Discussion Of

Environmentally processed asphalt can at best be described as user-friendly. There currently exist a multitude of uses for cold-mix EPA incorporating affected soil. One of the more viable and creative is keeping contaminated soils out of landfills as a waste and placing it in landfills as an end product [7]. The imminent closure of many of the nation's Class III and municipal landfills creates the potential use for hundreds of thousands of tons of contaminated soils incorporated into asphalt for use as a landfill liner or cap. The cost effectiveness of this method of capping landfills is very attractive to financially strained municipalities. Prior to the advent of EPA for use as a liner or a cap, clay was the specified material. In addition to environmental concerns associated with mining vast quantities of clay for these uses, the cost of landfill closure had no cost recovery options. By using EPA, the municipalities and landfill owners can charge attractive fees for the acceptance of affected soil. In most cases, this acceptance fee pays for the cost of on-site processing of the affected soil into the asphalt end product. The effectiveness of the cost recovery is obvious as the capping materials production process becomes a profit center. By the use of on-site material, not only is the cost of obtaining the clay canceled, but transportation costs also are eliminated. In essence, the capping process of landfill closure is more affordable, makes use of a product far superior to the traditional clay method, and reduces a broad spectrum of environmental concerns by keeping affected soil out of landfills as a waste. Instead it places affected soil as environmentally sound end products such as caps or liners.

Studies of asphalt, clay, and other membrane liners subjected to a variety of aging tests in exposure columns at various temperatures, pH conditions, oxygen concentrations, and hydrostatic pressures have been discussed [8]. The conclusions were that the asphalt liners and membranes were extremely stable chemically and physically. An aging period equivalent to 7 years produced penetration of reaction products to only 0.5 mm (0.5% of the 10-cm liner thickness). The results showed that if the asphalt content of the liner exceeded about 6%, these liners would perform adequately under impoundment conditions for over 1000 years, conditions that are similar to those expected for cold-mix EPA [17]. Catalytically blown asphalt was considered the best liner material and was selected for long-term field testing. Field tests of catalytically blown asphalt over a 2-year period showed superior performance of the asphalt liners compared to that of the clay liners. This will be especially true for the petroleum constituents in cold-mix EPA's liner; overall, asphalt is a much better liner material for this application than clay.

Its use as a cap or liner is only one example of this product's cost effectiveness and versatility, but what of its more traditional use as a pavement? To best describe "user-friendly," one should visualize a typical multilane high-traffic-volume freeway and the load-bearing capability and durability that must be designed into the asphalt product used in its construction. Now visualize the typical bicycle path winding its way through our urban areas. The point being that both the freeway and the bicycle path are asphalt pavements, but their end uses are drastically different. Cold-mix EPA pavement is certainly nothing new. There are very few, if any, state and county road departments that do not use variations of cold-mix EPA. The end use of asphalt dictates its specifications, or better said, if the asphalt mix will perform its required function, from freeway to bicycle path, it is within specifications. In fact, the ASTM procedure for cold-mix asphalt design includes a section that states that the mix must fulfill the requirements of its intended application. Recalling the term "user-friendly" it becomes apparent that the function of the end product will determine the asphalt mix design.

Pavement for a heavy equipment yard has been constructed from EPA made with affected soil recovered from leaking underground tanks. By producing parking lot pavement for on-site use, the generator eliminated the inherent liability of disposing of their contaminated soil in a dump site. Approximately $80.00/ton of disposal taxes were saved as the materials were recycled and not disposed of. The pavement produced not only kept the project's pricing below any other option but created a paved parking lot of extremely low permeability to prevent further adverse subsurface impact. The mix design was not the same as that required to construct a freeway, but then a freeway was not the intended use. The intended use was for low traffic volume but required extremely high load-bearing strength. Another project used affected soil from an oil tank spill for paving loading and unloading facilities at an oil refinery. Again, the affected soil was not disposed of as hazardous waste but was recovered and used in a cold-mix asphalt pavement to remediate the affected soil and prevent further contamination, and the mix design was consistent with the end use.

Stability or strength (as measured by the Marshall test) achieved by various mix designs of cold-mix EPA is presented in Table 4. The minimum Marshall stability required for paving mixtures, for example, is 2224 [18]. Mix designs used for actual applications range from a 95% contaminated soil (native silt, sand, and gravel contaminated with diesel fuel to 32,000 ppm total petroleum hydrocarbons) with a 5% emulsion, to a 5% contaminated soil (heavy black clay contaminated with machine cutting oils to 55,000 ppm total petroleum hydrocarbons) plus 90% Class II 3/4-in. or less base rock and 5% emulsion. To date, EPA has been successfully used on projects ranging from road base and road pavement to containment dikes and drain channels. The procedure was to determine the requirements, then design the EPA mix to fit the use. As the equipment used to produce EPA is portable and certainly not complex, field test batches of 20 tons or more are used rather than bench-scale tests. In this manner the actual field

Table 4 Summary of Marshall Test Results for EPA Stability

75/25 Blend; 3/4-in. Class II base and contaminated soil

Asphalt in emulsion"

62-64

62-64

62-64

62-64

62-64

62-64

Residual asphalt in mixture" 6

5

5

5

6

6

6

Total mix water"

5.2

5.2

5.2

5.2

5.2

5.2

Compacted specimen data

(emulsion in percent)

Bulk density

2.08

2.07

2.11

2.05

2.07

2.05

Weight in air

1116.1

1125.1

1130.0

1120.1

1122.6

1120.7

Weight in water

584.4

586.5

599.0

577.2

584.4

577.5

Weight SSD

1120.1

1129.0

1134.1

1124.0

1126.5

1124.9

Thickness

2 5/8"

2 11/16"

2 5/8"

2 11/16"

2 11/16"

2 11/16'

Stability

3100

2350

2800

2450

2250

2200

Adjusted stability

2880

2090

2600

2180

2000

1960

Flow

30

27.5

31

31

30

24

Average stability

NT(c)

2520

NT

NT

2050

NT

Sample number:

7

8

9

10

85/15 Blend; 3/4-in. Class II

base and contaminated soil

Residual asphalt in mixture"'6

6.5

6.5

6.5

6.5

Bulk density

2.02

2.02

2.00

2.00

Stability

3548

NT

3260

NT

24-Hour soak

NT

1410

NT

1056

Sample number:

11

12

13

14

85/15 Blend; 3/4-in. Class II

base and contaminated soil

Residual asphalt in mixture",b

6

6

6

6

Bulk density

2.01

2.03

2.01

2.03

Stability

3158

NT

2640

NT

24-Hour soak

NT

1577

NT

1201

Moisture absorbed

X

X

X

Maximum total voids"

X

X

X

0 In percent b Emulsion c Not tested

0 In percent b Emulsion c Not tested

Figure 4 California bearing ratio for Class II base using cold-mix EPA.

PENETRATION INCHES

Figure 4 California bearing ratio for Class II base using cold-mix EPA.

mix is tested rather than a small hand-mixed batch. The bearing ratio for processed EPA for Class II base is presented in Figure 4.

0 0

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