An Aquajet HVD6000 hydrodemolition robot is currently being used for rehabilitation work onthe Medway Bridge project in Kent, UK.
The new M2 road bridge across the River Medway is situated at the western end of a 17km-long motorway widening project on the A2/M2 route between London and the Kent coast.
A new four-lane bridge is being built to carry west bound (London bound) traffic over the river. The new structure is located between the existing Medway Bridge and the new Channel Tunnel Rail Link crossing.
While the new bridge is being constructed the old bridge is being modified for use of coast bound (east bound) traffic.
The bridges form part of an upgrading project of the M2 motorway, which has been deemed necessary because of expected traffic volume increase over the next decade.
The UK's Highways Agency awarded the £124mil. road widening project to the CSM Joint Venture, which comprises Costain, Skanska and Mowlem.
The 17km-long project was awarded to the joint venture in November 1999 and is scheduled for completion in 2003.
The entire project involves widening the route to four-lanes in each direction, which will be achieved by constructing a new bridge for London bound traffic alongside the existing bridge, and then modifying the original motorway bridge for coast bound traffic.
UK-based Rentajet - a specialised hydrodemolition company – has been sub-contracted to aid rehabilitation and bridge strengthening of the old Medway crossing.
Using its Aquacutter HVD6000 hydrodemolition robot from Aquajet Systems AB, the contract requires that sections of the old concrete bridge deck be removed so that new rebars can be inserted. This work is necessary according to the Highways Agency to allow the old structure to cope with heavier traffic volumes and larger trucks.
The old bridge deck is being strengthened at intervals close to its abutments, which are located near to the bridge access roads.
The Aquacutter HVD6000 is removing concrete to a depth of 300mm with each section 300mm wide by approximately 15m-long. The robot not only removes the old concrete deck in these designated sections but also cleans the rebars of any debris and rust.
Rentajet says that it is removing three identical sections on either end of the old bridge. As the deck is 300mm thick in these areas, a gantry has been set-up underneath the bridge to collect debris from the hydrodemolition operation.
Being supplied with 227litres of water per minute by a Woma 550hp high-pressure pump, the Aquacutter is advancing 1m every 15 minutes.
Another section close to the western end of the old bridge is also to be removed to allow for new rebar insertion. Measuring 500mm x 500mm, the Aquacutter robot will aid removal of this section by cutting around its perimeter, while a crane lifts the section out in one piece.
According to John Ward, Rentajet's on-site foreman, the Aquacutter was chosen for this project because of its speed and reliability. “We could do this work with hand lances but that would be more time consuming and need more manpower,” he says. “With the Aquacutter we just need one operator.”
Previously, the Aquacutter robot was used for removing sections of the old bridge's central parapet, which previously divided east bound traffic from west bound. The robot removed concrete to depths varying from 200mm to a maximum of 450mm – close to abutments, with two lengths of 160m completed in five weeks.
For more information visit Aquajet's website http://www.aquajet.se