SE-136 44 Handen
Ponti Del Valico is an aging and heavily trafficked double viaduct that straddles the Swiss-Italian border at Chiasso, just north of Milan. The 118m long, slightly curved reinforced concrete viaduct, supported on a series of piers, carries the main E35, which is one of the major trunk routes to and from the nearby Gotthard Tunnel. It was chosen for a hydrodemolition restoration.
During the CHR 7 million repair and strengthening of the major Ponti Del Valico, the contractor Wan-Jet used Conjet ACR™ robots.
Wan-Jet worked with fellow Swiss contractor Hydrodemolizione as the specialist hydrodemolition subcontractor for the main contractor Consorzio Viadot-to Brogeda. A joint venture of Swiss and Italian contractors Muttoni, CST and Pizzarotti, was able to quickly and easily adapt the Conjet ACR™ robot to suit the varied selective concrete removal tasks on its approximate CHR 0.5 million hydrodemolition contract.
Hydrodemolition is a very good system and method of removing concrete. It takes off concrete to a preset depth either above or below reinforcement and provides a rough surface to give a good bond with new concrete. Hydrodemolition also leaves reinforcement clean and undamaged and doesn’t cause any cracks in the concrete left behind, unlike jackhammers which can hit and vibrate the rebar and do a lot of extra damage by breaking the bond between the reinforcement and good concrete.
Before Wan-Jet could start the hydrodemolition work, Consorzio Viadotto Brogeda initially cut off the existing parapet with a diamond saw to expose the decks’ edge beams. Wan-Jet used the Conjet ACR™ robot with built-in automatic quality depth control, then followed on behind selectively removing an approximate 1.5 m high vertical swath of concrete to a depth of about 150 mm. In addition, the robot was also used to cut out the viaduct’s two old 450 mm wide by 300 m deep joints, one 80 m long and the other 50 m, which ran diagonally across the curving viaduct.
In both instances, the original reinforcement was left exposed, undamaged and cleaned by the ACR™ robot’s high-pressure water jet. After Wan-Jet had successfully completed hydrodemolition of the joints and edge beams, Consorzio Viadotto Brogeda returned to link in additional reinforcement prior to casting the new, stronger and heavily reinforced concrete parapet and replacing the joints.
Wan-Jets remotely operated, computer controlled Conjet ACR™ robot relies on a jet of high-pressure water exiting from the special nozzle at supersonic speed, forcing its way into the concretes porous surface. The water creates a hydraulic over pressure in the concrete which break away when the pressure rises above the tensile strength of the concrete. Water at a pressure of 1500 bar and flow of 105 liters/min was fed through a flexible hose to the robot’s nozzle from a high-pressure pump driven by a 333kW diesel engine housed in a silenced 20ft long ISO container.
The nozzle, set at a predetermined angle of attack to the concrete, was mounted on an oscillating cassette. This was attached to a traversing cradle running back and forth along a feed beam which was mounted on the Conjet ACR™ robot’s standard rotating arm. This boom gives the operator considerable flexibility to use the hydrodemolition machine in a wide variety of tasks on horizontal and vertical surfaces, ceilings and soffits.
Wan-Jet also has an optional bridge boom arm which could reach under a bridge deck soffit while the Conjet ACR™ robot stayed on the deck above. When the cradle reached the end of its travel the nozzle swiveled over to maintain the same angle which enables the jet to operate with a sweeping action to cut away concrete behind the reinforcement. At the same time the machine moved back a predetermined distance ready to make the next adjacent cut. The entire nozzle assembly was covered by a protective shroud.
After removing the concrete from the edge beams and joints, Wan-Jet simply replaced the Conjet ACR™ robot’s cassette mounted single nozzle assembly with the optional rotor cutting head to scarify the concrete abutment and the bridge deck.
The hydraulically operated spinning rotor, complete with four nozzles, was set a small distance above the concrete surface before removing a nominal 20 mm of concrete from the viaduct’s deck at about 23 m2/hour. Consorzio Viadotto Brogeda followed on behind bonding a new thin concrete overlay to the deck. The concrete was covered with a 5 mm thick layer of polymer insulation prior to asphalt subbase and base course overlay and final asphalt wearing course topping.
In summary, the versatility of the robot, equipped with different water jetting attachments, was prepared and scarified the concrete deck for a new overlay, cut out concrete to install new joints and removed concrete from the edge beams to expose reinforcement in preparation for casting on wider and stronger concrete parapets. A hydraulically driven spinning rotor head, equipped with four nozzles, was used to scarify the concrete deck, while a standard single oscillating nozzle selectively removed concrete from the bridge joints and beams.
By using the high-tech ACR™ technology, the viaduct could be repaired easily and safely. In addition, the viaduct will last for many years to come thanks to no micro-cracks and a new, strong concrete surface.
MISSION: Repair and strengthening
the double viaduct Ponti Del Valico, Chiasso, Italy
ROBOTS Used: 320-series
Conjet ACR™ robot 557 features 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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