Substitutes for Mining Products
Used in Road Construction
Rural Conservation Alliance
June 2004 ~
2. Road construction materials
3. Alternative materials used in road construction
4. Glass material and uses in road construction
The use of cullet in base course
The use of cullet in Glassphalt
Other uses of cullet
5. Plastic materials and uses in road construction
The use of plastic in plasphalt or as an asphalt cement additive
Other uses of plastic
Businesses in New Mexico and elsewhere
6. The Supply Side and Current Uses
7. Other waste material utilization in road construction materials
8. Program development with the public and private sector
Partnership and collaboration
9. Benefits and recommendations for action
10. Acknowledgement and References
Highways and roads demand enormous amounts of materials for their construction. The necessity for earth-based materials creates impacts of resource depletion, environmental degradation, and energy consumption. In New Mexico, gravel and other minerals for road construction-aggregate, base course, crushed rock, and sand-are mined from riverbeds and hillsides to serve the highway construction and building construction industries, leaving mines un-reclaimed. Environmental degradation accompanies the mining activities and remains after the mine ceases operations, with air pollution, scars on the landscape, and threatened surface waters and groundwater. Local residents and entire communities also feel the affects of industrial traffic and noise, which cause true public nuisances.
As numerous engineers, scientists, and business people in the United States have observed and demonstrated, waste materials can replace some of the natural materials used in highway construction projects. Research Engineer Warren Chesner has observed, "Waste residues can be substituted for natural aggregate materials in paving applications. To achieve acceptable performance properties consideration should be given to the types of natural aggregate materials used in the mix and the specific materials that the waste residues will replace." Such alternative materials protect the environment by conserving natural resources, including the lands for mining and for landfills. Benefits also include economic development opportunities and reduced pollution hazards, thus protecting human health.
The use of "waste" materials in road construction contributes to needed environmental solutions. The U.S. Environmental Protection Agency indicated that in 2000, only 37 percent of plastic soft drink bottles and 31 percent of glass beverage containers were recycled each year. If a greater demand for recyclable materials from landfills existed for local road construction, local governments that operate waste management facilities could find a market for the materials, and divert a greater amount of material from their landfills.
Several state transportation agencies in the US have played important roles in the development and utilization of glass and plastic materials. They have written and published specifications for road construction, guiding highway project contractors and local government agencies. New Mexico's Department of Transportation was not an active player in these developments, but under the current administration it has recognized that it could be transformed to a more responsible agency. In May, 2003, Secretary Rhonda Faught signed a commitment to environmental and energy action, calling upon employees to actively engage in nine principles. Principles numbered one and eight of particular interest:
"1. Incorporate sound environmental practices and energy efficiency throughout the organization, by instilling a culture of environmental stewardship and energy conservation awareness at all levels and in all operations;" and
"8. Promote energy efficiency and conservation using innovative approaches to transportation design, construction, and maintenance operations, through the use of alternative energy sources for the Department's fleet of vehicles and through the use of alternative and recycled materials and innovative construction techniques."
Solid waste materials are categorized into four types: Agricultural, Domestic, Industrial, and Mineral. Glass, or cullet, can be used for unbound base course, asphalt fine aggregate, and pipe bedding material. Plastic waste is usable for asphalt-cement modifier, as well as fence and signposts, plastic lumber, delineators, geotextile manufacture, and composite pipe pilings. This paper will report on the status and utility of alternative road construction materials for base course, aggregates, and asphalt-cement modifier using glass and plastics.
2. Road construction materials
As reported by Steve Blodgett in the accompanying report, "Environmental Impacts of Aggregate and Stone Mining in New Mexico", highway construction projects utilize these natural rock materials: aggregate, crushed rock, base course, sand and gravel. All of these materials can be fully or partially replaced with recycled materials. In addition, ingredients in asphalt can be partially substituted with recycled materials.
--Surfaces - Asphalt is a residue produced when crude oil is refined for gasoline. It is combined with aggregate materials, including sand and gravel, in an asphalt mix, which is used for flexible pavements on roads.
A rigid pavement, typically used for bridges and overpasses, consists of a concrete mix made of cement and aggregates.
--Base course unbound or bound materials.
--Subbase aggregate, unbound material.
--Subgrade is needed in some situations where the soil and drainage features demand more stability. Embankment fill is typically used.
3. Alternative materials used in road construction
The development of "recycled roads" was initiated by the early 1990s in the United States. The Intermodal Surface Transportation Efficiency Act of 1991 required the use of scrap rubber in asphalt, and that helped to focus federal involvement on the issue. By the mid-1990s, nearly every state had some project that utilized a waste product in their highway program; most states had used at least three materials, including fly ash, rubber, roofing shingles, plastic, and glass. Glass was used as a fine aggregate in asphalt mixes.
Transportation agencies are said to have been "curious but conservative" in their projects to reuse waste materials. The key to recycling, particularly for pavements, was to maintain competitiveness with other products and maintain the standard of a 20 year service life. Engineering and product associations involved with issuing reports and conducting studies included the National Asphalt Pavement Association and the American Association of State Highway and Transportation Officials. The Materials Engineering Division of the American Society of Civil Engineers conducted several sessions at their national convention in 1992 regarding the utilization of waste materials in construction. In a thorough study published in 1994 by the National Research Council, Robert Collins and Stanley Ciesielski described criteria for suitable use of waste materials and by-products: 1. Be of consistent quality and meet specification requirements; 2. Be economically competitive with the material it replaces, and specifically, though the initial cost may be incrementally higher, the life cycle cost should be comparable; and 3. enjoy a societal benefit of avoided disposal costs of materials.
NMDOT sponsored a study of the use of recyclable materials in New Mexico, resulting in a published report in 1996. James Brogan considered the use of recycled asphalt, or RAP, reclaimed concrete pavement, plastic, scrap rubber, and numerous other waste products, including glass and plastic, but only RAP and concrete pavement were being recycled, and only in a few communities. It appears that no recyclable materials derived from solid waste facilities were in use at that time.
In other states, innovative recycling companies and road builders have utilized a variety of waste materials. Glass, plastic, wood, sheetrock, asphalt roofing shingles, and tires have been recycled and reused, preventing hundreds of thousands of tons of waste from filling landfills. Road systems in New Hampshire and Maine use recycled material products produced by Commercial Paving and Recycling, based in Scarborough, Maine. The company offers discounts to the contractors, state agencies and municipalities in exchange for construction and demolition debris for waste derived products. It has invented its own products, including "C&R" and "R&R," materials used for shoulders, sub-base, and base course, and "Jack's Patch," for pavement patching.
4. Glass material and uses in road construction
Recyclable glass, or cullet, is recovered from glass containers used for food and beverage. Beer and soft drink bottles comprise the largest amount, followed by food bottles and jars, and then by wine and liquor bottles. Glass generation declined in the 1980s due to the availability of other materials, especially aluminum and plastics. Nationally, it was 10 percent of the municipal solid waste stream in 1980, declining to 5.5 percent in 2001.
