6.10.2 Heat shrink sleeves

Heat shrink sleeves may be used to encapsulate corrosion protection compounds which cover the surface of a steel element.

The heat shall be applied during shrinking in such a way that other elements of the corrosion protection system remain within standard requirements, e.g. not deformed nor burnt by heat application or otherwise damaged to the impairment of serviceability.

The shrinkage ratio shall be such as to prevent any gaps from opening in the long term. The wall thickness of the sleeve after shrinkage shall be not less than 1 mm.

6.10.3 Seals

Mechanical joints are sealed with O-rings, gaskets or heat shrink sleeves.

The seal or other equivalent device shall prevent any leak of packing or any penetration of water from outside, whatever the subsequent relative movements between adjacent elements being sealed.

6.10.4 Cement grout

Cement grout injected into boreholes is permitted as temporary protection provided that the cover to the tendon is not less than 10 mm throughout its length.

Dense cement grout injected under factory or equivalent controlled conditions is permitted as one of two permanent protection barriers provided that the cover between the tendon and the outer barrier is not less than 5 mm, and provided that the crack width during serviceability loading has been proven not to exceed 0,1 mm (see 6.12).

In the case of tube-á-manchette type anchors where the steel or plastic corrugated duct is at least 3 mm thick, surrounded by a minimum of 20 mm grout cover injected under a pressure of not less than 500 kPa, then crack widths in the grout between the tendon and the duct shall be proven to be less than 0,2 mm wide under the serviceability loading condition.

The distribution of cracks and their widths may, in certain conditions, be controlled by the distribution of ribs on a bar tendon.

Quality control and volume checks should be made during encapsulation grouting.

6.10.5 Resins

Resin grouts injected or placed in a controlled manner with a minimum cover to the tendon of 5 mm are permitted as one permanent barrier providing they are contained, are unstressed and do not crack.

6.10.6 Corrosion protection compounds

Corrosion protection compounds based on petroleum waxes and greases are commonly used.

Guidelines for the acceptance criteria for viscous corrosion protection compounds and examples of test methods to measure properties of viscous corrosion protection compounds are given in annex C.

The properties of corrosion protection compounds should include stability against oxygen and resistance to bacterial and microbiological attack.

Corrosion protection compounds used for permanent corrosion barriers shall be contained within a robust moisture-proof sheath, duct or cap which itself shall be resistant to corrosion. In these circumstances such compounds also act as lubricants and void fillers which are able to exclude gas and water.

Non-contained corrosion protection compounds may be used as temporary corrosion barriers when applied effectively as a coating. Tape impregnated with corrosion protection compounds may only be used as temporary protection since there is a tendency for it to deteriorate whilst exposed to air or water.

6.10.7 Sacrificial metallic coating

Sacrificial metallic coatings shall not be applied to tendons.

Sacrificial metallic coatings may be used on other steel components such as bearing plates, caps and sleeves.

6.10.8 Other coatings on steel parts

Tar-epoxy, tar-polyurethane and fusion bonded epoxy coatings may be applied to steel surfaces which are sand blasted and free from any deleterious matter. They may be used as corrosion protection to tendons of temporary anchors if they are factory applied.

They are acceptable as a corrosion protection barrier for the tendon on a permanent anchor if the layer is applied in the factory and the thickness is not less than 0,3 mm and if application faults like pin holes are excluded by appropriate fabrication control.

Coatings are only permitted in the bond length if the bond and the integrity of the corrosion protection are verified by testing (see 6.12).

6.10.9 Steel tubes and caps

Steel parts may provide permanent corrosion protection barriers where they are themselves externally protected. Such protection may be provided by dense cement grout or concrete, by hot dip galvanising or by multiple application of coating materials approved by the Client's Technical Representative.

Steel parts with coatings which become stressed during anchor loading are only permitted if the bond and integrity of the corrosion protection are verified by testing (see 6.12).

Where a duct used for grout injection is considered as a protective barrier then it should be demonstrated that the grout ports do not allow the ingress of water after grout injection.

The duct shall be not less than 3 mm thick, surrounded by a minimum of 20 mm grout cover and the bond capacity and integrity of the corrosion protection verified by a system test (see 6.12).

Any potential degradation of the steel or coating shall be considered in the design of the anchor in the selection of element thickness and sizes.

EN 1537:1999 Execution of special geotechnical works – Ground anchors