Construction and Infrastructure

Bridges

Corrosion in infrastructure represents an ongoing clear and present danger. The corrosion protection of bridges is provided by a complex sets of coatings that need to be regularly monitored and maintained. The painting of bridges is an extensive and never ending job especially on large bridges like the Sydney Harbour Bridge (AU), the Golden Gate Bridge (USA) and the Firth of Forth Bridge (UK). Corrosion prevention on these structures is essential to prevent any damage or chance of collapse due to lack of or improper maintenance. Any issues with these pieces of infrastructure becomes world headline news. An example of the critical impact that corrosion can have is illustrated by the collapse of the Morandi Bridge in Genoa (Italy) in August 2018. The tragedy killed 43 people and left 600 homeless, disrupting the traffic on a key European transportation axis for almost 2 years. Replacing or closing bridges of this size and importance is also not a viable option as it has significant direct and indirect costs to the local economy. Therefore their corrosion security in this sense is paramount. The Sydney harbour bridge has 485,000 m2 of steelwork requiring 30,000 litres for a single coat. Bridges which are exposed to challenging environmental surroundings such as marine environment have greatly increased rates of corrosion if not sufficiently protected from the harsh climate conditions. This will often require multiple coats of paints to provide sufficient protection from the elements.

Inhibispheres® can be used to enhance currently available bridge corrosion protection coatings. The patented Inhibispheres® controlled release mechanism allows for the delivery of organic or organometallic inhibitors in the coating. For example Inhibispheres A has been added to a 2 coat paint system to give it a similar level of corrosion protection performance to a 3 coat system designed to give long lasting protection to structural steel (>20 years) in a corrosive environment (coastal/salt water). Inhibispheres® A was added to an epoxy based zinc rich primer coating over sandblasted steel. A polyurethane top coat was added over the zinc rich epoxy containing Inhibispheres®. Normally in a three coat anticorrosive system a general purpose epoxy coat would be added as a build coat between the primer and the topcoat. In this case the anticorrosive performance without the intermediate epoxy coat and the inclusion of Inhibispheres A anticorrosive agent provided a superior corrosion protection to the standard three coat structural steel protective system recommended.

This reduction in the number of coatings can yield great benefits to asset owners with the additional benefit of greater corrosion protection while also reducing the amount of anti-corrosive paint used in coating the bridge. This translates into cost savings and reduced environmental footprint. The use of environmentally benign inhibitors in the formulation of Inhibispheres® means that waterways are protected from toxic zinc based corrosion inhibitors. The reduction in the number of coatings also reduces the Volatile Organic Content (VOC) released in the atmosphere during the painting. More significantly, the cost of labour is also reduced as the time required to complete the anti-corrosive paint job is reduced. The cost of the closure or reduction in capacity of the bridge during the paint is also reduced due the faster time taken to repaint the bridge with two coats rather than three coats.

Inhibispheres® from Ceramisphere offer a step change in the corrosion protection solutions for coating formulators when protecting infrastucture.

Transmission Towers

Australia has invested a staggering AU$15.6 billion just in electricity transmission towers (aka electricity pylons). Australia has a relatively small population compared to the size of the country with the majority of its population concentrated on the East Coast. Yet, the energy network extends about 918.000 km through remote areas and often harsh marine and tropical environment. Transmission towers can be made from steel, lattice, wood and concrete. Here our focus is on towers made from galvanised steel.

A transmission tower has to last between 80-120 years. Hence the goal is to have a long service life and low maintenance. This is particularly important for towers in remote and difficult to access locations. Most transmission towers in Australia are finished in hot dipped galvanized steel lattice. Their corrosion performance is usually very good but with Zinc being a heavy metal, potentially toxic to the environment and becoming a scarce resource it is now important to consider alternative options to protect towers from rusting.

There is about 225 million tonnes of Zinc reserves in the world and the world production of Zinc is stable at around 12 million per year. Zinc recycling accounts for about 39% of consumption. Zinc reserves are depleted at about 5.9 million tonnes per annum. Based on those numbers at the current rate the world Zinc reserves will run out in 35-40 years. Australia has about 28% of these reserves and China is the largest producer with just over 43%. About 50% of the Zinc produced is used for galvanising. As the cost of Zinc and galvanising increases in the years to come, there will be a big driver to find other ways to protect infrastructure against corrosion.

