Robotic Equipment in Hydrodemolition

Stefan Hilmersson, Aquajet Systems AB
Special Collaboration

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
The typical high pressure pump range required for concrete hydrodemolition applications is between 1000 bar and 1300 bar. Water flow rates range from 150 l/min up to approximately 400 l/min for heavy concrete removal machines.

Removal capacities in deteriorated concrete is accepted to average 0.4 to 1 m³/h but rates above 1.5 m³/h are possible.
It is possible therefore to evaluate the hydrodemolition capacity in different concrete structures by measuring the concrete strength compared with the fluid-dynamic impact energy directed towards the material to be removed.

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 selection of the robotic working tools is dependent on the task to be solved. Several removal tools are available for horizontal, vertical and overhead work, and work on curved surfaces.

Surface quality
It is proven that hydrodemolition produces an excellent clean surface quality.
With robotic hydrodemolition, once programmed, the jet moves rapidly and continuously over the selected area removing the concrete down to a desired quality level.

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.
In contrast, concrete with hard solid aggregate exhibits a more uneven surface and a high amount of undamaged aggregates.

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.

Hydrodemolition is today used in a wide variety of renovation applications around the world. These include, for example:

Bridges With traffic generalyl increasing in major cities around the world it is becoming necessary to frequently repair highways and bridges. Hydrodemolition is used to remove the deteriorated concrete before new fresh concrete is applied. Apart from bridge decks pillars, abutment walls, parapet beams and, underneath the deck are also much more in need of maintenance and rehabilitation.

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.
During refurbishment of the United States’ fifth largest electricity producer, the Robert Moses Niagara power plant, a total of 32 000 m2 of concrete was removed and replaced in the intakes and abutments. Using Hydrodemolition machines, the contractor removed more than 2800 m2 to a depth of 150 mm where deteriorated parts had to be removed. Some of the abutment work was carried out at heights of 32 m which could only be reached by robotic units.

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