Robotic Equipment in Hydrodemolition
Hydrodemolition is the selective removal of concrete using high-pressure water, selectively removing deteriorated concrete and retaining sound concrete below the intended level of removal. This process will not damage rebar or cause micro cracks in the concrete, as will mechanical methods such as jackhammers.
Over the years the hydrodemolition process and equipment has developed. Today the robotic units are capable of performing vertically, horizontally, and overhead as standard units. A variety of attachments are available allowing removal from the underside of bridge decks, columns, and parapet beams to name a few.
The high-pressure water is delivered to the robot through a flexible high-pressure hose. The water travels down a lance where it meets a nozzle. The nozzle orifice is sized according to pressure and flow requirements of the pump. The lance manipulates the jet of water as it leaves the nozzle. It will either oscillate or rotate the water jet nozzle depending on the type of application.
Hydrodemolition leaves the surface that has been cut with a jagged or craggy surface (profile) much like that of an English muffin that has been separated with a fork rather than with a knife.
Concrete suppliers have commented on the great bonding area left by hydrodemolition. Jackhammers, for example, tend to leave a flatter surface which result in fewer peaks and valleys providing a reduced bonding surface.
On concrete, the water jets accomplish their destructive action by means of different processes such as direct impact, pressurization of micro- and macro-cracks and cavitations. These processes reach their maximum efficiency when the water jets strike the bonding agent. The water jet is therefore moved rapidly and continuously over the area to be removed.
However, jet efficiency is only maximized when the jet itself is stable, and stability is influenced by distance from the nozzle to surface, shape and configuration of the nozzle that accelerates the water exit speed, jet movement and the angle of attach.
The high pressure jet of water passes across the surface, penetrating into the weak concrete. When the water “washes away”, it takes the damaged concrete with it; only removing concrete down to a preset “quality depth” and leaving a good rough bonding surface for the new concrete.
To meet the requirements of the European Union’s EN 1504 standard for the repair of concrete structures – pull off strength of 2.0 MPa for structural and 1.5 MPa for non structural structures – the old concrete must be removed using hydrodemolition techniques.
Techniques and tools
Removal capacities in deteriorated concrete is accepted to average 0.4 to 1 m³/h but rates above 1.5 m³/h are possible.
The dynamic combination of the pump pressure and the delivered water flow from the high pressure plunger pump, through the specially designed orifice nozzle, will generate a reaction force by the working tool. Reaction forces up to 3000 N can be achieved at certain pressures and flow.
Automatic robots are used for precise hydrodemolition. The robot can use rotating multiple nozzle carriers but single nozzle heads are generally used on machines for selective removal. They will however, work with much higher water flow rates.
Complete hydrodemolition units comprise a high pressure pump, driving engine and control system housed in the acoustically treated container and a hydrodemolition robot with a series of standard tools.
Computerised control plays a key role in the performance quality and design of hydrodemolition equipment, allowing the machines to carry out repetitive tasks automatically.
All movement parameters are fully adjustable from the control panel. Which can also be remote.
The surface geometry achieved after hydrodemolition also depends on the type and size of the aggregate with soft aggregates such as limestone, for example, has a comparatively smoother surface.
Compared with other removal methods, hydrodemolition generates a very large contact surface between the concrete and applied repair material.
Hydrodemolition is generally used to describe the process of using high-velocity water jets to remove or demolish concrete. Hydrodemolition is particularly effective as a restoration tool to remove deteriorated, delaminated or contaminated concrete.
A surface prepared using hydrodemolition provides the best possible bond for all types of repair material. The aggregate protruding from the existing surface provides excellent shear resistance across the bond line.
Parking garages Many parking garages were constructed many years ago .The wearing on have been affected by water and salt dripping from cars, air pollution and mechanical wear from cars driving in and out. Necessary renovation projects using hydrodemolition are ongoing throughout Europe.
Harbors and dry docks These are also able to take advantage of hydrodemolition techniques for rehabilitation of concrete and steel reinforcement, with extensive chloride deterioration, caused by the sea water salt penetrating the concrete. Large harbor and dry dock renovation projects around the world are ongoing projects where robotic hydrodemolition systems selectively removes deteriorated concrete from high vertical walls and below sea level as well as horizontal surrounding areas.
New concrete Hydrodemolition is also used on new concrete. During the erection of large engineered constructions it is sometimes necessary to remove some of the newly cast concrete. As an example the Storebaelt Bridge, in Danemark, it was necessary to remove and replace a large amount of concrete on one of the pylons. Air pockets in the newly cast concrete caused problems to depths of 300 - 500 mm requiring the heavy and narrow sitting rebars to be cleaned. Hydrodemolition was used to remove some 500 m3 successfully to the required depths in the limited time period.
The power and nuclear industries are also taking advantage of the hydrodemolition technique for concrete removal and repair.
A recent application in Spain required an opening to remove the steam generators. The concrete wall around the generator hall was 1400 mm thick and reinforced with eight layers of heavy 53 mm bars reinforcement. The total reinforcement density was 500 kg/m3 of concrete. Hydrodemolition was selected as the most efficient and safest method available.
Two robots for vertical operation equipped with heavy high-pressure pumps were used to complete the application.
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