[[wiki-architecture]] · [[Building Materials]] · [[ARCHITECTURE]] · [[000]] # Geomembrane A geomembrane is a very low permeability synthetic membrane liner or barrier used with any geotechnical engineering related material so as to control fluid (liquid or gas) migration in a human-made project, structure, or system. Geomembranes are made from relatively thin continuous polymeric sheets, but they can also be made from the impregnation of geotextiles with asphalt, elastomer or polymer sprays, or as multilayered bitumen geocomposites. Continuous polymer sheet geomembranes are, by far, the most common. == Manufacturing == The manufacturing of geomembranes begins with the production of raw materials, which include polymer resin and various additives such as antioxidants, plasticizers, fillers, carbon black, and lubricants (as a processing aid). These raw materials (i.e., the "formulation") are then processed into sheets of various widths and thickness by extrusion, calendering, and/or spread coating. A 2010 estimate cited geomembranes as the largest geosynthetic material in dollar terms at US$1.8 billion per year worldwide, which is 35% of the market. The US market is currently divided between HDPE, LLDPE, fPP, PVC, CSPE-R, EPDM-R and others (such as EIA-R and BGMs), and can be summarized as follows: (Note that Mm2 refers to millions of square meters.) High-density polyethylene (HDPE) ~ 35% or 105 Mm2 Linear low-density polyethylene (LLDPE) ~ 25% or 75 Mm2 Polyvinyl chloride (PVC) ~ 25% or 75 Mm2 Flexible polypropylene (fPP) ~ 10% or 30 Mm2 Chlorosulfonated polyethylene (CSPE) ~ 2% or 6 Mm2 Ethylene propylene diene terpolymer (EPDM) ~ 3% or 9 Mm2 The above represents approximately $1.8 billion in worldwide sales. Projections for future geomembrane usage are strongly dependent on the application and geographical location. Landfill liners and covers in North America and Europe will probably see modest growth (~ 5%), while in other parts of the world growth could be dramatic (10–15%). Perhaps the greatest increases will be seen in the containment of coal ash and heap leach mining for precious metal capture. == Properties == The majority of generic geomembrane test methods that are referenced worldwide are by ASTM International (ASTM) due to their long history of work in the field. More recently, the International Organization for Standardization (ISO) has also developed its own test methods. Lastly, the Geosynthetic Research Institute (GRI) has developed test methods to fill gaps not addressed by ASTM or ISO. Individual countries and manufacturers often have specific (and sometimes) proprietary test methods. === Physical properties === The main physical properties of geomembranes as-manufactured are: Thickness (smooth sheet, textured, asperity height) Density Melt flow index Mass per unit area (weight) Vapor transmission (water and solvent) === Mechanical properties === There are a number of mechanical tests that have been developed to determine the strength of polymeric sheet materials. Many have been adopted for use in evaluating geomembranes. They represent both quality control and design, i.e., index versus performance tests. Tensile strength and elongation (index, wide width, axisymmetric, and seams) Tear resistance Impact resistance Puncture resistance Interface shear strength Anchorage strength Stress cracking (constant load and single point) === Endurance === Any phenomenon that causes polymeric chain scission, bond breaking, additive depletion, or extraction within the geomembrane must be considered as compromising to its long-term performance. There are a number of potential concerns in this regard. While each is material-specific, the general behavior trend is to cause the geomembrane to become brittle in its stress-strain behavior over time. There are several mechanical properties to track in monitoring such long term degradation: the decrease in elongation at failure, the increase in modulus of elasticity, the increase (then decrease) in stress at failure (i.e., strength), and the general loss of ductility. Obviously, many of the physical and mechanical properties could be used to monitor the polymeric degradation process. Ultraviolet light exposure (laboratory or field) Radioactive degradation Biological degradation (animals, fungi or bacteria) Chemical degradation Thermal behavior (hot or cold) Oxidative degradation === Lifetime === Geomembranes degrade slowly enough that their lifetime behavior is as yet uncharted. Thus, accelerated testing, either by high stress, elevated temperatures and/or aggressive liquids, is the only way to determine how the material will behave long-term. Lifetime prediction methods use the following means of interpreting the data: Stress limit testing: A method used by the HDPE