Spanning the years

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The Huntingdon rail bridge, built in 1897 by A Handyside and Co of Derby and London, is one of hundreds of iron and steel constructions still in heavy daily use on busy network lines. Held together by literally thousands of rivets, the bridge is a testament to the builders, but surface deterioration over the years meant that maintenance and future protection was required as part of Network Rail’s National Upgrade Plan.

The bridge takes the East Coast Main Line between Cambridge from London over Ermine Street, a busy road into the town centre. Network Rail announced in late 2015 that the bridge was to undergo “strengthening work, minor repairs and receive a special protective coating to improve long term reliability”.  It had been painted grey for decades, but is now to be finished in holly green.

Moisture cure

Following successful projects by London Underground, Network Rail opted for Steelpaint’s single-pack moisture cure coating system – a key reason being that the coating would enable application to be carried out without the need for any conditioning or heating, and suffering fewer interruptions from cold or damp.

Perry Poppelaars, International Business Development Manager for Steelpaint, says

“Projects like this usually hit problems with the weather, and this becomes critical when the time needed for road closures is taken into account.

“We started to work on projects a few years ago for London Underground. They involved almost exclusively night work, often only two to three hours a night – the trains would be running and returning to their garages until 1.30 or 2.00am, and moving again as early as 4.30am. This kind of job is very difficult with ordinary epoxies because of the short time available, the low temperatures and the high humidity. Epoxies usually require humidity levels below 80 – 85% but our moisture cure products can be used in much damper conditions.

“We are selling a different technology which can do things which can’t be done with regular epoxy coatings. We are not relying on a chemical reaction between the two components – it is a one-part coating that uses moisture from the air as its curing agent. It meant that on the London Underground we were able to continue work with very few interruptions, even in cold conditions.

“After our work for the Underground we decided to focus on Network Rail, since many of these old bridges are suffering from their age and need work.”

Time pressures

Under pressure of road closures and other inconveniences to traffic and public, maintenance work had to be executed within as short a time frame as possible. The project, under main Network Rail contractor AMCO Rail, went to subcontractor Specialist Painting Group with close cooperation from Steelpaint.

Challenges included safety and environmental regulations, strict quality standards and work procedures laid down by Network Rail, as well as the practical difficulties such as the thousands of rivets, requiring brush and roller stripe coat application before spraying in freezing night conditions.

The Steelpaint single-pack moisture cure polyurethane chosen for the job is a PU-Zinc coating containing 93% zinc in the dry film, to ensure corrosion protection. Its quick-dry formulation means it can be recoated after 2 hours, and can be applied under very humid conditions: up to 98% RH with no dew point restrictions. It can also be applied to slightly
damp surfaces (not wet) and cures down to -5°C.

Preparation key

The coating system used on Huntingdon rail bridge was 90µ of steelpaint-PU Zinc Grey, followed by 90µ of Steelpaint-PU HS Medium Grey, and a topcoat of 60µ Steelpaint PU Cover (UK – BS 14C39) in Holly Green, providing high impact and abrasion resistance.

The project was carried out in two phases. Work on the parapets was done first, in November and December 2015 with work restricted to weekends, night hours only, and no road closures. The parapets were abraded with powertools to ST-3 followed by a solvent wipe. Application of the PU-Zinc coat was completed in temperatures ranging from minus 3°C to plus 7°C, validating the decision to avoid the use
of epoxies.

In the second phase of the project, the road was closed while rail traffic continued as usual. The bridge was encapsulated and the underside completely gritblasted to SA2.5. Testing showed the resulting anchor profile to be 83 microns.

A stripecoat and first coat of PU-Zinc was applied to a dft of 119µ, followed by a stripecoat and full second coat using Mica HS to a total depth of 188µ.

Given the low ambient temperatures during application of the coatings, painting contractors SPG chose to use a hopper pump with heating device. The advantage of this setup is that the temperature of the material can be regulated at all times, and it is also possible to spray the paint at very low pressure and prevent over-application. A stripecoat and full coat of cover UV Holly Green followed. The end of road closures was achieved well within the
scheduled time.

Cold conditions

Poppelaars continues: “The fact that we can apply our products without heating and dehumidification means we are able to give much better prediction about schedules and
are far less likely to lose time.

