Geofoam Applications in the Design and Construction of Highway Embankments (2004) / Chapter Skim
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Pages 522-543
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From page 522... ...
8-1 CHAPTER 8 GEOFOAM CONSTRUCTION PRACTICES Contents Introduction...................................................................................................................................8-2 Design ...........................................................................................................................................8-2 Block Layout .............................................................................................................................8-2 Longitudinal Geometry .............................................................................................................8-3 Block Layout Design.................................................................................................................8-4 Mechanical Connectors .............................................................................................................8-5 Manufacturing...............................................................................................................................8-5 Introduction ...............................................................................................................................8-5 Flammability .............................................................................................................................8-6 Dimensional Tolerances ............................................................................................................8-8 Manufacturing Quality ..............................................................................................................8-9 Pre-Construction Meeting .........................................................................................................8-9 Construction................................................................................................................................8-10 CQC/CQA ...............................................................................................................................8-10 Site Preparation .......................................................................................................................8-11 Block Shipment, Handling, and Storage .................................................................................8-13 Block Placement......................................................................................................................8-15 Accommodation of Utilities and Road Hardware ...................................................................8-16 Pavement Construction ...........................................................................................................8-16 Post Construction ........................................................................................................................8-18 Summary.....................................................................................................................................8-19 References...................................................................................................................................8-19
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From page 523... ...
8-2 Figures ........................................................................................................................................8-21 ______________________________________________________________________________ INTRODUCTION The focus of this chapter is construction related issues for EPS-block geofoam embankments. However, numerous aspects of both design and manufacturing of EPS-block geofoam for lightweight fill applications, including manufacturing quality control (MQC)
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8-3 • Blocks should be placed with their smallest (thickness) dimension oriented vertically.
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8-4 the first layer of EPS blocks. Additionally, the upper surface of the EPS blocks should be horizontal when viewed in cross-section so any crown desired in the cross-section of the final pavement surface should be achieved by varying the thickness of the pavement system (2)
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From page 526... ...
8-5 Mechanical Connectors If the calculated resistance forces along the nominally horizontal planes between EPS blocks are insufficient to resist the horizontal driving or imposed forces, additional resistance between EPS blocks is required to supplement the inherent inter-block friction. This is generally accomplished by adding mechanical inter-block connectors (typically prefabricated barbed metal plates)
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8-6 Flammability The primary manufacturing issue that impacts construction is flammability. Like most polymeric materials, polystyrene is inherently flammable as is the blowing agent, pentane (butane also has been used but not in the U.S.A.)
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8-7 expandable polystyrene raw material for cost reasons (it can be slightly cheaper) , the recommended practice incorporated in the provisional standard in Appendix C of this report is to require the use of flame retardant EPS.
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8-8 shipped in any type of enclosed vehicle as any accumulated outgassed blowing agent will pose a potential explosion hazard when the vehicle is opened. Dimensional Tolerances The dimensional tolerances of EPS blocks for geofoam applications affects construction through the ability of the blocks to fit together with minimal gaps and maintain a planar or horizontal surface as subsequent layers of blocks are placed.
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8-9 accept a greater, but incalculable, uncertainty with regard to overall final performance of the EPS embankment. Manufacturing Quality MQC/MQA is discussed fully in Chapter 9.
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8-10 geofoam. This is important as the use of EPS-block geofoam in road embankments is still a relatively new technology in many parts of the U.S.A.
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8-11 working with EPS-block geofoam. Therefore, both the designer as well as the CQA agent should also be present at the pre-construction conference to review necessary tasks.
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8-12 where the consequences of eventual ground thawing beneath the fill have been explicitly considered by the designer. • There should be no debris on or large pieces of vegetation protruding from the subgrade on which the EPS blocks are to be placed.
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8-13 assemblage of EPS blocks (and, therefore, the bottom as well) should always be parallel with the grade of the finished road surface in the longitudinal direction (as noted previously, any crown of the road in the transverse direction is, however, achieved by varying material thickness within the pavement system)
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8-14 blocks have gotten longer with newer molding equipment placed on line during the 1990s. Because the lightweight EPS blocks must be securely strapped to prevent their movement during shipment, it is not uncommon for EPS blocks to arrive at the job site with numerous indentations of the edges along the sides of the blocks from the strapping as well with breakage at the end corners of the blocks.
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8-15 temporarily with a dark-colored geomembrane built up sufficient heat to locally melt and distort some of the EPS. EPS is not an inherently dangerous or toxic material (other than the flammability issues discussed previously)
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8-16 review by the project designer because the mud slab will induce an additional permanent vertical stress on the foundation soil which needs to be evaluated. If necessary to field cut blocks, the most precise cutting can be done with a portable hotwire device that the EPS molder can provide or at least provide assistance with assembling.
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8-17 In addition, care must be exercised during placement of the separation material so that the EPS blocks are not damaged, unleveled, or moved so that gaps occur between the blocks. In general, the pavement system can be constructed in the normal manner with only a few cautions related to the presence of the EPS blocks.
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8-18 The most effective type of compaction equipment to utilize to meet the desired compaction requirements will depend on the characteristics of the material to be compacted. For example, in (11)
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8-19 SUMMARY Various aspects of both design and manufacturing of EPS-block geofoam for lightweight fill applications interact with and impact construction. Two construction issues that directly impact the design of an EPS-block geofoam embankment is placement of blocks and mechanical connectors.
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8-20 11. Duskov, M., "EPS as a Light-Weight Sub-Base Material in Pavement Structures," Doctor of Engineering thesis, Delft University of Technology, Delft, The Netherlands (1998)
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FIGURE 8.1 PROJ 24-11.doc 8-21
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FIGURE 8.2 PROJ 24-11.doc 8-22
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