Summary of Extensive Research Program on NPA Tough-Cells Conducted at University of Kansas

Neoloy (NPA) Tough-Cells demonstrated reduced vertical stresses, permanent deformations, and increased elastic modulus, stiffness, and bearing capacity of base courses.


This summary of various studies on Neoloy Tough-Cell reinforcement validates that NPA Tough-Cells increase bearing capacity and stiffness, while reducing permanent deformation and vertical stresses. A series of static and cyclic plate loading tests, full-scale moving wheel tests, and numerical modelling was conducted on a variety of infills by the research team at the University of Kansas. In particular, these tests found that Neoloy Tough-Cells can increase stiffness by a factor of up to 3.2x and can reduce vertical stress by approximately 50%. Consequently, Neoloy Tough-Cells can reduce the required base thickness, lowering construction costs.

Challenge – High-quality roads with optimal resources

There is a constant need to optimize natural and financial resources while constructing high-quality roads. Rajagopal, and Mandal & Gupta demonstrated that geocells increase strength and bearing capacity, although most research until then focused on planar geosynthetics such as geogrids and woven geotextiles.

Validation – Wide variety of field testing

Researchers at the University of Kansas conducted a series of tests in order to investigate the strengths and properties of NPA Tough-Cells. The results were further confirmed by a three-dimensional numerical model developed by Yang:

Static plate-loading tests

Vertical stress was compared in unreinforced, single NPA Tough-Cell reinforced and multi-layer NPA Tough-Cell reinforced samples. The deformation of the base course was recorded at 5-minute intervals with increments adjusted via air pressure. The following results were recorded:

  • Neoloy confinement significantly increased the bearing capacity of Kansas River sand
  • Stiffness of Kansas River sand and RAP bases was increased significantly by Neoloy
  • Neoloy confined bases recorded a stiffness improvement factor of between 1.2x and 3.2x
  • An increase in Neoloy confinement produced a decrease in creep deformation

Cyclic plate-loading tests

Earth pressure cells and strain gages were used to compare the performance of NPA Tough-Cell-reinforced and unreinforced bases over weak subgrade. The tests found that NPA Tough-Cell-reinforced bases performed like a slab and the following results were recorded:

  • Neoloy Tough-Cell reinforcement reduced permanent deformation and vertical stress
  • In RAP bases, Neoloy Tough-Cell increased elasticity
  • The ratio of the loading cycles for the Neoloy Tough-Cell reinforced section, to that for the unreinforced section was approximately 10x

Full-scale moving wheel tests

Strain gages were used to compare NPA Tough-Cell-reinforced and unreinforced samples over various bases. The following results were recorded:

  • By distributing loads over a wide area, Neoloy reduced the rut depth and vertical stresses transferred to the subgrade
  • The vertical stress recorded in the Neoloy-reinforced sample was approximately 50% of that in the unreinforced sample

Benefits – Stronger pavement base, lower cost

The tests summarized in this paper validate that Neoloy Tough-Cell is a cost-effective solution to strengthening pavements, bringing the following benefits:

  • Reduced required thickness of pavement, reducing construction costs
  • Stronger, stiffer pavement
  • Longer life-cycle, reducing maintenance costs

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