“On the Huntingdon bridge the painters told us they had never been able to work in such cold conditions before – there were temperatures as low as -7°C

“The minimum life expectancy for the coatings depends on the level of surface prep – on this bridge the underside was blasted to SA2.5 and will last for at least 25 years. The fact that trains still had to operate through the night meant that the topside parapets could only be cleaned with powertools to ST3 standard, so the life expectancy in those areas is 15 years.”

Achieving Network Rail certification is a long process, usually taking at least a year. But future work is on the cards for Steelpaint as the company establishes a list of reference projects, and they are working with the painting contractors to find more ways to streamline
the work.

CO2 blasting

The surface preparation process always brings difficulties, especially when projects are located close to public areas. Poppelaars continues: “We will be trying a new surface prep method for the next project which has some very interesting potential advantages. We will be working with high density CO2 blasting that may turn out to be a very attractive option. Although CO2 blasting is not new, the new high density techniques can avoid the need for any grit blasting, and all the difficulties that come with that. With only paint residue to collect, the job becomes much cleaner and brings less interruption and environmental hazard. Of course CO2 blasting will not create an anchor pattern or surface key in the metal, but for projects such as the older bridges there is usually already a very good underlying profile.

”Another option for surface preparation on some more modern bridge designs is to use heat induction. We will be using this on another project that has a lot of straight beams and does not include a lot of riveted construction. The heat induction technique uses heat from what looks like a large vacuum cleaner, and is very fast.

The extreme heat causes the existing coating system to disbond completely, after which it can be scraped off very easily.

“In cooperation with SPG, who are the specialist contractor for both High Density CO2 blasting and Heat Induction coating removal in the rail industry, we are starting two rail bridge projects shortly for Network Rail Principal Contractor CML.

Both methods will be employed. We are hoping to be able to move onto further similar projects for Network Rail over the coming year.”

Industrial icon

The world’s first iron bridge, crossing the River Severn in Shropshire, is receiving £1.25m for repairs and maintenance, to include structural repair and full re-coating.

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he 235-year-old Iron Bridge is an icon of the Industrial Revolution, the world’s first single span arch bridge made of cast iron. It is now at the heart of the Ironbridge Gorge World Heritage Site.

The bridge is currently suffering from cracking due to stresses in the ironwork
dating back to the original construction,
ground movement over the centuries and
an earthquake late in the 19th century.

Conservation

The conservation of Iron Bridge follows three years of investigations, including surveys by engineering experts abseiling from the bridge. As part of the restoration, different parts the bridge, including the iron radials and braces which hold it together, the main iron arch and the stone abutments on either side of the gorge are being examined and repaired. The bridge will also be fully repainted. It is the largest single conservation project undertaken by English Heritage to date.

Much of the older coating record for the bridge before 1980 are thought to have been lost, but in that year the bridge was blast cleaned and painted with a five coat system, prior to being Grade I listed in 1983. In 1999, the structure was inspected, following which cracks in the original cast iron parapet railings were repaired with 3.8mm thick carbon fibre reinforced epoxy plates. The repairs were almost invisible and circumvented the difficulty of welding cast iron in situ. The paint was retouched and a new top coat applied to all the ironwork. In 2006 the bridge was extensively re-painted at a cost of £100,000.

Ancient monument

Iron Bridge was designed by Shrewsbury architect Thomas Pritchard, who died in 1777. It was erected in 1779 by Abraham Darby III and officially opened on New Year’s Day in 1781, having cost £6,000 and used 378 tons of iron. It was in full use for 150 years, before it was closed and classed as an ancient monument in 1934. It was always intended as a monument to the achievements of Shropshire ironmasters as well as a river crossing – it was an advertisement that gave their ironworks a competitive edge over their rivals.

English Heritage’s major conservation programme will involve work on iron radials and braces holding the bridge together, the deck plates and wedges, the main iron arch, and the stone abutments on either side of the Severn.

The cast iron pieces will be carefully cleaned and conserved, reinstalled or replaced where “absolutely necessary” and as part of the project, the bridge will
be repainted.

Kate Mavor, English Heritage’s chief executive, said the renovations will ensure the Iron Bridge Gorge site “will continue to inspire us for generations to come”.

