Lecture 22Geosynthetic clay liners and geomembranesGeosynthetic materialsTimeline for geosyntheticsGeosynthetics - 1967Historical growth in geosynthetic marketHistorical growth in geosynthetic marketEPA regulations for geosyntheticsComposition of geomembranesPlastics in geomembranesPlastics in geomembranesPlastics in geomembranesPlastics in geomembranesGeomembrane additivesGeomembrane additivesComposition of geomembranesComposition of geomembranesGeomembrane manufacturingHigh-density polyethylene (HDPE)Linear low-density polyethylene (LLDPE)Coextruded HDPE and LLDPECoextruded HDPE and LLDPEFlexible polypropylene (fPP)Polyvinyl chloride (PVC)Chlorosulphonated polyethylene (CSPE) (Hypalon)Chlorosulphonated polyethylene (CSPE) (Hypalon)Butyl rubber and ethylene-propylene rubber (EPDM)Geomembrane testing methodsGeomembrane stress-strainLiner leakageLiner leakageLiner leakageWater vapor permeationSolvent vapor permeation of 0.8 mm HDPESummary of most common geomembrane materialsGeomembrane and GeosynthenticSeaming of geomembranesThermal seamingHot wedge seam weldingThermal seamingExtrusion or fusion weldingExtrusion welderExtrusion welding gunOther seaming methodsSolvent seamingAdhesive seamingGeomembrane seam alternativesSpecial seaming considerationsSeam testingSeam strength testsSeam testsSeam testingVacuum testsVacuum boxDestructive testsGeosynthetic clay linersGCL installation in Bourne landfillForms of GCLsSeaming GCLsHydraulic conductivity of GCLsGCL – permeability vs. compressionGCL – permeability recoveryGCL – freeze-thaw resistanceAdvantages of GCLsDisadvantages of GCLsLecture 22Geosynthetic clay liners and geomembranesGeosynthetic materialsGeotextiles – filter fabricsGeogrids – reinforcement materialsGeonets – drainage Geomembranes – containment Geosynthetic clay liners – containment Geopipe – buried plastic pipeGeocomposites – combinations of aboveGeo-Others – specialty productsSource: Koerner, Robert M., 1998. Designing with Geosynthetics, Fourth Edition. Prentice Hall, Upper Saddle River, New Jersey.Timeline for geosyntheticsLate 1950s – First use of geotextiles for erosion control1960s – woven fabrics in use as geotextiles1968 – First commercial product: needle-punch fabric by Rhone-Poulec Textiles in FranceLate 1970s – First non-woven geotextiles used in US imported from NetherlandsSource: Koerner, Robert M., 1998. Designing with Geosynthetics, Fourth Edition. Prentice Hall, Upper Saddle River, New Jersey.Early historical information from: Hsu-Yeh Huang and Xiao Gao, 1999. Geotextiles. http://trcs.he.utk.edu/textile/nonwovens/Geotextile.htmlGeosynthetics - 1967MR. MCQUIRE Ben - I just want to say one word to you - just one word -BEN Yes, sir.MR. MCQUIRE Are you listening?BEN Yes I am.MR. MCQUIRE Plastics.BEN Exactly how do you mean?MR. MCQUIRE There is a great future in plastics.Think about it. Will you think about it?BEN Yes, I will.MR. MCQUIRE Okay. Enough said. That's a deal.“The Graduate” 1967Historical growth in geosynthetic market Geotextiles Geomembranes Geocomposites GeonetsGeogridsGeosynthetic clay liners5004504003503002502001501005001970 1972 1974 1976 1978 1980 1982 1984YearAdapted from: Koerner, Robert M. Designing with Geosynthetics. 4th ed. Upper Saddle River, New Jersey: Prentice Hall, 1998.QuantityMillions of Square Meters1986 1988 1990 1992 1994 1996Historical growth in geosynthetic market Geotextiles Geomembranes GeocompositesGeonetsGeogridsGeosynthetic clay liners70060050040030020010001970 1972 1974 1976 1978 1980 1982 1984YearAdapted from: Koerner, Robert M. Designing with Geosynthetics. 4th ed. Upper Saddle River, New Jersey: Prentice Hall, 1998.SalesMillions of Dollars1986 1988 1990 1992 1994 1996EPA regulations for geosynthetics1982 – RCRA regulations require FMLs1982 – single geomembrane1983 – double geomembrane1984 – primary geomembrane, secondary composite1985 – geonet for leachate collection1987 – primary composite, secondary compositeComposition of geomembranesGeomembranes consist of:Polymers (plastics)FillersPlasticizersCarbon blackAdditivesScrim reinforcementPlastics in geomembranesThermoplasticsExample: polyvinyl chloride (PVC)Thermoplastics soften upon heating and can be moldedThermoplastics can be heat welded at seams in the fieldPlastics in geomembranesCrystalline thermoplasticAlso called semicrystallineExamples: HDPE, LDPE, polypropylenePolymeric chains are folded in a crystal latticeFolded chains form lamellae (plate-like crystals)Plastics in geomembranesCrystalline thermoplasticNon-crystalline tie-molecules connect lamellae: more tie molecules create more flexibilityVariations in molecular content change stiffness/brittlenessPlastics in geomembranesThermoplastic elastomersExamples: chlorinated polyethylene (CPE), chlorosulfonated polyethylene (CSPE, Hypalon)ElastomersExample: butyl rubberThermoset plasticsRarely used due to lack of good seaming methodsGeomembrane additivesAdditives address these concerns:Ultraviolet degradation – UV radiation breaks polymer chains, make membrane brittleSwelling – exposure to liquids causes polymers to swellOxidative degradation (aging) – oxygen reacts with polymers, makes membrane brittle rather than flexibleNote: this takes 100’s of years, accelerated by heatGeomembrane additivesAdditives address these concerns:Delamination – Separation of polymer layersExtractive degradation – Extraction of particular component (such as plasticizer) from polymerChemical degradation – Reaction of leachate components or organic chemicals with linerComposition of geomembranesOther components:Fillers – small mineral particles to reduce cost and increase stiffnessCarbon black – increases stiffness and retards UV degradationPlasticizers – increases flexibilityScrim reinforcement – embedded nylon or polyester fiber to increase strength, reduce tears and puncturesComposition of geomembranesOther components:Fungicides and biocides – prevent fungal or bacterial attackAntioxidants – reduce oxidative degradationGeomembrane manufacturingExtrusion – molten polymer is extruded in a non-reinforced sheetSpreading – coating of fabric with polymerCalendering – heated polymer passed through series of rollersSometimes with two sheets or with scrimsHigh-density polyethylene (HDPE)Semicrystalline thermoplasticTypical content:97% polyethylene3% carbon black (for UV resistance)traces (up to 1%) of stabilizers and