Recycled Materials and Byproducts in Highway Applications—Scrap Tire Byproducts, Volume 7 (2013)

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1 Background Approximately one scrap tire is generated per person in the United States every year (Zicari 2009; RMRC 2008). Approximately 30 million of these tires can be used for retreading, which leaves about 250 million scrap tires in need of alternative uses or disposal. For disposal purposes, about 75 tires take up a volume of one cubic yard of landfill space (Choi et al. 2007). The types of scrap tires generated in the United States are shown in Table 1. Truck tires differ in composition com- pared with passenger and light truck tires. Truck tires con- tain a higher percentage of natural rubber, whereas passenger tires have higher percentages of synthetic rubbers. Natural rubber is more tolerant of heat generated from tire–pavement interactions; hence, its preferred use in commercial tires. A brief overview of uses for scrap tires, provided by Zicari (2009), show the three main current uses as (1) a fuel source (main current use), (2) ground rubber byproducts, and (3) civil engineering applications (Table 2). Byproduct used in high- way applications will vary substantially between states. Types of scrap tire byproducts not used as a fuel source include: • Whole tires: used as-is with no post-processing. • Slit tires: cut in half or sidewalls separated from the tread. – Shredded or chipped tires: 4 by 4 in. (100 by 100 mm) to as large as 9 by 18 in. (229 by 457 mm) (Note: there are no equivalent sieve sizes for these measure- ments; sizing is done by manual measurements or visual observations). • Ground rubber: ranging in sieve size from ¾ in. to the No. 100 sieve (19 mm to 0.15 mm) and regular in shape. • Crumb rubber: ranging in sieve size from No. 4 to the No. 200 sieves (4.75 mm to less than 0.075 mm). Ground rubber is produced using granulators, hammer mills, or fine grinding machines. Crumb rubber can be pro- duced by one of three methods: cracker mill, granulator, or micro-milling. There are two methods of grinding: mechani- cal and cryogenic processing. The mechanical process reduces tires to chips and granulates the chips while at the same time removing the loose steel and fibers. Once contaminates have been removed, the granules are further ground to produce fine crumbs of rubber. The cryogenic process freezes the tire chips in liquid nitrogen (approximately minus 80°F), which makes the scrap tire brittle and easier to grind. Once cooled and crushed, the steel and fibers are removed. This process produces rubber particles with a range of sizes between 4.75 and 0.6 mm. The ASTM D6270 (2008) Standard Practice for Use of Scrap Tires in Civil Engineering defines tire-derived aggre- gate (TDA) as “. . . pieces of scrap tires that have a basic geo- metrical shape and are generally between 12 mm and 305 mm (0.5 to 12 inch) in size and are intended for use in civil engi- neering applications.” This definition covers a portion of both the shredded, chipped, or ground rubber definitions cited in the RMRC (2008) reference. Further definitions for ground tire rubber byproducts are provided by the Rubber Manufacturers Asso- ciation (RMA 2009). This reference notes ground tire byprod- ucts are generated by tire buffings and processed whole tires that are sorted into four size-based categories: • Tire buffings: byproduct of the retreading industry • Coarse rubber: No. 4 to 1 in. sieve sizes (4.75 to 25 mm) • Ground rubber: No. 80 to No. 10 sieve sizes (0.177 to 2.0 mm) • Fine ground rubber: No. 40 to No. 80 sieve sizes (0.037 to 0.177 mm). Information found in the literature uses all of these defini- tions, sometimes interchangeably. The lack of consistency in the use of terms and definitions makes it difficult to compare results from various studies. Additional information can be found at the following websites: • Rubber Manufacturer’s Association: www.rma.org • Rubber Pavement Association: www.rubberpavements. org • Recycled Materials Resource Center: www.rmrc.unh. edu/ • Turner–Fairbanks Highway Research Center: http:// www.fhwa.dot.gov/research/tfhrc/ • U.S. EPA Resource Conservation Challenge: http:// www.epa.gov/epawaste/conserve/materials/tires/civil_ eng.htm. chapter one Scrap Tire ByproducTS

2 The University of Maine website (2010) provided a sum- mary of specific gravities and water absorption values for tire byproducts (Table 4). The water absorption capacity varies between 2.0% and 9.5%. Specific gravity of TDA materials depends on the amount of nonrubber components still in the particles. Specific gravities range from 1.02 to a high of 1.27 when steel wire is still in the TDA (Barker- Lemar 2005). Ranges of unit weights (Table 5) were also reported in a number of previous research documents. Unit weights increase with increasing compaction effort (energy). The loose densities of TDA are on the average about 28 lb/ft3 and the compacted densities are generally about 40 lb/ft3. Although limited data were provided, the use of a surcharge can be expected to further increase the density of the TDA layer. phySical and chemical properTieS Scrap tires vary in chemical composition based on the type of tire. Table 3 shows the differences between passenger and truck tire scrap rubber. Truck tires are higher in natural rubber content than passenger tires and significantly lower in synthetic rubber. Carbon