“An iconic symbol of the Industrial Revolution, it is arguably the most important bridge ever built, and without doubt one of the most important sites in our care,” she explains.

The bridge over
the Lotsekanal

How Pasquick is enabling high-quality corrosion protection, significantly higher film thicknesses per pass and thus cost savings for the Zitadellenbrücke bridge in Hamburg.

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orrosion protection has one crucial role on bridges: It has to prevent moisture – such as precipitation, melt water or de-icing salt solutions – from penetrating the underlying structure and causing dangerous damage. When it comes to public infrastructure in particular, German authorities are uncompromising with respect to quality and thus safety, despite pressure to reduce costs.

Quality tested in practice

Polyaspartic coatings are ideal, for particularly cost-effective coating of a range of different substrates without compromising on quality. Fewer coats are generally required than with conventional anticorrosion systems. Curing is also faster, saving time and money.

The new Zitadellenbrücke bridge across the Lotsekanal canal in Hamburg-Harburg was built for the Landesbetrieb Strassen, Brücken und Gewässer der Freien und Hansestadt Hamburg (Hamburg state authority for roads, bridges and waterways). It was the first time Pasquick had been used for a public infrastructure project. Government customers like these only use technologies that have proved to be absolutely reliable and efficient in years of use.

Anticorrosion coating with Pasquick

“We have been using products based on Pasquick technology since 2012 with great success,” said Joachim Rother, authorised signatory and technical manager wind power at the novatic GmbH & Co. KG coatings factory in Dresden. novatic worked closely with Covestro to manufacture the coating material for the swing bridge. “Our primary customers are bulk buyers who fabricate concrete sections for wind turbine towers. Over the last few years, many concrete wind turbine towers have been coated this way.”

His experience using products based on Pasquick technology shows that they make outstanding topcoats in anticorrosion systems. novatic developed extremely successful anticorrosion systems for ‘5-M high’ environments according to DIN EN ISO 12944. The coatings factory used this type of anticorrosion system for the Zitadellenbrücke across the Lotsekanal
in Hamburg.

Rapid corrosion protection

The Zitadellenbrücke is in the inner port of Harburg. The bridge structure has an asymmetric movement and crosses the 44-metre-wide Lotsekanal that separates the Harburg Schlossinsel and the city centre in Hamburg. Opening the moving section of the bridge, which is for pedestrians and cyclists, allows ships to pass through an 18-metre gap into the Ziegelwiesenkanal and the Harburg Holzhafen.

The high quality required by the Hamburg Landesbetrieb Strassen, Brücken und Gewässer makes Pasquick the ideal anticorrosion product. Its polyaspartic technology enables significantly higher film thicknesses per pass than conventional polyurethane coatings. As a result, only three coats are required for this structure instead of four, as the last two coatings are combined into one. “Instead of the two finishing coats previously necessary, we can achieve the film thickness required for at least 25 years of protection in a single pass,” added Rother.

“Both facility operators and the contractors performing the work benefit from this,” said corrosion protection expert Thomas Baeker of Covestro. “Eliminating one of the coating steps saves contractors time and labour costs. They gain flexibility, meaning they can meet tighter deadlines or take on more projects in the same period.”

Outstanding long-term stability

For Rother, another advantage is the excellent long-term weather resistance with excellent colour stability and gloss retention. “A long-term chemical resistance immersion test demonstrated that the topcoat exhibits the outstanding resistance to water, salts, various chemicals, oils and fuels required to protect bridges, industrial facilities and hydraulic steelwork.” Coatings formulated with Pasquick also have a very low VOC content, significantly reducing solvent emissions.

The bridge over the Lotsekanal is thus an example of what Pasquick can do, and that is every bit as impressive to public and private customers as its cost and resource efficiency. The long-term corrosion protection is a perfect illustration of what the Pasquick developers mean when they say “Inventing for you.”

Award winning ingredients in Prague

The Troja Bridge over the River Vltava in the Czech capital Prague won the ECCS’s Steel Bridge Award in 2015. The 262m long bridge carries pedestrian and cycle traffic, four lanes of road traffic, and a double-tracked tram line. Designed by Mott MacDonald, constructed by Metrostav and coated by Hempel, it is a landmark in Prague, and famous for its slender arch and low height-to-span ratio.

