RHINOCEROS

The contract was always going to present special problems, and RHINOCEROS sent an experienced Contract Manager, Bill Prendergast, to inspect the Bridge and prepare their plan. Time was already tight - the deadline was April 2012 and the contract was only awarded in December 2011. Inspections revealed extensive corrosion and failure of existing coatings, most visibly on the parapets and handrails. The beams underneath were worse: pigeons had deposited up to 7" of guano throughout the structure, and the existing chlorinated rubber coatings were severely damaged.

Refurbishing any transport infrastructure can be a logistical headache. The Bridge had to be kept open to road and foot traffic throughout the operation, and there were plenty of minor inconveniences, such as a one-way system which meant a City centre detour to move supplies and plant from one end of the Bridge to the other. On top of that, work was to start in February, when cold and damp could be expected to be at their worst.

RHINOCEROS built its early reputation on graffiti removal and anti-graffiti coatings, but are now just as likely to be seen tackling large infrastructure maintenance projects all over the country, and beyond. Lateral thinking and problem-solving approach has won the RHINOCEROS team friends in many maintenance departments. Bill cut his teeth in the Southampton marine industry and works both as a Contracts Manager and as a Paint Inspector with ICORR Level 3 accreditation. His team are all ICATS accredited, or working hard to complete their ICATS training under Bill's active supervision.

Concrete refurbishment was being done concurrently by Graham Structural Solutions of Belfast, and they planned to control the temperature and humidity at levels which would allow painting by installing a Wacker Neuson ground heater. This powerful US built heater is designed for thawing out frozen ground and heating very large buildings. Calculations showed the device could heat the entire structure by 1 degree C in 24 hours, so less than a week would be needed to take it from 0 degrees C to a workable 5 degrees Celsius. In fact, Bill says the heating was so efficient that his workmen were able to do most of their work at a comfortable 15 degrees C.

The bridge had previously been painted with up to 6 coats of chlorinated rubber. Consultations between RHINOCEROS, Belfast's Road Agency and Mike Taylor of PPG/Sigma resulted in a specification for 40% blast cleaning to SA 2.5, with the remainder of the structure being sweep blasted to remove only the top chlorinated rubber.

Mike Taylor says "From experience with Highways Agency bridges, over-coating these types of systems can be fraught with difficulty. Applying an epoxy system such as HA115, HA116, HA168, over the physical drying chlorinated rubber systems has led to experiences of cracking, delamination and crazing.
Success is measured on the long term adhesion of the coatings to all the different surfaces of the structure. External areas on outer beams that are subject to sun and temperature rises and falls are far more difficult to coat successfully because of the difference in thermal characteristics of the chlorinated rubber compared with the epoxy. The chlorinated rubber will expand and contract with temperature whereas the epoxy is more rigid and if applied over the chlorinated rubber is likely to crack.

Experience from other Highways Agency bridges has shown that on outer beams the best option is to remove the existing chlorinated rubber system by abrasive blast cleaning and apply a new epoxy system.
The under deck areas, where the existing chlorinated rubber system is more sheltered from the temperature fluctuations, can possibly be treated with an epoxy system. It has been found that spot priming with HA Item 115 and then applying HA Item 112 and HA Item 168 can be successful. HA Item 112 is preferred because from experience it is more flexible than HA Item 116 and therefore less prone to cracking because of the micaceous iron oxide pigmentation. It has also been found that the chlorinated rubber systems can have a powdery surface and this is best removed by slight sweep blasting before over coating with the epoxy system."

The choice of abrasive was also critical. Gerry Bourke of Scangrit said Olivine was the preferred option when blasting above rivers: "Olivine AFS30 and Olivine AFS 20 will achieve "Medium" blast profiles on mild steel as defined by BS EN ISO 8503-1:1995. A medium blast profile is defined as being between 50 and 70 microns and up to 85 micron.

"In an independent Testing of Expendable Abrasives conducted by PERA on behalf of Scangrit, Olivine AFS30 achieved a blast profile of 52.9µm and Olivine AFS20 achieved a blast profile of 68.5µm. The tests were conducted with a compressor rated at 350cfm at 100psi delivery pressure. The blast nozzle was a venturi type having a nozzle bore of 3/8". Pressure measured in the grit delivery hose, behind the blast nozzle, was 60psi."

RHINOCEROS Manager Duncan J MacLean says Olivine also has the advantage of being a natural mineral - in the event of a spill or a tear in the containment sheeting no environmental contamination would be caused. "In practice this has proved to be a smart move. The men like it and say they never want to go back to using copper slag. It has proved to be highly efficient in removing the 6 coats of chlorinated rubber. The AFS30 or medium grit has proved to be ideal for sweep blasting the chlorinated rubber. The AFS20, a coarser grade, has produced a profile which exceeds that required by the paint and has satisfied the client that his paint is going to stick to the bridge for a very long time!"

After heating the area, it took over 100 tons of Olivine for blast cleaning, the waste having to be vacuum cleaned off the Terram protective sheeting and hauled up to the road surface in large buckets.
The first coating of Sigma 690 was applied by airless spray to a depth of 150 microns. A stripe coat over joints and rivets followed, using Sigma Micaceous Iron Oxide (MIO) to 75 microns. This was covered with a further full sprayed coat of MIO to 150 microns, and finally a top coat of Sigma 550 to 50 microns, in Belfast signature colour Neptune.
The parapets and handrails were taken to bare metal SA 2.5, then coated with Sigma 690, a stripe coat of Sigma 456, a further spray coating of Sigma 456 and a top coating of Sigma 550 in Blueberry and Turquoise.

The Titanic continues to generate controversy; latest theories suggest its hull failure might have been quickened due to excessive sulphur content in the steel. But above water level Belfast is about to unveil a very attractive example of the best modern refurbishment techniques.