Comparing Nonreinforced and Internally Reinforced GCL

Water is one of the most destructive forces on the planet, eroding everything from continents to human-made wonders. Water is also a vector by which contaminants spread from landfills and other waste reservoirs. Therefore, creating effective water seals has been a top concern in construction.

For many years, factory-fabricated clay products have been the barrier of choice against water and other migrating liquids. While the traditional tools have been useful, innovations with geosynthetic clay liners (GCL) have produced flexible solutions that are not only more efficient but also more quickly deployed.

GCL are helpful in a broad range of construction projects from pollution control applications such as landfills and containment tanks to geotechnical and transportation projects. Mostly a layer of bentonite sandwiched in between geotextiles or geomembranes, GCL are available reinforced or nonreinforced. Here, we examine the differences between the two categories, identify important properties of various GCL types, and discuss some test methods used to verify GCL quality.

What are the differences between reinforced and nonreinforced geosynthetic clay liners?

Nonreinforced GCLs are either geotextile-related, geotextile/polymer-related or geomembrane related. These liners have geotextiles and/or geomembranes on both surfaces. These GCLs are normally recommended only in applications that are relatively flat, i.e. <10:1 slopes as they have minimal needle punch reinforcement.
Reinforced GCLs, on the other hand, are more common than their nonreinforced counterparts. They are most commonly reinforced with needle-punched nonwoven geotextile through the bentonite and opposing geotextile.

What are important properties to consider in geosynthetic clay liners?

Choosing the right kind of GCL for a project can be daunting, due to the large number of physical, hydraulic, mechanical, and endurance properties to consider (see Tables 1, 2, 3, and 4).

Knowing the clay type, for instance, is important to understand the geosynthetic clay liner’s overall permeability. Using high-grade sodium bentonite carries the benefit of having the lowest permeability of any natural geologic material. For projects with less stringent permeability requirements, the more common calcium bentonite can be a cost effective alternative.

Table 1. Physical Properties

Property Test
Clay Type X-Ray Diffraction, methylene blue analysis
Mass Per Unit Area ASTM D5993 Standard
Coverings Measure the geomembrane/geotextile properties
Moisture Content ASTM D5993 Standard; moisture content divided by oven-dry weight.

Table 2. Hydraulic Properties

Property Test
Hydration Liquid Hydration response to various liquids
Swell Index Swell index, ASTM D5890 Standard
Moisture Absorption Plate water absorption, ASTM E946 Standard; Enslin-Neff test
Fluid Loss ASTM D5891 Standard, under pressure
Permeability and Flux ASTM D6766

Table 3. Mechanical Properties

Property Test
Tensile Strength ASTM D6768
Permeability of Overlap Seam Estornell and Daniel test
Permeability Under Deformation LaGatta test
Direct Shear Product-specific direct shear tests
Peel Strength ASTM D6496

Table 4. Endurance Properties

Property Test
Freeze-Thaw Daniel et at. Test; GCL-flow box assembly
Shrink-Swell Boardman and Daniel test
Adsorption Giroud et al. test
Water Breakout Time Permeability test
Solute Breakout Time Permeability test
Geotextile Durability ASTM D5819

How does Agru America test for manufacturing consistency?

ASTM International operates over 12,000 standards including some that help qualify different kinds of geosynthetic clay liners. Agru America applies these and other standards in conjunction to help inform their high-quality manufacturing process.

Looking to incorporate a geosynthetic clay liner in your next project? Reach out to an Agru America representative who can help walk you through the various GCLs available as well as their respective properties.


  1. Koerner, R. M., “Designing with Geosynthetics.” 5th Ed. Ch. 6. Prentice Hall. (2005). Link
  2. GRI-GCL3 Specification. Geosynthetic Institute. (2016). Link.