PP Geogrid vs Steel Geogrid: Tensile Strength, Corrosion and Weight

Overview: Two Different Reinforcement Philosophies

Polypropylene (PP) geogrid and steel geogrid represent two fundamentally different approaches to soil reinforcement. PP geogrid is a polymer grid that mobilises tensile resistance through elongation — it stretches slightly under load, developing tension that confines the surrounding soil. Steel geogrid (steel strip or welded steel mesh) is a metallic reinforcement that mobilises tensile resistance at very low strain — it is much stiffer than PP geogrid and develops its full tensile strength with minimal deformation.

This difference in stiffness has important implications for design. Steel geogrid is preferred in applications where deformation must be minimised — tall reinforced soil retaining walls where even small movements are unacceptable, or bridge abutments where differential settlement between the reinforced soil mass and the bridge structure must be controlled. PP geogrid is preferred in applications where some deformation is acceptable and where the lower cost, lighter weight and corrosion resistance of polymer reinforcement are advantageous.

A third category — polyester (PET) geogrid — combines the high tensile strength of steel with the corrosion resistance of polymer. PET geogrid is the preferred choice for high-strength applications (tensile strength > 100 kN/m) where steel geogrid would be used but corrosion is a concern. This comparison focuses on PP versus steel, with PET noted where relevant.

Tensile Strength Comparison

Published biaxial polypropylene grades often sit in a band of about 15–40 kN/m. Elongation and secant modulus belong on the data sheet. This page does not state them, and it does not set a wall height the product can serve.

Steel strip is a stiffer, higher-strength class than biaxial polypropylene. Read the strip strength and the strain on the data sheet. This page does not state a modulus, and it does not set a maximum wall height.

Welded steel mesh geogrid: tensile strength 50–150 kN/m. Elongation at break 2–5%. Stiffness intermediate between PP geogrid and steel strip. Suitable for reinforced soil retaining walls and steep slopes.

The useful difference is the strain at which tension is mobilised. Polymer grid generally needs more strain than steel strip. Use the design tensile load at the strain the code or the data sheet names. This page does not state those strains, and it does not say polymer grid is the lower-cost option.

Corrosion Resistance

Corrosion is the fundamental limitation of steel geogrid. Steel strip is often hot-dip galvanised, and it may carry a further coating. Coating thickness is on the data sheet. This note does not state a micron. In mild, well-drained soil the designer may accept galvanised steel with a sacrificial thickness. The soil limits are in the design code and the soil report. This note does not state them, and it does not state a life in years.

In aggressive soils (low pH, high chloride, high sulphate, organic soils, marine environments), the corrosion rate of galvanised steel increases dramatically. In soils with pH < 5 or chloride > 500 mg/kg, the design life of galvanised steel strip may be shortened by the designer. Stainless reinforcement is one response in aggressive soil. This note does not state a year or a cost ranking or a change to polymer reinforcement.

PP geogrid has no steel-wire rust mechanism. It is not immune to every soil chemistry, and it is not maintenance-free. Name the pH, the salts and the exposure before treating it as the mesh for an aggressive site. This note does not state a cost fraction.

The corrosion immunity of PP geogrid is particularly valuable in coastal and marine environments, in acid sulphate soils (common in reclaimed land and tidal areas), in industrial sites with chemical contamination, and in tropical climates where high temperature and humidity accelerate corrosion.

Weight and Installation

PP biaxial geogrid: unit weight 200–500 g/m². A 100 m² roll weighs 20–50 kg — easily handled by one or two workers without mechanical assistance. Installation requires no specialised equipment: unroll, overlap, pin and cover with aggregate.

Steel strip geogrid: unit weight 3,000–8,000 g/m² (3–8 kg/m²). A 100 m² panel weighs 300–800 kg — requires mechanical handling (crane or forklift) for placement. Installation requires precise positioning and connection to the wall facing panels.

Welded steel mesh geogrid: unit weight 1,500–4,000 g/m². Intermediate handling requirements between PP geogrid and steel strip.

The weight difference has significant implications for installation cost and logistics. PP geogrid can be installed by unskilled labour with no mechanical equipment, making it suitable for remote sites, steep slopes and confined spaces where mechanical access is difficult. Steel geogrid installation requires mechanical handling and skilled labour, increasing installation cost and limiting application to sites with good mechanical access.

A light roll can be unrolled ahead of the aggregate. This page does not state an area per day or a daily cost. Ask the contractor to price the crew.

Cost Comparison

PP biaxial geogrid (15–30 kN/m): ask for the current quotation. Price depends on grade and order size. Do not treat it as the cheaper option by default.

Steel strip geogrid (50–100 kN/m): price it on strip spacing, coating and grade. This note has no yuan rate, and it does not say steel costs more.

Welded steel mesh geogrid (50–100 kN/m): compare quotations. This note has no yuan rate. Less expensive than steel strip but significantly more expensive than PP geogrid for the same tensile strength.

For applications where PP geogrid provides adequate tensile strength (road base reinforcement, slopes up to 6 m, embankments on moderate subgrade), do not state a percentage saving versus steel. For high-strength applications (walls > 6 m, bridge abutments) where steel or PET geogrid is required for stiffness, the cost premium of steel is justified by the performance requirement.

Application Selection Guide

Polypropylene biaxial geogrid is discussed for road base, unpaved tracks and slopes where its strain and strength fit the design. Aggressive ground is a reason to compare it with coated steel. This page does not set a height, a gradient or a CBR limit.

Use PP multidirectional geogrid for: heavy haul roads, port yards and aircraft pavements where omnidirectional loading requires uniform aggregate confinement.

Use steel strip geogrid for: reinforced soil retaining walls above 6 m height where low-strain stiffness is required, bridge abutments, and applications where the design code specifically requires metallic reinforcement.

Use PET geogrid as an alternative to steel strip for: high-strength applications (tensile strength > 100 kN/m) in aggressive soil environments where steel corrosion would require stainless steel or frequent replacement.

Do not use PP geogrid as a direct replacement for steel strip geogrid in tall reinforced soil walls without redesigning the wall for the higher strain and lower stiffness of PP reinforcement. The design methodology for polymer-reinforced walls differs from that for steel-reinforced walls.