## 3 Challenges and Applicability of Blockchain and Smart Contracts in AEC  
Despite the omnipresence of the blockchain topic and the fast-growing number of articles about the use of smart contracts in the construction context, there is a lack of implementation and easy-to-integrate solutions. Several researchers have also referred to the need for validation and empirical analysis of the applicability regarding the proposed theoretical approaches [2; 3; 20]. [PERSON] et al. [5] reviewed 21 papers from 2019 to 2020 on blockchain applications in the construction industry. However, less than half of the reviewed papers (38%) discussed technological components that allow for interaction with blockchain applications. It emphasized the skepticism about the usability and readiness of the industry for the adoption of blockchain solutions. Indeed, many issues will need to be addressed before the new technology can be integrated into daily business and reach its full potential. [PERSON] et al. [2] analyzed the current state of DLT in the construction sector and presented, beyond the opportunities, an extensive list of identified challenges that concern various social, political, or technical issues. The concept at hand addresses many of these obstacles and tries to propose an adequate solution. The main idea of the proposed BIMcontracts framework is a gradual and coordinated process of integrating new technologies and organizational changes while considering the current conditions of the construction industry. Some authors emphasized the resistance to change and the unreadiness of the industry for the adoption of blockchain-based solutions [2; 3]. However, even if the digitization level is not high enough to take full advantage of them [2], certain digital technologies, processes, and standards have already been established. The research should now use that stage as a springboard for striking concepts that inspire new possibilities. This may help to create new long-term incentives for solving the typical AEC problems with the quicker sharing of information, trust, and collaboration [2]. Clear communication of the benefits--such as faster accounting, quality, control, transparency, and reduced risk of human error through automation--to the target audience is enormously important. The early involvement of experts from the practical field (general contractors, subcontractors, construction law specialists) in the concept phase of BIMcontracts ensures that feasibility and acceptance are checked at an early stage. To increase acceptance, the solution has to be integrated into the existing systems that people in the AEC industry are familiar with. Many SMEs may not have the resources to invest in new IT infrastructures or new software. Usability, cost issues, complexity, and a lack of skills and know-how are frequently mentioned barriers [2; 3; 6]. The proposed concept considers a smart contract as a service ecosystem using an API-based approach; it supports the conclusion and execution of the contract and provides pre-programmed and construction-compliant smart contract templates that are easy to configure. The use-case-specific template with all necessary inputs will be deployed on the blockchain. The final users of the system should adjust the desired settings and provide all necessary inputs for the automatic generation and deployment of smart contracts on the blockchain. In this way, neither the coding of smart contracts nor DLT skills are required. Data protection and data security are other important issues for blockchain applications [2]. To ensure these, this concept proposes the storage of all of the sensitive and important information in off-chain storage. Only secure resources, such as a CDE, that meet all requirements for data storage should be used. For the data stored in a CDE, a hash value is saved within the smart contract as the immutable checksum of the file. The privacy of the data stored on-chain is secured by the private consortium blockchain GoQuorum, which also improves the scalability and performance.