USING SOLID WASTES IN HIGHWAY CONSTRUCTION DA VID MANUGIAN Ciemson University Clemson, South Carolina pii3j 7 /./ 2,gc hf ABSTRACT As concerns about solid waste management continue to grow, new uses for these wastes are being investigated. One solution in the area of disposal of solid waste materials is to use them in highway construction. While providing a use for solid wastes, highway engineers are also finding replacements for costly and disappearing conventional highway materials. Some materials, such as rubber from waste tires, have qualities that form a better asphalt concrete than those used before. Tires are a plentiful source of material, and have been successfully used in many cases. Reclaimed paving materials and slags and ashes have found practical uses in highway construction. Glass, building rubble, and sludge have also found limited uses. These uses may provide an economically competitive solution for a growing disposal problem. In addition, legislation passed by federal and state governments in the last few years regarding use of solid wastes has created an additional incentive to use these materials. However, more research must be done. Issues such as recycleables' recyclability, long term durability, environmental impacts, constructability, and quality must be addressed before a total commitment can be made to solid waste materials in highway construction. INTRODUCTION The management of solid waste materials focuses on three areas; source, collection, and disposal.' To look at the management of these areas without considering political and economic consequences would be a waste of engineering skills. For example, if the cost of disposal of solid waste included environmental costs, people would lower their costs by dumping their waste on the side of a highway. Thus solutions must be found that are acceptable to the capitalist society we live in. One possibility is to use of these materials in highway construction. With continued research in a number of currently known areas this could become a feasible business in the near future. The use of solid waste materials in highway construction is an important area of research today for many reasons. Research of alternate materials in pavement construction is important because new supplies of conventional materials are disappearing or gone in some parts of the country, and are becoming prohibitively expensive. Alternate solutions for the deposition of solid wastes is important because current space for them is quickly being used up. This paper reviews what has been done, what is being done, and what will be done with solid waste materials in highway construction. It focuses on tires, reclaimed paving materials, and slags & ashes, and includes the use of plastics, glass, sludge, and building rubble. Finally it addresses concerns for future research. TIRES About 285 million vehicle tires are discarded each year.' In addition, it is estimated that over 3 billion tires are stockpiled above ground, legally and illegally, across the country. In addition to the space consumed, another problem is that the tires are a fire hazard because of the extreme difficulty in stopping one from burning once it has started, and they create an excellent breeding area for mosquitoes. Current methods for disposing of waste tires are using them as an industrial fuel source, recycling them as a raw material in the production of other rubber materials, and using them in ' P. Aarne Vesilind, Environmental Engineering (Butterworth; 1988): 261 Elizabeth Pennisi, "Rubber to the Road," Science News 7 March 1992: 155. 1
highway con~truction.~ In a questionnaire given to every state by the Transportation Research Board (TRB) regarding use of waste materials in highway construction, 38 of 45 respondents used scrap tire^.^ They are used in embankments to retain soil and in asphalt pavements. Tires have been used in asphalt pavement in a number of areas. They are ground up to form a "crumb rubber additive" which is used in two processes, a wet process and a dry process. In the wet process the crumb rubber additive is mixed with the asphalt in asphalt mixing tanks to produce an asphalt-rubber binder. In the dry process the crumb rubber additive is mixed with the hot dry aggregate before it is combine with the asphalt. The hybrid asphalt-rubber pavement is then used as a wearing surface. It is also used as a crack/joint sealant and a surface/interlayer treatment. Research has suggested that the use of rubber can prolong the life of an asphalt pavement. However, it also increases the cost of the asphalt. Thus in addition to new uses for the rubber in the asphalt, methods for