CONJET CHECKS IN AT HEATHROW

2004-08-10 — A Conjet Robot 322 hydrodemolition machine, on hire from Doornbos Rental UK in Southampton, has been playing a key role removing damaged concrete in the first phase of a major structural renovation of Heathrow Airport’s central area Car Park 1A/B. Contractor Taylor Woodrow Corrosion Engineering & Concrete Repairs, is using the Doornbos Rental Conjet Robot 322 to remove decaying concrete from the decks and soffits of the multi-storey car park as part of its £8M concrete repair and refurbishment contract for client BAA/Heathrow Airport Ltd.

The six-storey car park was built in the 1960s to provide parking for up to 1900 cars in the main central area of the very busy airport. But de-icing salts, brought into the car park and deposited when vehicles are parking, combined with water leaking through the deck joints, has since caused extensive chloride decay, which has led to cracking and spalling of the concrete floors. Some localised patch repairs have been done over the past 20 years, but it is now necessary for BAA to carry out a major refurbishment to extend the life of the car park and improve its general appearance.

Part of the major three-year renovation requires removal and replacement of all the defective concrete, including all previous repairs, using, in the first phase, the Swedish specialist Conjet Robot 322 high-pressure water-jetting machine. Up to one fifth of the total deck area of the car park has to be removed to a target depth of 50mm from the reinforced concrete floors, which in many places is just 152mm thick.

Taylor Woodrow’s and its client BAA’s commitment to health and safety, along with an extremely tight program, resulted in the consideration of hydrodemolition techniques over the more traditional methods.

“The remotely operated Conjet Robot 322 is technically very good, as it preferentially finds and removes defective concrete,” says Taylor Woodrow construction manager Dave Cullen. “This is my first experience of hydrodemolition with the Conjet Robot, which does an excellent job taking out only the damaged concrete above and below the reinforcement. It leaves a rough, clean, uneven textured surface to give a good key for the repairs, and does not cause micro-cracking in the surrounding parent concrete. It also leaves all the reinforcement intact and cleaned of any rust. This is an added bonus as conventional pneumatic breakers can damage the reinforcement and undermine the bond between the reinforcement and surrounding concrete.

The use of hydrodemolition also eliminates the risk of the operatives suffering from hand arm vibration syndrome, commonly referred to as vibration white finger, which is caused by the operation of percussive breakers and drills. Currently about 30,000 new cases are reported each year in the UK and as hydrodemolition completely eliminates this risk these removal techniques have got to be beneficial. Specifically, the Conjet Robot has distinct safety advantages over the other hand lance hydrodemolition methods. Reaction forces are contained by the self weight of the Robot, while the cowl over the cutting head prevents any debris from affecting the Conjet operator, or other persons in the area.”
Using a high pressure water jetting track mounted Conjet Robot to selectively remove the damaged concrete also has other major benefits for the operatives and local environment as the water totally removes the risk of generating any dust. “The Robot completely eliminates dust during breakout operations,” adds Dave Cullen. “Dust is an irritant and a nuisance and prolonged exposure to concrete dust has the potential to cause silicosis.”

The water used in the hydrodemolition gets contaminated with suspended concrete particles and Taylor Woodrow devised a system to manage the contaminated water working above live floors of the car park. “Managing the waste water, which can be raised from pH7 to pH10, proved a major challenge,” says Dave Cullen. “The final scheme diverted the existing car park drainage system into a central collection point, with a series of settlement tanks on the ground floor. Testing was undertaken on the water after settlement, and permission granted from the Environment Agency to discharge the particulate free, raised pH water into the existing storm water drain. Originally, plans were in place to treat the waste water to reduce the pH, but with the volumes and durations involved, approval was given based on the fact that the high pH water is diluted in a series of balancing ponds with the entire run off from the car parks, roads and runways at the airport. Further testing undertaken at the point of discharge, from the balancing ponds, into the public water course confirmed that no further treatment is needed.”

After removal of defective concrete and repair, an impressed current cathodic protection system will be installed to prevent further corrosion of the reinforcement steel, new expansion joints constructed, and a waterproof coating applied to the deck surfaces, in order to give a new lease of life to the ageing car park.

For further information please contact:

Lars-Göran Nilsson or Carl Strömdahl

Conjet AB
P.O. Box 507
S-136 25 Haninge
Sweden.

Tel: +46-8-556 522 40
Fax: +46-8- 556 522 60
E-mail: conjet@conjet.se
Internet: www.conjet.com

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