In today's world, despite improved construction practices, a large amount of construction waste is being generated, requiring significant planning and continuous management. Inadequate disposal and mishandling of generated construction waste led to serious issues, such as massive land space utilization, environmental pollution, continued depletion of finite resources, added cost, additional time, poor recycling, and re-use practices, thus making the overall situation challenging to manage effectively. Moreover, inert construction waste (ICW), as a dominant fraction of construction waste, generally ended up going to landfills without significant value recovery, which causes a severe threat to global sustainability.

Applying reverse logistics (RL) concepts to address construction waste p...[ Read more ]

In today's world, despite improved construction practices, a large amount of construction waste is being generated, requiring significant planning and continuous management. Inadequate disposal and mishandling of generated construction waste led to serious issues, such as massive land space utilization, environmental pollution, continued depletion of finite resources, added cost, additional time, poor recycling, and re-use practices, thus making the overall situation challenging to manage effectively. Moreover, inert construction waste (ICW), as a dominant fraction of construction waste, generally ended up going to landfills without significant value recovery, which causes a severe threat to global sustainability.

Applying reverse logistics (RL) concepts to address construction waste problems is a promising topic nowadays. The RL concepts contribute significantly towards improving the overall sustainability by promoting material recovery practices. Consequently, it eases the additional pressure on landfills by sending less waste and offers other key benefits such as improved environmental performance, better economic situations, resource conservation, re-use, and recycling of waste materials. However, due to the multitude of complex processes and stages involved in managing ICW, the overall management of RL becomes a complex network problem, and its visualization for effective planning is undeniably a difficult task. Consequently, achieving the RL network's improved performance is questionable and a matter of concern for stakeholders. To address this issue, the research thesis aimed at providing the effective reverse logistics management of ICW material by delivering three quantifiable research objectives.

The first objective develops a unique lean thinking-based multi-layer value stream assessment (MVSA) approach deriving from a conventional value stream mapping (VSM) technique to assess the overall RL network of ICW management. RL network design entails facility-based and non-facility-based processes, with four different value streams, i.e., time, cost, environmental quality, and process efficiency. A case study of Hong Kong demonstrates the developed MVSA approach. The case study features an assessment of the RL network's current and future states, considering multiple scenarios. Furthermore, a detailed sensitivity analysis is conducted to provide valuable insights and discussions. An agenda for the continuous improvement related to the proposed MVSA approach is expounded using the famous PDCA approach. The research findings verify that the proposed MVSA approach can significantly contribute to the overall process improvement, better visualization, and RL network assessment, leading to effective construction waste management.

The second objective develops a multi-stage network-based model to minimize the overall cost for the reverse logistics management of ICW across its entire life cycle. This model takes a unique two-type costing approach to overcome the ambiguities and deficiencies existing in the previous models. Type-I cost refers to facility-based costing (FBC), and Type-II cost refers to non-facility-based costing (NFBC). The mixed-integer linear programming technique is applied using the LINGO software. A case study of construction waste management in Hong Kong is conducted to validate the developed model, which includes waste generation point as the starting node, public fill reception facility and recycling facility as an intermediate node, and landfill as an ending node. The result shows about a 24% reduction in the total cost compared to the base case. Furthermore, a detailed scenario-based sensitivity analysis is presented to evaluate the impact of uncertainties on the cost parameters. The optimal result shows that a larger portion of the total cost comes from the NFBC component. Therefore, NFBC is critical in defining the overall reverse logistics network and thus, should be given more emphasis in designing an effective construction waste management system.

The third objective blends the traditional queuing theory into the design of the RL network by providing a queuing system assessment and impact reduction (QueSAIR) approach for ICW management. The network consists of four types of facilities: waste generation, waste collection, waste recycling, and waste disposal. The scope of the queuing system assessment encompasses both time-based KPIs and other adverse queuing effects. To boost the approach's applicability, simulation models were developed for different facilities in the queuing system of the RL network. Later, simulation results are validated against the analytical results, and it is found that all the developed models are employed efficiently. In addition to this, three crucial scenarios for the queuing impact reduction are considered, i.e., enhancement in the service rates, distribution of truck arrival patterns, and improvement in the capacity utilization. A comprehensive case study based on the Hong Kong ICW scenario provides an in-depth analysis and insights to substantiate the research findings. Conclusively, the proposed approach can significantly improve the overall management of waste collection and transportation activities by considerably reducing the queuing delays and their negative impacts within the RLN of ICW.