1.
Leachate
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A leachate is any liquid that, in the course of passing through matter, extracts soluble or suspended solids, or any other component of the material through which it has passed. It is most commonly used in the context of land-filling of putrescible or industrial waste, leachate from a landfill varies widely in composition depending on the age of the landfill and the type of waste that it contains. It usually contains both dissolved and suspended material, the generation of leachate is caused principally by precipitation percolating through waste deposited in a landfill. Once in contact with decomposing solid waste, the water becomes contaminated. The use of linings is now mandatory within the United States, Australia, in addition, most toxic and difficult materials are now specifically excluded from landfilling. When water percolates through waste, it promotes and assists the process of decomposition by bacteria and these processes in turn release by-products of decomposition and rapidly use up any available oxygen, creating an anoxic environment. The decomposition processes themselves release more water, which adds to the volume of leachate, leachate also reacts with materials that are not prone to decomposition themselves, such as fire ash, cement-based building materials and gypsum-based materials changing the chemical composition. The physical appearance of leachate when it emerges from a landfill site is a strongly odoured black-. The smell is acidic and offensive and may be very pervasive because of hydrogen-, nitrogen-, in older landfills and those with no membrane between the waste and the underlying geology, leachate is free to leave the waste and flow directly into the groundwater. In such cases, high concentrations of leachate are often found in nearby springs, as leachate first emerges it can be black in colour, anoxic, and possibly effervescent, with dissolved and entrained gases. As it becomes oxygenated it tends to brown or yellow because of the presence of iron salts in solution. It also quickly develops a bacterial flora often comprising substantial growths of Sphaerotilus natans, in the UK, in the late 1960s, central Government policy was to ensure new landfill sites were being chosen with permeable underlying geological strata to avoid the build-up of leachate. This policy was dubbed dilute and disperse, proposed landfill locations also had to be justified not only by geography but also scientifically. Many European countries decided to select sites in groundwater-free clay geological conditions or to require that the site have an engineered lining. In the wake of European advancements, the United States increased its development of leachate retaining and this quickly led from lining in principle to the use of multiple lining layers in all landfills. There are many components to a system including pumps, manholes, discharge lines. However, there are four main components which govern the overall efficiency of the system and these four elements are liners, filters, pumps and sumps. Natural and synthetic liners may be utilized as both a collection device and as a means for isolating leachate within the fill to protect the soil, the chief concern is the ability of a liner to maintain integrity and impermeability over the life of the landfill
2.
Geotextile
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Geotextiles are permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain. Typically made from polypropylene or polyester, geotextile fabrics come in three forms, woven, needle punched, or heat bonded. Geotextile composites have been introduced and products such as geogrids and meshes have been developed, Geotextiles were originally intended to be an alternative to granular soil filters. The original, and still used, term for geotextiles is filter fabrics. He used different styles of woven monofilament fabrics, all characterized by a high percentage open area. He discussed the need for both adequate permeability and soil retention, along with adequate strength and proper elongation and set the tone for geotextile use in filtration situations. Usually geotextiles are placed at the surface to strengthen the soil. Geotextiles are also used for sand dune armoring to protect upland coastal property from storm surge, wave action, a large sand-filled container within the dune system prevents storm erosion from proceeding beyond the SFC. Using a sloped unit rather than a single tube eliminates damaging scour, erosion control manuals comment on the effectiveness of sloped, stepped shapes in mitigating shoreline erosion damage from storms. Geotextile sand-filled units provide a soft armoring solution for upland property protection, Geotextiles are used as matting to stabilize flow in stream channels and swales. Geotextiles can improve soil strength at a lower cost than conventional soil nailing, in addition, geotextiles allow planting on steep slopes, further securing the slope. Geotextiles have been used to protect the fossil footprints of Laetoli in Tanzania from erosion, rain. In building demolition, geotextile fabrics in combination with wire fencing can contain explosive debris. Coir geotextiles are popular for erosion control, slope stabilization and bioengineering, coir geotextiles last approximately 3 to 5 years depending on the fabric weight. The product degrades into humus, enriching the soil, hard landscape materials Sediment control Koerner, R. M. Designing With Geosynthetics, 6th Edition, Xlibris Publishing Co.914 pgs. Geotextiles, From Design to Applications, Woodhead Publishing Co, john, N. W. M. Geotextiles, Blackie Publishing Ltd
3.
