The Arstein Bridge in the north of Norway was built in the 1940s from reinforced concrete. It is a single carriageway structure with 11 pairs of columns joined at a low level but above water by a crosshead beam. Each column has a diameter of 1.5 m (4.9 ft) below the crosshead beam, tapering to the bridge deck above to a diameter of 1 m (3.3 ft). The concrete and steel of these columns had suffered from extensive degradation, especially around the splash zone.
Specialist UK high pressure water jetting contractor Rentajet Group Ltd (RGL) was appointed by Norwegian main contractor Multibetong to undertake the removal of all growth from around the columns and any damaged concrete below the crosshead beam down to the bed of the fjord, a depth of 16 m (52.5 ft).
To carry out the work, RGL purpose ordered the new Aqua Spine system from Aquajet Systems’ UK distributer, Aquapower Ltd, together with a bespoke 1.5 m (5 ft) diameter pile ring multi-modular frame system with special clamp legs to fix to the column. The goal was to prepare each column for the installation of stainless steel reinforcement to be fixed before reinstatement of a new concrete casing.
Working remotely, from a barge, the operator was able to set the jet angle, number of passes and speed of travel of the hydrodemolition head. The system was set to make a controlled traverse in a complete circle of the column, before ‘auto indexing’ to the next level and continuing until the cycle was completed – i.e. the length of the Aqua Spine at 6 m (19.7 ft). Divers then released the clamps and the frame was lowered by crane to the next level and reclamped. The cycle then continued.
The depth of damaged concrete on the 22 columns ranged between 25-150 mm (1-6 inches) and in total more than 1,500 square metres (16,146 square feet) was successfully treated by the new Aqua Spine system.