Linking permissioned blockchain to Internet of Things (IoT)-BIM platform for off-site
production management in modular construction
Liupengfei Wu 1, Weisheng Lu 2*, Fan Xue 3, Xiao Li4, Rui Zhao5, Maohong Tang6
This is the peer-reviewed post-print version of the paper:
Wu, L., Lu, W., Xue, F., Li, X., Zhao, R., & Tang, M. (2022). Linking permissioned
blockchain to Internet of Things (IoT)-BIM platform for off-site production
management in modular construction. Computers in Industry, 135, 103573. Doi:
10.1016/j.compind.2021.103573
The final version of this paper is available at https://doi.org/10.1016/j.compind.2021.103573
The use of this file must follow the Creative Commons Attribution Non-Commercial No
Derivatives License, as required by Elsevier’s policy.
Highlights
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A novel blockchain-enabled IoT-BIM platform (BIBP).

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The business process of off-site production in modular construction is reviewed for
designing BIBP.

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A novel three-layer system architecture of BIBP.

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The prototype for BIBP was proven for avoiding a single point of failure in IoT
networks.

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The prototype for BIBP was proven for ensuring the provenance of BIM
modifications.

1

Ph.D. student, Department of Real Estate and Construction Management, The University of Hong Kong,

Hong Kong SAR. Email: liupengfeiwu@connect.hku.hk,
2

Professor, Department of Real Estate and Construction Management, The University of Hong Kong,

Hong Kong SAR. Email: wilsonlu@hku.hk,
3

ORCiD: 0000-0003-4674-0357; *: Corresponding author

Assistant Professor, Department of Real Estate and Construction Management, The University of Hong

Kong, Hong Kong SAR. Email: xuef@hku.hk,
4

ORCiD: 0000-0003-2217-3693;

Postdoctoral Fellow, Department of Real Estate and Construction Management, The University of Hong

Kong, Hong Kong SAR. Email: xl1991@hku.hk,
5

ORCiD: 0000-0001-9702-4153;

Research Assistant, Department of Real Estate and Construction Management, The University of Hong

Kong, Hong Kong SAR. Email: ruizhao@hku.hk,
6

ORCiD: 0000-0002-3768-9142;

ORCiD: 0000-0003-1993-3129;

Research Assistant, Department of Real Estate and Construction Management, The University of Hong

Kong, Hong Kong SAR. Email: maohongt@hku.hk,

ORCiD: 0000-0002-0540-7315;

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Abstract
Traditionally, construction managers were considered more experienced in project
management than off-site production management, although the latter is gaining importance
with the renaissance of modular construction worldwide. Various Internet of Things (IoT)enabled Building Information Modelling (BIM) platforms have been developed to facilitate
production management by providing better information visibility, traceability, and a more
collaborative working environment. Nevertheless, by and large, existing platforms suffer
from two shortcomings: (a) the ‘single point of failure’ problem of IoT networks and (b) how
to guarantee the provenance of BIM modifications from multi-sources. This research aims to
develop a blockchain-enabled IoT-BIM platform (BIBP) for off-site production management
in modular construction (OPM-MC) that can overcome the shortcomings. A design science
research method is adopted to develop a three-layer BIBP system architecture. The system
architecture is implemented and then compared with the existing IoT-enabled BIM platform.
It was found that BIBP can avoid a single point of failure in IoT networks and ensure the
provenance of BIM modifications with reduced storage costs in OPM-MC. The system
architecture developed in our study can help the industry advance beyond the rhetoric to
develop practical blockchain-enabled IoT-BIM applications. Future works are recommended
to fine-tune the platform and test and evaluate it in various scenarios.
Keywords: Blockchain, Internet of Things, BIM, Off-site Production Management, Modular
Construction

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1. Introduction
Modular construction (MC) is a procurement innovation that is fostered from the
globalization of construction logistics and supply chain (CLSC). It allows a construction
project, traditionally cast in-situ on a congested site, to be designed in one place and
manufactured/produced building “modules” in an off-site factory and transporting them to a
construction site for installation (Darko et al., 2020). Widely propagated benefits of adopting
MC include enhanced cost-effectiveness, productivity (Wuni and Shen, 2020), quality of
works (Deng et al., 2017), site safety, sustainability, and reduced construction period and
wastage (Lu et al., 2018).

