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Demolition Methods
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DEMOLITION METHODS
Details of the various methods utilised in demolition and
dismantling work:
Pneumatic and
Hydraulic Breakers
Often used in concrete demolition projects involving bridge decks,
foundations and pavement, hand-held or boom mounted pneumatic and
hydraulic breakers are currently the tools of choice.
The amount of work accomplished using these methods depends on the
hammer size, strength of the concrete, the amount of steel
reinforcing used in the concrete, and working conditions.
Machine-mounted breakers are able to deliver a range of 100 to
20,000 foot-pounds at 300 to 800 blows per minute. Machine-mounted
breakers may utilize:
- A telescoping boom for easy reach and maneuverability
- Remote control operation
- Underwater demolition capabilities
- Some limitations of machine-mounted breakers include
the generation of noise, dust and vibration.
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Dismantling
By cutting concrete elements, and then removing them by crane, the
demolition of an entire concrete structure may be carried out with
a minimum of noise, dust, and impact on surrounding structures.
This may be done by Sawing, Water-Jetting or Thermic Lance, and is
a particularly good method of demolishing portions of a structure,
especially portions of walls or slabs.
Water-jetting
- Minimizes dust and eliminates dust and fire hazards
- Can be used to cut both straight lines and contours
- Requires the use of an abrasive and water-catching
system during the cutting process
Thermic lance
- Excessive heat causes some deterioration of the
concrete adjacent to the cutting
- Works particularly well in the presence of reinforcing
steel
- Eliminates vibration and dust problems
- May create smoke and fire hazards
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Pressure
Bursting, Mechanical Bursting and Chemical Bursting
Pressure bursting can be used in cases where relatively
quiet, dust-free, controlled demolition is preferred.
Both mechanical and chemical pressure bursting split the concrete,
either with a splitting machine operating on hydraulic pressure
provided by a motor in the case of mechanical bursting, or through
the insertion of an expansive slurry into a pre-determined pattern
of boreholes in the case of chemical bursting.
The split concrete is then easily removed, either by hand or by
crane. Hydraulic and chemical pressure bursting break up concrete
structures with a minimum of noise and flying debris. Both methods
work by applying lateral forces against the inside of holes
drilled into the concrete, and can do virtually any job other
demolition methods are capable of. However, rather than shattering
the concrete into bits as dynamite and impact tools would, the
lateral forces build up over time to crack the concrete into
smaller sections.
Mechanical bursting highlights
- Inexpensive, quiet, no vibration
- Initial drilling of holes for splitter does produce
some noise and vibration
- Diamond-tipped coring machine greatly reduces noise and
vibration during hole drilling, but is much more expensive
- Controlling crack direction and movement of demolished
concrete can be difficult
- Hand-held or machine-mounted breaker may be needed to
expose reinforcing bars for cutting
Chemical bursting highlights
- More costly method of pressure bursting
- Can split concrete in a controlled manner
- In excess of 4300 psi of expansive pressure may
be generated to produce concrete cracking within 10 to 20
hours
- Quiet, no vibration, little or no dust
- Temperature sensitive : freezing greatly reduces
effectiveness
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Explosives
Explosives are generally used for removing large volumes of
concrete via insertion of explosive devices in a series of
boreholes:
- Versatile and flexible in terms of work output
- Vibration and air blast may damage surrounding structures
- Heightened safety considerations involved when compared
to other demolition methods
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Ball
and Crane for Demolishing Masonry and Concrete Structures
One of the oldest and most commonly used methods for building
demolition, the ball and crane uses a wrecking ball weighing up to
13,500 pounds to demolish concrete and masonry structures. During
the process, the ball is either dropped onto or swung into the
structure that is to be demolished.
The ball and crane, however, is not suitable for all demolition
applications. Some limitations:
- While the concrete can be broken into rather small
pieces, additional work in the form of cutting rebar may be
necessary.
- Only highly skilled and experienced crane operators
should be used on ball and crane demolition projects --
smoothness in controlling the swing of the ball is important
since missing the target may tip or overload the crane and a
mild swing-back may cause the ball to hit the boom.
- The size of the building that can be demolished with this
method is limited by crane size and working room, including
proximity to power lines.
- This form of demolition creates a great deal of dust,
vibration and noise.
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Mechanical
Demolition & Dismantling
The intricacy of the demolition process is a function of the size
and complexity of each project. For the times when explosive
demolition is not appropriate, mechanical methods are applied.
Small scale demolition projects involving low-rise structures can
be carried out using ordinary machinery, methods and equipment.
Larger structures and complex projects require more extensive
planning as well as specialised procedures, equipment and
machinery.
When valued assets are present at the demolition site it is
essential to recover these items in order to lessen the cost of
demolition to the client. This often involves careful dismantling
of plant and equipment to recover the assets for reuse by the
client. Alternatively, Amity Contractors will purchase the
entire plant and its equipment and carry out a turnkey project
involving purchase and removal of the plant and equipment and
demolition of the site which leaves the client with a
rehabilitated site.
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