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Comparison of Clay and Asphaltic Materials for use as Low
Permeability Layers in Engineered Covers at the Rockv Flats
Environmental Technology Site
M.J. Glade arid P.A. Nixon' Parsons Engineering Science' Denver' Colorado
INTRODUCTION
The Rocky Flats Environmental Technology Site (RFETS) located northwest of Denver,
Colorado, operated five lined Solar Evaporation Ponds (SEPs) from 1953 until 1986 for the
disposal of liquid radioactive and hazardous waste. The U.S. Department of Energy (DOE) has
signed an Interagency Agreement (LAG) with the Colorado Department of Public Health and the
Environment (CDPHE), and the U.S. Environmental Protection Agency JOSEPH), and has agreed
to close the SEPs through an Interim Measures/Inter~m Remedial Action (INDIRA) accelerated
program. Through an alternatives analysis study, DOE selected an alternative to consolidate
contaminated pond liners, subsurface soils, stabilized sludge, and miscellaneous contaminated
debris from within the operable unit (OU) under an engineered cover.
Based on the Colorado hazardous waste landfill siting regulations (6 CCR 1007-2, part 2),
the DOE has designed an engineered cover closure system with an anticipated functional lifetime of
1,000 years. The engineered cover must also meet the Resource Conservation and Recovery Act
(RCRA) requirements for the closure of a surface impoundment (40 CFR 265.111 and 40 CFR
265.228~. Since regulatory guidance for long-term engineered barriers does not exist, the DOE,
CDPHE, and USEPA agreed that synthetic (human-made) materials that have limited long-term
performance testing results should not be included as fimctional components of the engineered
cover. Therefore, the engineered cover is designed with natural matenals that have expected long-
te~m durability. Figure 1 presents a cross section of the proposed engineered cover. The asphaltic
low-permeability layer consists of a composite of a fluid applied asphalt (FAA) over asphaltic
concrete.
GRAVEL MULCH
FINE-GRAINED SOILS -
SAND/GRAVEL
LARGE RIPRAP '
ASPHALT MEMBRANE -
GRAVEL BASE COURSE -
FTGURE ~Engineered Cover Cross Section.
f~
. ~ . . . , . , . ~ . .
f ' ~-~ , ~ ~%
VEGETATIVE SURFACE
TOPSOIL/ORAVEL ADMIX
-- SAND
~SMALL RIPRAP
- SAND
- ASPHALT CONCRETE
CONSOLIDATED CONTAMINATED MEDIA
~ SUBSURFACE BLANKET DRAIN
- EXISTING SOILS
D-9O
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APPENDIX DIAPERS PRESENTED
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Low-permeability clay and asphaltic materials (hot-mix asphalt concrete and fluid applied
asphalt) were compared for use in the engineered cover for the SEPs. Low-permeability clay layers
have been used in numerous engineered covers throughout the DOE complex as well as at many
other sites. Research has been conducted at the DOE Hanford Reservation, Washington, for 10
years with respect to engineered barriers in semi-arid environments. The Hanford researchers have
constructed an asphalt low-permeable layer in a prototype engineered cover with a 1,000-year
design life. DOE selected asphalt for the low-permeable layer In the engineered cover for the OU4
SEPs.
This paper presents a comparison of {ow-permeable clay and asphaltic materials with
respect to the specific environmental conditions In Colorado and the design criteria of the
engineered cover. The comparison factors include hydraulic conductivity, longevity, engineering
characteristics, constructability, and cost.
SELECTION CRITERIA
Selection criteria for the low-permeability layer were established based on the performance
requirements, engineering charactenstics, constructability, and cost. The following subsections
discusses each of the specific selection cntena.