black, fabric filler, accelerators, etc., are similar in content for both types. The percentage of natural and synthetic rubber is a significant factor in how the scrap tire rubber interacts when used with asphalt cements. In some cases, there is sufficient incompatibility so that the rubber and asphalt cannot be blended. This is a function of crude source chemistry differences that define the ability of the asphalt cement to interact with or partially dissolve the scrap tire rubber byproducts. Tire Type Millions of Tires Market, % Average Weight of Tires in Group, lb Light Duty Tires 264.2 88.2 22.5 Passenger tire replacements 202.3 67.53 Light truck tire replacements 36.0 12.02 Tires from scrapped tires 25.9 8.65 110 Commercial Tires 35.3 11.80 Medium, wide base, heavy truck replacement tires 17.8 5.94 Tires from scrapped trucks and buses 17.6 5.86 Total Scrapped Tires 299.6 100 32.8 After RMA (2006). TABLE 1 TIRE GENERATION IN THE UNITED STATES Use Percent of Use New York* United States** Tire-Derived Fuel 39 52 Ground Rubber 27 17 Civil Engineering 19 12 Use Not Identified 15 19 After Zicari (2009). *New York data from Empire St ate Development draft 2006 report. **United States data from Rubber Manufacturers Association draft 2007 report. TABLE 2 PERCENT OF CURRENT USES FOR SCRAP TIRES Property Passenger Tires Truck Tires Com position, % by weight Natural rubber 14 27 Synthetic rubber 27 14 Carbon black 28 28 Steel 14–15 14–15 Fabric, fillers, accelerators, and antioxidants, etc. 16–17 16–17 New Tires, lb 25 120 Scrap Tires, lb 22.5 110 After RMA (2009). TABLE 3 TyPICAL COMPOSITION AND WEIGHT OF PASSENGER AND TRUCk TIRES

3 After University of Maine website (2010); Barker-Lemar (2005). — = not applicable. Tire Type and Source Properties Reference (reported in Barker-Lem ar 2005) Specific gravity Water absorption, % Bulk Saturated surface dry Apparent Glass Belted — — 1.14 3.8 Hu mp hrey et al. (1992) 0.98 1.02 1.02 4.0 Manion and Humphrey (1992) Steel Belted 1.06 1.01 1.10 4.0 Manion and Humphrey (1992) Mixture 1.06 1.16 1.18 9.5 Bressette (1984) — — 1.24 2.0 Hu mp hrey et al. (1992) Pine State Facility Mixture — — 1.27 2.0 Hu mp hrey et al. (1992) Palmer Facility Mixture — — 1.23 4.3 Hu mp hrey et al. (1992) Sawyer Facility Mixture 1.01 1.05 1.05 4.0 Manion and Humphrey (1992) — 0.88 to 1.13 — — Ahm ed (1993) TABLE 4 SUMMARy OF PREvIOUSLy REPORTED SPECIFIC GRAvITIES AND ABSORPTION CAPACITIES Compaction Method Particle Size, in. Tire Type TDA Recycler Dry Unit Weight, pcf Loose 0.5 to 5.5 — — 26.0 Loose 3 Mixed Palm er Shredding 21.3 Loose 2 Mixed Pine State Recycling 30.1 Loose 1 Glass F & B Enterprises 30.9 Loose 2 Mixed Sawyer Environm ental 25.5 Loose 2 Mixed — 29.1 Loose 2 — — 24 to 33 Loose 1 Mixed — 30.5 Vibration 1 Mixed — 31.0 Vibration 0.5 Mixed — 29.5 50% Standard 1 Mixed — 38.3 50% Standard 0.5 Mixed — 40.0 60% Standard 3 Mixed Palm er Shredding 38.7 60% Standard 2 Mixed Pine State Recycling 40.1 60% Standard 1 Glass F & B Enterprises 38.6 60% Standard 2 Mixed Sawyer Environm ental 39.0 Standard 2 Mixed Sawyer Environm ental 39.9 Standard 2 Mixed — 39.6 Standard 1.5 Mixed — 40.2 Standard 1 Mixed — 40.7 Standard 0.5 Mixed — 39.5 Standard b 0.75 to 3 — — 37.0 Standard c 0.7 to 3 — — 35.0 Standard b 3 — Rodefeld 37.1 b Standard c 3 — Rodefeld 34.9 c Modified 2 Mixed Sawyer Environm ental 41.2 Modified 2 Mixed — 41.7 Modified 1 Mixed — 42.7 — 2 Mixed — 26 to 36 Surcharged with 3 ft Soil, Pavem ent, and Highway Traffic 2 — — 52 to 53 Full-Scale Field Tests 1.5 — — 44.3 Full-Scale Field Tests 3 — — 43.1 After University of Maine (2010); Barker-Lemar (2005). Compaction methods: Loose = no compaction; tire s hreds loosely dumped into compaction mold. Vibration = Method D4253. 50% Standard = Impact compacti on with com paction energy of 6,188 ft-lb/f t 3 . 60% Standard = Impact compacti on with com paction energy of 7,425 ft-lb/f t 3 . Standard = Impact compaction with compaction energy of 12,375 ft-lb/ft 3 . Modified = Impact compaction with compaction energy of 56,250 ft-lb/ft 3 . b 6-in. diameter mold compacted by 10-lb rammer falling 12 in. c 12-in. diameter mold compacted by 60-lb rammer falling 18 in . TABLE 5 SUMMARy OF PREvIOUSLy REPORTED vALUES FOR UNIT WEIGHTS

4 ASTM D6270 defines two gradations for TDA depending on use. The Type A gradation is used for drainage, insula- tion, and vibration damping. This gradation has 100% pass- ing the 4 in. sieve, with a minimum of 90% passing the 3 in. sieve and a maximum of 5% passing the 4.75 mm sieve. Type B is used for lightweight fill. The Type B gradation has 100% smaller than 18 in. and 90% smaller than 12 in. in the maxi- mum dimension with a maximum of 50% passing the 3 in., 25% passing the 1.5 in., and 1% passing the 4.75 mm sieve. The composition of scrap tires varies widely. Typical scrap tire components were reported by Bojenko et al. (2008) (Table 6). Scrap tires are not sorted by type, other than some recycling facilities separating truck tires from passenger car tires; therefore, the composition of any scrap tire byproducts will reflect all makes and models of tires. Bojenko et al. (2008) also reported information on the trace metal concentrations for scrap tires (Table 7). engineering properTieS A range of physical properties for TDA byproducts has been reported in the literature. The available information includes ranges of values for: • Thermal conductivity • Compressibility • Hydraulic conductivity (permeability) • Cohesion and angle of internal friction • Combustibility. Thermal conductivity describes the ability of a material to conduct heat (Barker-Lemar 2005). The thermal conductiv- ity of TDA is from 0.1 to 0.2 Btu/hr-ft, which is significantly lower than for granular soils (Table 8). These values indicate that TDA layers can provide good insulation for protection against frost heave. TDA is highly compressible because of the large void spaces between the particles. The larger the void space between the particles the more vertical movement will be seen when a load is applied. Surcharges are typically used to remove the majority of the vertical movement before using the TDA layer in the application (Table 9). Compressibility results in vertical settlement when loads are applied (Table 10). This information is necessary for guidance for the designer who must determine the amount of surcharge needed to reduce long-term settlement. Most vol- ume change occurs immediately upon loading and begins to decrease with increasing loads (Wartman et al. 2007). volume change occurs from both a reduction in voids and deformation of the tire particles. Compressibility is inversely proportional to the soil content when TDA is mixed with soils. The soil increasingly fills the voids spaces and supports the tire particles. Hydraulic conductivity is a measure of the rate of water flow through a porous material and is an important property for evaluating the ability of water to drain through a TDA layer (Table 11). A wide range of hydraulic conductivity has been reported and varies with TDA particle size, compac- tion energy, and other test-specific variables. The range of reported values is between a low of 0.0005 cm/s to a high of 59.3 cm/s. This corresponds to a drainage rate of 1.42 ft per day to 168,094 feet per day, respectively. Smaller sizes of TDA compacted to a maximum density provided the lowest values of conductivity. Hydraulic conductivity can also be reduced by mixing TDA with soil, which will fill the void space and reduce flow. Triaxial testing was used to determine cohesion, C, and the angle of internal friction, f, have been reported by a num- ber of researchers (Barker-Lemar 2005) (Table 12). Wartman et al. (2007) summarized research that showed that the shear strength was TDA particle size-independent. In other words, Material Components in Tires Percent of Average Tire % of tire lb/average tire 30 different kinds of synthetic rubber 24 4.85 Eight types of natural rubber 20 3.97 Eight types of carbon black 24 4.85 Steel cords for belts 5 1.1 Polyester and nylon 5 1.1 Steel bead wire 5 1.1 Different kinds of chemicals, waxes, oils, pigments, etc. 15 3.09 After Bojenko et al. (2008). TABLE 6 TyPICAL COMPOSITION OF SCRAP TIRES Trace Metal Concentration, mg/kg Al 280 Ba <20 Be <0.5 Bo <500 Cd 3.6 Cr 107 Cu 3.3 Fe 4,480 Hg 0.1 Mg <500 Mn 28 Mo 1 Ni 3.3 Se <5 Sr <100 Ti 48 Zn 15,500 After Bojenko et al. (2008). TABLE 7 TRACE METAL CONCENTRATIONS IN RUBBER TIRES METAL

5 research using tire chips produce similar results to experi- ments using larger shredded tire particles. The TDA has a low modulus as a result of the large strain. The deformation is primarily a function of the void space between tire particles. volume change (compressibility) and constrained modulus have a moderate degree of TDA par- ticle size dependence, with more compressibility resulting from using larger TDA sizes. Combustibility is the ability of a material to react vigor- ously with oxygen to produce heat and flames. The compo- nents in tires can be flammable and in-use conditions that may generate self-combustion of the TDA are a concern (Barker- Lemar 2005; Tandon et al. 2007; Cheng 2010). Self-starting fires have been documented when the layer thickness was at least 20 ft (compacted). Possible sources of internal heating include the oxidation of the exposed steel in belted tires, oxi- dation of rubber, and microbial action. Possible conditions of contributing to heat generation include access to air, access to water, retention of heat (function of high insulation value), smaller TDA sizes and granulated rubber particles, the pres- ence of organic nutrients, and layer thickness. TDA is reported to have a flash point of 580°F (University of Maine 2010). Sample (location designation) Density (pcf) Void Ratio Apparent Thermal Conductivity (Btu/hr-ft-°F) Surcharge Gravel 117.6 0.41 0.295 none 121.6 0.36 0.326 half 123.0 0.34 0.345 full TDA (F&B-g) 38.5 0.85 0.120 none 43.3 0.64 0.113 half 45.4 0.56 0.114 full TDA (F&B-s) 39.1 0.85 0.145 none 42.8 0.69 0.130 half 45.3 0.6 0.134 full TDA (Palmer) 39.7 1.00 0.159 none 45.1 0.76 0.119 half 48.5 0.63 0.125 full TDA (Pine State) 39.2 0.97 0.158 none 45.4 0.70 0.139 half 49.6 0.56 0.114 full TDA (Sawyer) 36.0 1.13 0.184 none 41.0 0.87 0.148 half 43.7 0.76 0.156 full After Barker-Lemar (2005). TABLE 8 SUMMARy OF THERMAL PROPERTIES FOR TDA Tire Shred Size (in.) Compressibility (%) Stress (lb/ft2) 0.75 to 1.5 30 1,440 0.08 to 2 33–37 4,176 (loose before load) 52 4,176 (compacted before load) 0.08 to 1 33–35 4,176 (loose before load) 45 4,176 (loose) 0.08 to 3 38–41 4,176 (compacted before load) 0.08 to 2 29–37 4,176 (compacted before load) 0.5 to 1.5 27 — 1.18 25 104 40 8,532 2 to 3 37 14,400 8 to 16 55 793 3 18–28 522 0.5 to 5.5 31 665 50 3,400 65 21,000 After Barker-Lemar (2005). — = data not provided. TABLE 9 COMPRESSIBILITy OF DIFFERENT SIZE TIRE SHREDS