Geomembrane
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Continuous polymer sheet geomembranes are, by far, the most common. These raw materials are processed into sheets of various widths and thickness by extrusion, calendering. Geomembranes dominate the sales of products, at 1.8 billion USD per year worldwide. Projections for future geomembrane usage are strongly dependent on the application, landfill liners and covers in North America and Europe will probably see modest growth, while in other parts of the world growth could be dramatic. Perhaps the greatest increases will be seen in the containment of coal ash, the majority of generic geomembrane test methods that are referenced worldwide are by the ASTM International|American Society of Testing and Materials due to their long history in this activity. More recent are test method developed by the International Organization for Standardization, lastly, the Geosynthetic Research Institute has developed test methods that are only for test methods not addressed by ASTM or ISO. Of course, individual countries and manufacturers often have specific proprietary test methods, the main physical properties of geomembranes in the as-manufactured state are, Thickness Density Melt flow index Mass per unit area Vapor transmission. There are a number of tests that have been developed to determine the strength of polymeric sheet materials. Many have been adopted for use in evaluating geomembranes and they represent both quality control and design, i. e. index versus performance tests. Tensile strength and elongation tear resistance impact resistance puncture resistance interface shear strength anchorage strength stress cracking, 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 concerns in this regard. While each is material-specific, the general trend is to cause the geomembrane to become brittle in its stress-strain behavior over time. Obviously, many of the physical and mechanical properties could be used to monitor the degradation process. Ultraviolet light exposure radioactive degradation biological degradation chemical degradation thermal behavior oxidative degradation, geomembranes degrade slowly enough that their lifetime behavior is as yet uncharted. Thus, accelerated testing, either by stress, elevated temperatures and/or aggressive liquids, is the only way to determine how the material will behave long-term. Rate process method, Used in Europe for pipes and geomembranes, 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 described in Koerner for both buried and exposed conditions and this reorganization results from an input of energy that originates from either thermal or chemical processes. These processes may involve the addition of polymer in the area to be bonded
4.
Geocomposite
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Thus, the benefit/cost ratio is maximized. Such geocomposites will generally be geosynthetic materials, but not always, in some cases it may be more advantageous to use a nonsynthetic material with a geosynthetic one for optimum performance and/or least cost. As seen in the following, the number of possibilities is huge — the only limits being ones ingenuity, there are five basic functions that can be provided, separation, reinforcement, filtration, drainage, and containment. Such geocomposites are regularly used in intercepting and conveying leachate in landfill liner and cover systems and these drainage geocomposites also make excellent drains to intercept water in a capillary zone where frost heave or salt migration is a problem. In all cases, the liquid enters through the geotextile and then travels horizontally within the geonet to a suitable exit, geotextiles can be laminated on one or both sides of a geomembrane for a number of purposes. The geotextiles provide increased resistance to puncture, tear propagation, and friction related to sliding, as well as providing tensile strength in, quite often, however, the geotextiles are of the nonwoven, needle-punched variety and are of relatively heavy weight. In such cases the geotextile component acts as a media, since its in-plane transmissivity feature can conduct water. Since some types of geomembranes and geogrids can be made from the material, they can be bonded together to form an impervious membrane barrier with enhanced strength. A needle punched nonwoven geotextile bonded to a geogrid provides in-plane drainage while the geogrid provides tensile reinforcement, such geotextile-geogrid composites are used for internal drainage of low-permeability backfill soils for reinforced walls and slopes. The synergistic properties of each component enhances the behavior of the final product, the core must be protected by a geotextile, acting as a filter and separator, on one or both sides. Various systems are available, each focused on a particular application, the first is known as wick drains in the U. S. and prefabricated vertical drains, PVDs, in Europe. The 100 mm wide by 5 mm thick polymer cores are often fluted for ease of conducting water, a geotextile acting as a filter and separator is socked around the core. The emergence of such wick drains, or PVDs, has all, the second type is in the form of drainage panels, the rigid polymer core being nubbed, columned, dimpled or a three-dimensional net. With a geotextile on one side it makes an excellent drain on the side of retaining walls, basement walls. The cores are sometimes vacuum formed dimples or stiff 3-D meshes, as with wick drains, the geotextile is the filter/separator and the thick polymer core is the drain. Many systems of type are available, the latest addition having a thin pliable geomembrane on the side facing the wall. The third type within this area of drainage geocomposites is the category of prefabricated edge drains, the systems are very rapid in their installation and extremely cost effective
5.