Hydraulic Conductivity
Hydraulic conductivity (permeability) is a matenal property that is a measure of the ease
with which a liquid can be transmitted through a porous material. Clay soils have been used In
traditional compacted clay cover systems to meet RCRA requirements and have been shown to
have permeabilities below 1 x 10~7 cm/s (USEPA, 1988). However, Day and Daniel (1985)
indicated that field-measured permeability values could be 1000 times greater than laboratory-
measured permeability values possibly due to the numerous hydraulic defects found in field
compacted clay liners. Factors that can influence the inherent permeability of a clay material
include the void ratio, composition, fabnc, and degree of saturation for the material. Field
placement factors such as compacted water content, compactive energy, and desiccation can also
influence the permeability of a clay material (USEPA, 19911. Large variabilities in the permeability
of clays can exist due to all of these factors.
The permeability of asphalt concrete is primarily controlled by the asphalt content, mineral
filler content, and air void content, which are determined from the mix design. As a general rule,
asphalt type, aggregate type, and batch production variables have only a minor Influence on the
permeability of the asphalt concrete. However, a well-graded aggregate is preferred. A low air void
content will reduce the permeability of the mix. Air void contents are not only controlled by the
mix design but also by the energy of compaction. Standard roadway construction equipment may
be modified to produce the desired permeability. Asphalt linings 2 inches thick having 4 percent or
less air voids will generally have a permeability less than 1 x 10-7 cm/s (Asphalt Institute, 19891.
Freeman, Romine, and Zacher (1994) conducted detailed laboratory and field permeability
tests on asphalt concrete samples for the Hanford project. Laboratory tests indicated a permeability
range of 1.05 x 10~~i cm/s to 6.96 x 10~~i cm/s for an asphalt content of 6.5 percent, and 2.09 x 10-~2
cm/s to 8.25 x 10~~ cm/s for an asphalt content of 7.5-percent. The Hanford researchers also
perfonned field permeability tests on a prototype barrier constructed of two 7.5 cm layers of
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BARRIER TECHNOLOGIES FOR E~IRONMENTAL MANAGEMENT
compacted hot-applied asphalt concrete with an asphalt content of approximately 7.5 percent and
compacted it greater than 95 percent of theoretical maximum density (151 Ib/ft31. A modified
falling head permeability test was conducted at five locations of the prototype barner, and
permeability results ranged from 1.91 x 10-9 cm/s to 1.08 x 10-7 calls. The Hanford researchers
believe these numbers are conservative due to the fact that the samples were not confined and that
the bentonite used to seal the rings of the test was still hydrating and taking up water. Permeability
changes of an asphalt concrete after placement are due primarily to an increase in cracks within the
asphalt concrete cover. These cracks can be generated by an improper mix design flow asphalt
cement content), by freeze-thaw cycles, through the mechanism of asphalt cement stripping by
water, by age hardening and embrittlement, or by stress cracks that develop due to consolidation or
settlement of underlying materials.
Research was conducted under the OU4 MYRA accelerated program to ensure that the
proposed Deery Oil, ~c., fluid applied asphalt would perform adequately during actual field
loading conditions. Confined permeability tests In accordance with ASTM D-5084 were performed
with an applied normal load of 480 pounds per square foot (psf). The FAA was first applied to
concrete to the desired thickness and was then covered with a layer of 1/4-~nch gravel prior to the
application of the normal load. The laboratory permeability test results for both 160-mil- and 87-
mil-thick FAA membranes were below 1 x 10~~ cm/s (the limits of the test apparatus) and indicate
that gravel embe~nent in the FAA should not influence the results of permeability testing and field
performance dramatically. Freeman et al. (1994) also conducted permeability tests on Deery Oil,
Zinc., FAA that were removed from an actual placement over asphalt concrete. The results from four
samples ranged between 1.18 x 10- cm/s and 2.51 x 10-~ cm/s. They concluded that no direct
correlation between sample thickness and permeability was apparent.
The IM/IRA accelerated program determined, based on permeability, that the variability of
clay materials would make it difficult to predict the field behavior of a compacted clay cover over
the 1000-year design life of the system. The local arid climate and the difficulty in locating a
borrow source with the desired properties made clay an inappropriate choice based on permeability.
