Degradation behavior of stressed polyester reinforcing products under alkaline conditions embedded in eluates and soils

The use of geosynthetic reinforcements in different applications has been proven over the last decades to be a very beneficial and valid technique. For a safe design of such structures the long-term behavior and especially the available resistant tensile force over the time under variable boundary conditions, such as temperature, chemical influences or loading conditions, must be well known and understood. The known effects, which lead to a reduction in tensile strength, are considered in the design by applying so called reduction factors. So far, those reduction factors are determined separately without considering a possible interdependency. Latest research results are indicating that this can lead to major misjudgements. The main mechanism of the chemical degradation of polyester in high alkaline environment is the so called alkaline or “external” hydrolyses. In contrast to the internal hydrolyses, which provokes an evenly distributed, very slow degradation of the whole cross-section of the synthetic material, the external degradation generates a much faster “surface corrosion” with creation of fissures or cracks. If this does occur while the material is loaded, the fissures are widened, and their propagation are dramatically accelerated. The understanding and consideration of chemical degradation under mechanical stress is from crucial importance. This research will present results for products made of PET with different production technologies, where above-described mechanism has been investigated in more detail and conclude with a recommendation, how to proceed based on those findings. Tests have been conducted with samples embedded in eluate as well as in partially and fully saturated soils under a constant load, which approximately equals the design strength.