What should I ask for in comparing geogrids used in pavement design?
Performance is not based on index properties of the geogrid, measured in a lab. It is determined empirically, using full-scale in-ground trafficking testing. Require a copy of the third-party testing on which the supplier is basing its claim of equivalency. This testing should include Accelerated Pavement Testing (APT), performed on paved sections, following the procedures defined by NCHRP report 512. There should be multiple sections tested over different subgrade conditions and different pavement section thicknesses. Require a third-party review, by pavement design experts, verifying that the design values and methodology used are supported by testing for that product, and follow the guidance of AASHTO in R50-09 (“Geosynthetic Reinforcement of the Aggregate Base Course of Flexible Pavement Structures”). Also require third-party field validation testing, following AASHTO T221-90 (2012), to demonstrate that the results obtained in the field support the assumptions used in the design methodology, and that deformations are in line with predictions.