Asphalt concrete materials and equipment are available locally. Previous laboratory and field tests
confirm that asphalt concrete should meet RCRA requirements for permeability for the closure of a
surface impoundment when placed at a higher asphalt content and lower air void content than
typical road base designs. The asphalt concrete In combination with the FAA should provide a
redundant system with added protection against the development of cracks within the low-
permeability layer.
Longevity
The longevity of the clay and asphalt materials were compared with respect to the ability of
the materials to retain the desired properties over the 1000-year design life of the cover system. The
longevity of a clay soil at the RFETS is expected to be influenced primarily by the ability of the
clay cover to retain low permeability characteristics. No chemical interaction with the contaminated
media should be expected within the cover. The major concern with utilizing a clay soil is that
desiccation cracks may develop both during construction and after placement. Should excessive
differential settlement occur under the cover system, the tensile stains could farther lead to cracking
of the clay laver. Since the climate is arid, the clay layer could have a relatively low water content,
which could enhance the cracking of the cover. Traditional longevity arguments for the use of
asphalts have centered around archeological excavation data. However, more specific data on the
, ,
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APPENDIX~PAPERS PRESENTED
D-93
longevity of"refined" or "modified" asphalts is required. The IM/IRA accelerated program focused
on reviewing the research conducted by the Hanford researchers and by the Strategic Highway
Research Program(SHRP, 19941.
The SHRP provided important insight into the oxidative aging of asphalts. Excessive
oxidative aging can lead to asphalt hardening and embrittlement, which may ultimately contribute
to cracking. It was found that the aging of asphalts is a injunction of their physical state and is highly
temperature dependent. Temperature typically determines the rate of oxidation, the amount of
oxidation, and the ultimate age hardening of the asphalt. The SHRP aged asphalts under pressure
and at temperatures specific to, and higher than, application temperatures. This is an important
factor, since the asphalt materials under the cover will not be exposed to I]V light. However, tests
to determine the mechanism of age hardening were specific to pavement temperatures (140°F) and
higher temperatures (266°F). It was found that "asphalts with different component compatibilities
may exhibit similar age-hardening kinetics in the low end of the pavement temperature range but
quite different kinetics in the high end." The program also determined that lon~-term changes in the
_
r ~. r ~
~ 4=
physical properties of an asphalt are a function ot temperature and asphalt composition. Plots
(Figure 2) of the changes in viscosity with temperature for different asphalts were constructed from
samples using aging index data Tom 144 hour tests. These plots indicated that aging characteristics
cannot be interpolated between two different temperatures. Another important trend of this plot is
how the aging index converges between the asphalts at the lower test temperatures. It is important
to note that the test temperature ranges were 140°F (60°C) to 180°F (80°C). This plot indicates that
the lower the actual field temperatures are from the aging test temperatures, the less reliable the
aging data. The SHRP concluded that the higher-temperature tests produced more oxidation and
more stiffening of the asphalts than when the asphalts were tested at lower temperatures. The SHRP
also determined that asphalts that were coated onto aggregates did not demonstrate significantly
different aging characteristics from when the asphalts were aged without aggregate. The aggregate
type did not appear to alter the aging of the asphalts.
30
25
20
o
AS
4,, As
c
CR
10
5
O
//
-
-
-
///W
/ ///'
-
-
55 640 65 70 75 80 85
Aging Temperature °C
+MM-1
MD-1
_~MF-1
MM-1
+MK-1
-MB-1
+MC-1
~0 MG-1
FIGURE 2 Aging Indices After Thin Oven Testing of Core Asphalts Aged by the Pressure Air
Vessel Method a Different Temperatures.