A galvanised tower may well stay rust-free for 30 to 50 years in a dry desert climate, however, in harsh tropical and marine climates (or industrial polluted areas), corrosion will take place at an accelerated rate and the tower may rust in 15 years or less. To give you an idea of the costs involved in remediating corrosion damages, the repair of one tower in the field in the early stages of corrosion with about 5% corrosion primarily around nuts and bolts has been estimated at $ 4,000. More extensive rust up where abrasive cleaning is needed, not only spot priming, but also priming and coating, the cost per tower goes up to about $8,000 and if the tower is corroded at 75% or more the cost goes up to more than $12,500. And this is not even the cost of accessibility to the tower which can be very substantial in remote areas.

There are two pressing needs for transmission towers. First, their asset owner and operators need to plan for the maintenance and extension of life for existing transmission towers. In most countries around the world, the majority of these structures have been built between 1960 and 1990. Many are undergoing maintenance or are in need of inspection and maintenance. A self-priming paint that needs little surface preparation could be part of that maintenance plan. For new transmission towers, an alternative to galvanising needs to be found going forward; a potential solution could be the use of corrosion protective powder coatings or wet coatings.

Inhibispheres® could be part of this solution. Inhibispheres® have demonstrated the capability to improve the corrosion resistance by itself and in combination with other corrosion inhibitors. They offer the benefit that there will be no leaching of heavy metal (Zinc) in the soil or water ways making them a sustainable & green technology for the future.

Cladding

Cladding for buildings come in many forms (brick, wood, metal or composite material). The functional objective of the cladding is the protection against wind and rain, as well as insulation and fire resistance. Appearance is also a key requirement, especially in new high rise buildings being built all around the world. Insulation is important for both energy efficient buildings and noise minimization. Fire resistance is becoming a hot topic especially after the Grenfell Tower fire in the UK in June 2017 (causing 72 deaths) where the cladding was found to have played a key role in the fire propagation. The cladding used on the Grenfell Tower was an Aluminium Composite Panels (ACP) applied in this case primarily for improving the cosmetic appearance.

Aluminium Composite Panels (ACP) are flat panels that are coil coated and are bonded to a non-aluminium core. The ACP core can differ but there are 3 general categories polyethylene (PE) core, fire retardant (FR) core and aluminium cores (either honeycomb, or solid aluminium panels). The so called APC’s are primarily used for facades of building, signage and container construction. These aluminium sheets are coated with PVDF (polyvinylidene fluoride), FEVE (fluoropolymer) or polyester. For corrosion prevention on these panels an epoxy primer coat is used. The purpose of the epoxy primer is to facilitate good adhesion of the topcoat onto the aluminium and to protect the aluminium from corroding. The corrosion inhibitor used in the primer is usually chromate. Chromate is an excellent corrosion inhibitor but also a known carcinogen.

Despite being recently banned by the European Union, hexavalent chromium is sadly still used in a lot of coating primers all around the world. Trivalent chromium was introduced in the 1990’s as an alternative to hexavalent chromium but is now also a suspected carcinogen. Whilst chromium is very effective as a corrosion inhibitor, there are ever growing environmental and occupational health and safety concerns, not only in production and installation (i.e. welding, cutting, or abrading) of chromate containing objects but also the leaching of chromate from structures in soils and water ways. Workers can be exposed to chromate in the production and application process but also when performing maintenance work on structures containing chromate. The cost of soil remediation, expensive disposal of cladding material containing chromate and potential worker’s compensation claims from exposure to chromate represent significant drivers for the elimination of chromate from cladding coating formulations.

Fortunately, there are alternative technologies for corrosion inhibition for aluminium available: Inhibispheres® is one of these alternatives. Inhibispheres® were initially developed as a sustainable and environmentally friendly alternative to the use chromate in the aerospace industry. There are currently 3 products that can be part of the solution to replace chromates: Inhibispheres® B, Ceramisphere® H and Inhibispheres® M depending on the specific requirements e.g. prevention of white corrosion, filiform or crevice corrosion. All of these Inhibispheres® can provide a greener, safer and sustainable alternative to chromates for the corrosion protection of aluminium.

Because the approval of alternative coatings systems is a long process which requires corrosion and weatherability testing over many years, it is especially important start to develop alternative solutions to chromates now.