6 environmenTal properTieS air Quality Emissions are a concern when using crumb rubber as an asphalt modifier because of the higher hot mix asphalt (HMA) plant and compaction temperatures needed to obtain a work- able viscosity and in-place density. General guidelines for best HMA management of emissions provided by the Rubber Pave- ments Association (RPA) include (2009): • Produce crumb rubber-modified (CRM) mixes at the lowest possible temperatures, preferably lower than 325°F. • keep flights in drum dryers in good shape to promote the best drying of the aggregate and reduce the extent to which the flames reach the CRM binder. • Maintain material temperatures so that scorching of the binder is prevented. • Lower rates of production to reduce visible emissions. • Tarp trucks, shorten windrows for belly dump operations, and use material transfer devices to minimize cooling of the mix. • Only pave when the weather will not speed cooling of the mix. Avoid cool and windy conditions. • Odor reduction additives may be helpful in the mixes. Average Vertical Stress, psi Anticipated Range of Vertical Strain, % 10 19 to 33 20 25 to 37 30 29 to 42 40 33 to 44 50 36 to 46 60 39 to 48 70 40 to 50 After Barker-Lemar (2005). TABLE 10 vERTICAL STRAIN THAT CAN BE ANTICIPATED WITH TDA SETTLEMENT Tire Size, in. Hydraulic Conductivity, cm/s Test Condition Information 0.18 0.002 3,132 psf 5x10-4 7,308 psf 0.75 0.79 to 2.74 Simulated overburden of 0 to 25 ft of MSW 1.5 1.43 to 2.64 Simulated overburden of 0 to 35 ft of MSW 2 0.7 2,500 psf (40 ft MSW) 0.53 5,000 psf (80 ft MSW) 0.25 10,000 psf (160 ft MSW) 0.12 15,000 psf (240 ft MSW) 1.2 — 0.04 to 1.5 6.9 Void ratio = 0.833 1.5 Void ratio = 0.414 0.2 to 0.6 0.03 ASTM D2434 0.2 to 2.0 3.8 to 59.3 — 0.25 to 0.5 0.16 — 0.4 to2 7.7 Void ratio = 0.925 2.1 Void ratio = 0.488 0.5 to 1.0 0.18 — 0.5 to1.5 0.58 — 7.6 Void ratio = 0.693 1.5 Void ratio = 0.328 0.5 to 3 16.3 Void ratio = 0.857 5.6 Void ratio = 0.546 0.5 to 5.5 0.65 3,400 psf, Compression—50% 0.01 2,1000 psf, Compression—65% 0.75 to 3 15.4 Void ratio = 1.114 4.8 Void ratio = 0.583 1.0 to 1.5 0.18 — 1 to 2 1 — 1 to 2.5 2.9 to 23.5 — 2.4 to 4.0 55 1,879 psf 20 3,132 psf 10 7,308 psf 6 11,484 psf 2 to 3 0.6 Stress (psf): 0 0.45 1,440 psf 0.4 2,881 psf 8 to 16 9 Void ratio = 2.77 3.2 Void ratio = 1.53 1.8 Void ratio = 0.78 After Barker-Lemar (2005). — = data not provided; MSW = municipal solid waste; psf = pounds per square foot. TABLE 11 RANGE OF HyDRAULIC CONDUCTIvITy FOR TDA LAyERS WITH vARIOUS TEST CONDITIONS

7 Four studies have been conducted over the last 15 years that evaluated emissions from the production of conventional HMA to that of CRM HMA. The first study that reported measured emissions was from the Michigan Department of Transportation (DOT) in 1994. The second study was con- ducted by the Texas Transportation Institute in 1995 and evaluated the recyclability of the CRM HMA by analyzing previously reported data. The Institute data mining research concluded that the CRM HMA is likely recyclable and air quality should not be compromised. Construction issues were not addressed in this study. The third reported research proj- ect was conducted by the Northern California Rubberized Asphalt Technology Center in 2001. This study evaluated if additional permitting would be required for CRM HMA by comparison to the standards set out the 2000 EPA AP-42 guide “Hot mix asphalt plant emission assessment report.” The RPA reported results for emission testing at a drum mix plant and the fourth study (Roschen 2002) provided simi- lar testing for batch plants. The data in the Roschen report appear to repeat (or be the original source of) the RPA drum mix plant data. Emissions are compared based on the pounds per ton of HMA produced, which is a parameter that reflects the pro- duction rate of the mixes at the plant. For the Roschen study, the production rates were reported as 206 and 336 tons per hour for conventional mixes at the batch and drum plants, respectively. The production rates for the CRM HMA at the same two plants were lower at 185 and 307 tons per hour, respectively. These production rates represent the maximum capacity of each plant for each mix. The operating tempera- tures of each plant were 318°F and 311°F for the conven- tional HMA mixes at drum and batch plants, respectively. The temperatures were increased when producing the CRM HMA to 335°F and 318°F, respectively. Results showed that the particulate emissions were similar for both mixes, but somewhat different between batch and drum mix plants (Table 13). TDA Size, in. C, lb/ft 2 Friction Angle, o Specific Test Conditions <0.04 100 30 Tested at dry unit weight of 33 pcf 0.04 to 0.16 70 31 — <0.08 0 45 Tire shreds without steel–triaxial tests under confining pressure of 720 to 1,148 psf 0.16 to 0.27 130 27 — 0.18 1,462 6 10% strain 0.2 to 0.6 147 27 ASTM D3080 <0.37 0 47 to 60 — 0.5 747 20.5 Standard co mp action and 20% strain as failure <0.74 0 54 — 1 818 24.6 Modified compaction energy and 20% strain as failure 694 25.3 Standard co mp action energy and 20% strain as failure 779 22.6 50% standard com paction energy and 20% strain as failure 1.5 69 38 Saturated 1.5 to 55.1 65 38 115 to 585 psf peak failure criterion 0 38 115 to 585 psf 10% failure criterion <1.5 180 25 Norm al stress range: 400–1,500 psf 0 57 — 1 to 2 80 27.5 — 1,482 11 15% strain 1,712 15 20% strain <2, 2–4, and 4–6 0 to 62.6 30 146–1,460 psf <2.0 90 to 160 21 to 26 — <3.0 240 19 — 2 150 27 — 0 17 to 35 17 degrees at 5% strain, 35 degrees at 20% strain 2 to 3 — 37 to 43 0 2-in. shredded 660 14 — 2-in. square 540 21 — 3 90 32 — After Barker-Lemar (2005). — = data not provided. TABLE 12 SUMMARy OF COHESION AND ANGLE OF INTERNAL FRICTION