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BARRIER TECHNOLOGIES FOR ENVIRONMENTAL MANAGEMENT
Concerns were raised during the IM/IRA accelerated program that "refined" asphalts may
age more quickly than "natural" asphalts. At this time, simple conclusions based on the refinement
of an asphalt cannot be made. The SHRP utilized a number of asphalts that demonstrated a wide
range of behavior patterns. The variability of the aging behavior of asphalts is more chemistry
related than process related. The SHRP stated that the physical properties of an asphalt are best
described by the effectiveness by which the polar associating materials are dispersed by a solvent
moiety consisting of relatively nonpolar aliphatic particles, rather than by strict parameters such as
elemental composition. The longevity of asphalt materials is specific to the type and properties of
each individual asphalt. Traditional aging indexes (aged viscosity divided by unaged viscosity) may
not be relevant for applications involving 1000-year criteria. The SHRP developed effective
accelerated aging procedures and used direct theological measurements (penetration, softening
point, viscosity, etc.) that have made aging indexes unnecessary. An accurate assessment of the
longevity of asphalt materials can not be made without the benefit of further testing. Furthermore,
aging mechanisms at lower temperatures (58°F for buried asphalts) have not been detailed In
previous investigations.
Total and differential settlement of the asphaltic concrete and the FAA should be limited
due to the degree of compaction of the underlying soils. The maximum estimated total settlement is
4 Inches, while the maximum estimated differential settlement is approximately 0.4 percent (about
1/2-inch for every 10 feet). The performance of the hydraulic grade asphalt concrete and FAA
should not be negatively impacted (by excessive cracks) due to the estimated settlements. The
selection and design of the materials was based on providing an asphalt concrete that would offer
some flexibility. In order to reduce the opportunity for cracking caused by settlement' the
underlying materials below the cover were specified to be compacted to 95 percent of modified
Proctor density.
Some other typical physical factors that may induce failures of normal asphalt concrete
applications include:
· freeze-thaw stress changes, which can cause cracking of the asphalt concrete;
· traffic dynamic loading, which can cause vertical and horizontal movements in the
asphalt concrete, which can lead to cracking; and
· shrinkage cracks, which cart occur in asphalt concrete mixes that have a high content of
low-penetration asphalt (Asphalt Institute, 19891.
lithe forces that produce these physical conditions on an asphalt concrete will not be present
after the cover has been constructed.
Engineering Characteristics
The controlling factor for the design of a clay cover at the RFETS includes the 20-percent
grade (11.3° slope) of the cover. Clay soils that will meet the permeability requirements may not
meet slope stability requirements. RFETS slope stability analysis must include adjustments for
seismic loading. The selection of a clay material must account for the large variabilities of Fiction
angels and cohesion found in clays. The changes in the strength parameters due to compactive
efforts should also be Investigated closely. Effective Fiction angle differences can be as great as 7
degrees, while the differences in effective cohesion can be as great as 400 psf for compactive
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APPENDIX~PAPERS PRESENTED
D-9S
efforts ranging between 85 and 100 percent maximum standard Proctor density (Moretto et al.
1963).
The important eng~neenng characteristics to be considered for the design of the asphalt
concrete cover include its stability, durability, flexibility, impermeability, and workability during
placement. The mixture design may require a trial and error laboratory testing program to
determine the optimal design for the RFETS site. Stability of an asphalt concrete is the ability of the
asphalt concrete to resist deformation from imposed loads (Asphalt Institute, 1989) and is
determined by the internal Fiction and cohesion of the mixture. internal *fiction of the mix is
dependent upon the surface texture, gradation of aggregate, particle shape, density of the mix, and
quantity and type of asphalt. In order to improve the stability of the mix, 70 percent of the
aggregate materials retained on the No. 4 sieve were specified to have a minimum of two
mechanically induced fractured faces. Stability is an important consideration, since 11 feet of cover
material, which includes large nprap, was designed to be placed above the asphalt composite.
