For heavy applications ... the DS-TS/D-LP 30 hydraulic wallsaw.

Historically, the idea of demolition work has brought images of large structures being destroyed using explosives or by a crane swinging a huge iron ball at the end of a chain. The image that demolition has to be noisy, dirty and dangerous is not necessarily the correct one.

Use of industrial diamonds to cut reinforced concrete structures has been prevalent in the construction industry for over 20 years and is widely accepted as a convenient method for demolition works.

As more and more research is done into the performance of diamond products, a greater understanding of the mechanics of the cutting system has developed. The major influences on the life and performance of diamond cutting systems are the type of power unit used to drive the diamond elements, the amount of steel reinforcement and the quality of the stone and sand aggregate in the concrete.

By understanding the influencing factors, manufacturers of diamond tools can modify their product offering to suit local conditions and, in doing so, improve efficiency and effectiveness.

The advantages of using diamond products in demolition are clearly defined below:

  • First and foremost is the ability to have the cutting completed to an exact line. This means that the amount of overcut is minimal and the amount of remedial work required to make good the remaining structure is very low.

  • Secondly, diamond systems are vibration free. The advantage of this is twofold. Firstly the amount of noise generated is greatly reduced. Typically, a diamond wallsaw system such as the Hilti D-LP30/DS-TS30 system only makes approximately 89 dB of noise measured 3 m from the source! The second advantage of being vibration-free is a structural issue. If any sort of mechanical method is used to remove concrete elements, then the continued hammering of the structure can lead to breakage of the bond between the remaining reinforcement and the remaining concrete, thus weakening the structure. Using diamond systems ensures that the structural integrity of the structure remains unchanged. With the lower noise levels and the assurance of structural stability, then continued occupation of the building could be maintained.

  • Diamond systems are very fast. It is possible to cut at a speed of up to 8 sq m of cut area per hour.

  • Finally, it must be remembered that these systems, as well as being very simple to operate due to the high level of electronic control systems built into the units, are also very safe.

    Diamond sawing equipment, which effectively uses a drive unit to power blades up to 1,600 mm diameter, is able to cut concrete up to 730 mm thick. Beyond this depth, diamond wires are used which give the contractor the ability to cut unlimited thicknesses of concrete.

    One such project where diamond saws and wires have been used successfully is on the removal of a bridge at the second junction of Sheikh Zayed Road in Dubai, UAE. This interchange, as well as being one of the busiest in Dubai, also passes over the main Dubai-Abu Dhabi highway. One of the restrictions of the main contractor, NWJ&P, on the completion of this project was that the highway must remain open at all times. This meant a great deal of strategic planning had to be made to allow for the rerouting of traffic during the two-year construction period.

    The use of traditional demolition methods on the existing bridge decks was not a possible, due to the debris that would have been generated. The possibility of it falling down onto the highway below was deemed too high a risk to be considered. Instead, NWJ&P used a specialist sub-contractor, Medi, a Dubai-based firm with over four years of experience in the special field of diamond sawing and explicit experience in demolishing large critical structures under tight deadlines. Medi has had a long and close business relationship with the Hilti Corporation, and the power tools it uses for diamond sawing applications, such as this project, are exclusively Hilti.

    Using a combination of the Hilti D-LP 30 hydraulic power pack and DS-TS 30 sawing head diamond wallsaw and Hilti WSS 30 wiresaw system, the bridge deck was cut into 24 sections. Each section weighed up to 100 tonnes and was lifted by a 400-tonne crane onto a special truck for removal from site.

    Medi undertook pre-engineering studies to ensure that handling and structural stability of the elements were maintained throughout the delicate operation.

    Indeed, the most complicated element to diamond demolition systems is the handling of the structural elements to be demolished. The cutting of the sections is relatively simple. The ability to handle this project was achieved via the flexibility that the D-LP 30/DS-TS 30 system gives, to be both a wallsaw and wiresaw solution to a problem.

    The operation was thus undertaken conforming to all the restrictions laid down by the client.

    In the Gulf region there is a very high concentration of steel reinforcement in concrete structures.

    The use of hydraulically-powered tools such as the D-LP30 and DS-TS 30 is often the only way for this heavy construction to be removed. For lighter applications of up to 28 cm of reinforced concrete, it has now become possible to use electric wallsaw systems such as the Hilti DS-TS-5E, which uses new technology in electrical motors. These allow the possibility of DIY (do-it-yourself) demolition for lightly reinforced structures.

    With the focus on new construction in the Gulf declining in favour of renovating older structures, the use of diamond demolition systems is expected to rise over the coming years. With the experience of projects such as the Sheikh Zayed Road project to call on, companies such as Hilti and Medi are well placed to continue to support the needs of the market.

    Hilti, one of the world's leading companies specialising in the field of fastening and demolition systems in the construction industry, has its regional office in Dubai.