# Leveraging Blockchain Usage to Enhance Slag Exchange
## 2 Background
### Blockchain Applications  
Blockchain technology [13] is the key enabler for the solution proposed in this paper, where parties with opposing interests must interact over common data. It shines at maintaining an agreed state in all the participants of the network [14]. This state is composed by data structures called blocks. Each block groups a series of transactions sent and signed by individual users and contains a hash of the previously mined block. This structure ensures data integrity, as any change to a past block alters the hash in the latest block. New blocks are added via a consensus algorithm agreed by all participants. Peers usually contain a copy of all the blocks previously agreed. Some networks also allow transactions to include program deployments or calls, known as smart contracts, which are verified by the same consensus mechanism.  
Thanks to the decentralization of the state (i.e., any party can locally access to it without relying on other participants), its immutable nature and to the fact that it is signed by the sender, blockchain and traceability are often seen as a perfect match [15; 16; 17; 18]. [PERSON] et al. [19] examine how blockchain technology has been applied to boost circular economy.  
[PERSON] and [PERSON] [20] analyze the benefits obtained thanks to blockchain in different phases of commodity trading and how it affects different markets. This study highlights how a fairer price can be achieved and can reduce price-setting threats. Unlike more mature markets, the slag market lacks established IT systems to help in its exchange, so blockchain and the solution we propose could fill this need.  
However, the cement generated with the slag is consumed by the construction industry, and many authors have explored how to use blockchain in this sector. [PERSON] et al. [21] describes the different approaches in which the construction industry could benefit from using blockchain. Some of the relevant applications it analyzes are supply chain management, asset management, construction management, building maintenance or waste management. Our solution sits at the beginning of the supply chain and helps to certify the origins of the cement [22].  
[PERSON] et al. [23] provide a comprehensive description of various auction applications that leverage blockchain networks. Using this survey as a reference, we can position our work in comparison to others. When it comes to the application domain, energy auctions are the most popular ones, and as a consequence have been thoroughly discussed in other reviews [24; 25; 26]. To the best of our knowledge, this is the first proposal that takes advantage of blockchain-based auctions to promote the circularity of by-products. As indicated by these reviews, setting up auction schemes requires a thoughtful analysis of several market-specific factors. These factors include the needs and preferences of those participating in the auction, the existing rules and standards, and the unique features of the market. The auction scheme we present in this paper is secure, transparent, and efficient, and it considers these factors specifically for the steel slag market.  
In addition to auctions, there are other ways in which blockchain technology has been utilized to improve the circular economy. A recent bibliometric analysis [27] provides insights on these applications. They primarily focus on conventional applications such as asset traceability in the supply chain applied to waste management. It is worth noting that the solution proposed in this paper can be extended to be used in the following steps of the supply chain too. For instance, an eco-cement produced with slag could be backed up with the trustworthy provenance information which comes from our blockchain-based solution. Similarly, when this cement was used in a construction site, one could track the origins of the building back to the slag.