Durability is a property of asphalt that is its ability to resist detrimental effects of air, water,
W exposure, temperature extremes and variations, and dynamic loading. The durability of an
asphalt concrete is generally improved by higher asphalt contents, well-graded aggregates and low
air void content. Increased asphalt contents result in thicker film coating of the mix aggregate.
Thicker fiIrns are more resistant to age hardening (Asphalt Institute, 1989~. Lower air void contents
seal the mix from exposure to air and water.
Mixtures involving high asphalt contents with low air void contents require care during
design. Asphalt contents that are too high produce a thick film thickness that may yield a mixture
that is more prone to rutting, shoving, or creep. Constructability of this mix may be difficult on a
sloped surface, and stability of the asphalt mix may be reduced due to the asphalt cement acting like
a lubricant rather than a binder. Flexibility of an asphalt is required to compensate for minor
differential or total settlements beneath the cover system. Higher asphalt contents with smaller size
aggregates will increase flexibility within the asphalt concrete.
The engineering and construction properties that are important in asphalts are consistency
and nur~tv. The consistency of an asphalt is described as the viscosity or degree of fluidity of the
~ ~ ~ ~1~ ~ A I ~ ~ l ~ r A An at l-=f-1 he T ~
asphalt at a given temperature. Consistency OI a paving a~r ~ any "~llU~" ~) ~
penetration or viscosity test. The asphalt cement selected for RFETS was graded by viscosity
methods at 140°F. The grade of the asphalt cement will effect the resistance of the asphalt cement
to weather and physical changes and the stability of the asphalt cement to remain stable on
significant side slopes. The purity of an asphalt can impact the longevity and performance of an
asphalt concrete. Refined asphalts are composed almost entirely of bitumen, with a bitumen content
of more than 99.5 percent. The impurities that may be present in the asphalt are usually inert and
should not impact the performance or the grading of the asphalt concrete. Hence, asphalts that are
graded the same may have dramatically different properties related to the longevity of the asphalt.
Natural asphalts, such as Gilsonite or Trinidad Lake asphalts, are not refined but possess
characteristics that make them difficult to use in high percentages in a asphalt concrete mix. These
materials generally require the addition of a flux of! to soften the mix to produce a usable asphalt
cement.
The potential for the FAA to creep was a primary concern with respect to the use of
asphaltic materials. Generalized creep testing of materials consists of the application of a constant
uniaxial tensile load at a constant temperature sufficiently elevated to cause creep. However, field
conditions at the RFETS will not be consistent with standard uniaxial tensile loading of an asphalt
membrane at elevated temperatures. Furthermore, the FAA has significant adhesive properties and
also will be under a significant normal load that will confine the FAA. Since asphalt materials
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BARRIER TECHNOLOGIES FOR ENVIRONMENTAL MANAGEMENT
generally demonstrate classic creep behavior, a creep-testing program was initiated during the
MYRA accelerated program to determine the influence of the f~eld-applied dead load on the creep
characteristics of the FAA. The asphalt concrete is not expected to creep significantly under the
11.3° slope and a constant temperature of approximately 58° F. Research conducted by Hills and
McAughtry (1986) indicate that creep deformation should be minimal for the RFETS conditions.
However, creep deformation may occur during construction operations during the hot application of
the asphalt concrete.
The testing program to study the creep behavior of the FAA over the asphalt concrete was
initiated to determine if it could affect the integrity of the overlying cover materials (biotic barrier
and topsoil). The testing program was developed to incorporate buttressing effects, cover specific
materials, and determine the maximum allowable slope of the cover. The test consisted of three
large-scale consolidation/creep test frames configured to evaluate downslope creep under an
applied dead load on an infinite slope. All tests were performed in an environmentally controlled
chamber that was held at a constant 58°F. Each test station incorporated devices to measure vertical
and horizontal deflections. The lower slope frame (sloped at 11.3°) was constructed of roughened
concrete with the designated thickness of FAA applied to the upper surface of the concrete. The
upper loading platen was a custom angled solid aluminum block with a test surface area
incorporating a 1/4-~nch sand representative of the site cushion sand firmly embedded into the
surface. The sustained applied dead load for each test was 480 psf, with a minimum testing duration
of 40 days. The FAA was placed over roughened concrete samples to simulate the asphalt concrete.