8 The toxic potency index was evaluated using Bay Area Air Quality Management District Regulation 2-1-316 for each plant (Table 14). The emissions produced at the drum plant were similar for both conventional and CRM HMA. The emissions at the batch plant showed significant differences between the productions of conventional compared with CRM HMA. In this case, the emissions increased approximately twenty-fold when producing the CRM HMA. The presence of benzene was attributed to the tailpipe exhaust in the truck load-out shed since neither the CRM nor the extender oil used in this mix contained benzene. Operational data, material conditions, and stack measure- ments are included in Table 15. The operational characteris- tics, continuous emissions measurements, and polyaromatic compounds (PAH) contents were consistent between the drum and batch plants. The National Institute for Occupational Health and Safety (NIOSH) (2001) reported on testing from personal breath- ing zone air samples from CRM and conventional HMA paving operations. Testing included measurements of total particulates (TPs), benzene soluble particulate (BSP), poly- cyclic aromatic compounds, organic sulfur-containing com- pounds, and benzothiazole (Table 16). Only the TP and BSP have occupational limits. Sampling was also completed to identify emissions from any solvents used to clean equip- ment in the field, diesel exhaust, and carbon monoxide. NIOSH checked if the asphalt fume was mutagenic by testing on bacteria, collecting questionnaires completed by paving workers, and testing breathing capacity of workers during the day. Findings from this research showed: • Personal breathing zone exposures were high during CRM paving. • Eye, nose, and throat irritation were the most commonly reported worker complaints and were associated with the TPs during CRM HMA paving. • Solvent levels were generally very low; however, ben- zene was detected at several sites. • High carbon monoxide exposures were measured near some workers, but exposure to diesel fumes was low. This was eventually traced back to sampling near a poorly tuned engine. • Benzothiazole was found at all sites, but it is not known if these levels would have a health effect. • None of the asphalt fume samples tested was mutagenic. The conclusion by NIOSH was that CRM exposures are poten- tially more hazardous than conventional HMA and that fumes should be reduced whenever possible. Discussion and review (possibly still unpublished) of the NIOSH (2001) report included information that reflected poorly on the precision/accuracy of the tests leading to the TP and BSP values. Exxon Environmental, Inc., in East Millstone, New Jersey, asked the question, “Why do BSPs sometimes exceed TPs as BSPs are only part of TPs?” After extensive testing and study, they concluded that filters used in the BSP testing could have significant quantities of BSPs invalidating the testing, and the large amounts of solvent used, even the pur- est grades available as recommended in the EPA/NIOSH test procedures, could have significant quantities of BSPs, likewise After Roschen (2002). Source of Data Particulate Emissions (pounds per ton) Conventional asphalt concrete CRM HMA Dutra (batch plant) 0.0013 0.0015 MVR (drum plant) 0.0025 0.0030 TABLE 13 COMPARISON WITH EPA AP-42 FOR SACRAMENTO COUNTy, CALIFORNIA STUDy Compound Reg 2-1-316 Threshold (lb/yr) Toxic Potency Index for Two Locations Dutra (batch plant) MVR (drum plant) Conventional asphalt concrete Asphalt rubber concrete Conventional asphalt concrete Asphalt rubber concrete Benzene 6.7 1.90E-07 5.12E-06 6.32E-06 5.40E-06 Toluene 39,000 5.77E-11 1.99E-09 5.20E-10 4.64E-10 Xylene 58,000 0 1.42E-08 3.40E-10 8.93E-10 1,3-Butadiene 1.1 0 0 5.00E-06 6.20E-06 Naphthalene 270 4.89E-08 5.35E-08 1.16E-08 2.17E-08 Benz(a)anthracene 0.044 2.73E-08 0 0 0 Total Toxic Potency Index 2.66E-07 5.19E-06 1.13E-05 1.16E-05 After Roschen (2002). Toxic Potency Index for each contaminant is calculated by dividing the measured emission factor (lb/ton) by the annual emission threshold (lb/yr). TABLE 14 COMPARISON WITH EPA AP-42 FOR SACRAMENTO COUNTy, CALIFORNIA STUDy

9 invalidating the testing. It is important that this possibility be considered when conducting environmental testing. Water Quality Liu et al. (1998) provided a summary of earlier leachate test- ing studies which are summarized in Table 17. There is a general agreement that lower pH conditions result in higher concentrations of metals being leached out of the TDA in unbound application, but the concentrations are usually below the primary drinking water standards. The most common metal that exceeds the secondary drinking water standards is iron. High concentrations of carbon black were leached out of the TDA at high pH levels. Only one study evaluated the occurrence of PAH in the leachate; however, both TDA and HMA leachate were found to generate PAH compounds. Further studies were recommended for these compounds. TDA Above the Ground Water Table Humphrey and Swett (2006) evaluated water quality index tests for TDA in unbound