UK Contractor Makes Significant Savings on Underwater Bridge Columns Contract in Norway

UK contractor Rentajet Group (RGL) employed hydrodemolition techniques during underwater surface preparation on a bridge project in Northern Norway; ensuring significant cost savings and improved safety by eliminating the need for divers or other operatives, to be in the work areas whilst material was being removed. As no jackhammers were used, the quality of bridge repair was also improved.

Specialist high pressure water jetting contractor Rentajet Group Ltd (RGL) has taken delivery of a purpose-built Aqua Spine system from Aquajet Systems for a bridge contract in Northern Norway - requiring surface preparation work on the bridge columns using hydrodemolition techniques.

Constructed in the 1940’s, the columns of the Arstein Bridge in Northern Norway had suffered excessive degradation of the concrete and steel reinforcement, particularly in the splash zone.

The concrete-constructed, single carriageway bridge includes 11 pairs of columns. Each pair of columns is joined at a low level, but above water, by a crosshead beam.

Below the beam, the columns are 1500 mm in diameter and, 1000 mm above the beam to the underside of the bridge deck.

The Norwegian contractor Multibetong appointed RGL to undertake the specified removal of all growth from around the columns, and any damaged concrete below the crosshead beam down to the Fjord bed level, a depth of approximately 16 m.

The columns were prepared ready for stainless steel reinforcement to be fixed prior to reinstatement of a new concrete case.

The depth of damaged concrete ranged between 25-150 mm and in total more than 1500 m² was treated.

Hampshire, UK-based, RGL, purpose ordered the new Aqua Spine system from Aquajet Systems UK distributor, Aquapower Ltd, together with a bespoke 1500 mm pile ring multi-modular frame system with special clamp legs to fix to the column.

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.
Divers then released the clamps, and the frame was lowered by crane to the next level and reclamped. The cycle then continued.

Jeremy Twigg, RGL’s commercial director, confirmed that, had the company employed divers for the underwater preparation work, it would have taken 10 times longer.

Supplied with a Power and Control Unit, it features Aquajet’s patented Intelligent Sensing Control (ISC). An advanced sensing system, it features no electronics, such as sensors or cables, exposed to the moisture environs – resulting in a more efficient production with fewer stops due to problems with, for example, sensors.

“We particularly liked the Aqua Spine’s wireless controller and ISC sensorless control,” commented Jeremy Twigg. “It greatly helped towards ensuring continuous reliability in the harsh environment at Arstein; working in deep water and temperatures below 4ºC.

“We have found the Aqua Spine to be the ideal solution both to the project requirements and to the tight schedule. It certainly allowed us to reduce the planned timeframe,” said Mr. Twigg.

Between 50-250 mm of concrete per pass was removed depending on the condition of the concrete, with only damaged concrete being removed. On average each column was completed in 2-3 days.

The depth of the fjord was 16 m which meant as work progressed, underwater checks were carried out both by divers on hand and through underwater camera surveillance to ensure that an even finish was achieved across each column.
The project ran for a total of three months with all 22 columns being completed.

Aqua Spine is a modular Hydrodemolition system for work on surfaces that previously had been inaccessible for the Aqua Cutter robots, such as very high constructions or difficult locations requiring equipment to be accessed through, for example, manholes. It can be extensively used on offshore or onshore construction projects including hydro and nuclear power plants.

The Aqua Spine system can be positioned directly on the concrete surface by anchor bolts or supported by a carrier such as hydraulic platforms, sky lifts, cranes or scaffolding. Two interchangeable rail systems are integral with the system’s design – Dual or Triple.

For more confined areas, or when it is necessary to fix several accessible attachment points to the rail, the Dual rail is preferred.

The Triple rail system is used for longer free spans of up to 6 m between supports and it can be operated horizontally or vertically, as well as free standing.

As a modular system, Aqua Spine can be tailor-assembled for each task with all sub-components fitting together. The system is suited for tough environments and features surface-treated welded steel to ensure an extended lifespan. Any of the Aqua Cutter power heads can be selected for the systems frames. Additional power heads are also available for confined spaces. The Aqua Spine can also be powered and controlled by any type of Aqua Cutter robot.

The traverse beam is supported on the frame by a heavy duty carrier operating on the Spine rail by four V-shaped roller wheels. It can be rotated ±180° for better access in both ends.

Hydrodemolition works by pressurizing and widening existing pores and micro cracks in a concrete structure using high-pressure water penetration.

The rate of removal is dependent on the amount of water directed towards the concrete surface, and consequently the area and depth of removal can be closely controlled. Using a high pressure water jet also makes it easy for the operator to work around obstructions; particularly when compared with, for example, conventional jackhammer or hand lance methods.

With hydrodemolition, once programmed the jet moves rapidly and continuously over the selected area for removal.
There is no percussive effect on the surface, with the water jet penetrating the deteriorated concrete, and there is no modification of the concrete microstructure or pore structure.

Apart from very effective cleaning there is also no effect on the rebar.

Source: Aquajet AB

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