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Perth is one of the world's smaller capitals but dumps over 500,000 tonnes of construction waste a year. It is impossible to avoid some degree of waste in the construction process. All estimators allow for waste factors when pricing a bill of quantities. Unless site management has tight control of all activities, waste can exceed by a large margin than the figure allowed for in the tender document. Today, keeping control of materials is more difficult, except where the main contractor still buys materials in bulk. If control procedures are in place, financial benefit can be obtained and excessive wastage can be avoided.
Recent studies have shown that about 10% of construction waste is generated from the cutting of building materials during the construction process. If designers could consider dimensions to match the material size standards at the design stage, cutting wastes can be significantly reduced. Another design concept is the use of alternative forms of design to minimise the need for temporary works for example, prefabrication. A recent study showed timber formwork contributes to about 30% of the waste identified on site.
Take off and specification waste is the waste that is formed at the beginning or before the beginning of the construction process. It usually starts with the incorrect taking off of materials in order to start the construction process. Suppliers, the contractor or the subcontractor contribute to this waste. At a point when excess material is delivered to site, more waste is generated. If too little material is delivered, waste can be created by a delay to the contract.
Delivery waste is the waste formed during transport of materials. It involves poor packaging and careless handling of materials and, miscommunication with suppliers. Delivery waste in the construction phase comes about from a number of areas. The main areas relating to delivery waste are the problems of incorrect specifications given to suppliers and when amendments have been made, suppliers are not informed or notified. This causes inconveniences of time, costs and labour. Another issue with delivery waste is the transport of damaged items due to poor packing and careless handling of materials.
Site waste is the wastage formed on site during the construction process. It is almost always in the hands of the main contractor and his subcontractors. Wastage on site is mainly due to poor storage and control of materials, faulty conversion ratios, careless use of materials, failure to protect goods after installation and, working to inaccurate dimensions causing for example over excavation and excess use of concrete.
This looks at ways in which waste can be reduced. The best way to manage waste is to avoid it in the first place. This involves reducing the generation of waste by looking at ways in which waste can be reduced and reused. Studies have shown that the generation of waste can be reduced drastically by the use of pre-casting system formworks. The cleanliness of a site also determines the amount of wastage produced. Clean sites usually produce less waste as they are more organised and this decreases the chances of damage to materials and goods. This also allows for reuse and recycle of materials. (Hariop).
Waste management plans can assist in reducing waste as they identify specific wastes and the amounts to be targeted for reduction, reuse and recycling. Including timelines in the waste management plans also identifies when specific waste will be generated during the construction process for example packaging waste from interior finishing. (hariop). By prior planning, waste prevention goals for specific materials can be established as well as arrangements for its storage, reuse, transportation and disposal. Construction sites should be clean and well organised to avoid damage and loss of materials. (Hariop).
Recycling is an alternative to waste disposal. Reaserch shows 60-90% of construction materials can be recycled. The use of recyclable materials such as concrete can be used in the construction of roads. In Australia, the process of converting concrete waste into road construction material is well established. Standard specification clauses were developed by roads authorities for recycled concrete and cement-treated recycled crushed concrete for sub-base pavement applications. This has opened the way for the use of recycled crushed concrete on major highway construction and increased use for local roads. Annually, about 350000 tonnes of recycled crushed concrete is produced in Victoria alone. This concrete can be used for non structural applications. According to AS2758.1-1985: concrete aggregates, concrete needs to contain three elements which are, cement, sand, aggregate. With appropriate aggregate properties and grading, recycled concrete aggregate (RCA) can successfully replace coarse natural aggregates, either in part or whole, for the production of plain and reinforced concrete for non-structural applications