reducing the cost of the rubber material are currently being explored. In 1991 the federal government passed the ISTEA Act. It requires asphalt in federally-funded highway projects to contain at least 5% rubber by 1994. While many states already have similar legislation, surveys have shown that some states have not done any work in this area. In 1997 the percentage will increase to 20%.6 And in that time it is believed that new technology and research will also promote and expand the uses of tires in asphalt pavement.' RECLAIMED PAVING MATERIALS Reclaimed paving materials have been used satisfactorily for many years. In the TRB survey 42 of 45 respondents indicated that they were using them. The increasing cost of oil and the resulting increase in the cost of asphalt is making the recycling of pavement materials a feasible source of aggregate. At the same time federal, state, and local governments are becoming more aware of the need to preserve natural resources. Additionally, the disposal of removed paving materials is a major concern. The recycling of reclaimed paving materials can be classified into three categories: hot mix, cold mix, and surface recycling. Hot mix recycling involves removal and mixing at a central plant. Cold mix recycling can be performed in place or at a crushing plant. Surface recycling is the refinishing of just the top inch of pavement.' Research is being conducted in these areas today. At Purdue University the use of cold in-place recycling (CIR) is being tried and has tentatively been considered as "showing satisfactory performance and considerable cost savings over conventional overlays."e In Iowa the state Department of Transportation has tried using reclaimed Portland Cement Concrete and found that: 1. 2. The recycled pavements exhibit good performance. The major problem has been a common occurrence of mid panel cracking. lmtiaz Ahmed, Use of Waste Materials in Highway Construction. Indiana Department of Transportation, 1991. Material not specifically documented in this section of the paper was taken from this report, p 25. R.J. Collins and S.K. Ciesielski. "Highway Construction Use of Wastes and By-products, "Utilization of Waste Materials in Civil Engineering Construction (American Society of Civil Engineers, 1992): 150. Hugo Martin, "A Scrappy Stretch of Road," Los Anaeles Times 8 June 1992. Ahmed23. ' Ahmed 56. 8 Ahmed 57. 2
The Connecticut Department of Transportation used reclaimed paving materials for a six year period. They found that: 1. Energy expenditures for the construction of each section was about equal. 2. Differences between sections paved with reclaimed paving materials and control sections were minimal in the areas of wear, structural soundness, and friction level. 3. Cracking in the recycled pavement was higher than in the control section, but no major structural failure had occurred at the time. In addition to their use in the asphalt binder, reclaimed paving materials can also be used as a cheap alternative to fill in embankments. When used in this capacity care must be taken to assure that the materials will not substantially break down and cause settling of the embankments. Research done at this time has indicated that using reclaimed paving materials is technically reliable and economically feasible. And as landfill requirements become more stringent and the cost of disposing of used paving materials becomes more prohibitive, their reuse will become more prevalent. SLAGS AND ASHES Slags and Ashes have been used in different forms for many purposes for tkousands of years. Romans used them in their roads 2000 years ago. In the nineteenth century their use was expanded extensively in the U.S, and is widespread today. Millions of tons of slags and ashes are produced each year, and their disposal is a major concern. In the TRB survey 18 of 45 respondents used iron and steel slags, 14 of 45 used bottom ash, and 42 of 45 used fly ash. Disposal problems are similar to other materials. Four categories of slags and ashes are iron blast furnace slag, steel slag, bottom ash, and coal fly ash. lron Blast Furnace Slag is produced in the selective cooling of the liquid slag. It can be cooled by air or water, granulated, or pelletized, and is considered to have the highest potential of all waste materials in highway construction. lron Blast Furnace Slag is used by many states and is considered to be Cost effective while performing well. Studies have shown that roads incorporating boiler slag in the top /ayers retain their black cdor longer and experience less aggregate pitting than conventional asphzilt mixes. 