The total amount of waste glass material in the US was 12.57 million tons in 2001. The recovery of usable glass from landfill operations was 22 percent, or 2.4 million tons. However, this was a better recovery percentage than in 1988, when Collins and Ciesielski reported that just 12 percent of waste glass was recycled.
Container manufacturers use most of the cullet to create new glass. Recycled glass melts at lower temperatures than new glass, thus creating energy savings. For this purpose, glass containers must be sorted by color. Glass can also be used in a base course in roads, (unbound construction aggregate), as well as glassphalt, pipe backfill and storm drains. One of the efficiency benefits to these uses is that the glass can be mixed colors, and not sorted by color. Storage of glass at facilities is not of great cost; it is considered benign, producing no pollutants, and is a stable material, though covering it in cold and wet weather is recommended.
By 1994, at least ten states used glass in an application that replaced sand/gravel materials, and the state transportation agencies had developed specifications, as indicated in Table 1.
Table 1. Utilization of Glass, 1994
Collins and Ciesielski
State Construction Use Specs by DOT Note CA AGG, SB Base course Source for AGG: ceramic waste CONN AGG, EMB Base course FL AGG, EMB AGG in AC IO AGG AGG in AC NH ABC Base course NJ AGG, SUB AGG in AC NY AGG AGG in AC PA AGG, ABC, ABF AGG and base VT AGG VIRG AGG AGG and base WA SB SB special provisions
AGG: aggregate in asphalt ABF: aggregate back fill
SB: stabilized base course
EMB: embankment borrow AC: Asphalt cement
ABC: aggregate base course
California used a unique material for an unbound base course near Santa Barbara: crushed porcelain from used toilets. (Large amounts of ceramic waste may also be present in Santa Fe, where building permits are linked to the replacement of water-wasting toilets.)
The Clean Washington Center states that the cost-effectiveness of substituting glass for conventional aggregate is highly dependent on the location, the quality and cost of local aggregates, and any credits available for using recycled materials in beneficial re-use applications. CWA notes that the "economics of glassphalt are a local issue and generally rely on recognition of the value of waste diversion."
The use of cullet in base course
As indicated in Table 1, by 1994, at least six states had specifications in place for base course. The Clean Washington Center states that glass aggregate can be used as part of the base course where the size of the glass particles can vary.
NMDOT created a specification for a base course using 10 percent glass in October, 2003. Working with the NM Recycling Coalition and NMED on the Recycling Task Force, it tested this material on six sites. ON one of the sites, Santa Fe County utilized cullet at the El Dorado Transfer Station when it paved the road leading from the front gate, a length of 4/10 mile, using 30 tons of glass blended with standard base course. The Materials Testing Bureau at NMDOT is monitoring test results. The specification is expected to be published in a manual addendum at some point in the future, but was not available from two personnel the NMDOT testing bureau (though phone messages were left, requesting return calls).
Cullet has been use in gravel mixes for a base course (Class 5 aggregate) in at least five counties in Minnesota since the 1990s. Some of the counties, located in rural areas, use their own local cullet, thus avoiding transportation costs to move the cullet to a larger site, as well as coping with fluctuations in glass container market prices, and the need to separate the cullet by color. Lake of the Woods County found that the mixture may be an improvement over aggregate. In two counties, support from the state's Office of Environmental Assistance was provided. As a result, Sibley County and Mn/DOT developed documentation that allows for local governments to use up to 10 percent cullet in Class 5 aggregate base if it is not used as a wear course. Lab results indicated that the mixed material performs better than standard aggregate in freezing and thawing conditions.
In Pennsylvania, a specification allows 10 percent glassy particles as a substitute for aggregate in Bituminous Concrete Base Course.
The use of cullet in Glassphalt
As indicated in Table 1, by 1994, at least six states had specifications in place for asphalt mixes.
Clean Washington Center describes glassphalt as "asphalt containing glass cullet as an aggregate", reporting that it has been widely tried as a means to dispose of surplus waste glass since the 1960's. "Glassphalt is basically the same as conventional hot-mix asphalt, except that 5 percent to 40 percent of the rock and/or sand aggregate is replaced by crushed glass."
Numerous other experiments with glassphalt have occurred. The City of Baltimore used glassphalt during the early 1970s when then Mayor William Schaefer initiated the revitalization of its downtown. Several streets were paved with glassphalt. The city received free cullet from local manufacturers, this in the days before recycling was common. When cullet became more valuable to the companies in the 1980s with the development of other markets, they had little incentive to continue donating the cullet.
Lessons learned in Baltimore included: glassphalt was cheaper due to the source of donated material, which replaced stone aggregate. But a steady supply of cullet was a necessity. At that time, the savings was 30 to 40 cents a pound (equal to $600 or more per ton). Second, only two companies knew how to apply glassphalt on city streets, and other firms felt that they were shut out from the city's procedures, and there were pressures from the "industry" to end its use. Third, glassphalt is durable; streets paved in the early 70s were outlasting the normal 20-year life of standard asphalt mix in 2000. The former mayor, now the comptroller of the State of Maryland, stated "If I had to do it all over again, I'd do most of the streets in the city of Baltimore" with glassphalt. "It worked out well." The largest glassphalt manufacturer in the Baltimore area, Reliable Contracting Co., now provides it for an undercoating on highways; as a surface coating, it raised concerns about children's exposure to cullet's edges. However, cullet can be crushed so that sharp edges are eliminated and the shape is rounded, or "pebbleized."
Glassphalt has also been proven in Hennepin County, home of Minneapolis, Minnesota. The county blended five percent crushed cullet in a bituminous asphalt wear course on a county road in 1996, and then again in 1997 for its Public Works Center for both base and binder courses.
Ocean City, MD uses glassphalt. Public Works Director Dick Malone initiated the program years ago as a spin off of a mandatory glass-recycling program, collecting bottles from all establishments within the city's limits that hold a liquor license. The city also paved its own properties with glassphalt, including the Convention Center Parking Lot.
The Director of Allentown, Pennsylvania's Public Works, Neal Kearn, highly recommends the glassphalt process. During seven years, Allentown used 120,000 tons of "glassphalt" to pave its streets. Allentown used the Pennsylvania Department of Transportation's specification of ten percent glass in the asphalt mix. In 1999, he reported, "Last fall, we held a roundtable of the city's paving gurus to determine whether to continue with glassphalt or not," Kearn says. "It was unanimous to continue with and increase the program. Our track record speaks for itself. If we were having problems, we wouldn't have included it for 100 percent of this year's road material." The glassphalt held up even under the heavy truck traffic entering a municipal garage facility. The project was discontinued due to a supply side issue: the glass vendor could not make reliable deliveries.
Only one negative conclusion was found in the literature review on cullet, with Vermont reporting that waste glass in asphalt was a poor performer.