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Nevertheless, MC also results in several new non-trivial challenges. Firstly, it is the quality
assurance and material authenticity in off-site production. This is particularly onerous as now
the production is taking place in a remote, off-site place with many embedded trades.
Stakeholders raised concerns about the nonappearance of systematic records of inspection
and operations (Li et al., 2021a) or the ones that may suffer input errors, document loss, and
even tampering (Zhong et al., 2020). Secondly, it is the fragmented CLSC. The high level of
off-site production in an MC project involves various stakeholders with diversified
backgrounds, including clients, designers, engineers, suppliers, manufacturers, transporters,
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contractors, and sub-contractors (Luo et al., 2019). To this end, a high level of coordination
and collaboration is much desired. However, it should be noted that many MC projects
involve numerous stakeholders who store, retrieve and manage information on their own
isolated systems (Li et al., 2019). In Hong Kong, the issue of CLSC fragmentation is
amplified when the production work of MC has been completely shifted to the Great Bay
Area of Mainland China. These issues hamper higher levels of trust, which is further
execrated by the travel restrictions of dispatching authorized persons as inspectors due to
COVID-19 outbreaks around the globe.

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Scholars and practitioners have been enthusiastic in developing platforms for off-site
production management in modular construction (OPM-MC) primarily by adopting Building
Information Modeling (BIM) and the Internet of Things (IoT) (Li et al., 2016; Zhong et al.,
2017; Xu et al., 2018; Zhou et al., 2021). These IoT-BIM platforms are designed to collect
near real-time data to enhance visualization and traceability. Construction stakeholders can
then supervise the progress and accumulated costs in practices such as OPM-MC. However,
centralized IoT-BIM platforms may bring a “single point of failure (SPOF)” problem. Here a
SPOF refers to one component of a system that, if it fails, will make the entire system unable
to perform its primary functions (ISO, 2020). For example, noisy and malicious data
produced by IoT sensors would affect the trustworthiness of IoT networks (Lu et al., 2021a).
It further compromises the integrity of the IoT-BIM platforms. Another example is to modify
BIM without providing provenance. The designer may change the window size from 750 mm
x 1400 mm to 1400 mm x 1400 mm without notifying all participants, resulting in rework
and additional costs. The current IoT-BIM platforms cannot ensure the single point of truth of
any modification in BIM (Das et al., 2021). Thus, it leaves room for manipulations of BIM
models without traceability (Xue and Lu, 2020). Together, these issues restrain the
performance of IoT-BIM platforms for OPM-MC.

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Blockchain, used most broadly to record bitcoin and other cryptocurrency transactions, has
been actively investigated for its various potentials in construction (Wang et al., 2020; Lu et
al., 2021b; Li et al., 2021a). A blockchain refers to a distributed database with cryptography
and decentralized consensus mechanisms (Kuhle et al., 2021). Lately, blockchain has also
been proposed for IoT and BIM to establish trust in distributed IoT networks (Reyna et al.,
2018; Li et al., 2021b) and record the history of BIM changes (Zheng et al., 2019; Xue and
Lu, 2020). Theoretically, integrating blockchain with IoT and BIM can eliminate the pain
points of the IoT-BIM platforms mentioned above. Nevertheless, configuring a blockchainenabled IoT-BIM platform (BIBP) for OPM-MC is still in the conceptual stage rather than a
developed system. At the current stage, there is a lack of an effective system architecture that
uses blockchain to prevent a SPOF of the IoT networks and ensure a single point of truth of
BIM modifications.

