Product category:
Ground Engineering
News Release from: Conjet AB | Subject: Hydrodemolition
Edited by the Buildingtalk Editorial
Team on 07 October 2005
Hydrodemolition specified for underpass
repair
Hydrodemolition was specified as the concrete removal technique to assist in the repair of the Fawdon Wagonway pedestrian underpass, which carries the main A1 trunk road.
Hydrodemolition was specified as the concrete removal technique to assist in the repair of the Fawdon Wagonway pedestrian underpass, which carries the main A1 trunk road, just north of Newcastle upon Tyne, over the former Old Havannah mineral line, now a footpath linking Wide Open and Brunswick Village A Conjet 362 Robot high pressure water jetting hydrodemolition machine is playing a major role in the repairs by selectively removing the defective concrete and exposing corroded reinforcement on the walls and abutments that have been chemically attacked and weakened by water leaking in from above
This article was originally published on Buildingtalk on 13 Jun 2005 at 8.00am (UK)
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The 32 m long reinforced concrete rectangular underpass is 4.5 m high and 4.9 m wide and was built in 1970.
In 1990 the structure's waterproofing and joints failed in the crown leading to salt contaminated water leaking through and on to the walls and abutments.
This eventually caused very high chloride levels in the 40 N/mm^2 to 50 N/mm^2 strength concrete and above the threshold recommended by the Highways Agency, which manages England's motorway and trunk road network on behalf of the UK government.
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The structure was rewaterproofed and joints repaired in the 1990s to eradicate the leaking, but the problem of dealing with the randomly defective concrete remained.
Routine inspection and testing of the underpass in 2003 and 2004 by the HA's agent Aone Integrated Highways highlighted the extent of the defective reinforced concrete in the walls.
Aone Integrated Highways proposed an approximate GBP150,000 scheme, taking around 10 weeks, of replacing it using a combination of the hydrodemolition technique of using very high pressure jets of water to cut away the damaged areas of concrete, renewing any damaged reinforcement and covering with a new sprayed concrete overlay.
"We specified hydrodemolition as it is also far more beneficial than mechanical concrete removal, which can damage the surrounding healthy concrete and rebar," says Aone Integrated Highways senior consultant Rob Mouzas.
"Hydrodemolition also reduces the effects of dust and using the Robot is also much better than concrete removal using hand lancing as there is no vibration for the Robot operator, unlike a percussive breaker".
"Buxton demonstrated their Conjet Robot and we were impressed and wanted to adopt that on this project".
"It was also quicker and far more advantageous than someone spending 8 hours a day hand lancing which is an important consideration for health and safety reasons".
"Hydrodemolition removes concrete above and below rebar and leaves a textured surface to give a good bond for the new concrete".
"It also cleans the steel as well and allows us to clearly see the corrosion losses to the reinforcement".
"We are undertaking the works in 3 phases of 1.1 m wide panels to maintain structural integrity".
"The Robot is performing exceptionally well and reaching up doing the areas required very quickly minimising the need for scaffold".
"The site is located within a busy residential area and the effects of noise have been considered by erecting acoustic noise barriers".
"On completion of the works the footway and street lighting are to be upgraded by Aone with local school children painting a mural on the repaired walls".
The contract to remove the underpass's 162 m2 of defective concrete was awarded to the UK specialist hydrodemolition contractor Buxton Water , based at Chester-Le-Street, County Durham.
Buxton Water used its wheel mounted Conjet Robot 362 running on the pedestrian walkway with its arm and shrouded jetting nozzle reaching up to the tops of the walls.
The 362 Robot was connected to a Hammelmann pump, driven by a 350 hp Caterpillar engine, delivering fresh clean water at a pressure of 1000 bar and flow of 197 litres/min to remove a nominal 100 mm deep layer of the defective and weakened concrete from the 400 mm thick walls".
""We have about 17m^3 of defective concrete to remove and we're doing that in three, three and a half day visits and taking about 6 m^3 each time," says Buxton Water director Mark Hothersall".
""We are removing about 0.35m3 /jetting hour".
"On average we are removing 100mm to expose the steel, however, were the concrete has seriously deteriorated a greater depth is being removed to ensure the remaining concrete has a consistent strength".
"The Conjet Robot has a far greater reach making it more versatile than our other Robots".
"Every project we complete using robotics proves to clients how selective removal of defective concrete works and customers are getting the benefit of that".
"The clients that have seen it operating are sold on the safety and speed benefits." After Buxton has finished the hydrodemolition, another contractor will follow on replacing any corroded rebar, which has lost more than 25% of its area, prior to a final overlay of sprayed 40 N/mm^2 strength concrete to complete the patch repairs.
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