Pennsylvania's DOT encourages recycling in transportation projects and has developed a Strategic Recycling Plan with the Department of Environmental Project. A glassphalt project in 2000 widened a road with mixes provided by a local asphalt plant. A DOT district crew placed three mixes for testing: a conventional asphalt mix, a mix with 5 percent cullet in place of aggregate, and a mix with 10 percent cullet, with the same machinery. The sections were marked for testing. The finished roadway looked like other re-paved, widened roads and signs of glass were not evident.
New Mexico's Recycling Task Force has worked on evaluating glassphalt and glass in a concrete mix. They negotiated on a mix with a local plant, Associated Asphalt, but without success. The concrete mix would have used 3/8" aggregate, but the plant stated that they could not switch between glass for one mix and all natural aggregate in another mix. (Associated Asphalt is a large operator, and it is associated with Richard Cook, who is also associated with Cerrillos Gravel Products.) Whether this is a legitimate processing issue was not confirmed in the documents reviewed for this report.
Other uses of cullet
PENNDOT currently provides specifications for "crushed glass" in these classes: Embankment fill, flowable fill, and pending is information on Pipe trench backfill. Glass beads for use in traffic paint were another tested product in at least two states in the early 1990s.
Key physical factors in the use of glass are the size of the glass pebbles or particles and the percentage that can be effectively substituted for natural materials in an asphalt or concrete mix. By 1992, Research Engineer Warren Chesner conducted a test program on the use of waste glass and other materials for asphalt pavements to assess the stability of the mixes. Potential stripping problems were noted with the introduction of 15 or more percent glass substituting for natural aggregate in a wearing surface course mix. Chesner modified the types and sizes of natural aggregates to arrive at a recommendation that waste glass should be substituted primarily for natural sand to produce minimal impact on quality. Thus, the processing of the glass cullet would require a uniform sand-size fraction (i.e. less than a No. 4 sieve). (A larger project by Chesner involved the creation of the Waste and Recycled Materials database for the National Cooperative Highway Research Program in 2000, which includes material and engineering properties and information on demonstration projects. This may be the most valuable reference for transportation agencies and researchers using glass.)
In 1996, the Clean Washington Center (CWA) reported: "Most installations of glassphalt have been designed to meet the standards of The Asphalt Institute for medium traffic asphalt, which specify a maximum speed limit of 40 mph. These standards include requirements for stability, flow, voids in mineral aggregate, percentage of air voids in the mix, and unit weight. The most common applications are as surface pavement for residential streets, secondary roads, parking lots, sidewalks, and curbing."
A key concern with glassphalt was skid resistance, though it is reparable. CWA reported, "When glassphalt is placed and compacted, larger glass particles will align themselves parallel to the road surface." Too much glass can cause the skid resistance to be slightly lower than that of conventional asphalt, yet a smaller amount of glass in the asphalt mix resolves this issue: "The skid resistance of glassphalt containing less than 10 percent glass by weight, with cullet particles smaller in size, shows no appreciable difference from asphalt containing 100 percent natural aggregate." This is similar to the conclusion on pebble size drawn by Chesner.
Container glass in a coarse condition is frequently used in Minnesota. According to an evaluation of waste materials in highway construction in Minnesota, which ranked wastes according to a four-class system, crushed glass resulting in flat, long articles with smooth surfaces and no porosity is used as a base and subgrade aggregate additive, and as a bituminous mix additive. The materials performed with improved thermal characteristics. They were classed as follows:
--Technical feasibility for aggregate use in base course: Class 1 (highest potential for use and requires a minimum of processing before use)
--Technical feasibility for aggregate use in bituminous mix: Class 1
--Technical feasibility for aggregate use in concrete mix: Class 1 AND Class 4 (little or no potential and at best might be used in small amounts as filler or in very specialized applications). The reason for the two classifications is not provided.
PENNDOT has worked with Pennsylvania's environmental department, a university and two glass providers to determine several physical, mechanical and hydraulic properties of glass materials, for the purposes of using glass cullet for drainage, slope stability, bearing capacity and lateral earth pressure. A summary is provided on the PENNDOT website.
CWA provides a best practices document on preparation and placement of asphalt mixes, indicating that glassphalt can be installed using the same equipment and procedures as conventional asphalt. (As previously indicated, PENNDOT used three consecutive mixes in the same road project to test glassphalt, and it appears that agencies and contractors in New Mexico could also apply glassphalt with standard equipment.)
5. Plastic materials and uses in road construction
Six main types of resins are used to make plastic products in the US:
1 PET, polyethylene terphthalate, from 2-1 soda bottles.
2 HDPE, high density polyethylene, natural, from 1 gallon milk jugs, grocery bags
HDPE, high density polyethylene, colored, from bottles
3 PVC, polyvinyl chloride, various bottle, pipes, flooring
4 LDPE, low density polyethylene, from film and trash bags, rigid containers
5 PP, polypropylene, from some food containers, battery cases, medical containers
6 PS, polystyrene, from carry-out containers, some food containers, vitamin bottles
The numerical coding system identifies plastics by resin types to help workers in recycling centers sort them by resin. The resin codes are molded onto the bottom of most plastic containers larger than 8 oz., with a recycling triangle surrounding the number. Separation has been necessary for many applications, but not for road construction materials.
Nationally, the municipal solid waste stream produced 6.1 million tons of plastics in nondurable goods in 2001. Durable goods containing plastics generated another 8 million tons. The recovery rate was nearly 36 percent for PET #1 and 28 percent for HDPE #2. In 1988, 30 percent of PET and 7 percent of HDPE were recycled. (Data was not available for other plastics; as in New Mexico, plastics commonly diverted from the waste stream are PET #1 and HDPE #2.)
As of 1994, 15 states had conducted research on plastic uses, with three state transportation agencies providing specifications, as indicate in Table 2. Four states had examined LPDE #4 pellets for use in asphalt mix, or ACM (asphalt cement modifier).
Table 2. Utilization of Plastics, 1994
Collins and Ciesielski
State Construction Use Specs by DOT CO ACM ACM NV ACM ACM NY ACM ACM RI ACM
ACM: asphalt-cement modifier
PENN DOT reported that it intended to research shredded tires and plastics in bituminous concrete and modified asphalt cement in 1994, but have not since defined it.
As of 1996, NMDOT, then NMSHTD, had not considered plastic as a pavement additive; though it seemed to be aware of its utility to form posts, guardrails and other products. Brogan noted in 1996 that research was underway on plastic as an additive in both asphalt mix and Portland cement concrete. Currently, NMDOT and the Recycling Task Force have discussed the use of plastics "briefly," according to a NMDOT staff Colleen Vaughn. The efforts of Tewa Technology to work with NMDOT on a plasphalt project are described in a later section.
The use of plastic in plasphalt or as an asphalt cement additive
By 1994, Colorado, Nevada and New York had mixed LPDE pellets (made from trash bags and sandwich bags) at approximately seven percent by weight to asphalt cement. In another mix, PET had been modified chemically for a polymer concrete.