2 Its environmental acceptability raises some concerns, but these concerns are mostly,with their use in embankments and subbases instead of their use in pavements. Steel Slag is a byproduct in steel production. Concerns are its expansive nature, and inappropriateness for use in Portland Cement Concrete. In asphalt pavements steel slags have been used and are considered economical, technically feasible, and environmentally acceptable. l3 Bottom Ash is the residue from burning coal. Over ten million tons are produced each year. Once again, disposal is a concern. Bottom ashes have potential for use in highway construction but are considered very corrosive. l4 F!y Ash is nearly 75% of all ash waste produced. It has been used in pavements in the U. S. for over 75 years. Its benefits include improved workability, reduced heat of hydration, increased Ahmed 56. lo D.W. Lewis, Resource Conservation bv Use of lron and Steel Slaas (ASTIM, 19821 35. Lewis 37. l2 Elizabeth Bretz Innovation key to finding unusual ash-disposal options, Electrical World July 1991: 57. l3 Ahmed 62-63. l4 Ahmed 65. 3
ultimate strength, improved resistance against aikali aggregate and sulfate attack, and reduced permeability. l6 Slags and ashes have also been used as fill in embankments. Two problems with their use are that they erode very easily and do not support vegetation. To solve these problems engineers have used a cover of about two feet of soil over the waste materials. Another issue that will have to be addressed is finding a universal set of specifications by which to judge the ash.16 Use of slags and ashes is well established in pavement construction, and as disposal costs increase their use will increase as well. OTHER MATERIALS Plastics, glass, sludge, and building rubble have been tried as highway materials to a lesser extent than tires, reclaimed paving materials, and slags and ashes. However, their uses are currently being explored. Plastic has been used in a highway project near Toronto. Polymers have been used in asphalt. They were found to make the pavement more flexible." Glass has been used in numerous studies for highway construction. In the TRB survey 9 of 45 respondents reported using waste glass. Problems have been encountered with skid resistance and reaction with the asphalt. Generally it is recommended that the glass be limited in use to small amounts on roads without high-speed traffic." Sludge use has been limited to highway embankments. Applications in pavements have not been explored. Incinerator residue has qualities and applications which are similar to bottom and fly ash, and its applications are similar. In the TRB survey 3 of 45 respondents reported using sewage sludge, and 5 of 45 reported trying incinerator residue. Building Rubble has been considered as a pavement material. In the TRB survey, 5 of 45 respondents reported using demolition rubble. It is estimated that around 20 million tons are produced each year, and thus disposal concerns are once again encouraging new uses. A problem is the variety of materials that can be in building rubble. It is hard to control the quality of the material when its contents can vary greatly. Thus its use in pavements has been limited. The Connecticut DOT has used it without many problems to date." Materials such as plastics, glass, and building rubble may prove to be useful in highway pavement construction. At this point, their use is still in the research stage, and little solid data is yet available for interpretation. THE FUTURE OF WASTE MATERIALS IN HIGHWAY CONSTRUCTION In a recent survey sent out from the Clemson University Civil Engineering Department to state highway agencies, researchers found that of the of the 41 states responding to the survey, 26 are currently using solid wastes in their highway construction, and 1 2 have legislation, "for including solid l6 Ahmed 66-67 l6 Buddhima Indraratna, "Problems Related to disposal of Fly Ash and its Utilization as a Structural Fill "Utilization of Waste Materials in Civil Enaineerina Construction September 1992: 175. l7 Fred Langen, "Ontario Turns Plastic Milk Jugs into a Road," The Christian Science Monitor 16 August 1991: 8. Donald Larsen, Feasibilitv of Usina Waste Glass in Pavements, Connecticut DOT, Bureau of Highways, and Office of Research and Materials. l9 Ahmed 71 4
