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Q: Are geosynthetics allowed to be used in marine structures? I am concerned about plastics in the environment and emission of plastic additives and their degradation by-products.
A: Geosynthetics have provided a wide range of solutions for many types of marine structures including revetments, levees, jetties, breakwaters and offshore structures for the past 40 years. Geosynthetics are long-term, durable polymers that are made to withstand environmental conditions. They are not single-use plastics, which produce debris. However, geosynthetics don’t last forever. They will age and degrade over time. Hence, all marine structures built with geosynthetics should be monitored and maintained according to a plan. One needs to assign a half-life to all geosynthetics and define property thresholds that forecast an appropriate reconstruction schedule.
The degradation by-product strongly depends on the geosynthetic’s polymer formulation and fabrication. For example, a properly stabilized submerged polypropylene geotextile, where the supply of oxygen is limited and the temperature is low, can last 100-plus years. However, some products will fail within a few decades under these same conditions if they were poorly formulated or carelessly fabricated and installed. The same reasoning applies to the environmental impacts of the emission of additives. The loss of additives is directly related to the aging of the geosynthetic.