DOT agencies contacted for the development of this report provided some current information: According to Colorado's DOT, plastic was used in the mix for toll road E-470 in the Denver metropolitan region, but it has not become standard practice; the DOT staff contacted for this report had no recollection of using plastic. (Due to the years that have passed since an experimental use, staff that knew of the DOT's involvement may have changed, but it may also indicate a lack of leadership and consistency in carrying out demonstration projects and documenting them for future utilization.)
Local governments in Pennsylvania recently demonstrated Plasphalt in the wearing course at ten locations, where treated plastics replaced about two percent of the coarse aggregate. A specification for "Plasphalt in HMA" may be forthcoming.
Other uses of plastic
Several communities and states have examined and utilized plastics for other uses related to highway and road construction, including fences or sign posts, sign blanks, barricades, delineators or cones, and plastic timbers, tables, and benches.
Plastics have been analyzed for a variety of construction related products. As reported by a team of engineers before the Materials Engineering Congress in 1992, unsaturated polyester resins based on recycled PET #1 offer the possibility of a lower source cost of materials to form useful polymer concrete for a binder and mortar products to replace natural aggregates. Collins and Ciesielski reported that by 1994, granulated plastic was used in a Portland-cement concrete structure in Elgin IL; and a "pedestrian bridge deck contained 30 percent plastic as a partial replacement of sand to reduce dead weight at comparable compressive strength."
The plastic resin, LPDE, has been recycled into pellets to modify asphalt mixes. By 1994, Colorado, Nevada and New York installed road pavements with LPDE pellets mixed in conventional hot-mix plants at about 7 percent by weight of polyethylene to asphalt cement. Western Plasphalt Products has conducted tests and patented several products that combine various types of unsorted waste plastic and incorporates the granulated material for seven to ten percent of the medium-sized aggregate in a typical asphalt cement mix. (As of May 2004, the company does not have a working phone number in its original location in California, and could not be located.)
Due to the abundance of discarded tires, many states have pursued the reuse of rubber in tires. Crumb Rubber is a product used in asphalt binders, and the addition of plastic waste was examined in 1995. A rubber tire-plastic composite was tested and found to be less reactive than a crumb rubber binder, with more stability when stored at high temperatures.
Businesses in New Mexico and elsewhere
Tewa Technology Corp., based in Albuquerque, developed a plasphalt additive product and tested it on a two-mile stretch of I-25, near Budaghers in the southbound outer lane, with NMDOT cooperation. TEWA developed their patented plastic aggregate from all types of plastic materials except LPDE #4, referring to their granulated mix as Treated Recycled Plastic Aggregate (TRPA). WIRED magazine recognized Tewa's efforts, citing its sources of plastic materials: Philips Semiconductors, Intel, Coca-Cola, and Sandia National Labs. LANL provided empty plastic buckets (and later awarded TEWA with recognition for environmental stewardship). One mile of roadway consumed 75 tons of plastic waste material. Overall, the potential impact on New Mexico's landfills was a reduction of 27 percent of all waste, since nearly all plastics could be diverted to use in TRPA.
One ton of the TRPA product would have cost $225 a ton, and the resulting plasphalt was reported to cost six to seven percent more than the typical product, but it would extend the road life for an additional 25 to 20 percent longer. Thus, the net savings was a long-term effect. One of Tewa's owners, Gary Bowers, described how difficult it was to convince the construction community of that value.
Tewa's experiment appears to be the first and possibly the only project utilizing plastic in pavement materials in New Mexico, and it failed. Tewa Technology filed for bankruptcy in 2002. Several causes have been suggested for the company's demise. NMDOT did not conduct other tests in other climate zones of the state, even though it approved the project on an interstate highway. AMEC, a local materials testing firm hired by NMDOT, was said not to have enough technical ability to fully evaluate the pavement. Also, NMDOT didn't approve the product for 13 months, which was more than double the agreed-upon six months. This created financial strains on the firm, since they were unable to sell their product to local governments (and they had stockpiled 100 tons of TRPA, with more plastic material on hand.) Also, the highway was paved in November, which is not an appropriate time of year.
It also was reported by Tewa that a contractor's bid for another paving project, using TRPA at Intel's plant in Rio Rancho, was over-priced at three dollars a square yard, though the material only cost $.67 more than standard material. Tewa's owner noted that the material does not require modifications to the machines used for laying asphalt. Another contractor cited "the unknown factor" of untested material as the reason for an unwillingness to price appropriately.
The entrepreneurial spirit was successful and acclaimed in another part of the US. Recycling company Conigliaro Industries has developed several products using plastic from discarded computers. The state agencies have worked with the company, and Beneficial Use Determinations were granted for asphalt matrix products, including road bedding material and other cold mix products. More recently, the Massachusetts Department of Environmental Protection and the American Plastics Council provided financial support in the amount of $155,000 for the development of a lightweight asphalt mixture for patching potholes.
Research Engineer Anthony Conigliaro developed and tested the product, using #3 through #7 waste plastics, and produced a report on the best formulation in 2000. The plastics are derived from the huge volumes of scrapped computers, monitors and, as analog signals become obsolete, older televisions are expected to provide more material. Conigliaro takes the plastic housings from the region's computer and electronics dismantling firms and produces a cold patch product that consists of over 75 percent of plastic regrind material in product volume. The product, now marketed as Boston's Best Patch, is effective in the northeast, and as Conigliaro states, other formulations will be necessary as the business expands to warmer parts of the country. As of 2000, the firm was producing over 100 tons of mixed plastic aggregate, and 10,000 buckets of cold patch per month. It was found to be cost-effective with other products, and has a lighter weight.
6. The Supply Side and Current Uses
The recovery of recyclable waste materials is reported by the NM Environment Department on an annual basis. NMED reports that the NM Solid Waste Act, adopted in 1990, "established a goal to divert 554,760 tons or 50% of the estimated waste generated in 1990 (the base year), by the year 2000. This goal will not be attained in the year 2000." During 1999, 290,427 tons of municipal solid waste (MSW) were diverted, equal to only 26% of the estimated MSW generated in the base year, or 9.7% of the current waste stream. "A significant increase in MSW diversion is not anticipated unless municipal governments and the solid waste industry adopt cost-effective diversion technology and practices." The most recent statewide data exists for 2002, when the total amount diverted from landfills was 156,699 tons. This amount was a major decrease from the largest recovery amount in previous years, 312,349, in 2000.
Table 3 indicates the great variations in the amount of recovered glass and plastics that can take place year to year. These variations could indicate that there is a supply side issue for a consistent and reliable supply of material for construction projects, should a demand for the materials occur. However, industrial and commercial sources may be more consistent, as indicated by Tewa Technology, which was supplied primarily with industrial/institutional plastic materials.
