Road Reinforcement Field Trial, KIWA Institute, NL, Van Gurp and Westera (2008)

NPA geocell pavement reduction factor exceeded the test values for geogrids by 30-40% in a controlled field trial of stiffness and deformation for road bases with 7 leading geogrids.

This controlled field trial, conducted by KIWA (formely KOAC-NPC), the leading road research and standards institute in Netherlands in 2008, compared the reinforcement factor of various geogrids in base courses of pavement structures and ballast beds. NPA Geocells were the only geocell among the tested geogrids from 7 leading geogrid manufacturers, and the only product tested that could accommodate inferior aggregate material as road base infill. The results showed that Neoloy Geocells had the highest Road Base Thickness Reduction Factor of any tested product (0.72), and substantially exceeded the values for geogrids.

Challenge – Comparing reinforcement products

CROW Publication 157 “Thin asphalt roads” highlights the importance of comparing results from matching projects, when measuring Life Extension Factor (LVF), Road base Thickness Reduction Factor (FRF) and similar variables. However, most studies did not have the requisite scope to compare the performance and response characteristics of multiple products.

Validation – Loading tests on multiple geosynthetics

Tests were conducted in the Netherlands on experimental pavement sections, constructed in large hangars (1,250 sq. m) with each geosynthetic installed on 55 cm clay subgrade (CBR=1.4%). The pavement was divided into 30 test sections (each 4×4 sq. m) of varying reinforcing geosynthetics, and including 7 unreinforced control sections. Each sample consisted of a road base, subbase and subgrade. It should be noted that the NPA Geocell sample was the only one tested using a recycled construction waste infill material.

Stiffness and deformation of the test sections were tested by FWD loading. Deformation was measured using 2 contact displacement transducers, while a penetrologger measured cone resistance of the clay subbase.

Results – Road base thickness reduction factors exceeds limits

Table 1. Results showing 0.73 Mean Reduction Factor (NO LIMITS) for NPA geocells exceeds test limits of 0.5 for geogrids

The comparative test results recorded a road base reduction factor (RF) for NPA Geocells of 0.73. This figure was off the charts, with the highest published RF for geogrids of 0.5 set as the maximum limit. NPA Geocells recorded a mean RF of 0.43, higher than all other products tested. In addition, the tests also demonstrated that Neoloy Geocells cause a significant reduction in deformation.

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This study validated that Neoloy Geocells are more effective than geogrids in reducing road thickness and deformation, resulting in the following benefits:

  • Highest Road Base Thickness Reduction Factor of any tested product –
    0.47 (limited), 0.73 (unlimited)
  • Base layer thickness reduction lowers construction costs
  • NPA Geocell performance was above and beyond geogrid capabilities
  • NPA was the only geosynthetic that could utilize inferior infill
  • Stronger, stiffer roads extend service life and reduce maintenance cycles