Towards a closed material cycle in the infrastructure

Abstract

The construction industry is a large generator of waste. The interest in improving the resource efficiency is growing. A move towards a Circular Economy (CE) has been assigned as the solution for a more efficient use of resources in the construction industry. The aim of a circular economy is to create a system in which waste and energy leakage is minimised and resource input is avoided by closing the material and energy loops. Despite the advantages of CE, the construction industry has not yet made a significant step towards
the CE. The theory of Reverse Logistics (RL) could be the enabler of circular economy in the construction industry. RL in the construction sector is defined as the management of collecting, sorting, processing and reusing construction waste. In the field of RL, quantitative models have proven to be a successful tool to combine environmental goals with financial constraints. However, such models are missing in the field of construction industry. In this context, this research proposed a general applicable RL-model that supports decision-makers in implementing circular principles in the return flow of their assets while minimising the costs.
Literature review has been conducted to obtain a theoretical framework for the model design. The first part of the literature study has provided a framework to prioritise different waste management strategies based on their level of circularity. The second part of the literature study has been conducted to get an insight in the characteristics of the reverse logistics in the infrastructure and how the principles of circular economy can be included in the RL-process.
The most suitable modelling approach for the proposed problem has been found to be linear programming.
The proposed RL-model has been designed as a transhipment model and is based on mixed integer linear programming (MILP). The proposed model design simulates the reverse flow of one asset moving from a deconstruction project, through the processing facilities to the final redistribution. The proposed model has been complemented by a guideline that supports the application of the model for specific cases.
To test the applicability of the model and the proposed guideline, the model has been applied on two different types of assets in the infrastructure: concrete and street lights.
The model for both cases have been run for multiple scenarios, based on the developments in the industry. The results of the model provides two types of information. Firstly, it provides a trade-off between the level of circularity and the costs. Secondly, it gives the corresponding network-design for the different outcomes. It was found that technical innovations in combination with efficient transportation will help to create return flow in the infrastructure, according to the principles of circular economy, which is financially feasible.
Overall the model has been proven to be general applicable and it supports decision-makers in making decisions about the reverse flow. The outcome gives information about the financial impact on implementing circular principles. The corresponding RL-network provides an insight in which aspects in the RL-process influences the outcome.