Table 3. Recovery of Waste Materials in New Mexico, tonnage
NMED Solid Waste Bureau
Year Glass Plastic 1993 3,423 460 1994 4,181 333 1995 2,223 853 1996 1,432 252 1997 1,926 621 1998 2,587 388 1999 3,511 425 2000 2,025 586 2001 1,808 630 2002 1,473 656
The data for plastics includes PET, HDPE and all other types. In 2002, PET comprised the largest amount with 42 percent, HDPE a slightly lesser amount with 33 percent, and other plastics with 25 percent.
Generation rates provide data on the actual amount of waste that is generated by households and commercial properties. Discrepancies in data are very common and sources often note their own limitations. Waste material data utilized in this report are used to provide illustrations of the potential supply.
According to the NM Environment Department, nearly 2.3 million tons of municipal waste was generated in 1999 (about seven times more than what was recovered). A steady increase in waste has occurred over the past decade, which NMED attributes to increases in population and support services, economic growth and increased reporting accuracy.
A national study by the American Plastics Council estimates that 200 pounds of glass and 35 pounds of plastics are generated per household per year. Using this average, estimates for the state's and urban counties' generation rates are listed in Table 4. The national generation rates may be appropriate for New Mexico's households, which are considered average waste generators by NMED's Solid Waste Bureau manager, E. Gifford Stack.
Table 4. Estimates of Annual Glass and Plastic Generation in NM
County / NM Number of Households Glass generation @ 200 lbs. per household Glass generation by ton Plastic generation @ 35 lbs. per household Plastic generation by ton Bernalillo County 220,936 44,187,200 22,094 7,732,760 3,866 Dona Ana County 59,556 11,911,200 5,956 2,084,460 1,042 San Juan County 37,711 7,542,200 3,771 1,319,885 660 Santa Fe County 52,482 10,496,400 5,248 1,836,870 660 New Mexico 677,971 135,594,200 67,797 23,728,985 11,864
With a population of approximately 1.8 million people that is very likely to grow, New Mexico could provide a much larger supply of materials than it has in the last decade.
The collection, storage and re-use and recycling of waste plastic and glass are in very preliminary stages in New Mexico's communities. The largest facility, operated by the City of Albuquerque, began its program in 1983 with a glass-collecting program. It now collects recyclable products at curbside for single-family residential units; 14 drop-off sites are provided for other residents who are willing and able to transport materials to one of the sites. The city has a limited storage area for the recyclables.
Waste Management of New Mexico Inc. of Browning Ferris Industries handles waste collection and locates buyers for the collected materials for many NM towns and cities. Other facilities are located in Native American communities and on federal installations of the Departments of Defense and Energy.
Glass Supply / Current uses
The City of Albuquerque has a glass crusher at its Cerro Colorado landfill that can produce ground, pulverized and tumbled cullet in accordance with manufacturing standards. It has produced _ to 3/8" sized pellets, and less than 1/8" size, producing a large sand-like material. Albuquerque sells its glass for $15/ton to 2 local vendors who markets and packages the cullet. The city could not supply the tonnage of cullet that it diverts and moves into markets.
The two vendors are Buildology and Glasscapes. Buildology sells ground glass at $70 per ton, and 20 lb. bags for $3.50. Their price for "Road Base" for base course is $19./ton; "concrete mix" with 1" rock and sand costs $15.75. Shipping is additional, at a cost of $4.30 per ton. Their dump truck handles about 13 tons, and a full truckload costs $60 for a delivery in the Albuquerque area.
Glasscapes sells the cullet as a landscaping material. A five-gallon bucket costs $10. A ton costs $75., and shipping is additional at $95 for a one-ton delivery (several sites can be on the delivery route). One ton covers an 11 by 11 foot area that is 2" deep.
The City, County, and the Santa Fe Solid Waste Management Agency collected approximately 4,000 tons of waste material in 2003. Santa Fe operates a glass crusher at the City of Santa Fe Solid Waste Transfer Station, producing 1,000 tons of cullet. The facility has the storage capacity for stockpiling glass. The City might charge only five dollars a ton (not including shipping) if a demand for it as base course developed, in the interests of remaining competitive with conventional sources. It was suggested that a business could take the lead in marketing the materials for road projects in the region.
The recycling coordinator at the Santa Fe Solid Waste Management Agency estimates that the county could use twice as much glass as what is now recycled throughout Santa Fe for road projects in the county alone. Approximately 20,000 tons of gravel are bought for County road projects. If the facility could recover the full amount generated, estimated at 5,248 tons (Table 4), it could reduce its purchases of gravel by more than 24 percent.
Taos was the first community to buy a glass crusher with capability of sizing 1/8" or 1/8 to 3/8." Many other communities have crushers, and they use the cullet for public projects.
Federal Departments of Defense and Energy are charged with the goal to divert forty percent of their installations' solid waste stream. Cannon Air Force Base, located near Clovis, has diverted glass and plastic since 1999. In fiscal year 2003, four tons of #1 and 2 plastics and ten tons of glass were diverted, which are small portions of the total diversion; the demolition of old housing units provided large amounts of diverted material. The base ceases diverting, or recovering, materials, once they have achieved their overall goal. Initially, they produced _ inch to 3/8 inch crushed glass with an old crusher, but they do not have a vendor who wants the material. They now donate the glass to a firm in Lubbock, TX and pay the shipping costs. They had considered Coors in Colorado, but the shipping was prohibitive. The base works alone in the eastern central region, since the Clovis Regional Landfill only diverts green waste from the landfill.
Recycling facilities only recycle PETE #1 and HDPE #2 plastics, a situation considered "tragic" by the NM Recycling Coalition's executive director, Nancy Judd. The "other" plastics found in the recovered waste are most likely sent to landfills.
Albuquerque sells its plastics to buyers in California, Missouri, and Georgia. The facility processed 285 tons of plastics in 2003. Santa Fe ships its plastic to Albuquerque for the same purpose, estimated by staff at approximately 200 tons annually. The 485 tons of plastic generated from the two facilities is only ten percent of the estimated generation of 4,784 tons (Table 4). The plastic collected at Cannon AFB is transported to McKinley Paper in Albuquerque, along with the base's waste paper. Similar out-of-state destinations are likely for their plastic material.
Albertson's grocery stores collect plastic bags made of LDPE #4, and send them to its warehouse near Phoenix, AZ. (The warehouse number is 1-602-382-5525).
7. Other waste material utilization in road construction materials
According to the FHWA's Office of Pavement Technology, which participates in the agency's recycling team, glass and plastic have not been of interest in recent years, and there is no current status report. A key issue, according to a staff person, is the available supply of the materials. As noted in the beginning of this report, recyclable waste materials are also derived from industrial, agricultural and mineral industries. Another key source for highway construction are road materials themselves. Nationally, recycling of asphalt into asphalt mix and base course are of greatest utility, as are fly ash in concrete, blast furnace slag in concrete, and recycled concrete for base course and in concrete mix. Another material is reclaimed roofing shingles, which contains asphalt and takes a long time to disintegrate. States that have banned the dumping of roofing shingles, or that impose a fee for disposal, created an incentive to develop a use for them.
