for high­ways, such as wood and plaster. However, demolition debris also includes concrete, glass, metal, brick, and asphalt, most of which can be reused in highways as aggregate. In order to be a viable resource and meet the standard specifications as aggregate when crushed, the construction and/or demolition rubble must be separated from the other debris and cleaned of detritus. Construction wastes generated and the associated annual tonnage produced are presented below. Tonnage estimates were collected from numerous sources and summa­rized in NCHRP Synthesis 199.

Reclaimed Asphalt. Asphalt pavement from the demolition of parking lots, roads, and highways can be reclaimed. Most states are making at least some use of reclaimed asphalt pavement (RAP) in highways, with use within asphalt pavement as the most prevalent use. Estimated tonnage of available RAP is 50 million tons annually. Because the use of RAP interferes with the ability to control hot-mix temperatures during formulation, asphalt mix­tures can contain only between 20 and 50 percent RAP. Achieving 50 percent RAP content is practical only in a laboratory setting, where thorough blending of the RAP and new aggregate can be controlled. When plant efficiency is a concern, 50 percent RAP in hot mix is not practical. The differential between the temperature of the discharged gases and the discharged asphalt mix reaches 70° F (21°C). High exhaust gas temperatures can lead to premature corrosion of plan equipment. Thus the percentage of RAP that can be incorporated efficiently is based on the plant efficiency that can be maintained. (U. S. Army Corps of Engineers, Hot-Mix Asphalt Paving Handbook, AC 150/5370-14, July 1991, Appendix 1, pp. 1-21, and 2-45.)

Reclaimed Concrete Pavement (RCP). The recycling of concrete pavement began in this country many years ago, first as unbound aggregate, then in asphalt-wearing surfaces, and later as concrete aggregate. Improved methods of breaking up concrete and separating out the rebar have made the use of RCP more cost-competitive. Many states now recycle con­crete pavements either as new concrete or as aggregate in subbase material or base course. This does not include demolition debris of concrete structures.

Roofing Shingles. Scrap and leftover materials from composite shingle manufacturing operations results in a large quantity of waste annually. The waste includes fragments, asphalt binder, and granules. These wastes can be recycled as asphalt paving material. Shingle waste from roofing contractors and demolition operations is less viable because of possible contamination.

Sandblasting Residue. Many uses of sandblasting grit are possible if the removed paint was not lead based. If the paint was lead based or contained other metals, the debris would have to be analyzed to determine if it was nonhazardous before suitable use.

Demolition Debris. Demolition debris is a major component of waste. Much of this debris can not be received in municipal landfills. To be viable for recycling, the debris has to be separated into homogeneous materials. Rubble material has many recycling uses in highways. Wood debris can be chipped and used for lightweight fill and mulch, but only if it is untreated. Disposing of asbestos-containing material (ACM, prevalent in buildings constructed before 1979) is difficult because chrysotile asbestos fibers are known to increase cancer risk if inhaled. If demolition of buildings with ACM from state trans­portation right-of-way is required in a project, it is possible in some states to arrange for on-site disposal in a state-monitored landfill.

Waste material can be categorized as construction wastes, industrial wastes, mining or mineral wastes, agricultural wastes, or domestic wastes (of which scrap tires are a signifi­cant subset). Many advanced recycling programs have been established to make use of these wastes, such as requiring identifying codes for the base resin in plastic products to enable more refined recycling of plastics. Some of these wastes are not suitable for or do not make a significant recycling contribution to highway use. For example, only a small amount of the total crop waste (estimated to be about 9 percent of all the total nonhazardous solid waste generated each year in the United States) has a beneficial highway use. Potential uses are as an asphalt extender or portland cement additive.

In another example, it has been shown that wastes can be rendered essentially benign when used in asphaltic concrete installations. In a demonstration to the Minnesota Department of Transportation, the toxicity of bottom ash from a municipal sewage sludge incinerator was shown to be less than or equal to the toxicity of the asphaltic concrete matrix to which it was attached (Request for Approval of WIA in MnDOT Asphaltic Concrete Non-Wear Course Projects, Final report, S. David, Jan 16, 2002).

The following articles contain brief descriptions of the types of wastes that research has indicated have the potential for use in highway projects (NCHRP Synthesis 199).

The Resource Conservation and Recovery Act (RCRA). RCRA classified solid waste management facilities and practices, required states to develop comprehensive state plans for solid waste management (Dufour, op. cit., p. 99). RCRA also emphasized the growing landfill capacity problem and the need to develop approaches to handling wastes. In the preamble of RCRA, attention was called to the vast quantity of recoverable materials that are placed in landfills and to the fact that the recovery or conservation of many of these materials would benefit the United States by reducing projected landfill capacity require­ments, retaining and expanding our national resources, and reducing the country’s depen­dence on foreign resources.

