In order to minimise the amount of natural resources being used and the energy involved in manufacturing these materials, a cautious approach to the disposal of C&D waste needs to considered. Reusing materials prevents the use of embodied energy. This is the energy that goes into the production and manufacturing of a new product. Reducing the amount of energy required in manufacturing, producing and transporting new products leads to a reduction in damage to the environment. The figure below shows a system which could be implemented in order to limit the number of materials being disposed of on construction sites.
There are a number of challenges which face deconstruction including (1) tools needed for deconstruction do not always exist; (2) disposal costs of C&D waste is relatively low; (3) deconstruction takes up more time than conventional demolition; (4) building and design codes do not always cover the reuse of building materials; (5) buildings are not designed to be dismantled; (6) the environmental and economic advantages of deconstruction are not recognized.
Along with imposing waste taxes, the Netherlands also implemented bans on sending recyclable and combustible waste to the landfill. This came into operation in 1997. This included separated C&D waste. The reason for this ban was to limit the amount of waste going to landfills which is seen as the least favoured method of disposal. The responsibility for implementing the ban lies with the landfill operators who are inspected regularly by the government’s waste management agency, SenterNovern. The introduction of the ban in the Netherlands proved to be a success in cutting down the amount of C&D waste sent to landfill. In 2009, 97% of C&D waste in the Netherlands is recovered. (defra.gov.uk)
The first step in dismantling a building is to check to see if the building contains any hazardous substances. One of the main hazardous wastes which cause concern in Ireland is asbestos. This is a natural mineral which is used in many buildings for fire proofing or thermal insulation. The danger with asbestos is that if it breaks up, the fibres which make up asbestos may then be inhaled into the lungs as dust. This increases the risk of lung cancer and causes lung tissue scarring. Under EU legislation it is no longer allowable to re-use asbestos or to even buy products containing asbestos in Ireland. This means that asbestos cannot be recycled; it must be disposed of after it has been removed from the building. (citizensinformation.ie)
This is the demolition technique where a heavy cast iron or steel ball is used to knock a building. The ball usually weighs between 500 to 5000kg. The balling technique can be used to demolish concrete, reinforced conrete and masonry. It has become less popular due to the level of disturbance which arises on site including vibrations, noise and dust.The ball can come into contact with the building in two ways (1) free fall (2) swinging. In the free fall process the demolition ball is lifted up into the air by a large magnet and then it is dropped onto the building which is to be demolished. In the swinging process the demolition ball is attached to a steel line which is attached to a machine with a rotating frame.
There are two types of breakers used in demolition (1) pneumatic (2) hydraulic. The difference between the two is pneumatic breakers are run using compressed air while hydraulic breakers use compressed oil. These type of breakers are used on concrete, brickwork and stone. Both types of breakers are mainly associated with minor demolition works, however they can also be attached to excavators for major demolition works.
Thermal cutting is used to cut steel and iron. Cutting torches are used for this process. There are three types of cutting torches (1) fuel/oxygen (2) powder (3) plasma. The fuel/oxygen cutting torches are run on a combination of oxegen and fuels such as natural gas, propane and acetylene which cuts at a maximum temperature of 3200 degrees Celsius. The choice of the fuel depends on the thickness of the metal.
Explosives can be used in the demolition of buildings. Explosives can be set of using a wide variety of detonators which allows different detonation speeds. Explosions can be set off immediately or can be delayed by milliseconds if required. By blasting certain components of the building before others, it will allow the collapse of the structure to be carried out in a controlled manner. Even though this may help in accurately collapsing the building, there are still numerous examples of demolitions that have gone wrong when explosives have been used. This is why a large area must be cordoned off around the demolition site before blasting takes place.
Immediately after a structure has been demolished it is transported a treatment plant where crushing and separating takes place. This enables new materials to be produced. The C&D waste must go through a number of processes before it is recycled. It must get sieved, pre crushed to prevent the lager materials from damaging the main crusher and all material such as steel, glass, plastics and timber must be removed manually, by air separation or by washing. The materials must then be sieved at the end of the process in order to get the requied sizing for the new material.