According to a survey conducted in 1996 by James Brogan, most NMSHTD districts reported that they were recycling asphalt pavement and some were also using broken concrete. Many counties also use recycled asphalt product for base course and overlay, and concrete on a more limited basis. These were the only recycled materials in common use. Recycled asphalt processes, or cold in-situ recycling, has been evaluated over time in New Mexico, and its performance is considered excellent and its use cost effective. NMDOT funded a technical evaluation of 45 projects around the state in 1996, indicating its serious intent toward this alternative process for road surfacing.
Of the nine out of 31 cities that responded to the survey, two-thirds used reclaimed asphalt pavement for base courses or for paving. Albuquerque also used recycled Portland cement concrete in a program initially suggested by local material suppliers of asphalt and cement concrete. The city established that waste asphalt and Portland cement concrete was a viable resource for materials, and developed specifications in 1992. The savings over three years was reported to be $12.1 million, representing disposal costs in landfill, extending the life of landfill and extending the source of natural aggregate materials. This amount of money is a powerful economic indicator of the public benefits that may be available with more extensive utilization of alternative materials.
Tire rubber is used as a binder in asphalt, and four contractors for Asphalt-Rubber Wet process are certified in New Mexico. The states of Arizona, California and Texas use 18 percent rubber in hot asphalt. Two inches spread onto a road uses about 2,000 tires per lane mile. The Rubber Pavements Association reports that producers of asphalt-rubber mostly use crumb rubber, or rubber pellets, from Canada. The only producer in NM was based in Socorro, but it closed after a fire.
8. Program development with the public and private sectors
Innovations in infrastructure design and construction often require the support of government agencies, elected officials, entrepreneurs and advocates. Both the private and public sectors are best served if they jointly cooperate in ventures that create highway construction applications for alternative waste materials.
As of 1994, NMSHTD was one of four state agencies that had not conducted any research on using waste materials for highway construction, though it was using reclaimed asphalt, scrap tires, and used motor oil. However, the only specification developed by the agency was recycled asphalt as an aggregate in asphalt applications. Other states had been engaged in developing a variety of specifications, including the uses of fly ash, scrap tires, blast-furnace slag, recycled motor oil, and steel slag.
As noted in the introduction, NMDOT's Secretary Faught is committed to principles that may encourage additional projects using recyclable materials, including domestic materials such as glass and plastics. NMDOT's State Materials Bureau manages the research of new materials and development of road specifications. Their mission is to be "internationally recognized leaders and innovators within the highway construction and maintenance industry in the fields of geotechnical, pavement, and materials engineering." This, in concert with the Secretary's environmental principles, could orient the Bureau toward using more local supplies of alternative materials that are environmentally appropriate. The bureau is already known for capabilities in innovation, as demonstrated by the appointment of its chief, John Tenison, as chair of the National Cooperative Highway Research Program Project Panel on Superpave Asphalt Binder Technology. The bureau is now working on uses for wood waste with the Recycling Coalition. Wood chips and mulch are replacing straw and other materials for preventing erosion and revegetating areas along highways. The DOT should also strive to overcome imposition of special interests on the development of alternatives, and the case of Tewa Technology should serve as a cautionary illustration of institutional and corporate obstacles.
States with recycling and market development programs have developed useful information and communication links. Some DOTs not only conducted investigations of waste materials in highway construction products by the early 1990s but also inventoried all waste material sources by town and county, and the uses of those materials. Missouri was considered "outstanding" for its materials inventory by type of storage (wet or dry), estimated annual production and accumulation, and product type rating. Collins and Ciesielski noted, "This report is an excellent example for other state highway agencies to follow." In 1996, Brogan reported that a key problem with NMDOT's recycling program was a lack of communication between NMDOT and local agencies, and he recommended that the DOT establish a conduit of information such as a newsletter. Even now, items such as the recycling program for waste wood, and the specification for glass in base course, is not apparent on NMDOT's website.
Of great importance are state environment agencies. They have been important partners in efforts to recycle and reuse waste materials due to their programs regarding mandatory recycling, landfill space and out-of-state waste reuse. By 1994, 38 percent of the states mandated recycling. Twenty-three percent indicated that they were out of landfill space or expected to be by 2004. Thus, they had a strong motivator to "close the loop" of recycling and reuse. New Mexico had only a "beneficial use provision," but no mandatory recycling, which is still the case. The Solid Waste Act of 1990 prioritizes waste reduction and recycling, but it was limited in scope, and there was no legislation for use of waste materials by DOT. No doubt, there was great optimism that goals of the act would be achieved without mandates, but as noted in Section 6, only half of the goal was achieved during the course of a decade. A mandatory recycling law for valued materials would be of great consequence in securing a steady supply of materials for reuse within the state.
The Massachusetts Environment Department played an important role in encouraging the reuse of the plastic from trashed computers that were demanding landfill space. The state's bottle bill, passed in 1981 after years of effort, provided a source of funding for entrepreneurial research and development of waste material reuse. Of the states that researched and/or used glass for road construction by 1994, Connecticut, Iowa, Maine, New York and Vermont had beverage container deposit laws (or bottle bills) in place.
Pennsylvania's Municipal Waste Planning, Recycling and Waste Reduction Act was passed in 1988 and then re-authorized in 2002. The act specifically directed PENNDOT to evaluate products and materials that may be recycled in transportation and civil engineering applications. Pennsylvania's DOT and Environment department enter into a Memorandum of Understanding to promote the use of recycled materials in construction and maintenance projects. Since 1998, they have renewed the MOU every two years, so that funds collected by the environmental agency from the Recycling Fund can be transferred to the DOT for its Strategic Recycling Program. The key focus areas of the program are Research, Specifications, Projects, Outreach, and Contracting; information is available to the public on the DOT's website.
Factors in the development and usage of an innovative material include the cautionary, if not stubborn, approach of highway engineers, as well as the organization's capabilities to efficiently release test results, reports and specifications. Allentown, Pennsylvania's Director of Public Works Neal Kearn admitted that there was skepticism about using glass in their road wearing courses, but when they observed the results in a test section at the municipal garage it allayed all fears. They also had PENNDOT specifications to utilize.
Other agencies that manage properties with roadways can play a role in demonstrating and utilizing road materials for their paved roads. For example, Pennsylvania's parks department used plasphalt in a state park for the roads and parking lots.
Partnership and collaboration
As described in the previous sections, local governments, federal installations, tribal governments, and a private corporation operate the waste recovery facilities in New Mexico. Several have indicated their interest in finding markets nearby that can use glass and plastic materials. Other entities that may be readily involved with partnering or collaborating on reuse projects include Sandia National Laboratories. Its four year old Manufacturing Science and Technology Center develops niche marketing for green technology.