applications that were placed above the ground-water table. The investigation monitored five projects for total dissolved solids (TDS), total solids, bio- logical oxygen demand, and contamination oxygen demand (Table 18). The measured pH was near neutral. The North yarmouth project showed that both the control and the TDS exceeded secondary drinking water standards, but the ini- tial preconstruction data showed that these levels of TDS Operating Data/Conditions/Measurements Control 2 RBR 1 HMA Production Rate (tons per hour) 351 357 Dry Aggregate Rate (tons per hour) 330 333 Asphalt Ce me nt Added (%) 5.75% 6.84% Materials Moisture Content 4.17% 5.21% Fuel Consum ption (gal/hr) 655 690 Exhaust Gas Te mp erature (°F) 311 324 Mix Tem perature (°F) 296 316 Sam ple Volume (SCF) 46.501 42.823 Sam ple Volume (cu. m) 1.317 1.213 Exhaust Gas Moisture (%) 27.00% 29.30% Stack Tem perature (°F) 260 271 Actual Exhaust Gas Flow (ACFM) 89,540 95,450 Dry Exhaust Gas Flow (DSCFM) 47,076 47,836 Dry Exhaust Gas Flow (DSCMM) 1,333 1,355 Continuous Emissions Measurem ents and Method 18 Results CO 2 , %, Orsat Result 5.79% 6.02% O 2 , %, Orsat Result 12.75% 12.10% N 2 , %, Orsat Result 81.46% 81.88% Carbon Dioxide (C O 2 ) 6.00% 6.48% Oxygen (O 2 ) 12.87% 12.18% Carbon Mo noxide (CO) PPM 430.5 259.5 Nitrogen Oxides (N O x ) PPM 139.3 124.4 Sulfur Dioxide (S O 2 ) PPM 74.4 76.7 Non Methane Total Hy drocarbons (NMTHC) as Carbon PPM 225.5 183.0 Methane (C H 4 ) as Measured PPM 27.7 10.6 Methane as Carbon PPM 20.7 7.9 Total Hydrocarbons (THC) as Carbon PPM 245.1 191.3 NMTHC as Carbon PPM 225.5 183.0 PAH Em issions Measurem ents (lb/hr) Acenaphthene 0.0018 0.0021 Acenaphthylene 0.0022 0.0026 Anthracene 0.0003 ND Benz(a) anthracene 0.0002 ND Chrysene 0.0003 ND Fluoranthene 0.0030 0.0024 Fluorene 0.0051 0.0055 Naphthalene 0.0502 0.0622 Naphthalene, 2-Methyl- 0.0578 0.0788 Phenanthrene 0.0120 0.0141 Pyrene 0.0030 0.0022 Cunene 0.0056 0.0069 o-Cresol (2-M ethylphenol) 0.0029 0.0011 m- /p-Cresol (3-/4-Methylphenol) 0.0052 0.0058 After RMA (2009). ND = not detectable. TABLE 15 EMISSION RESEARCH REPORTED FOR MICHIGAN DOT 1994 STUDy

10 were not related to TDA. Secondary drinking water stan- dard inorganic chemical compounds are “non-enforceable guidelines regulating contaminants that may cause cosmetic effects (such as skin or tooth discoloration) or aesthetic effects (such as taste, odor, or color) in drinking water” (EPA 2006). Thirteen inorganic chemicals for primary drinking water standards were measured on filtered samples, except for mer- cury (Table 19). All of the projects showed concentrations below the regulatory allowed limits with one exception. The C&E (climate and energy) project showed concentrations for antimony, arsenic, lead, selenium, and titanium, but no con- trol was taken; therefore, it was unclear where the contami- nation was coming from. These results appeared reasonable because none of these chemicals are commonly used in the manufacture of tires. Nine inorganic compounds related to secondary drinking water standards were directly monitored on filtered samples (Table 20). The C&E project compounds were higher than the limit for aluminum; however, there was no control sam- ple available for the preconstruction condition. The TDA was source of elevated levels of iron (Fe) and manganese (Mn). There was an elevated chloride content in two projects that was attributed to the use of road salts. The zinc was lower in TDA areas for two projects when compared with the control sections (statistically significant). Sulfate was lower than control on one project. Organic compounds were measured for two field studies where the water passing through the TDA was used for the analysis. volatile organic compounds (vOCs) per EPA Method 8260 are shown in Table 21. The semi-volatile organic compounds (SvOCs) were measured per capillary column EPA Method 8270. No difference between control and TDA projects were observed. Aquatic toxicity was evaluated for one project with the U.S. EPA (EPA 2006) freshwater short-term toxicity tests. The results showed no effect from TDA. Projects with adjacent wells (three) showed no statistical differences found between the control wells and those adjacent to the TDA projects. A summary for TDA used above the water tables were: • Drinking water standards are not exceeded when TDA is used above the ground-water table. • Would be unlikely to increase levels of metals above naturally occurring levels. • Secondary drinking water standards may be exceeded for concentrations of iron and manganese. • vOCs and SvOCs were generally below reporting limits. • Aquatic toxicity tests showed no effect from TDA. Compound Emission Factor (pounds per ton) RPA (2001) (drum plant) Roschen (2002) (batch plant) Conventional asphalt concrete Asphalt rubber concrete EPA AP-42 Conventional asphalt concrete Asphalt rubber concrete EPA AP-42 Benzene 4.23E-05 3.62E-05 3.90E-04 1.27E-06 3.43E-05 2.80E-04 Toluene 2.03E-05 1.81E-05 1.50E-04 2.25E-06 7.75E-05 1.00E-03 Ethyl Benzene 0 3.20E-06 2.40E-04 0 7.37E-06 2.20E-03 Xylene 1.97E-05 5.18E-05 2.00E-04 0 8.26E-04 2.70E-03 1,3-Butadiene 5.50E-06 6.82E-06 NA 0 0 NA Naphthalene 3.12E-06 5.87E-06 9.00E-05 1.32E-05 1.45E-05 3.60E-05 2-Methylnaphthalene 7.78E-07 1.60E-06 7.40E-05 1.12E-05 2.15E-05 7.10E-05 Acenaphthylene 1.71E-07 1.01E-07 8.60E-06 3.43E-07 3.99E-07 5.80E-07 Acenaphthene 1.66E-08 1.86E-09 1.40E-06 1.05E-06 1.63E-06 