waste materials in...pavements. 20 In a similar survey of the 50 states, 42 were using reclaimed asphalt pavements, 42 were using coal fly ash, and 38 were using scrap tires. This trend suggests acceptance of solid wastes as materials in highway construction on the local level, a trend which will continue. Locally, the government of South Carolina has mandated that by 1997 the amount of solid waste received by landfills and incinerators must be reduced by 30%. 22 The use of tires, reclaimed paving materials, slags and ashes, plastics, glass, sludge, and building rubble in highway construction would satisfy this law and also could provide an inexpensive alternative to conventional aggregates and asphalt materials. However, for these materials to become more prevalent in the near future, present concerns about them must be met. In the survey sent out by Clemson University, a number of issues were identified by state agencies as needing more emphasis in future research. Issues identified by many states were: 1. The re-recyclability of highway materials with solid wastes in them; 2. The long-term durability of waste materials; 3. The need for more thorough Cost/Benefit analyses of the use of waste materials; 4. Environmental impacts of using waste materials; 5. the suitability of materials for specific types of construction: and 6. Waste material quality control. These issues will have to be addressed before many states will commit to a highway program that includes waste materials. CONCLUSIONS Currently the use of solid wastes such as tires, reclaimed paving materials, and slags and ashes is becoming more prevalent in the pavement industry. In addition to the loss of landfills and cost of opening new landfills, this is motivated by increased legislation mandating their use, better knowledge of their qualities, and the disappearance of and increasing cost of conventional materials. Tires are a plentiful source of material and are used by many highway departments in pavements and embankments. Their use will continue to grow as more legislation such as the ISTEA Act are adopted by the country. Reclaimed paving materials have been used successfully for many years. They have been a cheap, reliable alternative to using virgin materials. In the future their use will be increased in both volume and frequency. Slags and ashes are also another plentiful material. However, valid concerns about chemical reactions with other materials in concretes and pavements have limited their use. Use of wastes such as glass, building rubble, and sludges is not as common as other materials, but IS currently being studied. In the near future, as the cost of waste disposal increases, alternative uses that are not economically feasible now will be given fresh consideration by both state agencies and the federal government. However, with new uses come new concerns. Recyclability, durability, costs, environmental impacts, constructability, and material quality will have to be studied before any comprehensive program can be endorsed. As in the past, a coalition of federal, university, and private entities can build a winning team for a potentially important engineering advance. One state, Michigan, has legislation prohibiting use of solid waste materials in their pavements. Collins 150. 22 South Carolina Department of Health and Environmental Control, Division of Solid Waste Management An Overview of the S.C. Solid Waste Policv and Manaclement Act of 1991. 5
BIBLIOGRAPHY Documentation formatting is based on the Modern Language Association format. Ahmed, Imtiaz. Use of Waste Materials in Hiahwav Construction Indiana Department of Transportation, 1991. Bretz, Elizabeth. "Innovation key to finding unusual ash-disposal options." Electrical World July 1991. Indraratna, Buddhima. "Problems Related to Disposal of Fly Ash and its Utilization as a Structural Fill," Utilization of Waste Materials in Civil Enaineerina Construction. Inyang, Hilary, Editor. New York: American Society of Civil Engineers, 1992. Collins, R. J. and Ciesielski, S.K. "Highway Construction Use of Wastes and By-Products,'' Utilization of Waste Materials in Civil EnaineerinQ Construction. Inyang, Hilary, Editor. New York: American Society of Civil Engineers, 1992. Langen, Fred. "Ontario Turns Plastic Milk Jugs into a Road." The Christian Science Monitor 16 August 1991. Larsen, Donald. Feasibilitv of Usina Waste Glass in Pavements. Connecticut Department of transportation, Bureau of Highways, Office of Research and Materials June, 1989. Lewis, D. W. Resource Conservation bv Use of Iron and Steel Slaas. ASTM, 1982. Martin, Hugo. " A Scrappy Stretch of Road." Los Anaeles Times 8 June 1992. Pennisi, Elizabeth. "Rubber to the Road." Science News 7 March 1992. South Carolina Department of Health and Environmental Control, Division of Solid Waste Management. An Overview of the South Carolina Solid Waste Policv and Manaaement Act of 1991. Vesilind, P. Aarne, Peirce, J. Jeffrey, and Weiner, Ruth F.Environmental Enqineerinq Butterworth Publishers, 1988. 6