A ready supply of products with recyclable materials is the responsibility of both waste recovery facilities and manufacturing and construction companies, depending on the complexity of the product. Cullet for base course can be provided by local recovery facilities with crushers. In addition, suppliers of construction materials should be readily able to crush cullet to specification for mixing with aggregate.
The state has procedures for the disposal and acquisition of public properties between state, city and county agencies. NMDOT, for example, provides for the disposal of public property that is usable to political subdivisions. Brogan cited NMSHTD Document AD 302-95 "Disposal of Public Property (1995) as a starting point for encouraging reuse of materials. However, NMDOT was charging local jurisdictions for their recycled materials, and some county responders and a district engineer suggested that it would be as cheap for NMDOT to give them to a project contractor with their value reflected in the bid price. Thus, if NMDOT had a supply of material on hand, they would indicate the available of that material in project requests in the locality. Creating an efficient and cost-effective for the dispersal of recycled materials is a key factor in promoting inter-governmental recycling programs for road construction.
Innovations in asphalt or cement mixes require research and development, with support from government agencies. Tewa Technology very likely failed in New Mexico due to several obstacles, including slow permitting, reluctant contractors in using the plasphalt product, and NMDOT's failure to conduct promised tests. The owners filed bankruptcy after their test effort with NMDOT, with great losses incurred during a two-year period, and laid off five workers. The New Mexico Business Weekly reported owner Eric Bowers as saying: "We wanted this to be a New Mexico product. All the original research and development was done here. We wanted to see New Mexico benefit from being the place where it began. At this point, we're going to have to leave the state and go to a market that is interested in an ecologically sound product like ours." Resistance to change can be a fatal obstacle in New Mexico, whether the resistance is from the government or private businesses with vested interests in the status quo.
The NM Recycling Coalition, composed of the staff from waste management facilities in New Mexico, works with NMDOT's State Materials Bureau and NMED on a Recycling Team in a joint problem-solving effort to use recyclable materials. Glass and tires were considered high priorities for the team at one time, but there was not a consistent demand for those materials, indicating a need for outreach and education regarding the use of glass and plastic alternatives. Their current efforts have been on uses for wood waste. The coalition could play an important role in collaboration with their members to develop efficient supplies of waste materials for reuse in road construction.
Sustainable development organizations may also provide partnership opportunities. Sustainable Communities/ZERI-NM is a non-government organization that creates environmentally sustainable applications of science and technology. By-products of industry are used to stimulate further production, creating jobs and programs in New Mexico and the international border area. ZERI conducted a workshop in March 2004 with the Governor's office and state agencies. ZERI and other related organizations may be appropriate providers of expertise on rethinking processes in materials development and road construction.
As reported by BioCycle magazine in 2004, "Recycling, remanufacturing, composting, and other green ventures have an even harder time than more "traditional" small companies in obtaining patient capital for start-up and expansion." It suggests that community development financial institutions, which serve economically distressed communities, could provide needed financial support. Recent initiatives from the state, including support from the Economic Development Department to support small businesses and the Governor's sustainable energy program may indicate that the state is prepared to support innovations in products with recycled materials.
9. Benefits and Recommendations for Action
As noted previously, the City of Albuquerque conducted an evaluation of their program that re-uses asphalt and Portland cement concrete materials for base course materials, in asphalt concrete, and for subgrade embankment. The city recognized that recycling road surface materials allowed it to have a new source of aggregate, thus extending the life of sand and gravel mines, extending the life of the regional landfill, and eliminating costs for processing the road waste materials at the landfill.
--Aggregate Supplier: Virgin source of pit life extended by 803,687 tons
--Landfill life extension: 32 ac/yd not used (457,941 CY @ 90 percent compaction)
--Savings in Solid Waste costs @ $15.00/ton
--Total savings: $12,055,300.00
This project evaluation proves that there are significant public benefits associated with the use of recycled materials.
Public benefits of glass and plastic resource utilization also include:
--Reductions in negative environmental impacts from mining operations, including noise from trucks and operations at pit, and air pollutants from the mines and trucks, especially fine particles (<PM10).
--Less neglect of rural communities. Road construction materials usually are mined from temporary (1-2 year) sites, but that itself leads to neglect of the local community, indicated by poor notification procedures, negligent operators, and unclaimed mining sites.
--Reductions or elimination of industrial mining traffic in local communities.
--Less need to open new mines for sand and gravel materials.
--Reductions in costs of vehicle damage in the vicinities of gravel mines, due to trucks casting gravel onto windshields and bodies. Vehicle companies and the insured public will benefit due to savings from fewer repairs to windshields and vehicle surfaces.
--Less conflict over siting new landfills, due to reduced demand on them.
--The use of recycled materials from domestic, agricultural and industrial sources offer benefits, but glass and plastics are very benign materials compared to other sources, thus are not likely to create additional pollution issues or health impacts when stored or used in road work.
--Preservation and greater protection of the landscapes of New Mexico, considered valuable resources culturally, historically, and as long-term assets contributing to the state's important tourism economy. Fewer un-reclaimed scars on the landscape would appear, and with greater recovery of glass and plastic materials, there could be less litter along the state highways and byways.
--Development of new business opportunities and jobs.
Collins and Ciesielski noted in 1994 that state legislation and regulation influences the development and use of waste materials in road construction. State legislation includes banning landfill disposal of certain wastes, allocating funds for research, development, and entrepreneurial support through its research institutions, and mandating state transportation agencies to investigate or use certain waste materials. If recycled materials are not found to be cost competitive with standard materials, the government should develop subsidies, or at the least eliminate barriers, for the use of recycled materials. It is likely that recycled materials will become more cost effective if they become widely used, and some materials have been shown to exceed the performance of standard materials, so cost savings are found in these material improvements.
Certainly, if legislation (state-wide and local) helped to create an assured supply of glass and plastic from that generated, and also required straightforward exchanges of materials for road construction projects, efficiencies could be met.
Strengthen research efforts at NM DOT using recyclable materials that local governments and other entities can provide. Utilize existing materials testing data from other DOTs, including PENNDOT, where appropriate. Ensure that evaluative tests of alternative products and specifications are developed in a timely manner. Consider specifications for lower-volume roads as opposed to high-volume roads such as interstate highways.
NMDOT and partners should inform the business community and contractors in all districts, as well as DOT staff engaged in design and construction projects, of experimental projects, test results, and specifications for materials using recycled waste products. For example, the NM Recycling Coalition will participate with NMDOT on educating DOT district staff during the next year on the use of wood waste materials. The team should also present information on the new specification for cullet for base course.
The state and partners should develop communications links that identify ready supplies of alternative waste materials, road projects with a demand for materials, businesses that prepare or re-use waste materials in construction products, and transportation/shipping providers. Include an inventory of the quantities, characteristics and appropriate end uses of waste materials and products. Information is essential in allowing municipalities, counties, sovereign tribes, and military and DOE installations to participate in and benefit from recycling and reuse opportunities.