Due to the accelerated schedule of the MYRA program, not enough time was available to cure
asphalt concrete properly prior to the creep tests.
Three tests were initiated under the stated testing conditions. FAA nominal thicknesses of
87, 1 1 S. and 160 mil were tested. The 87-mil sample saw an initial embedment of the upper surface
platen into the membrane within a period of 16 hours after which a time the platen did not creep.
The sample did not demonstrate any creep characteristics over the 40-day test duration. The 1 18-
mi! sample appears to have taken longer to become embedded into the FAA. It took approximately
22 days for the sample to become embedded into the FAA prior to the cessation of creep behavior.
The 160-mi] sample continued to creep at an unacceptable rate for a duration of over 75 days of
testing. The rate of creep was estimated to be at 0.07 inches per year. It was determined that over
the 1,000-year design life of the cover, this rate would be excessive. The results of the creep testing
indicate that a relationship exists between the thickness of the FAA and possibly the angularity and
size of the surface aggregate. Surface roughness of the underlying material (roughened concrete)
likely influences the creep behavior of the system. Following the results of the creep tests, it was
determined that no creep behavior characteristics would be allowed for the FAA materials. Hence,
the maximum allowable thickness for the FAA was established at 1 18 milt
Constructability
Clay Soils
The difficulty in constructing a clay cover at the RFETS would not be in the construction
equipment's ability to perform, but rather in the contractor's ability to control the conditions to
which the clay soil is placed and compacted. As discussed in earlier sections, a clay soil requires the
application of significant quantities of water to ensure that permeability requirements are met and
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APPENDIX DIAPERS PRESENTED
D-97
that desiccation cracking be kept to a minimum. Furthermore, dust suppression is an important
issue at the RFETS. The application of water to clay layers during construction by water trucks is
generally a "less than scientific" operation. One of the important factors in modeling the leaching of
contaminants from under the cover at RFETS was the insurance that excessive water would not
exist in the contaminated zone. The introduction of free water that could infiltrate the waste zone is
against the design basis for the construction of the cover at the RFETS. Quality Assurance/Quality
Control (QA/QC) operations for the construction of a clay cover must be enforced strictly. Areas of
the cover that are out of compliance would require significant operations to recompact or replace
the clay materials. The use of large rototillers to blend the clay soil could disturb underlying layers
of the cover. Lifts of the clay soils that are not correctly bonded, through scarifying or other
methods, may provide channels for water migration.
Asphalt Concrete
The construction of the asphalt concrete cover would not require any construction methods
that would introduce excessive moisture into the waste zone. Dust suppression would not be an
issue during the placement of the asphalt concrete. The difficulty in constructing the asphalt cover
would be in the placement of the high asphalt content hot mixture on the sloping surface (11.3°
slope). Shoving and inadequate compaction could result if the operations are not performed
properly. Excess shoving could lead to the development of transverse hairline cracks. A test pad is
recommended for the asphalt concrete and FAA application to confirm the placement methods and
any unique behavior properties that may occur during placement.
Cost
The costs for the construction of a clay or asphalt cover will be dependent upon many
variables. The estimated in-place cost for the asphalt and base course materials for the currently
designed cover ot the ~1xA Is ~:z per square yard. The total cost of the asphalt for the 12-acre
engineered cover would be $1.8 million. Estimates for the in-place cost of a 2-foot-thick clay cover
(only the clay portion) are approximately $8 per square yard depending on the borrow location. The
total cost of the clay layer for the 12-acre engineered cover would be $465,000.
