A large amount of recycled asphalt pavement (RAP) material is created every year in the United States (approximately 100 million t each year in the 2000s) during the rehabilitation and reconstruction of existing flexible pavements. Several studies exist on blending RAP with virgin aggregates and stabilizing RAPs using chemical additives. However, limited research has been conducted to investigate the performance of RAP stabilized with geosynthetics, especially geocells. No study has been conducted to investigate the effect of subgrade strength on the performance of geocell-reinforced RAP bases under cyclic loading.


Validation – Comparative cyclic plate loading tests

Four cyclic plate loading tests were conducted on unreinforced and geocell-reinforced RAP bases over weak subgrade while five cyclic plate loading tests were conducted on unreinforced and geocell-reinforced RAP bases over moderate subgrade. The samples tested were of varying thickness.

The subgrade was comprised of 25 percent kaolin and 75 per cent Kansas River sand. In the reinforced samples, RAP cover was added on top of filled NPA Geocell in large test boxes. This was compared with the same tests on unreinforced samples. The main results are summarized below.

  • The NPA Geocell improved the resilient behaviour of the RAP bases
  • All NPA Geocell-reinforced sections displayed more resilient deformation in comparison to corresponding unreinforced sections.
  • The NPA Geocell-reinforced bases improved the permanent deformation performance of the test sections by a factor of 1.1 to 11.4, when compared to the unreinforced sections.
  • The NPA Geocell-reinforced sections constructed over the weak subgrade had more resilient deformation and a lower percentage of resilient deformation compared with those over the moderate subgrade.
  • An increase in NPA Geocell-reinforcement, the subgrade strength and the base course thickness reduced the amount of surface heave and compression. Increasing base thickness by 150 mm improved the RAP permanent deformation performance by a factor of 1.1–2.7.
  • The subgrade strength was a more sgnificant factor than NPA Geocell confinement in reducing permanent surface deformations. Increase of the subgrade CBR from 2 to 5% improved RAP base permanent deformation performance by a factor of 1.2–17.2.

Benefits – More resilient, longer lasting paving

The results demonstrate that NPA-Geocell reinforcement makes RAP pavement more resilient and less susceptible to deformation, especially when combined with strong subgrade and thick base course.

  • A longer lasting RAP paving solution
  • RAP pavement which requires less maintenance and reconstruction
  • A more cost-effective RAP paving solution

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