Long-term performance of PET geogrids with LLDPE coating in alkaline conditions

The increasing demand for sustainable construction practices and cost minimization has driven interest in utilizing locally available soil for reinforced fill structures. However, cohesive soils often require chemical stabilization to meet engineering standards, creating highly alkaline conditions that can affect the durability of polymeric reinforcements. Conventional PET geogrids are generally considered unsuitable in environments where pH exceeds 9 due to their susceptibility to hydrolysis. While this concern is valid, it may not fully consider the various types of coatings and industrial production processes available, which can significantly impact reinforcement performance. This study investigates the long-term performance of high-strength PET geogrids with LLDPE coatings in highly alkaline environments through laboratory experiments and real-world exhumation campaigns. The research examines the role of PE sheathing in mitigating the penetration of alkaline solutions, preserving the mechanical properties of geosynthetic reinforcements. Findings from field tests at multiple sites in the UK and Italy, where geogrids were exposed for up to 20 years, confirm that the protective LLDPE coating effectively prevents degradation, with residual tensile strengths exceeding 96% of the characteristic values. The results highlight the need to reconsider existing durability standards, which primarily assess uncoated PET, to account for the protective role of advanced coatings.