Large amounts of construction waste are produced annually in Switzerland. The volume of 11 million tons in 1997 are likely to increase in the future because of the increasing requirements of accommodation space per capita and the decreasing availability of construction land, leading to demolition of old buildings. In 1997 the overall recycling rate of construction waste in Switzerland was quite high (82%), ranging from 67% in the Canton of Basle City to 87% in the Canton of Valais. Reused mineral construction materials from buildings are usually down-cycled and used as uncompounded foundation layers. That is, in Switzerland recycling is not equally accepted nor applied in all regions. These emergent phenomena are mostly related to decisions made at the level of the individual system agents. It is considered that parameters such as acceptance, risk perception, lack of experience with alternative materials or lack of trust on recommendations have an important influence on reducing demand for recycling material. Furthermore, the main agents affecting the demand for recycling construction materials, i.e., contractors, architects, engineers and the awarding authorities, are likely to have different ways to impact the system. However, so far, it has not been analyzed what the decision-making trees of these agents are, how their decisions interact, and how they cumulatively affect the demand for recycling materials.

Together with the division 'Social and Industrial Ecology' at the University of Zürich a master thesis has been started to analyse the decision structure of the important system agents and to simulate the process with agent based modeling (ABM). ABM allows for generating results concerning present and future demands based on agents´ decision trees. This study aims at building a specific decision tree regarding the utilization of recycling materials for each agent group. Each decision in these trees is based on various internal (e.g., required accommodation space or personal experience) and external (e.g., material prizes or norms and laws) parameters. Decisions are modeled based on probabilities, e.g., a higher demand for recycling materials occurs if these materials are recommended by the Canton; a lower demand results from a lacking competitiveness against virgin materials. The interaction between the agents finally leads to a specific demand for recycling materials. Changes in the internal and external parameters are modeled in form of scenarios providing different input values. The decision trees are developed in semi-structured expert interviews and calibrated against the agents´ behavior analyzed in structured interviews from a larger sample. Several scenarios for recycling of construction materials will be presented and the effects of planned policies regarding the demand for recycling materials discussed.

The result of this master thesis is an integrative part of a Ph.D. project "Demand and supply of the mineral fraction of construction materials: A modeling tool to support decision-making processes" that is conduced jointly at the division 'Social and Industrial Ecology' at the University of Zürich (supervised by Prof. Dr. Claudia Binder) and the Technology and Society Laboratory (H.-J. Althaus).

Keywords: Agent based modeling, decision-making process, recycling mineral construction material, recourse management.

Contact: Christof Knoeri

    
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