The Growth of Bentofix and the Geosynthetics Industry
During the EuroGeo 4, the Fourth European Conference on Geosynthetics, in Edinburgh, Scotland, the International Geosynthetics Society (IGS) awarded NAUE GmbH & Co. KG an IGS Award in recognition of the company’s activities on development and research on needlepunched Geosynthetic Clay Liners.
This is the second award for NAUE this year from the IGS. In March, the company was recognized for its 20+ years of membership in the IGS, which itself is celebrating its 25th anniversary.
The needlepunched Geosynthetic Clay Liner Bentofix was developed in 1988, and since then a good number of refinements to the product’s construction and the manufacturing process have separated it from similar products in the field. Also, the field has benefited from these refinements in that these discoveries have improved product performance, spurred greater use of GCLs across numerous sectors, expanded design options for engineers and clients, and given standards committees, laboratories, universities and institutes more data with which to work and improve overall quality control.
In short, it has had a ripple effect.
The 1988 discovery of the needle-punch nonwoven geotextile method of manufacturing (Bentofix’s launching point) stands as a key example. The advance enabled not only the rapid, safe production of GCLs but the efficient shipping of GCLs in rolls. Also, the previously low friction coefficient of the sought-after clay used in GCLs—bentonite—ceased to be of concern because this new method of manufacturing transferred the shear stress from the clay to the highly engineered geotextile to which the bentonite had been bonded.
The speed of manufacturing, shear stress transfer, and ease of installation that needle-punching led to cannot be measured simply by square meters of materials produced; but the volume of production is worth noting and emblematic of the field’s growth.
It’s estimated that more than several 100 million square meters (includes licence manufacturing) of GCLs have been put into service and needlepunched GCL's have reached more than 90 % market share..
The Refinement Process
All manufactures find ways to improve their products at the point of production, and these stories are valuable. Some of the key refinements to Bentofix have been:
• A unique fibre-bonding process locks the needle-punched fibres into place. This creates a high internal shear-strength with unsurpassed creep resistance.
• The complete impregnation of the non-woven cover of the Bentofix with bentonite powder creates an ideal, intimate contact condition between the Bentofix and a geomembrane. This discovery came about during investigations into the flow rate between GCLs and geomembranes in composite systems (studies which were being conducted in 1992).
• Similarly, the 50-cm-width impregnation of GCL panel side overlaps with bentonite powder creates a self-sealing overlap and reduces additional on-site overlap treatment.
• Continuous development of the needling process has brought about a low (10%) moisture content in the Bentofix range of products.
• The addition of continuous needle detection and removal devices during manufacture has improved product quality.
Expanding Reach
Manufacture, of course, is not the only place in which companies expand expertise and realize product potentials. Expansion in application is key—again, not just for the manufacturer but for the entire profession—and NAUE has taken GCLs quite a ways.
For example: underwater installations, such as for canals.
NAUE has used a combined sandmat/GCL system for underwater installation, and it has opened the potential for GCLs to be used in waterway sealing without disrupting active traffic. The GCL provides excellent impermeability. The bentonite powder-impregnated 50-cm-edge (ie, sealed overlaps) assures long-term performance.
In this application, homogeneous swelling of the GCL below water and a long-term peel strength are created through the installation of a top layer made of an uniform thickness of quartz. The quartz also provides the weight responsible for the immediate sinking of the entire GCL composite. And the sandmat acts as a protection layer against the loading of a riprap layer.
Another example: the waste management industry’s use of GCLs.
GCLs provide economical and environmental advantages when used as the base layer in landfills instead of cells relying on multiple layers of hard-to-construct compacted clay. Also, GCLs can increase the potential containment volume and reduce the amount of necessary excavation. From a logistical view, the advantages are easy to see: one truckload of Bentofix, for example, covers 4000m² compared to only 40m² (50 cm thick) for a similar truckload of clay.
Similar logic applies to the use of GCLs in landfill capping systems. The necessary cover thickness will be less with a GCL; meaning: more containment reserved for waste burial. And the simplicity of installation—no need for generators or welding machines—also assists with safety requirements for such sites.
The sealing of dykes and dams is another interesting application to which GCLs are and have been applied to great economic success, especially where there is a local shortage of natural sealing material with a low hydraulic conductivity. The Sainte-Marguerite Dam in France is an exemplary case. The 42-year-old, 20m-high structure was lined with Bentofix GCL as the primary watertight barrier.
The dam’s cross section reveals some interesting aspects of the project’s scope and hints at the degree to which geosynthetics may aid this piece of the water management field:
• Foundation of 20m layer of compacted coarse sand
• Watertight trench with a maximum depth of 65m
• Sealing of the slope with Bentofix
• One metre of protection backfill in two layers of sand and gravel and stones
For other instructive water management applications, NAUE does not need to look outside of Germany, where the devastating flooding of 2002 has led to various dyke construction projects. A basic “three-zone dyke” principle is guiding the refurbishment: a barrier, dyke core and a down-stream load filter. Bentofix GCL has been the choice for several hundred thousand square metres of up-stream barriers: it is a very cost-effective alternative to a 60cm clay layer.
More Growth to Come
The advantages for GCLs are many. In addition to the aforementioned ease of installation and long-term performance, NAUE has found that truly outstanding sealing properties (k < 5 x 10E-11 m/s) can be engineered, and the ability to install these products in all weather conditions has only expanded the scope of what can be done.
As can be seen, Bentofix is an extremely versatile clay-based lining product. Once hydrated it is an effective barrier against liquids, vapours and gases.
With many years of successful installations, the range of Bentofix applications is virtually limitless; waste and contaminated soil caps; landfill base liners; gas and vapour seals; surface impoundment liners; secondary containment; dams, canals and water courses; tailings containment; groundwater protection; sorptive barriers; vertical barriers; waterproofing; and others.
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