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Corrosion Protection

Pre-Grouted Bars Epoxy Coating
Hot Dip Galvanizing Extruded Polyethylene
Corrosion Inhibiting Grease or Wax Coal Tar Epoxy
Heat Shrink Tubing Epoxy Coating Patch Kits
Anchor Head Protection Field Splice for Bars
The level of corrosion protection for an earth anchor is primarily dependent on the service life of the anchor, the aggressivity of the environment, installation methods and consequences of failure. An anchor with a service life greater than 24 months is generally considered permanent. Permanent anchors should always have some type of corrosion protection incorporated into their design.

Ground aggressivity is generally influenced by the following:

  1. Electrical resistivity of the soil (Soil is aggressive if resistance is less than 2000 ohm-cm.)
  2. pH value of the soil (Soil is aggressive if less than 5.5)
  3. Chemical characteristics of the ground water, rock, or soil (salt water, slag fill, industrial waste, organic fill etc.)
  4. Moisture seepage
  5. Presents of oxygen
  6. Stray electrical currents
Governing Specifications for each anchor application may specify different protection schemes and these specifications should always be followed in designing the appropriate corrosion protection level. The following “Decision Tree” published in the PTI Recommendations for Prestressed Rock and Soil Anchors, assists designers in following a logical approach to corrosion protection selection:
Corrosion Protection Decision Tree

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.

Methods of Corrosion Protection
Corrosion Protection Type Abrasion Resistance (4=best) Typical Thickness Relative Cost (4=highest) Lead Time Can be applied to accessories? Applied in the Field?
Hot Dip Galvanizing 4 3-4 mils 2 2-4 weeks yes no
Epoxy Coating 1 7-12 mils 1 2-3 weeks yes no
Pre-Grouted Bars 3 2", 3" or 4"
tubing
3 2 weeks no yes
Extruded Polyethylene Coating 2 23-25 mils 1 2-4 weeks no no
Corrosion Inhibiting Compound 2 N.A. 2 2-4 weeks yes yes
• Other thicknesses can be applied, contact a Williams representative for issues regarding threadability of fasteners
• Combination of protection methods are available (i.e. epoxy bar with a pregrout section, galvanizing with epoxy)
• Field patch kits are available for galvanized and epoxy coated products
• Field procedures are available for coupling (2) pregrouted anchors
• Contact Williams for more information regarding the appropriate corrosion protection level and corresponding governing reference specifications/documents.

Epoxy Coating
Epoxy Coating Fusion bonded epoxy coating of steel bars to help prevent corrosion has been successfully employed in many applications because of the chemical stability of epoxy resins. Epoxy coated bars and fasteners should be done in accordance with ASTM A-775 or ASTM 934. Coating thickness is generally specified between 7 to 12 mils. Epoxy coated bars and components are subject to damage if dragged on the ground or mishandled. Heavy plates and nuts are often galvanized even though the bar may be epoxy coated since they are difficult to protect against abrasion in the field. Epoxy coating patch kits are often used in the field for repairing nicked or scratched epoxy surfaces.
Pre-Grouted Bars
Pre-Grouted Bars Cement Grout filled corrugated polyethylene tubing is often used to provide an additional barrier against corrosion attack in highly aggressive soils. These anchors are often referred to as MCP or Multiple Corrosion Protection anchors. The steel bars are wrapped with an internal centralizer then placed inside of the polyethylene tube where they are then factory pre-grouted. When specifying couplings with MCP ground anchors, verify coupling locations with a Williams representative.
Hot Dip Galvanizing
Hot Dip Galvanizing Zinc serves as a sacrificial metal corroding preferentially to the steel. Galvanized bars have excellent bond characteristics to grout or concrete and do not require as much care in handling as epoxy coated bars. However, galvanization of anchor rods is more expensive than epoxy coating and often has greater lead time. Hot dip galvanizing bars and fasteners should be done in accordance with ASTM A-153. Typical galvanized coating thickness for steel bars and components is between 3 and 4 mils. 150 KSI high strength steel bars should always be mechanically cleaned (never acid washed) to avoid problems associated with hydrogen embrittlement.

Extruded Polyethylene
Extruded Polyethylene Williams strand tendons contain an extruded high density polyethylene sheathing around each individual strand in the free-stressing portion of the anchorage. The sheathing is minimum 60 mils thick and applied once the 7-wire strand has been coated with a corrosion inhibiting compound. Extruded polyethylene sheathing provides a moisture tight barrier for corrosion protection and allows the strand to elongate freely throughout the free-stressing length during the prestressing operation.
Corrosion Inhibiting Wax or Grease with Sheath
Corrosion Inhibiting Wax or Grease with Sheath Williams corrosion inhibiting compounds can be placed in the free stressing sleeves, in the end caps, or in the trumpet areas. Often bars are greased/waxed and PVC is slipped over the greased/waxed bar prior to shipping. Each are of an organic compound with either a grease or wax base. They provide the appropriate polar moisture displacement and have corrosion inhibiting additives with self-healing properties. They can be pumped or applied manually. Corrosion inhibiting compounds stay permanently viscous, chemically stable and non-reactive with the prestressing steel, duct materials or grout. Both compounds meet PTI standards for Corrosion Inhibiting Coating.
Coal Tar Epoxy
Coal tar epoxy has shown to be abrasion resistant, economical and durable. This product when specified should meet or exceed the requirements of (a) Corp of Engineers C-200, C200a and (b) AWWA C-210-92 for exterior. Typically the thickness is between 8 and 24 mils. Make sure that the surfaces of the bar are clean and dry before coating.
Heat Shrink Tubing
Coal Tar Epoxy Heat Shrink Tubing provides a corrosion protected seal when connecting smooth or corrugated segments.
Epoxy Coating Patch Kits
Coal Tar Epoxy Epoxy Coating Patch Kits are available upon request.
Anchor Head Protection

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.

Fiber Reinforced Nylon End Cap Strand End Cap Screw-On PVC End Cap Steel Tube End Cap welded on flange with threaded screw connections
Fiber Reinforced Nylon Cap Strand
End Cap
Screw-On
PVC Cap
Steel Tube Welded on Flange with Threaded Screw Connections
Field Splice for Bars
Continuous corrosion protection can even be accomplished for the MCP Pregrouted anchors manufactured from Williams Form Engineering. To achieve the equivalent levels of corrosion protection the coupled sections of bar anchors can be wrapped in a grease impregnated tape that is further protected with heat shrink sleeving. This scheme is acceptable by most governing agencies and is specified in the PTI Recommendations for Prestresed Rock and Soil Anchors.
Field Splice for Bars
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