Geogrid Carbon Savings Require a Redesigned Pavement

The grid does not save carbon by itself

A geogrid adds polymer and embodied carbon to a pavement. If it is simply inserted beneath an unchanged pavement section, the material saving is zero and the carbon balance may be worse. The benefit emerges only when a defensible structural contribution is converted into a thinner section, longer service life, lower maintenance demand or another measurable change.

A 2025 study by Polisetti and Baadiga illustrates that distinction. The authors combined three-dimensional numerical modelling with field static plate-load testing, then used the calculated reinforcement benefit to redesign flexible pavement sections. The resulting cases showed embodied-carbon reductions of approximately 6–24%.

The environmental claim came from the redesigned pavement—not from the presence of a geogrid alone.

What the study assessed

The researchers considered flexible pavements over subgrades with California Bearing Ratio values of 2%, 5% and 10%. The starting pavement sections were designed for 50 million standard axles using Indian Roads Congress procedures. Polypropylene biaxial geogrids were represented with axial stiffness values from 400 to 1,500 kN/m.

PLAXIS 3D models simulated static plate loading of reinforced and unreinforced sections. Base, subbase and subgrade materials were represented using the Mohr–Coulomb model. Field plate-load tests, carried out in accordance with ASTM D1196 on reinforced and unreinforced sections of India’s NH-53 Raipur bypass, were used to check the numerical response. The reported difference between modelled and field settlement was less than 10%.

That field comparison strengthens the load–settlement evidence, but it does not turn the whole study into a long-term trafficking trial. The design reductions and carbon results still depend on the adopted static-load model, material assumptions and pavement-design framework.

Placement depended on the pavement structure

The study did not identify one universal geogrid location. With H defined as the combined granular-layer thickness, the preferred modelled positions were:

• CBR 2%: approximately H/4 below the top of the granular pavement.
• CBR 5%: approximately H/3 below the top of the granular pavement.
• CBR 10%: the base–subbase interface was adopted; H/3 gave slightly lower settlement, but the interface was considered more practical and produced similar performance.

The result is a useful warning against specifying the grid location by habit. Aggregate confinement and interlock need to develop within the active deformation zone, with enough overburden and compatible aggregate to mobilise the reinforcement. Axial stiffness alone cannot describe that interaction.

The US Federal Highway Administration similarly describes tensile resistance to lateral aggregate movement as a key reinforcement response, while noting that a geogrid does not replace the filtration and separation functions that may be required at the subgrade interface.

Stronger was not proportionally better

Increasing the modelled axial stiffness reduced settlement across the three subgrade cases. At 1,500 kN/m, the reported settlement changed from 17 mm to 10 mm for the 2% CBR case, from 8.2 mm to 4.4 mm for the 5% CBR case, and from 5.5 mm to 3.2 mm for the 10% CBR case.

The improvement curve flattened beyond about 1,200 kN/m in the modelled cases. The weaker subgrade obtained the greatest benefit, while the incremental response reduced as the surrounding pavement became stiffer. This does not establish 1,200 kN/m as a general optimum; it shows that the value of additional grid stiffness depends on whether the pavement can mobilise it.

That qualification is supported by broader pavement research. A PennDOT-sponsored accelerated pavement study found that some reinforced test sections showed no statistical improvement where measured grid strains were very low. A high nominal capacity is not useful if the installed system never engages it.

How the reported carbon reductions were created

The study calculated a Modulus Improvement Factor from the initial load–settlement response and used it to develop reinforced pavement sections. Reported MIF values ranged from about 1.3 to 3.0. The redesigned cases reduced asphalt and granular-layer thicknesses by approximately 15–30%, producing calculated embodied carbon of about 24–47 kg CO₂e/m² across the cases.

Compared with the study’s conventional and optimised unreinforced baselines, calculated carbon reductions varied with subgrade and geogrid stiffness. For the 2% CBR cases they ranged from about 15% to 24%; for 10% CBR they ranged from about 5% to 20%. The paper summarised the overall reduction range as approximately 6–24%.

The baseline is critical. A reinforced option can appear to save more carbon when compared with a conservative catalogue pavement than when compared with an already-optimised unreinforced design. Emission factors, layer densities, quarry and haul distances, asphalt source and the geogrid’s own manufacturing impact also affect the result.

What should not be transferred directly to Australian projects

The reported percentages and Modulus Improvement Factors are study outcomes, not universal product or design factors. The work used Indian pavement procedures, a 50 MSA design case, local material assumptions, static plate loading and a relatively simple Mohr–Coulomb representation of pavement materials.

• Do not apply the 6–24% carbon range without recalculating the actual pavement sections and project emission factors.
• Do not select a grid from axial stiffness alone; aperture compatibility, junction response, interface shear, installation damage and construction quality also affect mobilisation.
• Do not treat a static plate-load validation as proof of long-term behaviour under repeated moving wheel loads, wet-season weakening, rutting and maintenance cycles.
• Do not copy the reported grid positions without checking the Australian pavement structure, aggregate, subgrade condition, drainage and construction sequence.
• Do not omit separation or filtration where the subgrade and aggregate combination requires those functions.

For Australian work, the defensible path is to apply the relevant project and road-authority requirements, use evidence suited to the nominated geogrid and materials, and document how the reinforced design changes the quantities and expected performance.

A credible comparison starts with two designs

The sustainability case should compare a properly designed unreinforced section with a reinforced section developed using project-specific ground, traffic, material and construction inputs. The comparison can then quantify aggregate and asphalt volume, excavation, haulage, geosynthetic contribution, construction effort, expected maintenance and design life.

If the grid does not materially change one of those outcomes, the carbon claim is weak. If it produces a verified section reduction or service-life benefit, the saving becomes an engineering result that can be audited.

For unsealed roads, temporary access and working platforms, Kontain’s free pavement screening tool provides an early comparison between unreinforced and geogrid-stabilised concepts. It is a feasibility tool, not a sealed-pavement design or substitute for project-specific engineering.

Source study: Sai Meghana Polisetti and Ramu Baadiga, Engineering geogrid enabled low carbon and aggregate efficient flexible pavements, Scientific Reports 15, 33944 (2025). Mechanism guidance: US Federal Highway Administration, NHI-05-037, Chapter 7. Accelerated pavement evidence: Palomino, Tang and Stoffels, Determination of Structural Benefits of PennDOT-Approved Geogrids in Pavement Design, FHWA-PA-2010-012-PSU 018 (2010).