9.00E-07 Fluroene 5.27E-08 3.68E-08 3.80E-06 6.61E-07 1.37E-06 1.60E-06 Phenanthrene 1.09E-07 8.02E-08 7.60E-06 1.28E-06 1.83E-06 2.60E-06 Anthracene 1.19E-07 4.79E-09 2.20E-07 4.09E-07 5.04E-07 2.10E-07 Fluoranthene 8.28E-09 4.04E-09 6.10E-07 6.15E-08 4.00E-08 1.60E-07 Pyrene 1.16E-09 3.52E-09 NA 2.78E-07 1.64E-07 NA Benz(a)anthracene 0 0 2.10E-07 1.20E-09 0 4.60E-09 Chrysene 0 0 1.80E-07 7.55E-09 2.55E-09 3.80E-09 Benzo(b)fluoranthene 0 0 1.00E-07 0 0 9.40E-09 Benzo(k)fluoranthene 0 0 4.10E-08 0 0 1.30E-08 Benzo(e)pyrene 0 0 1.10E-07 5.56E-09 2.82E-09 NA Benzo(a)pyrene 0 0 9.80E-09 0 0 3.10E-10 Perylene 0 0 8.80E-09 1.51E-09 0 NA Indeno(1,2,3 - c,d)pyrene 0 0 7.00E-09 0 0 3.00E-10 Dibenz(a,h)anthracene 0 0 NA 0 0 9.50E-11 Benzo(g,h,l)perylene 0 0 4.00E-08 0 0 NA After RMA (2009) and Roschen (2002). NA = not available. TABLE 16 EMISSION RESULTS FROM ENvIRONMENTAL STUDIES

11 Source of Inform ation pH Range Metals Other Inform ation Comments Minnesota Pollution Control Agency (1990) 3.5 to 8.0 As, Ca, Cr, Se, and Zn were over the Mn drinking water standards in some cases. Fe exceeded secondary drinking water standards. Leach mo re in lower pH water PAHs were exceeded for all conditions for both TDA and HM A. Use TDA above the water table Limit infiltration of water through scrap tires Drain surface water away from TDA base Wi sconsin (1992) Neutral If any com pounds leached, the concentrations decreased with tim e except for Ba, Fe, Mn, and Zn. Fe and Mn were at or above the drinking water standards. NA Not a hazardous waste Little or no influence on ground-water quality Scrap Tire Management Council Study (1991) Neutral No regulatory limits were exceeded. NA No differences in results from TCLP and EP Tox test results Virginia DOT TCLP 1-yr study showed no concentrations exceeded lim its. Metals leached most readily at lower pH. Fe concentrations were highest. Significant amounts of carbon black leached at higher pH. Som e gas generation observed after two weeks at very low pH. Illinois DOT (1990) EP Tox Metals were usually below or close to detection limits. Organics were below or close to detection limits. Kent State University, Ohio Field study No regulation limits were exceeded. Wageningen Agricultural University, Denm ark Field study NA Measured the release of CO 2 from TDA– soil mixtures, which was attributed to the degradation of TDA particle com ponents such as steric acid. Liu et al. (1998). NA = not available; TCLP = Toxicity Characteristic Leaching Procedure. As = arsenic; Ba = barium; Ca = calcium; Cr = chromiu m; Fe = iron; Mn = manganese; Se = selenium; Zn = zinc. TABLE 17 SUMMARy OF RESULTS FROM PREvIOUS STUDIES After Humphrey and Swett (2006). NA = not available. *Results for unfiltered sample reported. **Results from a single sample reported. References: Wisconsin (Edil and Bosscher 1992; Eldin and Senouci 1992; Bosscher et al. 1993); North Yarmouth (Humphrey and Kat z 2000); Witter Farm Road (Humphrey 1999); Ohio Monofills (Chyi 2000); Binghamton (Brophy and Graney 2004); Secondary standard (EPA 2006). Analyte Secondary Standard Wisconsin North Yarmouth Winter Farm Road** Ohio Monofills Binghamton, NY West 4-in. TDA East 2-in. TDA Control TDA Section C TDA Section D C&E American Control TF2 TDA TF 1 pH 6.5–8.5 7.5 7.5 7.21 7.11 7.05 NA 7.29 7.51 7.06 6.79 Total Dissolved Solids, mg/L 500 1,883 230 1,096 1,049 902 320 NA NA NA NA Total Solids, mg/L NA NA NA 1,117 1,062 925 610 NA NA NA NA BOD, mg/L NA 16.3 38.7 1.79 1.34 2.04 NA NA NA NA NA COD, mg/L NA 163 279 56.6 58 61.1 NA NA NA NA NA TABLE 18 MEAN vALUES OF WATER QUALITy INDEx TESTS FROM FIELD STUDIES WITH DIRECT COLLECTION OF SAMPLES

12 Constituents RAL Wisconsin North Yarmouth Witter Farm Road** Ohio Monofills Binghamton, NY West 4-in. TDA East 2-in. TDA Control TDA Section C TDA Section D C&E American Control TF2 TDA TF1 Sb 0.006 NA NA 100% <0.05 100% <0.05 NA 0.129 100% <0.005 NA NA As 0.01 NA NA NA NA NA NA 0.31 67% <0.001 NA NA Ba 2 0.346 0.281 0.0688 0.0339 0.0395 0.017 0.218 0.0603 0.796 0.392 Be 0.004 NA NA 100% <0.005 100% <0.005 NA 100% <0.1 100% <0.001 NA NA Ca 0.005 NA NA 95% <0.0005 100% <0.0005 96% <0.0005 <0.0005 80% <0.1 67% <0.001 0.0325 0.008 Cl 0.1 NA NA 0.0118 0.0126 0.0119 <0.006 NA NA NA NA Cu 1.3 NA NA 91% <0.009 91% <0.009 96% <0.009 <0.009 80% <0.02 67% <0.01 NA NA F 4 NA NA NA NA NA NA 0.8018 0.7356 NA NA Pb 0.015 90% <0.003 0.008 88% <0.002 88% <0.002 94% <0.002 <0.002 0.19 67% <0.001 NA NA Hg 0.002 NA NA 100% <0.0005 100% <0.0005 NA NA NA NA NA NO 3 10 NA NA NA NA NA NA 0.9217 0.8933 NA NA Se 0.05 NA NA NA NA NA NA 0.231 100% <0.001 NA NA Ti 0.002 NA NA NA NA NA NA 80% <0.002 100% <0.002 NA NA After Wartmen et al. (2007). **Results from a single sample reported. NA = not available; RAL = regulatory allowed limits. TABLE 19 MEAN CONCENTRATIONS OF INORGANIC ANALyTES WITH PRIMARy DRINkING WATER STANDARDS FROM FIELD STUDIES WITH DIRECT COLLECTION OF SAMPLES Analyte Secondary Standard Wisconsin North Yarmouth Winter Farm Road** Ohio Monofills Binghamton, NY West 4-in. TDA East 2-in. TDA Control TDA Section C TDA Section D C&E American Control TF2 TDA TF1 Al 0.2 NA NA 81% <0.07 100% <0.07 100% <0.07 <0.07 7.97 67% < 0.1 NA NA Cl 250 477 600 345.8 331.9 338. 