The life cycle of concrete structures is usually 40 to 90 years. During this life, structures often meet with some situations like disasters, changing functions, city reconstruction, or higher residence demand due to population, all these lead to demolition or reconstruction of existing structures. In developed countries demolition is very essential for development of new structures for various residential and industrial purposes. Any kind of demolition work needs labor forces for executing the work. Today various kinds of demolition methods are available, but the method of implementation for demolition work varies with the site condition, safety and cost. The demolition method also varies with the time available for demolition and need of site clearance for the new structure.
The word demolition means destruction, breaking down or removal. Demolition of building is the process of dismantling or destroying of a structure after its life of serviceability by pre-planned and controlled methods.As we know that every design of a building or a structure has a lifespan know as design life.
Before execution of demolition work, the careful study of site condition, the type of structure, structural member, demolition range, rural or urban area and frequency. The application of method for demolition depends upon actual site condition and available space. The demolition technology that is practiced to demolish the concrete structures in a controlled way especially in Indian conditions. The important methods practiced in this field are mentioned. Demolition is the deliberate destruction of structures and materials by means of explosives, mechanical devices, fire, chemical agent, etc.
Different steps are involved in the process of demolition of building structures which are:
- Removal of hazardous materials
- Preparation of plan
- Safety measures
- Demolition Methods for Buildings and other Structures
There are two types of demolition methods used for buildings and structures
Non-explosive demolition: A non-explosive demolition / cracking agent is a soundless and safe demolition agent that is quite different from other ordinary demolition agents such as explosives and dangerous materials. It does not cause any fly rock, noise, ground vibration, gas, dust or any other environmental pollution when used properly. As requirements for demolishing rock and reinforced concrete in construction are increasing in tight quarters, the use of explosives and explosive agents is becoming more restricted as far as safety and environmental pollution problems are concerned. Non-explosive demolition / cracking agents are the solution.
Explosive demolition: In the controlled demolition industry, building implosion is the strategic placing of explosive material and timing of its detonation so that a structure collapses on itself in a matter of seconds, minimizing the physical damage to its immediate surroundings. Despite its terminology, building implosion also includes the controlled demolition of other structures, such as bridges, smokestacks, towers, and tunnels. Building implosion (which reduces to seconds a process which could take months or years to achieve by other methods) typically occurs in urban areas and often involves large landmark structures.
Deconstruction: A new approach to demolition is the deconstruction of a building with the goal of minimizing the amount of materials going to landfills. This “green” approach is applied by removing the materials by type material and segregating them for reuse or recycling. With proper planning this approach has resulted in landfill diversion rates that exceed 90% of an entire building and its contents in some cases. It also vastly reduces the CO2 emissions of the removing of a building in comparison to demolition.The development of plant and equipment has allowed for the easier segregation of demolition waste types on site and the reuse within the construction of the replacement building. On-site crushers allow the demolished concrete to be reused as type 1 crushed aggregate either as a piling mat for ground stabilization or as aggregate in the mixing of concrete. Timber waste can be shredded using specialist timber shredders and composted or used to form manufactured timber boards, such as MDF or chipboard. Safety is paramount; a site safety officer is usually assigned to each project to enforce all safety rules and regulations.
Different kind of demolition equipments
Before any demolition activities can take place, there are many steps that must be carried out beforehand, including performing asbestos abatement, removing hazardous or regulated materials, obtaining necessary permits, submitting necessary notifications, disconnecting utilities, rodent baiting and the development of site-specific safety and work plans.
Hydraulic excavators may be used to topple one- or two-story buildings by an undermining process. The strategy is to undermine the building while controlling the manner and direction in which it falls. The demolition project manager/ supervisor will determine where undermining is necessary so that a building is pulled in the desired manner and direction. The walls are typically undermined at a building’s base, but this is not always the case if the building design dictates otherwise. Safety and cleanup considerations are also taken into account in determining how the building is undermined and ultimately demolished.
In some cases a crane with a wrecking ball is used to demolish the structure down to a certain manageable height. At that point undermining takes place as described above. However crane mounted demolition balls are rarely used within demolition due to the uncontrollable nature of the swinging ball and the safety implications associated.
High reach demolition excavators are more often used for tall buildings where explosive demolition is not appropriate or possible. Excavators with shear attachments are typically used to dismantle steel structural elements. Hydraulic hammers are often used for concrete structures and concrete processing attachments are used to crush concrete to a manageable size, and to remove reinforcing steel. For tall concrete buildings, where neither explosive or high reach demolition with an excavator is safe or practical, the “inside-out” method is used, whereby remotely operated mini-excavators demolish the building from the inside, whilst maintaining the outer walls of the building as a scaffolding, as each floor is demolished.
