ASTM A975

ASTM A975 is the authoritative North American standard for manufacturing, testing, and specifying double-twisted hexagonal wire mesh gabions and revet mattresses. Unlike general-purpose fencing, this standard dictates the performance of heavy-duty structural systems used in critical infrastructure such as gravity retaining walls, channel linings, and rockfall protection.

For the civil engineer or infrastructure consultant, citing ASTM A975 is the primary method of ensuring quality control. It guarantees that the gabion units function as a monolithic structure that will not unravel under tension and possesses sufficient coating mass to survive the environmental corrosivity of the project site for its intended design life.

Technical Principles

ASTM A975 classifies gabion materials into distinct “Styles” based on the wire coating technology. The standard ensures the mesh can withstand high hydrostatic pressure and earth loads without rupture or deformation.

The Three Gabion Wire Material:

1. Galvanized Wire: Zinc-coated steel wire (Heavy Galvanized). Suitable for dry, non-aggressive environments.
2. Galfan Wire: Zinc-5% Aluminum-Mischmetal alloy-coated steel wire. This advanced alloy provides approximately 2-3 times the corrosion resistance of standard zinc and is the modern standard for long-term durability.
3. PVC Coated Wire: Metallic-coated steel wire (galvanized wire and galfan wire) with an additional extruded Poly(Vinyl Chloride) (PVC) sleeve. This is mandatory for aggressive environments (marine, acidic soils, or high-abrasion zones).

Key Performance Metrics:

• Double-Twist Geometry: The wire is twisted around itself at least three half-turns. This prevents the mesh from unraveling if a single wire is cut, keeping the damage localized.
• Tensile Strength: The mesh must meet strict strength thresholds parallel to the twist (the load-bearing direction).
• Punch Strength: A localized strength test simulating the pressure of sharp rocks against the mesh face.

Specification Notes

When defining specifications for public works or commercial infrastructure, referencing “Gabions” without ASTM A975 opens the door to “commercial grade” substitutes that lack structural validity. To ensure performance, specify the following parameters explicitly:

1. Define the Coating Style:

Clearly state whether the project requires Galfan wire (Zn-5Al-MM) for general use or PVC gabion wire (PVC Coated) for corrosive environments. Advisory Note: Standard Zinc is rarely recommended for permanent infrastructure due to lower life-cycle value.

2. Enforce Minimum Structural Values:

Require the manufacturer to provide a Mill Test Certificate (MTC) verifying the following minimum values derived from ASTM A975:

3. Verify Coating Weights (ASTM A641 Class 3):

Low-quality wire often skimps on zinc mass. Ensure your specification table matches these Class 3 minimums to guarantee corrosion resistance:

4. PVC Integrity (PVC Coated Gabion Only):

Common failures in PVC gabions occur when the polymer cracks or fades.

• Specific Gravity: 1.30 – 1.35 (Ensures dense, high-quality compound).
• UV Resistance: The coating must show no cracking or blistering after 3000 hours of exposure testing (ASTM G154/G155).