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Concrete repair

Concrete repair and corrosion protection

An understanding of how corrosion protection products are applied to a range of reinforced concrete structures gives concrete repair contractors, owners of concrete structures, project managers and specifiers an insight into the benefits of innovative solutions over some of the more expensive, disruptive traditional concrete repair methods. Download the SRCP concrete repair guide, or below you will find a brief review of new durable and easy to apply concrete repair methods.

Balconies

Balconies

Conventional patch repairs require extensive breakout which is noisy and may destabilise the balcony unless expensive support is installed.

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Balconies should be built to a high reliability because of their low redundancy and proneness to user abuse but codes make no provision for this and sometimes corrosion occurs and this can be critical. The problem with balconies is that they are small elements often repaired in isolation and provision of impressed current cathodic protection used on large structures is often not practical, economic or in the realms of the repairer. corrPRE’s galvanic cathodic protection systems and Metalnastri’s ZincTape are simply installed to provide active corrosion protection to concrete reinforcement and exposed steel. They are the answer for small and large concrete repair contractors who want to provide a long lasting repair with the minimum of disturbance.

Basements, Tunnels, Tanks and Pools

Basements, Tunnels, Tanks and Pools

A range of mechanisms may occur other than just reinforcement corrosion.

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Cracks may leak leading to corrosion of reinforcement at cracks. Water flowing over the concrete surface from leaks at cracks and joints running over the atmospheric surface and evaporative concentration leads to a high build-up of chlorides at the surface which diffuse back into the concrete and cause corrosion in the run off area.

If there is a high pressure head of water and the concrete is not high performance water penetrates the concrete under a pressure head. Evaporation of the water arriving at the atmospheric concrete face and chlorides or sulphate ions back diffuse to the reinforcement. The process is referred to as transpiration.

Bases, Plinths & Pedistals

Bases, Plinths & Pedestals

On mining and industrial plants concrete is frequently used to support steel plant and structures. These bases, plinths and pedestals are frequently damaged.

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If nothing is done to prevent the corrosion then full patch repairs involves breaking out around the reinforcement. This can lead to issues as the load is sometimes very high. The cost of supporting the load while repairs are undertaken can be intense. In other cases extensive breakout may cause misalignment of equipment or the need to stop operations while repairs are undertaken. This makes for difficult and expensive structural repairs for bases.

These problems are largely eliminated if the breakout of the sound but contaminated concrete becomes unnecessary and the only way of achieving this is by the application of cathodic protection.

Bridge piers in the tidal zone

Bridge piers in the tidal zone

Learn about the structural benefits of using roll anodes for bridge piers in the tidal zone.

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Tidal and splash zones are the most common place to find corrosion of bridge elements. Where bridge piers extend to these zones, roll anodes are the preferred SACP system for corrosion protection because they are suitable for immersed concrete. Typically the anodes are inserted in 32mm drilled hole between reinforcement bars, terminating just below the concrete surface.

Bridge piers are subject to bending and in rare cases, the 32mm diameter holes with no structural grout at the extreme fibre is an issue. In some cases small diameter anodes and holes may be the solution. In others the roll anodes can be pushed deeper into the concrete towards the neutral axis and the hole at the extreme fibre can then be filled with a high strength grout.

Columns

Columns

Problems are eliminated if breakout becomes unnecessary with the application of cathodic protection.

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Whether the column is built into a wall and exposed only over a limited area or is a free standing and exposed over its full circumference Zinc Layer Anode (ZLA) provides the lowest cost and simplest repair systems. Just remove the loose concrete and patch, apply the ZLA to the concrete surface, make a connection to the reinforcement and the reinforcement is protected by cathodic protection. A cementitious coating is applied for and aesthetic and waterproof finish.

Because the reinforcement is barely exposed there is very little breakout and no need to consider structural aspects.

Cracks & Joints

Cracks

Zinc layer anodes and roll anodes applied to the concrete surface provide full cathodic protection to reinforcement.

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Where saline water penetrates down leaking cracks there is a risk of corrosion continuing at the crack even once the crack has been sealed. There is also a corrosion risk of corrosion at wide cracks if they are not sealed at an early stage. ICCP systems are too complex for practical installation along cracks and galvanic anodes don't generally have the power to provide cathodic protection.

corrPRE's ZLA and Roll Anodes have a high power output and either can be applied to the concrete surface along the line of the cracks to provide full cathodic protection to reinforcement at the cracks over the life of the anodes. The anodes will have a hybrid effect of providing cathodic protection as soon as installed and during their life will bring about repassivation of the reinforcement.

Historic Structures

Historic Structures

Ease of installation of cathodic protection allows the system to be replaced with the coating.

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Many of Australia's Historic Buildings were built during a period where steel sections were embedded in coke breeze concrete. Ultimately corrosion of the steelwork occurs, particularly in wetted areas, and this can be stopped using corrPRE galvanic anodes or conductive paint impressed current systems without changing the appearance of the structure. An assessment of various elements of one project is given here to indicate how these anodes can be used in these difficult sections.

Roll Anodes and Zinc Layer Anode can be used in conjunction with each other to provide great flexibility in designing cathodic protection to structural steel embedded in coke breeze concrete in historic buildings.

Lintels

Lintels, Sills and Arches

Corrosion of the steel or concrete lintel can lead to collapse but more typically the corrosion damages the surrounds (window, door or masonry).

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Lintels are beams that span an opening and distribute the load from above the opening into the structure on either side of the opening. These elements are frequently an issue for small buildings because the manufacturers and builders are not equipped to make judgements on the low cost elements durability.

The critical structural nature of lintels works against using a standard patch repair. Where reinforcement corrosion is due to chlorides it is almost always necessary to break out behind the reinforcement to remove contaminated concrete unless cathodic protection is applied.

Patch Repairs

Patch Repairs

Learn about a low cost patch repair with simple galvanic cathodic protection for high performance repair providing full cathodic protection to the reinforcement such that concrete does not need to be broken out behind the reinforcement.

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Some owners don't realise the risks they take when authorising low cost repairs. The risks include further spalls falling and injuring someone or causing damage, insurance cover prejudiced due to inappropriate maintenance and accelerating damage arising due to the method of repair. A simple way to assess if the problem is likely to be local or wide spread is to measure the cover thickness over the steel and do a visual survey.

Building owners will often first notice a corrosion problem when a crack appears in the concrete and rust stains start to appear. In other cases a piece of concrete may spall off. By the time this occurs contaminants may be widely spread through the concrete such that global repairs or protection should be considered.

Slabs

Slabs

A key determinate of choice of cathodic protection is whether it can be applied to the top or bottom of the slabs.

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All concrete repairs suffer from the problem that breakout around the reinforcement to remove contamination is required unless cathodic protection is applied. Conventional cathodic protection suffers from the problem of high design, installation and maintenance costs and high output sacrificial systems are now being considered as an alternative. In this page galvanic and impressed current systems for corrosion protection of concrete slabs are discussed.

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