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he innovative design of the Troja Bridge lies in the fact that it reconfigures the hangers of the classic bowstring arch from a conventional vertical arrangement to a diagonal one, thus providing four times more rigidity, and improving overall performance. Such innovation could not go unnoticed, which is why it won the ECCS’s Steel Bridge Award. In the words of the jury: “The beautiful design is developed to suit the construction process and carries the heavy loads of tramways, cars, and pedestrians into the heart of Prague. The bridge promotes the qualities of steel by its visible slender structure and elegance. The effective lighting accentuates the expressive form. Troja Bridge is like a sculpture, and a beautiful addition to the city of Prague.” 

Simple start

Significant words of praise for a project that for Hempel started like any other, with its coating advisors defining the most appropriate system for the customer’s specifications. However, its unique design called for a unique solution and finally a high zinc primer was specified. The company’s two-component, zinc-rich epoxy primer Hempadur Zinc 17360 cures to a hard-wearing, highly weather-resistant coating and is used as a versatile, long-term primer on steel in severely corrosive environments. On this occasion, the primer was applied in the workshop before the main steel parts were transported to the site. Following touch-up work in assembly areas, a second primer and intermediate layers were applied with Hempadur Fast Dry 15560, which enabled work to progress smoothly, while also reducing the risk of affecting property around the site. Finally, the bridge was roller-coated with Hempathane HS 55610, the fast-dry version of the company’s polyurethane topcoat with zinc phosphate, which provides the highest standards of long-lasting colour fastness and dries to touch in just three hours at 20°C.

An extra intermediate layer of Hempadur Fast Dry 15560 was used on structural steel parts anchored in concrete, and the entire system was successfully validated in accordance with Ministry of Transport regulations for 30 years’ service life and tested in an accredited laboratory for high durability in C5-I environments.

Eliminating
the problems

Stirling Lloyd’s Eliminator system has been specified for the waterproofing of the historic Reading Bridge, with a total of 950m2 of Stirling Lloyd primer, Eliminator membrane and Bond Coat 3 being applied by VolkerLaser to the reinforced concrete bridge deck.

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key transport link in the UK between Reading town centre on the south bank with Caversham on the north bank, the bridge carries some 24,000 vehicles every day. With this level of traffic, the bridge required major strengthening works in order to bring it in line with 21st century infrastructure, capable of withstanding increasing volumes and axle-weights of traffic and help ensure it continues to keep traffic moving for many years to come.

The Berkshire bridge encompasses a
three-lane highway and two footways, and
its importance to traffic flow meant disruption on this section of the B3335 had to be kept to
a minimum.

Eliminator is a cold, spray-applied waterproofing membrane with rapid curing properties, allowing for a fast and efficient application. Stirling Lloyd’s Bond Coat 3, a high performance heat activated bond coat, was used in conjunction with Eliminator to enhance the bond between the waterproofing and surfacing, completing the robust, durable system that is designed to outlast the life of the structure.

Eliminator provides a tough, seamless, flexible membrane and the Bond Coat 3 cures to provide a hard tack free protective finish – both being resistant to contamination and damage from site traffic. This allowed other trades and phases of works to take place throughout the duration of the waterproofing works without damage.

Innovative solution

Peter Weaver, Estimator at VolkerLaser, comments “For such a key transport link in Reading, it was critical that as few vehicles as possible would be affected with this waterproofing work. Closing the bridge meant that the application could be carried out quickly, without interruption.

“The use of carbon fibre strengthening on the project was innovative; thin, strong and flexible, carbon fibre plates can be designed and installed to provide a cost effective solution, which does not detract visually from the original design of the structure. These plates were applied to the soffit of the bridge deck and beams; enabling an increase in the carrying capacity for the bridge. Spandrel columns were also carbon wrapped to assist with the management of the constraints of the loadings and the vehicles above. This mitigated risk to the overall delivery of the project.

“The project also led to VolkerLaser being shortlisted for the Construction News Awards for Structural Specialist of the Year.”

Built at the end of the 19th century and opened in 1923, Reading Bridge is a historical spandrel arch structure over the River Thames. The bridge was built using an early form of reinforced concrete developed by the French engineer François Hennebique.

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