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Thus, this research aims to develop a spanking-new BIBP for OPM-MC. The specific
objectives of this research are to: (1) define the objectives of the proposed platform; (2)
propose a system architecture of the BIBP based on the defined objectives; (3) substantiate
the proposed system architecture by implementing a prototype and evaluate its performance
by comparing with existing centralized IoT-BIM platforms. The remainder of this paper is
organized as follows. Section 2 introduces the related works of BIM, IoT, blockchain, and
their integrations. Section 3 reviews the current business process of OPM-MC. Section 4
presents the research methodology. Section 5 gives the details of the BIBP system
architecture. Section 6 shows the developed platform and evaluates its performance. Section
7 offers our discussion, and Section 8 concludes this research.

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2. Background

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2.1 Building Information Modeling (BIM)

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In recent years, the introduction of BIM has been perceived as one of the critical
developments in industrialized construction. BIM is a nomenclatural term employed to refer
to a series of technologies and associated works utilized to describe and manage information
used and produced for the process of designing, constructing, and operating buildings (Xue et
al., 2021). The taxonomy of BIM information differentiates geometric, semantic, and
topological types (Xue and Lu 2020). Open BIM supports the definition of the above
information, and the Industry Foundation Class (IFC) (an open BIM standard) is usually used
for data exchange for BIM interoperability.

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BIM has been widely adopted in MC in various stages of a project lifecycle, including
feasibility study (Li et al., 2020), design (Alwisy et al., 2019), production (Li et al., 2019),
transportation (Bortolini et al., 2019), installation (Zhang et al., 2016), and maintenance
(Wang and Piao, 2019). However, rare works contribute to BIM security, e.g., BIM
modification audit and provenance (Zheng et al., 2019). For instance, the design of modular
products in BIM may be modified due to budget or client requirements. The modification of
BIM information is usually updated rather than keeping revision history. Even if the
modification records are stored, it is difficult to guarantee the integrity of historical
information (Xue and Lu, 2020). In addition, the modification records rely on complete trust
in the central operator. Once the internal operators misbehave, the tampered information will
lead to production rework and even legal proceedings. In short, the main challenge is the lack
of an effective way to safely track BIM changes (Das et al., 2021). Therefore, this research
aims to link the blockchain with BIM to track off-site production information in modular
construction.

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2.2 Internet of Things (IoT) and IoT-enabled BIM
IoT can provide accurate and timely information collection (Trappey et al., 2017).
Practitioners and scholars have suggested many core components of the IoT, such as RFID
(Radio Frequency Identification) tags, NFC (Near Field Communication) tags, and GPS
sensors to help realize its concept (Zheng et al., 2018). Besides, Niu et al. (2016) proposed
smart construction objects (SCOs), an IoT model with sensing, processing, and
communication capabilities, to facilitate the information exchange among construction
resources.

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To fully achieve the potential of BIM in MC projects requires accurate information
collection, timely information exchange, and automatic decision support throughout the
project life cycle. Thus, several researchers have developed IoT-enabled BIM platforms for
construction safety management (Xu et al., 2018), construction logistics and supply chain
management (Zhong et al., 2017), on-site assembly services (Li et al., 2016; Zhou et al.,
2021), and facility management (Hu et al., 2016). Tang et al. (2019) summarized five IoT and
BIM integration methods: (1) employing the Application Program Interfaces (APIs) of BIM
tools’ and relational databases; (2) adopting novel data schema to reconstruct BIM data; (3)
formulating novel query language; (4) applying semantic web technologies; and (5) adopting
a hybrid approach. However, integrating the IoT and BIM cannot guarantee information
security (Lu et al., 2021a). For example, the IoT may provide noisy or malicious data to BIM,
thereby reducing the trustworthiness of the IoT-enabled BIM platforms. Thus, this study aims
to use blockchain to avoid a SPOF in IoT networks.

