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Marine Corrosion Protection

Deterioration of concrete marine structure such as wharves, jetties, marinas and piers is a common problem and the cause is invariably chloride ingress leading to reinforcement corrosion. Cathodic protection is commonly the only sensible answer due to the widespread reinforcement corrosion activation by the time concrete repair is initiated.

 

Impressed Current Systems

On major projects impressed current systems are frequently the preferred method as the high cost of design and control systems can be spread over the large project cost and anodes long life (50 years). There are many impressed current anode systems available and all these systems should be evaluated. For example the BCRC method of anode system appraisal considers all the client selection criteria to determine the appropriate system for the project.

MMO Mesh – MMO Mesh is an open mesh pinned to the concrete surface and covered in mortar (trowelled or sprayed) to make ionic contact. Excellent for large walls not subject to tidal/swell inundation and access is simple

MMO Ribbon – MMO Ribbon is a fine MMO mesh cast into slots cut in the concrete. The anodes are embedded in a cementitious mortar or grout. They are excellent for large beams not subject to tidal/swell inundation and access is simple. If used in splash zones extreme care is required to safeguard against current dumping. Cutting the slots can be expensive or even impossible in some restricted confines.

MMO Discrete – MMO Discrete Anodes (large diameter) can be used in beams and columns provided the anode current density is kept low but average reinforcement density is kept high to safeguard against non-uniform current. Often used when it is perceived there is no time to undertake optimisation by trials

DurAnode4 – DurAnode 4 are an engineered small diameter discrete MMO anode with proprietary grouting and connection systems and inbuild resistor. It is used in splash and atmospheric where trials enable design to higher anode current density based on the more uniform current distribution and where the small diameter holes required is useful for rapid installation, low structural and tenant interference and lower installation cost.

Cassette – Cassettes are a MMO ribbon anode mounted on the concrete surface in an inert rigid frame. They overcome the issues of acidification of grouted ribbons due to current dumping in wet areas. They are extremely fast to install and overcome many problems where access is limited. Ideal for basements, bridges, tunnels, industrial structures and wharves where finished appearance is not so critical.

 

Sacrificial Zinc Anodes

The sacrificial anode Cathodic protection systems offered here are all true CP systems. They provide high polarisation so that true CP in accordance with Standards is achieved. Sacrificial Anodes for cathodic protection (rather than the lesser level of cathodic prevention or corrosion control anodes) are finding great favour where the 20 year replacement interval is acceptable and a low install cost is required.

Zinc Layer Anode – The is a sheet of zinc with self-adhesive backing that also acts as an activator. It is ideal for the upper level beams in the atmospheric zones as it is the lowest cost, simplest to install anode. It is not suitable to areas of inundation as even with the recommended waterproofing membrane water will seep in and lead to early failure.

Roll Anodes – These are a zinc anode in an activator paste that are inserted into drilled holes in the concrete. The holes are sealed and these anode can be used in splash and tidal zones. Typically, in marine structures in water anodes are used to protect underwater and up to mid height of the tidal zone, Roll Anodes are used for the mid tidal to atmospheric level and ZLA used in the atmospheric zone.

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