Geosynthetics/Geomembranes/Geotextiles
Polyethylene sheet products are regularly referred to using several different terms, but the specific definitions between manufacturers, distributors, and users can overlap or conflict, sometimes making it difficult to be sure you’re talking about the same thing. The broad term geosynthetics, however, can be used to refer to all types of this material.
Woven and Non-woven Geotextiles
Woven geotextiles are generally analogous to traditional woven fabrics like silk or cotton, but are made from extremely durable synthetic filaments, derived using very long polymer chains, which are spun into threads and finally woven to make geotextile fabric. The woven construction provides strength, durability, and a limited amount of permeability. Perhaps the most popular use for woven geotextiles is in construction, where they’re used to separate different layers of soil and other materials. For example, a woven geotextile may be placed between a layer of wet soil or mud and a bed of gravel above. Without separation, the layers would inevitably merge, but the addition of a textile layer permits extremely long-term functionality.
Nonwoven geotextiles are produced by extruding essentially solid sheets of ethylene polymers and bonding multiple layers together using thermal, chemical, or mechanical techniques. Post-processing is used to fine-tune desired properties like pore-size and mechanical durability. Nonwoven geotextiles are characterized by their strength, flexibility, low-cost, and permeability. Since the polymer chains making up the sheet material are inherently durable, non-woven geotextiles are ideal for erosion control and stabilizing soil and rocks along embankments, dams, and steep hills. Permeable products like this are best used where it’s important to allow water to flow while maintaining control over larger particles. Filtration parameters can be fine-tuned during manufacture by controlling final pore-sizes.
Geotextiles vs Geomembranes
The terms geotextile and geomembrane are some of the most interchanged because the actual defining line between the two is not an industry standard. In some cases, the term geotextile is used to refer to any type of permeable geosynthetic sheet material which allows liquid to pass through at different flow rates. In contrast, other industry members may instead distinguish between geomembranes and geotextiles based only on the thickness of the sheets. If the product is 30 mil or below, they sell it as a geotextile, while products above 30 mil are called geomembrane.
In other cases, geomembranes are defined as impermeable synthetic liners used to control or restrict the movement of fluid. When a distinction is made, these polymeric sheets are manufactured just like geotextiles, but they typically incorporate special additives like polymer sprays or other materials that enhance the properties of the geomembrane for a specific use. In these cases, geomembrane liners are commonly used as liners for potable water storage, fishponds, hazardous liquids, and other applications, where it’s imperative that no liquid escapes or seeps through the liner material. It can be confusing when you consider that, in some applications, non-woven geotextiles are considered more permeable than their woven counterparts, while in others, they’re considered impermeable.
Geosynthetics is another term that includes these products, but it also generally covers all types of polymeric sheet products, including geomembranes, geotextiles, as well as geogrids, geonets, geofoam, geocells and geocomposites.
The intermixing of these terms is not only confusing, but it can also spell big trouble for the materials manager who doesn’t thoroughly understand their supplier’s taxonomy. After all, nonwoven geotextiles, no matter how thick or thin, aren’t appropriate to use for containment jobs dealing with storing water, hazardous waste, or ponds. In this series of articles, we’ll refer to impermeable liner products as geomembranes, regardless of the material’s thickness.
Composite Geomembranes
A composite geomembrane is a combination product of two or more layers, usually a geotextile and a geomembrane (using impermeability as the defining characteristic). Composites are designed to reflect the various strengths of both individual materials, while canceling out each other’s weaknesses.
The leading geomembrane composite is known as reinforced polyethylene (RPE), an affordable material made by sandwiching a layer of reinforcing scrim between HDPE and LDPE layers.
The combined layers of composite geomembranes give RPE one of the best perfomance in the industry, including unmatched puncture and tear resistance, as well as robust chemical and UV resistance. The multilayer reinforced design provides strength, wrinkle resistance, adaptability to a wide range of temperatures, and the ability to conform to unusual curves all at once. These combine to give RPE one of the best physical profiles in the industry.