Geogrid
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A geogrid is geosynthetic material used to reinforce soils and similar materials. Geogrids are commonly used to reinforce retaining walls, as well as subbases or subsoils below roads or structures, compared to soil, geogrids are strong in tension. This fact allows them to transfer forces to an area of soil than would otherwise be the case. Geogrids are commonly made of materials, such as polyester, polyvinyl alcohol. They may be woven or knitted from yarns, heat-welded from strips of material, or produced by punching a regular pattern of holes in sheets of material, used as such, the major function of the resulting geogrids is in the area of reinforcement. This area, as many other geosynthetics, is very active, with a number of different products, materials, configurations. The ribs of some geogrids are often quite stiff compared to the fibers of geotextiles, as discussed later, not only is rib strength important, but junction strength is also important. The junctions are, of course, where the longitudinal and transverse ribs meet and are connected, currently there are three categories of geogrids. The first, and original, geogrids were invented by Dr Frank Brian Mercer in the United Kingdom at Netlon, a conference in 1984 was helpful in bringing geogrids to the engineering design community. A similar type of drawn geogrid which originated in Italy by Tenax is also available, the second category of geogrids are more flexible, textile-like geogrids using bundles of polyethylene-coated polyester fibres as the reinforcing component. They were first developed by ICI Linear Composites LTD in the United Kingdom around 1980 and this led to the development of polyester yarn geogrids made on textile weaving machinery. In this process hundreds of continuous fibers are gathered together to form yarns which are woven into longitudinal, the cross-overs are joined by knitting or intertwining before the entire unit is protected by a subsequent coating. Bitumen, latex, or PVC are the usual coating materials, geosynthetics within this group are manufactured by many companies having various trademarked products. There are possibly as many as 25 companies manufacturing coated yarn-type polyester geogrids on a worldwide basis, the third category of geogrids are made by laser or ultrasonically bonding together polyester or polypropylene rods or straps in a gridlike pattern. Two manufacturers currently make such geogrids, the geogrid sector is extremely active not only in manufacturing new products, but also in providing significant technical information to aid the design engineer
6.
High-density polyethylene
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High-density polyethylene or polyethylene high-density is a polyethylene thermoplastic made from petroleum. It is sometimes called alkathene or polythene when used for pipes, with a high strength-to-density ratio, HDPE is used in the production of plastic bottles, corrosion-resistant piping, geomembranes, and plastic lumber. HDPE is commonly recycled, and has the number 2 as its identification code. In 2007, the global HDPE market reached a volume of more than 30 million tons, HDPE is known for its large strength-to-density ratio. The density of HDPE can range from 0.93 to 0.97 g/cm3 or 970 kg/m3, although the density of HDPE is only marginally higher than that of low-density polyethylene, HDPE has little branching, giving it stronger intermolecular forces and tensile strength than LDPE. The difference in strength exceeds the difference in density, giving HDPE a higher specific strength and it is also harder and more opaque and can withstand somewhat higher temperatures. High-density polyethylene, unlike polypropylene, cannot withstand normally required autoclaving conditions, the lack of branching is ensured by an appropriate choice of catalyst and reaction conditions. For example, in Rotational Molding, to identify the environmental stress crack resistance of a sample the Notched Constant Tensile Load Test is put to use, HDPE is preferred by the pyrotechnics trade for mortars over steel or PVC tubes, being more durable and safer. HDPE tends to rip or tear in a malfunction instead of shattering and becoming shrapnel like the other materials. Milk jugs and other goods manufactured through blow molding are the most important application area for HDPE, accounting for one-third of worldwide production. There is some evidence that this form of recycling is less intensive than conventional recycling. Above all, China, where beverage bottles made from HDPE were first imported in 2005, is a market for rigid HDPE packaging. In India and other highly populated, emerging nations, infrastructure expansion includes the deployment of pipes, HDPE for Robotics Advantages & Disadvantages How to Recycle Plastic
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