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2.3 Blockchain

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Three essential components keep the functioning of a blockchain: cryptography, distributed
ledgers, and a consensus mechanism (Xue and Lu et al., 2020). Cryptography (e.g., hashing
algorithms) embodies the principles and methods for transforming data to hide their semantic
content, restrict their unauthorized use or prevent undetected modification (ISO, 2020).
Distributed ledgers involve an accounting technique to record when anything of value is
transacted. These ledgers are shared and synchronized among users using a decentralized
consensus mechanism (Li et al., 2021a). Consensus mechanisms are procedures used to reach
an agreement on the order and correctness of data (ISO, 2020). Besides, blockchains can be
configured with smart contracts. Smart contracts are digital contracts that can self-execute
processes when preset conditions are satisfied (Kuhle et al., 2021). Some studies classify
blockchain platforms as permissioned or permissionless based on whether platforms provide
access control on their network. Users are pre-authorized to use a permissioned blockchain
platform, such as Hyperledger Fabric.

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Only a few studies have explored blockchain in OPM-MC. Cao et al. (2019) demonstrated a
blockchain-based system to improve the transparency of information between steel
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production companies and buyers. Li et al. (2021a) proposed a two-layer blockchain-based
model to supervise off-site production in modular construction and protect the privacy of
participants. Wang et al. (2020) designed a blockchain-based framework to improve the
information sharing of off-site production, transportation, and on-site assembly in precast
construction. It is observed that more studies are focused on the use of blockchain to enhance
the traceability of the construction supply chain (e.g., Zhang et al., 2016; Zhong et al., 2020)
and the overall management of information (Sheng et al., 2020; Lu et al., 2021b). However,
the benefits of using blockchain in OPM-MC cannot be cultivated with an incomplete,
inaccurate, and untimely data exchange and lack of real-time visibility (Lee et al., 2021). To
deal with these challenges, this study aims to link blockchain with IoT-BIM platform for
OPM-MC.

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2.4 The Integration of Blockchain, IoT, and BIM

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Recently, researchers have been studied the integration of blockchain and BIM or the
integration of blockchain and IoT separately. For example, Xue and Lu (2020) developed a
semantic differential transaction (SDT) approach to lessening information redundancy for
blockchain and BIM integration. Zheng et al. (2019) proposed a blockchain-based model
called “bcBIM” for BIM modification audit and provenance. Additionally, several studies
have found that integrating blockchain and IoT can help immerse trust into IoT-oriented data
sources and secure IoT networks (Reyna et al., 2018; Li et al., 2021b). Therefore, previous
studies have shown that blockchain has great potential to avoid a SPOF in the IoT networks
and ensure the provenance of BIM modifications, which are the two main challenges of the
current IoT-BIM platforms. Lee et al. (2021) proposed an integrated IoT-BIM and blockchain
framework to support accountable information sharing in construction. Nonetheless, the
integration of blockchain and IoT-BIM is still in its infancy.

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The research gaps identified can be summarized as follows. Firstly, there is a lack of system
architecture to guide the integration of BIM, IoT, and blockchain for specific OPM-MC
functions. Secondly, the integrated blockchain-enabled IoT-BIM has not been compared with
the current centralized IoT-BIM platform for evaluation. Thus, this research aims to define
the objectives of the BIBP for OPM-MC; propose a system architecture of the BIBP based on
the defined objectives; substantiate the proposed system architecture, and evaluate its
performance.

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3. Off-site Production in Modular Construction
The OPM-MC business process generally contains production preparation, production, and
inspection. The scope of the OPM-MC process has been identified as follows: (1) this process
begins when the contractor’s project manager signs the contract to confirm production; (2)
the inputs are the production plan and the design drawings; (3) this process ends when project
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manager confirms the delivery order; and (4) the outputs are the qualified modules. As shown
in Figure 1(a), the main contractor works with the manufacturer and designer to propose a
production plan after placing an order. After confirming the design drawings, the
manufacturer’s design department formulates detailed shop drawings. The project client and
the contractor need to approve shop drawings when these drawings are ready. After approval,
the manufacturer can develop a master production plan. Then, a bill of materials will be
formed according to the production execution plan. Next, the manufacturer’s procurement
department will order materials such as 2D panels from suppliers. The supplied materials will
only be utilized after passing inspections and tests. Materials that pass the inspections will be
sent to the factory, and then the production department will start production.

