Developing a sustainable construction waste estimation and management system

Construction waste is a major source of urban waste and usually accounts for 10-30% of the total waste disposed of at landfill sites in many cities around the world. As the construction industry is a major user of natural resources, the enormous amount of construction waste imposes great stress on the limited natural resources and places a burden on sustainable development of all the cities in both developed and developing countries and regions. A number of construction waste management policies have been established with the aim of reducing the volume of construction waste and improving its recycling rate. Comparison and analysis of typical waste management policy instruments shows that (1) the emphasis of instruments shifts from the end of construction waste management chain to the beginning of the chain; (2) the instruments tend to internalize the externalities; and (3) more and more economic instruments are introduced to effectively promote sustainable construction waste management. Under the increasing political and financial pressure, construction companies need to adopt more sustainable waste management strategies to reduce the associated costs of waste disposal, especially for those with multiple projects in hand. Efficient construction waste management necessitates a systematic approach with the collaboration of various stakeholders in the construction industry. This study focuses on one of such key issues, construction waste estimation. In order to make improvements on the existing methods, a quantitative construction waste estimation model for building projects is proposed to enhance the estimation accuracy of construction waste at the project level, to predict the quantities of various kinds of construction waste in each period of the whole construction process of a building project and to track the sources of construction waste. In the development of this model, a theoretical material flow analysis of the construction process and the construction waste generation process has been conducted. Specifically, this model integrates the mass balance principle, work breakdown structure, material quantity takeoff, conversion ratios between different waste measurement units and the wastage levels of various materials used in different work packages. Furthermore, a more sophisticated construction waste model is presented by considering the waste generation mechanism of different materials in various kinds of construction processes and waste generation time. The construction processes are categorized into three classes based on the input-output analysis: onsite processing process, material extracting process and element-construction process. These processes are corresponding to terminal work packages in the work breakdown structure of a building. On the basis of material flow analysis of these three kinds of processes, waste generation mechanism is discovered for deriving construction waste estimation from each terminal work package. Project schedules and waste generation distributions are also incorporated to quantify construction waste over the construction period. As a result, construction waste in a specific project is forecasted by type and in total over the construction period more accurately. A web-based construction waste management system was also developed based on the proposed estimation method. This system provides user-friendly interfaces to enter the necessary information and display construction waste estimation graphically. Based on the accurate waste estimation, the suitable waste management method for each construction waste stream can be determined for a specific construction companies, in particular those with multiple projects. Sustainable attributes (including economic, social and environmental attributes) are taken into account to choose the favorite waste management methods with respect to the major construction waste streams. In evaluating these attributes, some of them can be represented by numerical values while others expressed in linguistic variables due to the human being's i ability to assess these complicated attributes. The proposed utility-based linguistic multi-attribute decision making model enables computing with words without loss of information, overcomes the gap between numerical values and linguistic descriptions, employs the utility functions to transform multiple scales of different attributes into a common one for easy comparison and finally chooses the appropriate methods for the major construction waste streams. With the accurate waste estimation and optimizing waste management method, construction companies can extract the maximum benefit or spend the minimum expense under the current local policy framework. At the same time, the government and public should be happy to see the twofold benefits brought by the greatly reduced construction waste: one is the saving of natural resources and the other is reducing the waste disposal.