DESIGN OF SELECTED MATERIAL
The following section discusses the detailed design of the asphaltic low-permeability layer
in the engineered cover. The objectives of the total design for the asphalt concrete and FAA were to
design a cover that meets RCRA requirements for the closure of a surface impoundment, has the
longevity and durability to last the 1,000-year design life of the cover, and be constructable using
common construction equipment and techniques.
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BARRIER TECHNOLOGIES FOR ENVIRONMENTAL MANAGEMENT
Asphalt Composite Design
The composite design of the FAA installed above asphaltic concrete was selected as a fail-
safe measure. It is believed that the FAA will span the cracks in the asphalt concrete that may occur
due to settlement. The FAA also appears to have "self-healing" properties, as demonstrated during
the performance of the creep tests with sand embedment. The design specifications called for an
asphalt concrete that would meet the following requirements as determined by American Society
for Testing and Materials (ASTM) D 1559:
Air Voids: 4 percent maximum
Asphalt Content: 6-9 percent
Marshall Stability: 750 pound minimum
Design compaction by the Marshall Method is limited to 35 blows on each end of the
specimen
.
Voids in Mineral Aggregate: 15 percent minimum
The asphalt cement was specified as an AC-10 grade. The aggregate material was specified
with 100 percent passing the 5/8-inch sieve. These design specifications are subject to change
following the performance of more detailed laboratory tests.
The FAA was specified as Deery Oil Co. Membrane 6 or approved substitute. The tests for
the MYRA project were performed utilizing this matenal. Specific required tests for the FAA
;~1.~A^. mixer Saint {~Tl\/r n ~ ~ne~it1~ ~v1tV (AN l M ~ /~: penetration (ASTM 3407);
lll~lU~I~. vVlL~ll~l~ ~V~1~ ~ *~ ~ ~ ~^ ~ JO 7 vim ~ _
viscosity (ASTM D4402)7 and elongation (ASTIR D4885).
Long-Term Testing
Current tests that simulate the chemical and physical property changes in asphalts during
hot mix plant operations traditionally have been used as indicators for the longevity of an asphalt.
However, the SHRP determined that the extended fumes and high temperatures of traditional tests
cause excessive loss of volatiles and the tests are not a reliable source for predicting the behavior of
asphalt aging at lower temperatures.
The behavior of asphalt materials over the life of the cover is one of the few factors that is
not predictable. Available data on the performance of asphalts does not provide enough detail to
confirm that the properties will remain acceptable. It is suggested that accelerated age-testing
followed by physical performance tests be conducted on the asphalt samples under "aged"
conditions. Freeman and Romine (1994) provide details of a testing program to provide valuable
information on the performance of aged asphalts. The Hanford researchers recommended the
following activities be conducted to provide data to support the longevity of an asphalt cover
system for a 1,000-year design life cycle:
1. Develop a defensible, accelerated aging test procedure to allow for measurements of
asphalt baIlier properties as a fimction of age for a minimum of 1,000 years. Accelerated test
procedures would be based on the procedures developed by the SIP. The procedures would be
modified to account for the conditions expected in the subsurface conditions versus highway
exposures.
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APPENDIX~PAPERS PRESENTED
D-99
2. Age potential the asphalt materials over the conditions expected in the actual subsurface
environment.
3. Measure the changes of the asphalt chemical and physical properties using standard and
modified testing procedures.
4. Supplement and validate the laboratory aging data by comparing the chemical properties
with several-hundred- to several-thousand-year-old asphalt artifacts.
5. Estimate the response and performance of aged asphalt materials to a range of
performance tests including settlement and permeability tests.