More specifically, a government agency should develop an interactive database and mapping system detailing the locations of management facilities that have the capabilities to supply waste materials, the locations of road projects, and manufacturers of glassphalt and plasphalt. Other considerations could be applied: supplies of alternative materials and their proximity to areas where fewer sand and aggregate mines are desirable, such as areas of sensitive air quality; scenic and cultural locations that attract tourists and economic development dollars; and sites considered spiritually significant by American Tribes. Identify rational markets, such as counties with numerous unpaved roads and few local sources of aggregates for base course (Torrance is an example). Provide this information via a website that is regularly updated with current information.
Inform the general public of new uses for their waste materials, creating incentives for greater recovery rates in New Mexico, and marketing the environmental stewardship of the partners.
Working in collaboration with other agencies has provided other states with funding, markets and projects for DOTs engaged in fulfilling their environmental stewardship objectives. Thus, it is recommended that DOT or staff from the legislature or the governor's office determine the need for resources to enhance the collaborative strengths' of the NMED/NMDOT's Recycling Task Force. The task force and the agencies' directors may develop a project schedule for a period of time, such as 2 to 5 years. Ensure that testing and specification development, outreach and contracting activities are considered in planning and implementing projects.
Provide resources that strengthen the work of the NM Recycling Coalition.
Support materials, research and editorial support were provided by:
American Recycler, "Commercial Paving and Recycling Named Business Recycler of the Year," July 2003, at http://www.americanrecycler.com/july2003/misc.htm.
Aven, Paula, "Stapleton asphalt hits recycling pile," Denver Business Journal, April 21, 2000.
Bahia, Hussain; Davies, Robert; and Martinez, Victor, "Recycling of Scrap Tires and Plastic Waste in Modification of Asphalt Binders," in Transportation Congress: Civil Engineers-Key to the World Infrastructure, Proceedings of the 1995 Conference, 1995, p734.
Blodgett, Steve, Center for Science in Public Participation, "Environmental Impacts of Aggregate and Stone Mining in New Mexico," January 2004.
Brogan, James D., A Manual of Good Practice for Recycling/Reuse of Highway Construction Materials," NM State Highway and Transportation Department, 1996.
Brogan citing Barker: Barker, Martin, Recycled Construction Materials Waste Asphalt and Portland Cement Concretes as Base Material, City of Albuquerque, nd.
Brogan citing Han and Johnson: Han, Chunhua and Johnson, Ann, "Waste Products in Highway Construction," Sixth International Conference on Low-Volume Roads, pp. 62-69.
City of Albuquerque, Solid Waste Department, phone and correspondence, April, 2004.
Cannon Air Force Base, previous and current coordinators (Carla Givens), phone interviews, April and May, 2004.
CDOT, Colorado DOT, correspondence with Donna Harmelink, April, 2004.
Chesner, Warren, "Waste Glass and Sewage Sludge Fris Use in Asphalt pavements," in Utilization of Waste Materials in civil engineering construction: proceedings of sessions sponsored by the Materials Engineering Division of the American Society of Civil Engineers, 1992, page 296 307.
Civil Engineering, Materials Section, "Potholes Filled with Computers," June, 1999,
Cohen, Charles, "All that glitters is not road," Baltimore City Paper Online, March 1-7, 2000, http://www.citypaper.com/2000-03-01/charmed.html.
Collins, Robert J. and Ciesielski, Stanley, "Recycling and Use of Waste Materials and By-Products in Highway Construction," NCHRP Synthesis 199, Transportation Research Board, National Research Council, 1994.
Conigliaro, Anthony; Watson, Phil, "Determining the Best Formulation for Unique Asphalt Cold Patch Product Made with #3-7 Rigid Plastic Aggregate," for the Chelsea Center for Recycling and Economic Development, University of Massachusetts Lowell, 2000.
CWA / Clean Washington Center, Best Practice in Glass Recycling, November 1996, available at:
CWA, Preparation and Placement of Glassphalt, November 1996, available at: http://www.cwc.org/gl_bp/gbp4-0202.htm.
EPA, Office of Solid Waste and Emergency Response, "Municipal Solid Waste in the US: 2001 Facts and Figures," 2003.
FHWA, Recycling Team, Office of Pavement Technology, Mike Rafalowski, phone conversation, May, 2004.
Glass in Roadways and Runways, Slippery Rock University Recycling Program, http://www.sru.edu/depts/finance/recycling/glass.htm, October 11, 1999.
Kearn, Neal, Director of Public Works, Allentown, PA, phone conversation, March, 2004.
Madapati, Raghu Ram; Lee, K. Wayne; and Franco, Colin, "Evaluation of Crumb Rubber in Asphalt Pavements," in Transportation Congress: Civil Engineers-Key to the World Infrastructure, Proceedings of the 1995 Conference, 1995, p755.
Martinez, Lorenzo, LANL, phone conversation, March 2004.
McKeen, R. Gordon, "Cold Insitu Recycling Evaluation," NMSHTD Research Bureau, 1996.
NM Recycling Coalition, Directory, 2002; and phone conversation, Nancy Judd, Executive Director, April 2004.
PENNDOT, correspondence, May, 2004, with Robin Sukley; and "PENNDOT Paves the Way with Glass Pavement," from Strategic Recycling Program website; and "What's Ahead for Recycling in 2002," March, 2002; and "PENNDOT partners with private industry on glass recycling," available on
Pentz, Michelle, "Plasphalt," Wired, Feb. 2002, p. 25.
Rebeiz, Karim; Fowler, David; and Paul, Donald, "Properties of Composites Using Recycled Plastics," in Materials: Performance and Prevention of Deficiencies and Failures: Proceedings of the Materials Engineering Division of the American Society of Civil Engineers, 1992, p. 373.
Rubber Pavements Association, FAQ, at http://www.rubberpavements.org/faq.asp and phone interview with Doug Carlson, Executive Director, March, 2004.
Rural Conservation Alliance, website, http://www.raintreecounty.com/CMD.html.
Santa Fe County, phone conversation, Justin Stockdale, Recycling Coordinator, April 2004.
Stelmar, Hilary, Potting with Plasphalt, (letter to the editor), Civil Engineering, August, 1999.
Tarricone, Paul, "Recycled Roads," Civil Engineering, April, 1993.
UMN, University of Minnesota Technology Transfer Program, (Reprinted from The Resource, Minnesota Office of Environmental Assistance, spring 1998), http://www.cts.umn.edu/T2/archive/mixedglass.htm.
Vaughn, Colleen, NMDOT, phone conversation, May 2004.
Webb, Andrew, "Struggling Asphalt Company says state, local industry kept it from thriving," NM Business Weekly, Sept. 30, 2002.
ZERI, Sustainable Communities/ZERI-NM, website: http://www.scizerinm.org/.
~ Rural Conservation Alliance
PO Box 245
Cerrillos, NM 87010
Page managed by RIII http://www.raintreecounty.com/RecyAlte.html