pipe industry in the United States for determining the value of hydrostatic design basis stress. Rate process method: Used in Europe for pipes and geomembranes. The method yields similar results to stress limit testing. Hoechst multiparameter approach: A method that utilizes biaxial stresses and stress relaxation for lifetime prediction and can include seams as well. Arrhenius modeling: A method for testing geomembranes (and other geosynthetics) described in Koerner for both buried and exposed conditions. == Seaming == The fundamental mechanism of seaming polymeric geomembrane sheets together is to temporarily reorganize the polymer structure (by melting or softening) of the two opposing surfaces to be joined in a controlled manner that, after the application of pressure, results in the two sheets being bonded together. This reorganization results from an input of energy that originates from either thermal or chemical processes. These processes may involve the addition of additional polymer in the area to be bonded. Ideally, seaming two geomembrane sheets should result in no net loss of tensile strength across the two sheets, and the joined sheets should perform as one single geomembrane sheet. However, due to stress concentrations resulting from the seam geometry, current seaming techniques may result in minor tensile strength and/or elongation loss relative to the parent sheet. The characteristics of the seamed area are a function of the type of geomembrane and the seaming technique used. == Applications == Geomembranes have been used in the following environmental, geotechnical, hydraulic, transportation, and private development applications: As liners for potable water As liners for reserve water (e.g., safe shutdown of nuclear facilities) As liners for waste liquids (e.g., sewage sludge) Liners for radioactive or hazardous waste liquid As liners for secondary containment of underground storage tanks As liners for solar ponds As liners for brine solutions As liners for the agriculture industry As liners for the aquiculture industry, such as ponds used to raise fish or shrimp As liners for golf course water holes and sand bunkers As liners for all types of decorative and architectural ponds As liners for water conveyance canals As liners for various waste conveyance canals As liners for primary, secondary, and/or tertiary solid-waste landfills and waste piles As liners for heap leach pads As covers (caps) for solid-waste landfills As covers for aerobic and anaerobic manure digesters in the agriculture industry As covers for power plant coal ash As liners for vertical walls: single or double with leak detection As cutoffs within zoned earth dams for seepage control As linings for emergency spillways As waterproofing liners within tunnels and pipelines As waterproof facing of earth and rockfill dams As waterproof facing for roller compacted concrete dams As waterproof facing for masonry and concrete dams Within cofferdams for seepage control As floating reservoirs for seepage control As floating reservoir covers for preventing pollution To contain and transport liquids in trucks To contain and transport potable water and other liquids in the ocean As a barrier to odors from landfills As a barrier to vapors (radon, hydrocarbons, etc.) beneath buildings To control expansive soils To control frost-susceptible soils To shield sinkhole-susceptible areas from flowing water To prevent infiltration of water in sensitive areas To form barrier tubes as dams To face structural supports as temporary cofferdams To conduct water flow into preferred paths Beneath highways to prevent pollution from deicing salts Beneath and adjacent to highways to capture hazardous liquid spills As containment structures for temporary surcharges To aid in establishing uniformity of subsurface compressibility and subsidence Beneath asphalt overlays as a waterproofing layer To contain seepage losses in existing above-ground tanks As flexible forms where loss of material cannot be allowed == See also == Electrical liner integrity survey == References == - [[Wiki-Architecture/Building Materials]] - [[Wiki-Architecture]] - [[Urban and Planning/Town & Country Planning]] - [[Professional Practice/Codes & Standards/National Building Code of India/Part 06 - Structural Design/Section 4 - Masonry]] - [[Building Construction/Structural Systems/Masonry Structures]] - [[Environmental Design/Thermal Comfort]] - [[Design/Building Typologies/Hospitality Architecture]] - [[Professional Practice/Codes & Standards/National Building Code of India/Part 06 - Structural Design/Section 2 - Soils and Foundations]] - [[Building Construction/Construction & Materials/Building Material]] - [[Digital Architecture/ePractice/BIM and Digital Modeling]] == Further reading ==