111 44.2 34.6 NA NA Cu 1 NA NA 91% <0.009 91% <0.009 96% <0.009 <0.009 80% <0.02 67% <0.01 NA NA F 2 NA NA NA NA NA NA 0.8 0.736 NA NA Fe 0.3 0.71 1.13 0.0198 0.0795 0.555 0.158 0.19 0.103 0.255 15 Mn 0.05 1.129 1.522 0.0421 4.38 2.56 2.53 2.72 1.93 0.26 6.21 Ag 0.1 NA NA NA NA NA NA 80% <0.00 5 100% <0.001 NA NA SO 4 2 250 115 213 25.3 18.9 11.4 3.51 468.5 600.7 NA NA Zn 5 0.093 0.23 1.1 0.0111 0.0111 0.082 0.492 100% <0.005 0.3 0.0343 After Humphrey and Swett (2006). Units = mg/l. NA = not available. When possible, the calculated mean is reported; if the mean c ould not be calculated because of limited number of samples with concentrations above the dete ction limit, then the percent of the results below the detection limit is reported. *Results for unfiltered sample reported. **Results from a single sample reported. References: Wisconsin (Eldin and Senouci 1992; Bosscher et al. 1993); North Yarmouth (Humphrey and Katz 2000); Witter Farm Road (Humphrey 1999); Ohio Monofills (Chyi 2000); Binghamton (Brophy and Graney 2004); Secondary st andard (EPA 2006). TABLE 20 MEAN CONCENTRATIONS OF INORGANIC ANALyTES WITH SECONDARy DRINkING WATER STANDARDS FROM FIELD STUDIES WITH DIRECT

13 After Humphrey and Swett (2006). RAL = regulatory allowable limits; ND = not detectable; MRL = 0.0005. *MRL = 0.005. **MRL = 0.010. # = not included in analysis on that date. — = not available. 1 Cis-1,2-dichloroethene also known as cis-1,2-dichloroethylene. Compound RAL Sampling Date (mg/L) 12/28/1995 4/5/1996 6/22/1999 11/8/2000 1/1/2002 North Yarmouth Project 1,1-dichloroethane VOC 0.005 ND* ND* ND* ND# ND# cis-1,2-dichloroethen e 1 VOC 0.07 ND* ND* ND* ND# ND# Toluene VOC 1 ND* ND* 0.07 ND# ND# 4-methyl-2-pentanone VOC — ND* ND* ND* ND** ND** Acetone VOC — ND** ND** ND** ND** ND** Aniline SVOC — ND** ND** ND** ND* ND* bis(2-ethylhexyl)phthalate SVOC — ND** ND** ND** ND* 0.006 3&4-methylphenol SVOC — ND** ND** 0.1 ND* ND* Benzoic acid SVOC — ND** ND** 0.025 ND* ND* Phenol SVOC — ND** ND** 0.074 ND* ND* North Yarmouth—TDA Section C 1,1-dichloroethane VOC 0.005 ND* ND* ND* 0.0013 ND# cis-1,2-dichloroethen e 1 VOC 0.07 ND* ND* ND* 0.0015 ND# Toluene VOC 1 ND* ND* ND* ND# ND# 4-methyl-2-pentanone VOC — ND* ND* ND* ND** ND** Acetone VOC — ND** ND** ND** 0.014 0.024 Aniline SVOC — ND** ND** ND** 0.005 ND* bis(2-ethylhexyl)phthalate SVOC — ND** ND** ND** ND* ND* 3&4-methylphenol SVOC — ND** ND** ND** ND* ND* Benzoic acid SVOC — ND** ND** ND** ND* ND* Phenol SVOC — ND** ND** ND** ND* ND* North Yarmouth—TDA Section D 1,1-dichloroethane VOC 0.005 ND* ND* <0.005 On 11/8/2000 and 1/1/2002 the sample was a composite from Sections C and D—see above for results cis-1,2-dichloroethen e 1 VOC 0.07 ND* ND* ND* Toluene VOC 1 ND* ND* ND* 4-methyl-2-pentanone VOC — ND* ND* <0.005 Acetone VOC — ND** ND** ND** Aniline SVOC — ND** ND** ND** bis(2-ethylhexyl)phthalate SVOC — ND** ND** ND** 3&4-methylphenol SVOC — ND** ND** ND** Benzoic acid SVOC — ND** ND** ND** Phenol SVOC — ND** ND** ND** TABLE 21 CONCENTRATIONS ON ORGANIC ANALyTES FROM THREE PROJECTS

14 TDA Below the Ground-Water Table Humphrey and katz (2001) studied the use of TDA below the ground-water table in three types of soil studied (peat, marine clay, and glacial till). The TDA was placed in a trench 2 to 6 ft wide at a depth below the water table and oriented perpendicular to the ground-water flow. Monitoring wells were set up so that one well was placed upgrade for control mea- surement, one directly in the TDA, between one and three wells were placed 2 ft down grade of the TDA, and one 10 ft down grade. An analysis for the primary drinking water standards showed that the TDA had a limited potential for raising the barium concentration slightly, but not above the standard lim- its. The secondary drinking water standards analysis showed that water in direct contact with the TDA (trench) showed an increase in the levels of Fe, Mn, and zinc (Zn). The concentra- tions of Mn and Zn decreased with time and were seen in both the trenches and down grade. The vOC analysis showed cis-1,2-dichloroethene and benzene were found at most sampling dates, but at concentra- tions below standard limits. The TDA slowly released these compounds, but increases were only detectable close to the TDA location. Other compounds found in the water included 1,1-dichloroethane, 4-methyl-2-pentanone, and acetone that were also released at low levels in the trenches, but did not migrate down grade. SvOC measurements showed that the concentrations of aniline increased but remained at low levels. The m,p-cresol was above the detection limits about half of the time in the trenches, but was not found in the down-grade wells except in the clay soils. This compound may be released but tends not to migrate. Benzoic acid was found in about half of the trenches and N-nitrosodiphenyl-amine was found in about one-third of the trenches, but did not migrate to the down-grade wells. Aquatic toxicity showed only a limited effect on the sur- vival rate of Ceriodaphnia Dubai (species of water flea) in water in direct contact with the TDA. Concentration should not influence survival rate after some dilution. The summary for using TDA below the water table was: • The concentrations of iron, manganese, and zinc increased when TDA was in direct contact with water; however, the increase did not extend to more than 3 m down-gradient from the trench. • The concentrations decreased to background levels a short distance away from the submerged TDA. • Only low levels of vOCs and SvOCs were found in water in direct contact with the TDA and would be below the detectable limits a short distance away.