In reference to recycled materials, Section 6002 of RCRA requires that federal, state, and local agencies receiving funds from the federal government must procure supplies and other items composed of the highest practical percentage of recovered or recycled materials, consistent with maintaining satisfactory levels of

• Product quality

• Technical performance

• Price competition

• Availability

Also, under RCRA, specifications cannot be written to discriminate against materials with recycled constituents. In addition, EPA was authorized to prepare guidelines for recy­cling, and resource recovery guidelines addressing procurement practices and information on research findings about the uses and availability of recycled materials. Guidelines cov­ering coal fly ash in portland cement, recycled paper, retreaded tires, building insulation, and rerefined oil have been developed. While not specifically required by EPA, the guide­lines encouraged most state highway programs to prepare specifications allowing the sub­stitution of fly ash in concrete.

Intermodal Surface Transportation Efficiency Act (ISTEA). ISTEA authorized DOT to coordinate with EPA and state programs in developing information on the economic savings, technical performance qualities, and environmental and public health threats and benefits of using recoverable resources in highway construction. TEA-21 provided technical corrections to ISTEA. ISTEA specifically calls out requirements for the per­centage of asphalt pavement containing recycled rubber from scrap tires.

In addition, state legislation has been developing to promote both research into the per­formance and viability of recycled materials and the procurement of such materials. Many have established mandatory recycling laws and most have used wastes or waste by­products in their highway programs.

Given the vast amount of building materials required to construct and maintain the trans­portation infrastructure in the United States, the country’s highway system represents a tremendous opportunity for the beneficial use of reclaimed and recycled resources. However, the reclamation and reuse of waste material must be done in an environmentally responsible manner.

The handling, disposal, and reuse of solid waste is regulated by a number of environ­mental statutes. Increased cost of complying with these requirements has increased the appeal of recycling and resource management. Because solid waste material is not as uni­form as raw materials, the characteristics, performance, cost of preparing, and application of solid waste vary with the source and type of the material. Results in highway applica­tions vary considerably and depend on such parameters as climate, composition, material handling practices, and construction procedures. Factors to be considered when recycling a waste to a highway construction end use include the following [National Cooperative Highway Research Program (NCHRP), Transportation Research Board, Synthesis 199, Recycling and Use of Waste Materials and By-Products in Highway Construction: A Synthesis of Highway Practice, Washington D. C., 1994]:

Environmental Threats and Benefits. Along with the considerable environmental bene­fit of reducing the landfill burden, potential threats to the environment caused by the use of

recycled material must be considered and compensated, mitigated, or otherwise overcome before use of recycled material is feasible.

Regulatory Requirements, Guidelines, and Restrictions. The federal and state legis­lation and guidance regarding recycled materials reflect reduced landfill capacity in the United States and the recognition that there is a net benefit to producing resources from waste. The federal government as well as some states now have recycling mandates in place. Permits are often required when conducting recycling activities, and/or when creat­ing an authorized disposal site in using certain wastes as embankment fill. If the recycling activity falls under the RCRA classification of “use constituting disposal,” additional reg­ulations apply.

Economic Cost and Benefit. Economic considerations are often the driving force behind recycling efforts on the county and city level, because of the increased landfilI costs and increasingly limited capacity. Recycling for highway departments may become more attractive as budget cuts increase and the price for recycled waste materials decreases. In some cases, recycled materials extend the service life of highway components, making the life-cycle costs of using such materials attractive.

Engineering Properties and Technical Performance. Because of the variability of the composition of waste materials, performance results for end products may vary signifi­cantly, requiring careful evaluation before identifying suitable applications for their use. The primary question is “does the performance of the material compare favorably with the same material constituted from raw materials?” In some instances, the use of waste material has consistently improved performance. For instance, silica fume use in portland cement results in higher compressive strength and higher resistance to corrosion of steel reinforcement due to the increased density and reduced porosity of the resulting concrete. (“Silicon,” Minerals Yearbook, U. S. Bureau of Mines, Washington, D. C., 1989.)

