Corrosion Protection

Ground aggressivity is generally influenced by the following:

Grout Bonded Rock or Soil Anchors

The standard permanent grout bonded rock or soil anchor consists of an epoxy coated or galvanized anchor rod, grouted in an oversized drill hole. Centralizers should be used to assure good grout cover (approximately 25 mm) around the bar. Additional corrosion protection may be desired if the rock or soil is considered to be aggressive, consequences of failure are high or anchoring into material where good grout cover is difficult to achieve. Williams Multiple Corrosion Protection (MCP) systems offer increasing barriers against corrosion attack. Williams MCP systems allow the anchor bar to be engulfed in a pre-grouted poly-corrugated tube. Protective end caps may also be used to seal the nut and washer from the environment when the outer end of the anchorage will not be encased in concrete.

Grout Bonded Multi-Strand Anchors

Williams also offers permanent and temporary multi-strand ground anchors. Williams strand anchors are offered with a corrosion inhibiting compound under an extruded high density polyethylene in the anchor unbonded length. The permanent anchors are protected with corrugated high density polyethylene (HDPE) over the entire length of the anchor excluding the stressing tail. The corrugated HDPE offers one level of corrosion protection while the field grouting operation inside the corrugated HDPE offers an additional level of protection. Temporary anchors are not manufactured with the corrugated HDPE over the anchor bond and unbonded lengths. Upon request, the 0.6” diameter, 270 KSI, 7 wire strand is offered epoxy coated or galvanized.

Mechanical Rock Anchors

Williams Spin-Lock mechanical rock anchors are used when anchoring into competent rock. The standard Williams Spin-Lock anchor relies on cement grout for corrosion protection. Williams Spin-Locks can be specified with a hollow anchor bar, allowing the system to be grouted from the lowest gravitational point in both up and down bolting applications. This provides a solid grout cover surrounding the anchor rod. Unlike the bonded rock anchor, the Spin-lock is grouted after the anchor is stressed so cracking of the grout column due to prestressing is eliminated. Spin-Lock anchors have been in service since 1959 and in most cases have relied strictly on cement grout for corrosion protection. If so desired, additional corrosion protection can be provided by step drilling a larger diameter drill hole, which provides additional grout cover, or by galvanizing the steel anchor rod. Protective end caps may also be used to seal the nut and washer from the environment when the outer end of the anchorage will not be encased in concrete.

The most important section of a ground anchor that needs adequate corrosion protection is the portion of the anchor exposed to air/oxygen. This is typically defined as the "anchor head", which generally consists of a steel bearing plate, a hex nut and washer for a bar system, or a wedge plate and wedges for a strand system. For permanent ground anchors it is best to galvanize the hex nut and plates even if the bar is epoxy coated. Galvanized components, if scratched during shipping, are less likely to cause corrosion concerns than scratched epoxy coated components. The end of the steel bar protruding out from the hex nut is often protected by the use of a plastic or steel end cap packed with grease or cement grout. Williams offers several different types of PVC and metal end caps to provide corrosion protection at otherwise exposed anchor ends.