One of the multi-story car parks at telecommunications company Ericsson’s headquarters just outside Stockholm was desperately in need of repair. Built in the 1970’s, a combination of frost and de-icing salts had caused extensive decay to the intermediate floors and supporting columns.
Hydrodemolition contractor NCC, with its fleet of seven Conjet ACR™ robots, was commissioned to renovate the car park.
The bulk of the repair was to the 220 mm thick reinforced concrete floor slabs. NCC used one of its remotely operated Conjet ACR™ robots to selectively remove only the badly decayed concrete. The damage was inconsistent, so the robot had to take out substandard concrete to depths varying between 50 mm and 120 mm. In some instances, it required cutting right through the floor slab.
The scope of the project included NCC restoring the deck, and after the decayed concrete was cut out, fresh concrete was poured in to complete the repair. The contractor supplemented its Conjet ACR™ robot with a high-pressure handheld lance to cut out similarly decayed concrete from around the cases.
NCC’s Conjet ACR™ robot uses a jet of high-pressure water exiting from a special nozzle at supersonic speed and forcing its way into the damaged concrete’s porous and cracked surface. The water creates a hydraulic overpressure in the concrete which breaks when this pressure rises above the tensile strength of the concrete. The water pressure and flow are fed through a long flexible hose to the robot nozzle from a high-pressure pump driven by a diesel engine housed in a silenced ISO container at ground level.
The nozzle, set at a predetermined angle of attack to the concrete, is mounted on an oscillating cassette, which is attached to a traversing cradle running back and forth along a feed beam. When the cradle reaches the end of its travel, the nozzle swivels over to maintain the same angle which enables the jet to operate with a sweeping action to cut away concrete behind reinforcement. At the same time the machine moves back a predetermined distance ready to make the next adjacent cut. The entire nozzle assembly is covered by a protective safety shroud.
NCC removed the damaged concrete reliably and without leaving any micro-cracks in the surface – so the structure was fully intact. The rebar was unharmed and the surface that remained was ideal for bonding of new concrete. The owner of the car park was extremely satisfied with the work done, on time and on budget, as the car park is such an important part of the company workplace.
CUSTOMER: NCC
STRUCTURE: Parking decks
MISSION: Restore car park
with hydrodemolition
RECOMMENDED ROBOTS: Robot 557 MPA
and Jetframe 137/157
Conjet ACR™ robot Robot 557 MPAfeatures the latest technology in hydrodemolition. Combining the reach of Robot 367, the flexibility of Robot 327 and the diesel engine of Robot 437, this robot has it all.
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Conjet has more than 35 years of experience in the hydrodemolition business. Our goal is to create the best products for every type of hydrodemolition application, providing you with the widest range of ACR™ hydrodemolition equipment.
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