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E- 1 APPENDIX E GLOSSARY OF TERMS
E- 2 APPENDIX E GLOSSARY OF TERMS Block Molding is the second step in the two-step manufacturing process of EPS-block geofoam whereby the pre-puff is placed into a mold which is essentially a closed steel box that is rectangular in shape and steam is injected into the sealed mold to resoften the polystyrene and further expand the pre-puff causing the pre-puff to fuse thermally. Blowing Agent is the naturally occurring petroleum hydrocarbon, almost always pentane (Japan is the only known country where an alternative, butane, is used routinely) mixed in the raw material of expandable polystyrene. Compressive Strength is a traditional material parameter of EPS that is defined as the compressive stress at some arbitrary strain level. There is no universal agreement as to what this arbitrary strain level is. However, it is typically defined at 10 percent strain. Creep is the additional strain or deformation that occurs with time under an applied stress or load of constant magnitude. Density Gradients are variations in density within an EPS block caused by the inherent variability in the EPS manufacturing process. Differential icing is a condition that develops during cold temperatures whereby ice forms on the pavement surface overlying lightweight fills while the adjacent pavement underlain by natural soil is ice free. Elastic Limit Stress is the compressive stress at 1 percent strain as measured in a standard rapid- loading compression test. Expandable Polystyrene (EPS) is the raw material that is used to manufacture EPS-block geofoam. Expandable polystyrene consists of fine to medium sand-size spherical particles of solid polystyrene with a naturally occurring petroleum hydrocarbon, almost always
E- 3 pentane (Japan is the only known country where an alternative, butane, is used routinely), mixed in as a blowing agent. EPS is sometimes referred to as beads or resin. External (global) stability is one of the three primary design phases where consideration is given to how the overall embankment, which consists of the combined fill mass and overlying pavement system, interacts with the existing foundation soil. Failure is the loss of function of an embankment due to the embankment loads exceeding the resistance of the embankment and foundation and/or postconstruction settlement exceeding the maximum acceptable deformation. Fill mass is the portion of the embankment that primarily consists of EPS-block geofoam, although some amount of soil fill may also be used between the foundation soil and bottom of the EPS blocks, and the soil or structural cover placed on the sides of the EPS blocks. It is one of the three major components of an EPS-block geofoam embankment. Foundation soil is the existing natural soil that will support the embankment and is one of the three major components of an EPS-block geofoam embankment. Also referred to as soil subgrade. Fusion refers to the thermal fusion between pieces of prepuff (and regrind when used) that occurs during the second stage of manufacturing, which is known as final block molding. Initial Tangent Youngâs Modulus is the slope of the initial (approximately) linear portion of the stress-strain curve in a standard rapid-loading compression test. Mechanical inter-block connectors are typically prefabricated barbed metal plates placed along the horizontal interfaces between EPS blocks, when required, to supplement the inter- block friction and provide additional resistance against horizontal driving or imposed forces. Modified expandable polystyrene is a type of modified resin that contains an inorganic, bromine-based flame retardant that is sometimes used in the manufacture of flame- retardant EPS blocks.
E- 4 Molder is the manufacturer of expanded polystyrene blocks that buys the expandable polystyrene and, in a multi-stage process, transforms it into expanded polystyrene block. Oxygen Index (OI) is the minimum relative proportion (expressed as a percent) of oxygen in some mixture of gases that is required to support continuous combustion. Flammability of a polymeric material such as polystyrene is often measured or expressed by its OI. Pavement system includes all materials, bound and unbound, placed above the EPS blocks and is one of the three major components of an EPS-block geofoam embankment. Design of the pavement system is one of the three primary design phases. Pre-Expansion is the first step in the two-step manufacturing process of EPS-block geofoam whereby the expandable polystyrene raw material is placed into a large container called a pre-expander and then heated with steam. The expanded spheres of polystyrene are sometimes referred to as pre-puff. Pre-Puff is the expanded spheres of polystyrene that are formed by the pre-expansion manufacturing process of EPS-block geofoam. Regrind is recycled in-plant scrap or post-consumer recycled expanded polystyrene material that is reused by grinding it up into pieces that are generally sand-size. A small percentage of regrind is sometimes mixed in with virgin pre-puff during the final block molding process. Relaxation is the reduction in applied stress or load with time under a constant magnitude of strain or deformation. Seasoning is the process of allowing the EPS block to stabilize thermally (dimensional changes of the block occur during cooling) and chemically (residual blowing agent remaining in the cells of the EPS outgasses and is replaced by air) after the block is released from the mold. The block also dries during this seasoning period as a relatively significant amount of water vapor and liquid (which can artificially increase the apparent density of the EPS)
E- 5 that is condensed steam from molding remains in the block at the end of molding. Seasoning is also referred to as aging and conditioning in the EPS industry. Separation layer is a material placed between the EPS blocks and the overlying pavement system or between the embankment fill mass and the foundation soil. Serviceability limit state (SLS) is the state at which the deformation of the embankment exceeds the maximum acceptable deformation. Solar heating is a condition that develops during warm temperatures whereby the pavement surface overlying lightweight fills is warmer than the adjacent pavement underlain by natural soil. Ultimate limit state (ULS) is the state at which the resistance of the embankment to failure is less than or equal to the embankment loads producing failure. Ultra light cellular structures (ULCS) are a type of lightweight fill, sometimes called geocomb, because of their honeycomb appearance in cross section, that is similar to geofoam but with an open-cell structure that can flood and drain, and thus will not float. Yield Stress is the stress corresponding to the onset of yielding in a standard rapid-loading test. Sometimes referred to as "plastic stress" .
