When using polyester (PET) geosynthetic materials (fibers, yarns, straps or bars) for reinforcement of retaining walls, the long-term durability depends on the in-situ alkalinity levels (as measured by pH-values) within the backfill soil and masonry block facing. This paper describes such monitoring behind 25 segmental retaining walls in widely separated geographic regions of the USA. The ages of the walls vary between 0.5 to 8.0 years. Within this range, the potential leaching of alkali from the facing block to the adjacent soil was assessed; if indeed, such leaching occurred. It was found that the majority of pH-values were in the range of 5.8 to 8.8. Such values are not generally considered to be in the critical range insofar as alkalinity degradation is concerned.
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