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Figure 1. The business process of off-site production in modular construction: (a) production
preparation; (b) production and inspection (Adapted from Li et al., (2021a))

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Figure 1(b) shows that the standard module is produced through the following five main
procedures: structure, door/window, wall, paint, electrical and mechanical services, and
testing and commission. Workers need to apply additional wet trades to bathroom modules.
For example, they need to add waterproof layers and conduct flood tests. Various inspection
and testing means are employed to ensure quality control and assurance at each checkpoint,
as shown in Figure 1(b). For example, check the thickness of the fireproof coating on the
structural members at the structure stage, and check the dimensions of the windows at the
door/window stage.

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Several existing information security problems have been observed when applying IoTenabled BIM platforms in the current business process of OPM-MC. Firstly, the noise data
generated by IoT sensors reduces the data quality of BIM and further affects the
trustworthiness of the IoT-BIM platform. For instance, the erroneous production status
generated by IoT sensors is reflected in BIM, causing
decision-makers to make inappropriate decisions in the subsequent transportation preparation

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stage. Secondly, there is a lack of an effective method to ensure the provenance of BIM

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modifications. For instance, BIM has been modified in multiple versions due to design change

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requirements, so the manufacturer had to spend considerable time asking each stakeholder and

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its departments to provide signatures to confirm that the current version they hold is the “right

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version”.

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4. Research Methodology
In this study, the design science research (DSR) approach was adopted to develop a BIBP
system architecture for OPM-MC. DSR, as a scientific knowledge production philosophy,
seeks to develop innovative constructs to solve real-world problems and simultaneously make
prescriptive scientific solutions (Peffers et al., 2007). Our study used four steps, as shown in
Figure 2. In the first step, to define the objectives of the BIBP system architecture, the
research team visited a prefabrication factory for module production in Foshan, Mainland
China, between February and March 2021, understanding the challenges of the existing IoTBIM platform from the employees. Then, the research team analyzed the knowledge obtained
from the site visits in two research workshops in April 2021. In the second step, the research
team brainstormed in four meetings in May 2021, synthesizing the knowledge obtained from
the literature and defined objectives. This process was non-linear and required multiple
iterations to develop a promising solution (some solutions are feasible but not the most
promising) for which the system architecture was developed.

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Figure 2. Research methodology

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The third step involved a two-phase development of the prototype system. In the first phase,
the options of IoT plan and application development language were firstly compared and
selected with justifications. RFID has been widely used for production management due to its
bright advantages. Through numerous studies (e.g., Poon et al., 2009), RFID has been proven
to facilitate data collection and information sharing in production control efficiently. In
addition, it can react quickly and flexibly to the dynamic environment of the production chain
(Zhong et al., 2015). Compared to other IoT options (e.g., NFC and GPS), RFID technology
adoption with component-level tagging, from the research conducted by Bottani and Rizzi
(2008), shows that positive revenues for all production stakeholders could be achieved. Thus,
passive RFID is adopted as the IoT plan in this study. JavaScript was selected to develop
applications as it reduces the time required by other programming languages like Java for
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compilation (Sheikh, 2016). Its structure is simple for the research team to implement the
prototype, and it provides various standard components to create user interfaces.

