Blockchain-Enabled Provenance Tracking for Sustainable Material Reuse in Construction Supply Chains +
Footnote †: This paper is an extended version of our paper published in IEEE 19 th International Conference on e-Science (e-Science), Tracking Material Reuse across Construction Supply Chains, Limassol, Cyprus, 9-13 October 2023. The Ellen MacArthur Foundation [4] is one of the non-profit organisations that promotes the principles of the circular economy (CE). They have introduced the idea of a \"material passport\" (MP) to promote the traceability of products within a circular supply chain. An MP is a document that tracks a product's journey from the extraction of raw materials to the end of its life. It helps to share information across the supply chain in a timely manner. The MP contains comprehensive information about the composition of a product, its location, and its impact on the environment. Many industry projects have realised the potential of the MP and implemented it in their projects, such as Madaster [5], ORMS [6], and Buildings As Material Banks (BAMB) [7]. The use of MPs can help in tracking materials/products in the entire construction supply chain and identifying their origins. Having more details about construction materials can lead to more efficient and less wasteful building construction processes. Furthermore, MPs can also be utilised to dispose of materials properly once they are no longer useful. Although MPs have proven to be beneficial in the construction sector, there still remain limitations to achieving the desired sustainability outcomes. One of the significant challenges in generating MPs is the absence of unified approaches or standards. This lack of standardisation results in the use of different terminologies and processes in MPs, which reduces their usefulness for other partners in the construction industry. Additionally, the construction supply chain involves multiple stakeholders who manage a product at various stages of the process, which makes it challenging to always keep the MP updated throughout the life cycle of the product. There are also challenges associated with confidentiality while sharing business information in MPs. In this context, we will explain how MPs can be used while mitigating the impact of these limitations. Blockchain technology offers a promising solution for improving provenance tracking in the construction industry. Its decentralised approach eliminates the need for a central authority, resulting in a transparent and collaborative environment in which all stakeholders can access information. The immutability of a blockchain ensures that once a record is entered, it cannot be changed, resulting in a tamper-proof history of materials. This fosters trust and reliability. Smart contracts also automate and enforce transaction terms, making it easier to exchange information securely. By utilising these features, blockchain technology provides a high level of detail and accountability in provenance tracking. This is critical for certifying the quality, safety, and sustainability of repurposed materials. This not only supports environmental goals but also promotes the CE by extending the lifespan of resources. Our contributions are as follows:  
1. We propose a novel framework that uses a multilayer blockchain to improve data retrieval and provenance tracking, allowing for a reliable audit trail for material reuse. 2. We propose a privacy-centric storage solution that combines the InterPlanetary File System (IPFS) with backend servers, balancing decentralisation and robust data management to secure sensitive information while maintaining transparency in material provenance. 3. The framework implements efficient access controls, strengthens security and privacy, and promotes transparency and information sharing among stakeholders, all of which are vital for trusted material reuse in construction supply chains. This paper is an extended version of the work published in [8].