Emerald Group Publishing Limited
Copyright © 2008, Emerald Group Publishing Limited
Metallisation protecting Angleseys Aluminium Jetty
Article Type: Methods From: Anti-Corrosion Methods and Materials, Volume 55, Issue 4
Metallisation’s customer, Brookes Specialist Contractors Limited, has completed another anti corrosion project using Metallisation equipment. Brookes won a contract with Anglesey Aluminium to protect the reinforced concrete beams on the Anglesey Aluminium Jetty in Wales (Figure 1).
The offloading jetty is an essential asset for Anglesey Aluminium as it enables them to take delivery of raw materials directly into its UK aluminium processing facility. Being exposed to the harsh environment of the sea, the natural presence of salt has contaminated the concrete over time and has resulted in the corrosion of the steel reinforcing bars. The salt seeps into the concrete and erodes the steel reinforcing bar causing cracks and spalling in the concrete and eventually the potential for failure of the structure. The Anglesey Aluminium Jetty had deteriorated quite badly and was in need of urgent repair.
With the high level of salt contamination a simple concrete repair project would not provide sufficient long-term protection. There was also the risk of accelerated deterioration through incipient anode effect. One very effective, long-term solution is thermal spraying the concrete with Brookes Specialist Contractors “Asset Guard”. Using Metallisation’s Arc 140 spray system, Brookes applied Asset Guard to the concrete surface. Asset Guard is a unique aluminium/zinc/indium anode developed to provide electro-chemical protection of steel reinforced concrete structures.
The first step in the process was the hydro-demolition of damaged concrete, then the reference electrodes were installed and tested, followed by the thermal spraying of the concrete surface of the jetty. The Metallisation Arc Spray process produces high levels of productivity and can achieve between 10 and 30 m2 of coating to the concrete per hour. Typically Asset Guard produces between 2 and 20 ma/m2 of concrete surface area depending on the electrical resistance of the concrete itself.
Brookes’ sacrificial coating, Asset Guard, means that the coating itself will be what is attacked by corrosion, rather than the steel of the reinforcing bar. The metallurgical and electro-chemical properties of the Arc Sprayed Asset Guard have been optimised to meet the requirements of concrete cathodic protection. The unique alloy composition ensures the coating is easy to apply and provides consistent uniform sacrificial corrosion of the anode, minimal self protection, negligible wasted current capacity and high-anode efficiency.
The Metallisation Arc spray process has been used for over 80 years to protect steel structures from corrosion and since the 1980s to protect concrete structures from corrosion. In the Arc spray process the raw material, in the form of a pair of metallic wires, is melted by an electric arc. This molten material is atomised by a cone of compressed air and propelled towards the work piece. The molten spray solidifies on the component surface to form a dense, strongly adherent coating suitable for corrosion protection or component reclamation. Sprayed coatings may also be used to provide wear resistance, electrical and thermal conductivity or freestanding shape.
Major advantages of the Arc spray process are that the coatings are available for almost instant use, with no drying or curing times, and there is no risk of damaging the component. Finally, the use of compressed air and electricity alone provide much more economic coatings.
Using the Arc spray process means that, the surface coating can be applied in a single treatment, which saves both time and cost of materials used. The life of the concrete protection is determined by the thickness of the coating applied. Typically a 250 μm thick coat is applied giving anti corrosion protection for around 20 years. Owing to the sacrificial nature of Asset Guard there is usually no requirement for a power supply or monitoring and system adjustment. However, due to the exposed nature of the jetty, Brookes recommended that a simple monitoring system based on silver/silver chloride reference electrodes be installed. This provided additional confidence in the protection and allows periodical checks on the reinforcing bars to be undertaken.
Stuart Milton, Sales and Marketing Manager at Metallisation says: “This is yet another example of the effectiveness of our thermal spraying technology in one of the harshest environments. Following the success of the flame spray system we have worked with Brookes to develop an alternative solution, to ensure they can deliver the protection of Asset Guard across a diverse range of applications.”
Wayne Brierley, Commercial Director at Brookes, says: “This contract certainly challenged us, both technically and practically. With Metallisation’s experience and support, we managed to overcome all adversity to deliver a proven engineered corrosion prevention solution that satisfied both the financial and commercial demands of our client”.
For further information on surface coatings or the Metallisation equipment and processes, please contact Stuart Milton on Tel: +44 (0) 1384 252 464 or web site: www.metallisation.com