Sustainable Nonwovens: Please could you tell us a little about GEOfabrics and its activities?
Andrew Leech: GEOfabrics was formed in 1992 at the time when the landfill industry was making the transition from dilute and disperse to engineered containment. The use of geomembrane barriers to provide this containment meant that high-performance protection would be required to prevent their puncture, this was achieved through the development of thick needlepunched nonwoven geotextiles. Today, the company not only manufactures class-leading geotextiles, but also geocomposites.
SNW: What are the key sectors for the company?
AL: GEOfabrics operates in a number of key areas within the construction industry – landfill, rail, coastal defence, gas venting and green roofs.
SNW: What are the respective advantages and disadvantages of woven and nonwoven geotextiles?
AL: It’s about using the right materials for the right application. The use of woven textiles can be perfectly appropriate for soil reinforcement where high strength and modulus is required. It’s important that the right woven is selected in this type of application. The use of nonwovens is generally favoured in most applications, where their high elongation and isotropic tensile strength provides improved durability. The use of mechanically-bonded nonwovens provides an excellent filter for soils where the thickness of the fabric is at least 30 times thicker than the opening size. This thickness allows for depth filtration and prevents the development of a filter cake at the interface between the soil and the geotextile, which would reduce permeability.
SNW: What are the strengths of polypropylene as a fibre for needlepunched nonwovens?
AL: Polypropylene is an excellent fibre for geotextiles. The selection of the right polymer type for the manufacture of textiles for use in civil engineering applications is essential. Polypropylene fibres have a high resistance to acids, alkalis and most solvents. It is also inert to both acid and alkali attack and is suitable for most geotextile applications. It can, however, be susceptible to oxidation, but oxygen levels are normally well below soil level and GEOfabrics performs ongoing oxidation tests to ensure accurate assessment of oxidation rates in relation to long term durability Another polymer fibre that is used within geotextile manufacturing is polyester, of which the most common type is polyethylene terephthalate (PET) which is produced using condensation polymerisation. PET can offer good mechanical properties and is suitable for some applications, but the ester group can be hydrolysed in the presence of water, which is accelerated by alkaline conditions. Polyester can also be susceptible to heightened degradation where there is lime-treated soil, concrete or cement present.
SNW: The company also manufactures cuspates. What are they and what is their function?
AL: GEOfabrics cuspates are polymeric sheet materials that have been vacuum formed into either a stud or cup to provide a void space for the passage of either a liquid or a gas. They are available in a range of heights to suit design requirements. It is common for a cuspate to be used as a component in a geocomposite, in conjunction with a geotextile filter. They are commonly used in gas protection systems, cut off walls around contaminated land, at the rear of bridge abutments and retaining walls, and around buried structures.
SNW: You often use materials in composite combinations. Another example is your LFX range of products. What do they consist of and what are their key applications?
AL: LFX is a range of multilayer geocomposites designed specifically for use in landfill basal applications, providing both membrane protection and drainage. The use of LFX allows for the replacement of up to 250mm of the drainage aggregate used in the leachate drainage system at the base of the cell. The composite consists of a tri-planer geonet encapsulated between two specially-developed woven filters overlaying a lower interchangeable protection geotextile which can be engineered to suit specific site requirements.
SNW: Similarly, your Tracktex for railway track maintenance consists of a microporous filter media sandwiched by two spunbond layers with protective outer layers of needlepunched material. What benefits does this bring?
AL: The use of Tracktex is the most cost-effective way of preventing and correcting ‘mud pumping failure’ – a phenomenon whereby clay slurry is pumped up into the overlying rail ballast. Contamination of the clean ballast layer by the fine soil particles in the slurry very quickly reduces the load-bearing properties of the ballast and leads to loss of track alignment in the affected area.
Tracktex is a multilayer composite with a unique microporous filter media protected by specially-engineered protective nonwoven geotextiles. The filter is an orientated microporous polymeric film with a series of microcells and interconnecting pores, characterised by its relative strength and ability to transmit vapour. Tracktex is able to effectively facilitate the passage of liquid under pressure, but the pores are such that the passages of clay fines are prohibited. Without pressure, water cannot pass through the filter, therefore any underlying clay formation will, over time, dry out and have an improved modulus. The benefits to the operators are huge – Tracktex has been shown to increase track bed maintenance intervals due to pumping failure by more than 25 times, providing significant savings over any available alternative.
SNW: What other composites are common?
AL: The use of composes within our sector is growing year on year and when effectively selected can allow the user to benefit from multiple features in an optimal manner at minimal cost. The use of a composite materials allows for expanded functionality in a single material and can significantly increase construction speeds when compared with alternatives. Common combinations include geotextiles with nets, geotextiles with membranes and geotextiles with grids.
SNW: GEOFabrics also manufactures an orange geotextile. In what circumstances would this be required?
AL: With the ever-increasing demand to construct on brown field sites there is a need ensure that any contaminated soils are contained and that any future excavators are made aware of any potential hazards. HPS Orange is a high visibility geotextile that has all the benefits of the standard materials with the added advantage of being a vivid orange to act as a warning layer for future excavators and prevent disturbing contaminated soils.
SNW: How do you view the markets for geotextiles at present, both in the UK and regionally around the world?
AL: This is a complex question, since the market is very segmented. From the point of view of GEOfabrics our position remains strong, although I believe this is because the company has recognised the need to focus on niche markets where the end user needs a high level of support with products and applications. For basic geotextiles, what we would call commodities, the market remains very competitive, and it would be fair to say, over supplied.