An approach to Longevity and Durability of Bituminous Geomembranes (BGM)

Bitumen is a natural product – like clay – and its use for waterproofing dates to ancient times. Bitumen was primarily used for waterproofing irrigation canals in Mesopotamia, 4,000 years BC. Sections of these waterproofed canals are still existing today. A bituminous geomembrane (BGM) is manufactured by impregnating a polyester geotextile with an elastomeric bitumen compound. The geotextile provides a high mechanical resistance and a high puncture resistance.  The bitumen provides the waterproofing properties and ensures longevity of the framework by protecting the geotextile. The durability of a BGM is measured in terms of how its key components, namely the polyester geotextile and the bitumen, maintain their mechanical and low permeable properties under different applications and whether the BGM is to remain exposed under UV radiation or if it will be covered, subject to biodegradation by bacteria.

The paper will present the following information regarding the durability of BGM and it addresses the specific characteristics that justify its longevity. Its low thermal expansion coefficient leads to zero stress-cracking and therefore has no phenomenon of fatigue, unlike polymeric geomembranes, and has quick demonstrated relaxation over time demonstrated by laboratory CEBTP of the French Ministry of Transport.

• Concerning Longevity, laboratory tests results on samples will be described: samples of a newly prefabricated geomembrane. Tests imposed by the European standardization (CEN Standardization) for assuming a longevity of 25 and 50 years buried and exposed,
• Samples taken in the field of a geomembrane in service under covered and exposed conditions after 15 and 35 years,

Laboratory studies done in France and in USA determinates the longevity of a BGM for capping radioactive wastes of low and medium activity:

• Studies of the life expectancy carried out over 7 years by the French company Andra for the use of BGM to contain low and medium nuclear wastes. These studies are based on a mathematical model, compared to and corrected by tests results of samples taken on site after 5, 10, 15 years, calculating the rate of biodegradation of BGM in confined conditions after 300 years.
• The results of testing done in North America by the Department of Nuclear Energy in the Brookhaven National Laboratory (Upton, NY) and the Batelle Pacific Northwest Laboratory (Richland, WA) measures the biodegradation of bitumen in a cell submitted to different bacteria included in different types of soil. The conclusion published validates a life expectancy of bitumen up to 1,000 years in confined conditions. 

Field testing demonstrates that naturally aged BGM under covered conditions maintain their key features after many years of service.