CONJET ROBOT ASSISTS WITH BRIDGE DECK WIDENING IN UK

2004-09-16 — A Conjet Robot 322 hydrodemolition machine, has been playing a key role in the UK removing concrete at a major redevelopment project in the centre of Plymouth, Devon. The Robot 322 on hire from Doornbos Rental UK in Southampton, is being used to accurately cut out the concrete from the reinforced deck and heavily reinforced cantilevered finger beams of a viaduct carrying a major road above a bus station, shops and café.

Main contractor Mowlem Civil Engineering is using Doornbos Rental UK’s Conjet Robot 322 to remove concrete from the City’s Exeter Street Viaduct to expose reinforcement in preparation for tying in additional reinforcement and casting on a short extension to make a wider deck. The hydrodemolition, which was specified by Plymouth City Council, is part of Mowlem’s approximate £4M enabling works contract to divert all the utilities and services for the vast Drake’s Circus Redevelopment Project for client P & O Developments.

“My concern was to leave the original structure as intact as possible to add the crossover and suggested the hydrodemolition technique as I have used the method before,” says Plymouth City Council senior bridge engineer Hrach Agobiani. “Hydrodemolition provides a clean exposure of existing reinforcement to tie additional reinforcement onto and recast with fresh concrete in order to get an integral monolithic structure. The client’s consulting engineer Clark Nicholls and Marcel went along with my suggestion. They made it a contract requirement instead of breaking the concrete out manually with breakers, which would have caused damaged to the surrounding concrete from vibration. The hydrodemolition technique was adopted as it leaves a very good uneven textured finish, which gives a very strong bond for the new concrete we have to cast on.”

Mowlem initially planned the less efficient method of water jetting with hand held lances, but the company investigated alternative robotic hydrodemolition methods and opted for the safer and more environmentally acceptable Conjet 322 Robot from Doornbos.

Using the specified hydrodemolition method Mowlem had originally planned to take out all the concrete from a 30m long, 900mm wide section of the 500mm thick deck, plus an adjacent and parallel 100mm deep 1.4m wide swath of concrete of the same length. The reinforced deck, built in the 1960s, proved to be exceptionally strong and allowed Mowlem to modify and reduce the amount of healthy concrete needed to be removed by the Conjet 322 Robot. “We started on the hydrodemolition to the original plan, but found the concrete was much stronger than expected,” says Mowlem section agent Cris Peck. “We were able to reduce the amount and only take out a 150mm deep strip and a parallel and adjacent 100mm thick section. This proved adequate to allow us to tie in the required additional steel reinforcement and extend the width of the deck with a C40 concrete mix.”

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Conjet AB
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S-136 25 Haninge
Sweden.

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