Construction Materials Shortages and Alternative Resource Availability. Millions of tons of aggregate are used each year in the construction of highways. Resources from exist­ing quarry mining are being depleted and the new sources are often not used because of restrictive regulation and preferred uses of the land. In areas experiencing shortages, recy­cling construction materials, waste minerals, and other products into aggregate is more cost-effective than shipping aggregate from distant quarries. Steel is one of the most widely recycled materials used in highways. Steel reinforcement can be composed completely of recycled scrap steel, and steel girders can contain as much as 25 percent recycled scrap steel. Recycling scrap steel greatly reduces reliance on foreign sources for raw materials in the steel industry. (NCHRP Synthesis 199, p. 6.)

The following steps have been developed for managing lead-based paint removal projects based on procedures in Trimbler’s Industrial Lead Paint Removal Handbook.

Initial Project Evaluation. In the initial project evaluation, the owner or specifier must determine whether the coating contains lead-based paint either by reviewing earlier plans and specifications for the structure or by sampling and analysis.

Prebid Assessment of Paint Removal Methods and Debris Generated. The owner or specifiers should estimate how much waste will be generated by methods evaluated to be appropriate to the size and circumstances of the project. Designing a testing program to evaluate the toxicity of waste generated may be appropriate for large paint removal projects.

Understanding the Regulations before Preparing the Specifications. The regulations regarding air quality, water quality, soil cleanup, unauthorized releases, worker protection, and hazardous waste generators should be thoroughly understood. How these regulations are enforced should be discussed with both state and local officials.

Preparing the Project Specifications. Both painting and lead removal requirements should be addressed in the specifications. These should identify the methods for surface preparation and the coating system to be applied. The relevant regulations, the degree of containment, and the evaluation of performance criteria should all be specified.

Developing a Worker Protection Plan. Prior to start-up, the contractor should provide a worker safety plan that addresses exposure monitoring, the compliance program, the respiratory protection program, personal protective equipment, housekeeping issues, hygiene facilities and procedures, medical surveillance, employee removal for exposure to lead, employee training, signage, record keeping, and employees’ right to observe and review monitoring information.

Preparing Environmental Protection Monitoring Plans. The procedures developed to verify environmental protection should include high-volume air samplers, tests for visible air emissions (opacity), personal air quality monitors, measurement (and reporting requirements) of unauthorized releases, and pre – and postproject soil quality and water quality sampling.

Developing Procedures for the Control and Handling of Hazardous Waste. Assuming that hazardous waste is to be generated, plans should be developed for identifying the waste, obtaining a hazardous waste generator identification number from the EPA, prepar­ing for proper notification and certifications with each shipment, preparing waste mani­fests, packaging and labeling waste, implementing contingency plans, conducting waste treatment and analysis for on-site handling, and record keeping.

Designing a Containment and Ventilation Plan. The contractor should develop detailed plans to select appropriate support structures and containment, address ventilation and other worker safety issues, provide emissions control, achieve water and soil protection and debris recovery, and verify the integrity of the containment structure.

Monitoring the Project. The project manager should develop a plan to monitor the ade­quacy of all of the control measures; visually monitor the project regularly and use approved testing methods to evaluate adequacy of controls; regularly monitor the ventila­tion system and the integrity of the containment; regularly examine waste storage facilities, and the handling and transportation methods and procedures; and verify worker protection and hygiene procedures. OSHA standards must be observed. Figure 1.2 illustrates a deci­sion tree to aid in the management of lead paint removal.

Specifications for scraping or blasting lead-based paint from structures should be written with worker safety and environmental issues in mind, so that qualified contractors who can adhere to a high level of quality and compliance are selected for the project. These specifi­cations should

• Describe the extent of surface preparation and the degree of containment required and let the contractor propose how to accomplish this.

• Identify key health and safety and environmental regulations to ensure that the con­tractor is aware of these regulations and plans compliance strategies in the bid.

• Clearly state that the paint to be removed is lead based. The highway department should have had the paint tested prior to contract bid if there is any doubt whether the paint is lead based. The cost differential is too great to make the assumption or let a contract with the lead concentration factor as an unknown.

• Specify how the waste is to be treated, tested, handled, and disposed of.

• Identify the worker protection standards and requirements that the contractor’s health and safety plan must meet at a minimum.

Bridges are public structures. Lead poisoning caused by lead-based paint has come to the forefront of public awareness. Any inconvenience to the public due to bridge mainte­nance calls attention to the structure and ongoing operations. If not handled well, lead – based paint removal from bridges can become a volatile community issue. Some states have passed regulations requiring public notice. The highway agency should be prepared to provide complete, accurate, and current documentation on the safety procedures that are implemented to protect the public health and the environment.

Gaining regulatory agreement with the removal and containment methods will also be valu­able in reducing public concern. Adjusting the timing for paint removal activities to be con­ducted during off-peak hours also serves to diminish the attention that the operation receives.