Barrier Technologies for Environmental Management Summary of a Workshop (1997) / Chapter Skim
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Comparison of Clay and Asphaltic Materials for Use as Low-Permeability Layers in Engineered Covers at the Rocky Flats Environmental Technology Site
Comparison of Clay and Asphaltic Materials for Use as Low-Permeability Layers in Engineered Covers at the Rocky Flats Environmental Technology Site
Pages 108-118
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From page 108... ...
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.
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From page 109... ...
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.
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From page 110... ...
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)
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From page 111... ...
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]
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From page 112... ...
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.
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From page 113... ...
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.
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From page 114... ...
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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From page 115... ...
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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From page 116... ...
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.
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From page 117... ...
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.
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From page 118... ...
1994. Hanford permanent isolation barrier program: Asphalt technology development.
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