When permissioned blockchain meets IoT oracles: An on-chain quality assurance system for off-shore modular construction manufacture

Advanced information technologies such as the In-ternet of Things (IoT) and Modular Construction (MC) bring new potentials to the construction industry. The trustworthiness is critical for MC quality assurance (QA), particularly in the off-shore manufacture stage. The emerging blockchain technology which enables transparent, traceable, and immutable information exchange in distributed systems opens a new avenue for managing off-shore MC. However, the real-time data collection and update, as well as permitted data access are two critical concerns in utilizing blockchain for MC. The permissioned blockchain and IoT is considered as feasible solutions. Thus, this paper presents a three-tier architecture of permissioned blockchain with IoT oracles: the infrastructure layer, platform layer, and service layer. IoT devices in the infrastructure layer act as oracles of the blockchain, feeding real-world data from MC components promptly on time through trusted APIs. A permissioned blockchain network in the platform layer provides authentication functions to ensure authorized access to QA-related channels. A mobile-based application named e-InStar in the service layer provides user-friendly UI for multi-stakeholders to access the QA system named e-inspection 2.0. The three-tier architecture design can thus respond to the data access and data updating needs for MC QA, specifically for multi-stakeholders cooperation requirements. An application case of a housing project validated the permissioned blockchain in the e-Inspection 2.0 system in two aspects: (1) system transparency and security, and (2) users' satisfaction with data collection and QA functions.