To control dust, fire hoses are used to maintain a wet demolition. Hoses may be held by workers, secured in fixed location, or attached to lifts to gain elevation.
Loaders or bulldozers may also be used to demolish a building. They are typically equipped with “rakes” (thick pieces of steel that could be an I-beam or tube) that are used to ram building walls. Skid loaders and loaders will also be used to take materials out and sort steel.
To demolish bridges, hoe rams are typically used to remove the concrete road deck and piers, while hydraulic shears are used to remove the bridge’s structural steel.
Non, explosive demolition
Some common type are:
Articulated Trucks- An articulated truck is a vehicle with a joint that allows for sharp turning. They accelerate hauling because they are fast and maneuverable.
Backhoe Loaders- Basic workhorse machine that allows for multiple attachments. Short reach machines. Can work in moderately small areas.
Hydraulic Excavators- They provide for longer reach and power. A step up from the backhoe. Can use multiple attachments.
Material Handlers- The primary purpose of these machines is to take dismantled material and load them on trucks for removal.
Multi Terrain Loaders- Small loaders that can work on various terrains. Very compact for small areas. Can use multiple attachments, but the most common is a bucket.
Skid Steer Loaders- Very versatile small loaders. Very compact for small areas. Can use multiple attachments, but the most common is a bucket.
Track Loaders- Powerful machines used for raising and lifting. Commonly used with a bucket.
Track-Type Tractors- The most powerful types of machines used for raising and lifting. Commonly used with a bucket.
Wheel Loaders- Great for hauling and loading scrap and debris.
The technique of Vérinage is used in France to weaken and buckle the supports of central floors promoting the collapse of the top part of a building onto the bottom resulting in a rapid, symmetrical, collapse.
The Japanese company Kajima Construction has developed a new method of demolishing buildings which involves using computer-controlled hydraulic jacks to support the bottom floor as the supporting columns are removed. The floor is lowered and this process is repeated for each floor. This technique is safer and more environmentally friendly, and is useful in areas of high population density.
Construction activities and demolition activities are like sightseeing for a tourism industry. Both are going hand in hand. Whereas construction is due to the rebuilding of old structures or new structures, demolition is growing due to old structures needs replacement with time and growing needs of the society. All such activities are generating the huge amount of waste, called the Construction and Demolition waste. Disposal of such debris in a safe environment is a big challenge for the builders, developers, and owners. When on one hand the disposal of debris is a challenge, then, on the other hand, there is an acute shortage of naturally available aggregates for the construction of buildings. Reduction of this demand is possible only with the reusing or recycling of waste generated from the construction activities.
Globally, building waste production of 2 to 3 billion tonnes per year is estimated, of which 30-40 % is concrete . C&D waste issues are more important for the developing countries, which are entering or already entered in construction boom era. According to the annual report of Dubai municipality’s Waste Management Department, a total of 27.7 million tonnes of construction waste were removed from various construction sites in the city in 2007, recording growth of 163 % in comparison to the waste generated in 2006, just 10.5 million tonnes. In their study, Vilas and Guilber to found that many countries in Asia do not have specific regulations designed for C&D wastes, although some countries include some sections in their solid waste management regulations and/or related policies. According to the study, developed countries generate 500 to 1000 kg per capita per year building & construction waste and waste in European Countries is estimated to be 175 million tonnes/year. It was also mentioned that very small percentage of waste from construction industry is reused or recycled, the majority being deposited or used as landfill. Like other developing countries, India is also enjoying construction boom. With the rapid growth in construction activities of India it is appropriate to link the generation of C&D waste with the growth of construction industry and related issues. It is also essential to study C&D waste generation and handling to develop accurate data and establish sustainable methods to manage construction waste.
Over the world, the growth of construction industry is enormous in the past decade. The pace of generation of C&D waste is also significant. In general, there are two sources for generation of waste materials, namely, bulk generators and retail or small generators. The classification of sources is given in The infrastructure development sector and real estate sector are the bulk generators of waste. Construction and repair of roads, bridges, flyovers etc. are classified under infrastructure development sector. Real estate sector consists of housing, industrial, and commercial building construction, demolition of unauthorized structures etc. Small commercial enterprises and individual house building teams are considered as retail or small generators. The project activities are to be planned at every stage by every personnel, who are involved, to minimize the overall waste generation.
India produces 25-30 million tons of Construction, Demolition and Excavation waste material annually. The traditional practice in India is to dispose of this waste in landfills or illegally dump in rivers and water bodies. Faced with growing environmental concerns and lack of landfill space. As per the Central Public Health & Environmental Engineering Organization (CPHEEO), the Indian Real Estate Industry alone is facing a shortage of aggregates to the extent of 55,000 million cum. An additional, 750 million cum of aggregates would be required to achieve the targets of road construction sector, which will lead to tremendous pressure on natural resources.
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