CONCLUSIONS AND RECOMMENDATIONS
Asphalt matenals were chosen over clay soils for use as a Tow-permeability layer to meet
RCRA requirements for the closure of a surface impoundment that will have a 1,000-year design
life. It is believed that the asphalt materials will outperform clay soils based on permeability,
longevity, and constructability considerations. However, the asphalt materials could cost as much
as 3-4 times more than clay. Creep testing should be conducted for the design of an engineered
cover utilizing asphaltic materials. Creep testing should be performed on the selected asphalt
materials and should be a combination of the asphalt concrete and FAA. The FAA will have to be
applied at a range of 60-118 mil at the OU4 SEPs, based on the specific side slope and loading
conditions. The 60-mil lower-thickness limit was developed from the acceptable permeability test
(below ~ x 10- calls), while loaded at 480 psf. The upper-thickness limit of 118 mil was
developed Tom the performance of the creep tests.
Age testing is necessary in order for asphalt materials to become widely accepted
throughout the engineering industry for use as long-term low-permeability layers in engineered
covers. The SHRP found that aging kinetics are highly dependent on how temperature will effect
the molecular structure of an asphalt. Aging tests need to be specific to the materials and
environmental conditions expected within engineered covers. It is important to determine the
mechanisms for the aging of asphalts and the subsequent physical and chemical changes in the
materials. Realistic tests could determine if premature age hardening may lead to a breakdown in
the performance of asphaltic materials.
BIBLIOGRAPHY
American Society for Testing and Materials (ASTM). 1990. Annual Book of ASTM Standards,
Part 3 1.
Asphalt Institute. 1989. The Asphalt Handbook, Manual Series No. 4 (DISC. Lexington, Ky.
Beckwith, G. H., G. D. Allen, and A. C. Ruckrnan. 1988. Asphaltic Concrete Leach Pads. Second
International Conference on Gold Mining. Gold Mining 88. Society of Mining Engineers.
Boynton, S. S., and D. E. Daniel. l9SS. Hydraulic Conductivity Tests on Compacted Clay. Journal
of Geotechnical Engineenng. 111~41: 465-478.
Day, S. R., and D. E. Daniel. 1985. Hydraulic Conductivity of Two Prototype Clay Liners. Journal
of Geotechnical Engineering. 111~: 957-970.
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BARRIER TECHNOLOGIES FOR ENVIRONMENTAL MANAGEMENT
Freeman, H. D., and R. A. Romine. 1994. Hanford permanent isolation barrier program: Asphalt
technology development. Pp. 491 -505 In Proceedings of the Thirty-Third Hanford
Symposium on Health and The Environment. In-Situ Remediation: Scientific Basis for
Current and Future Technologies.
Freeman, H. D., R. A. Romine, and A. H. Zacher. 1994. Hanford Permanent Isolation Barrier
Program: Asphalt Technology Data and Status Report - FY 1994. PNL-10194, UC-702,
Pacific Northwest Laboratory, Richiand, Wash.
Hills, I. F., and D. McAughtry. 1986. Deformation of Asphalt Concrete Linings on Slopes. Journal
of Engineenng Mechanics. 112~10~: 1076-1089.
Lambe, T. W., and R. V. Whitman. 1969. Soil Mechanics. New York: John Wiley and Sons, Inc.
Moretto, O., A. I. L. Bolognesi, A. O. Lopez, and E. Nunez. 1963. Propiedades Y Comportamiento
De Un Suelo L~moso De Baja Plasticidad. Proceedings of the Second Panamerican
Conference on SM and FE. Vol. II, p. 131. Brazil.
Strategic Highway Research Program (SHRP). 1994. Binder Characterization and Evaluation, Vol.
1. (SHRP-A-367), Vol. 2. (SHRP-A-368), Vol. 3. (SHRP-A-3694. Washington, DC.:
National Research Council.
U.S. Environmental Protection Agency (USEPA). 1988. Design, Construction, and Evaluation of
Clay Liners for Waste Management Facilities. EPA/530/SW-86/007F.
U.S. Environmental Protection Agency (USEPA). 1991. Design and Construction of
RCRA/CERCLA Final Covers. EPA/625/4-91/025
Representative terms from entire chapter:
engineered cover
