Z275 C4-Grade Corrosion-Resistant Ground Screw System

Product Overview

Soil is often more corrosive than air. A ground screw buried in acidic clay (pH 4.5–5.5), saline coastal sand, or waterlogged tropical laterite can lose zinc coating at 3–5× the rate of an above-ground HDG structure. A standard C3 ground screw in these conditions may reach critical coating loss within 12–15 years — far short of the 25-year project life.

The Z275 C4-Grade Corrosion-Resistant Ground Screw System is engineered for aggressive soil environments where standard galvanizing is insufficient. The Z275 coating specification provides 275 g/m² of zinc — approximately 35% more zinc mass than standard C3 ground screws (typically 200–220 g/m²) — translating directly to proportionally longer service life in corrosive conditions.

Beyond coating weight, this system incorporates three additional corrosion-defense measures:

Zinc-aluminum alloy chemistry: The Z275 coating includes 5% aluminum in the zinc bath, forming a denser, more adherent intermetallic layer at the steel-coating interface that resists under-film corrosion propagation

Optional epoxy base coating: For C4+ and C5 soil conditions, an epoxy-based primer is applied over the Z275 galvanizing on the below-grade portion of the pile, providing a dual-barrier system

Sacrificial anode option: For extreme conditions (saline groundwater, acidic peat, industrial contaminated soil), a bolt-on magnesium sacrificial anode provides cathodic protection that extends service life beyond the coating alone

Technical Specifications

Soil Corrosivity Assessment

If any two parameters fall in the High Risk column, specify Z275 C4 grade.

Applications

Coastal solar projects (within 5km of shoreline with saline groundwater)

Tropical laterite soil regions (West Africa, Southeast Asia, Northern Australia, Amazon basin)

Acidic peat and marsh soil solar installations

Agricultural land with fertilizer-contaminated soil (high nitrate/sulfate)

Industrial brownfield sites with soil contamination

Wetland and high-water-table solar projects

FAQ

Q. How do I know if I need Z275 instead of standard galvanizing?

We recommend Z275 C4 grade if your geotechnical report indicates any of the following: soil resistivity below 2,000 Ω·cm, pH below 5.0, chloride above 500 ppm, or if the project is within 5km of a marine coastline. Our engineering team can review your geotechnical data and provide a formal coating recommendation at no cost.

Q. Does the epoxy base coat affect the screw's ability to be driven?

The epoxy is applied only after the screw has been driven to final depth, as a post-installation treatment on the exposed above-grade portion and the soil interface zone. Alternatively, pre-coated screws with a factory-applied fusion-bonded epoxy (FBE) layer are available for projects where post-installation coating is impractical.

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