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Additionally, blockchain type, development platform, open blockchain BIM standard
extension method, and consensus mechanism were selected to implement the system
architecture. Among blockchain types (permissioned and permissionless), permissioned
blockchains can provide functions such as authorization and identification audit, meeting
business cooperation demands (Lu et al., 2021b). The permissioned blockchain was selected
as OPM-MC includes numerous stakeholders, and only approved parties can participate in
the network. Next, from among three popular permissioned blockchain platforms, namely R3
Corda, Neo, and Hyperledger Fabric (Lu et al., 2021b), Hyperledger Fabric was adopted as
the development platform because it provides developers with numerous security-enhanced
alternatives and resources due to its maturity (Li et al., 2021a). The SDT method developed
by Xue and Lu (2020) was chosen to extend the open blockchain BIM standard IFC. SDT
provides a higher IFC compression ratio (e.g., 791.2 for modular room) to minimize
information redundancy compared to existing solutions. In addition, it offers rapid IFC
restoration from the chain (complete ifcJSON restoration at 200MB/s). Then, the crash fault
tolerance (CFT) consensus was chosen. Compared with open consensuses such as proof of
work and proof of stake, CFT can avoid network partitions and is relatively fast compared to
Byzantine fault tolerance (Hyperledger Fabric, 2020).

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In the second phase, BIBP was implemented according to the designed system architecture.
Initially, RFID tags are affixed on material packages, prefabricated components, and
prefabricated modules to monitor the process states of OPM-MC. The user interfaces were
developed to allow input and inquiry production-related operations. Besides, the IFC standard
(ISO 16739-1:2018) was extended by appending a set of properties to the BIM family of the
precast components. In addition, the SDT method was introduced to compute the version
changes of the BIM over time. Next, the blockchain BIM system was implemented on
Hyperledger Fabric (version 1.4), and smart contracts were written through JavaScript. The
development environment was in Linux 5.4.0-58-generic-lpae (5.4.0-58.64~18.04.1) (Ubuntu
18.04.1 LTS), and the back-end was implemented using SpringBoot (version 2.4.0) allowing
the research team to quickly develop a database management system MySQL. The genesis
block of the blockchain BIM system was configured to initialize the CFT consensus
mechanism.

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In the four step, the developed BIBP was tested in the mock-up production phase of a
modular construction project. The evaluation was done through a comparative analysis
between BIBP and the existing IoT-BIM platform. In previous studies (e.g., Farzan et al.,
2008), comparative analysis has been used to test the effectiveness of various information

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systems before fine-tuning and further development. The evaluation results were
disseminated to audiences in manufacturing and modular construction.

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5. Architecture Design of the Blockchain-enabled IoT-BIM Platform
This section describes the architectural structure of the proposed BIBP platform. Section 5.1
illustrates the overall platform development objectives. Section 5.2 offers an overview of the
platform. The key components of BIBP are categorized into three dimensions, i.e.,
Infrastructure as a Service (IaaS), Blockchain BIM as a Service (BaaS), and Software as a
Service (SaaS), on data, information, and knowledge aspects, respectively. Section 5.2.1
describes the core components of the IaaS. Section. 5.2.2 introduces the BaaS structure and
interfaces. The SaaS Process Management and Quality Assurance (PM/QA) applications are
shown in Section 5.2.3.

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5.1 Platform Development Objectives
Based on the knowledge obtained from site visits and research workshops, the objectives of
the proposed system architecture are defined as follows: (i) it should reinforce the
authenticity of the information collected from RFID; (ii) it should record BIM modifications
with provenance; (iii) it should provide a foundation for practitioners to develop high-level
APIs. APIs developed based on the system architecture should be able to integrate with the
existing software in construction.

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5.2 Overall System Architecture of the Platform
The platform takes advantage of the XaaS (Anything as a Service) paradigm to bridge the
OPM-MC practices and the demands of multiple stakeholders. The whole architecture of
BIBP can be divided into three layers from the reality to the OPM-MC demands, as shown in
Figure 3(a). The first IaaS layer includes IoT module and user interfaces. The second BaaS
layer includes functionality structure to interoperate the information, semantics, and
meaningful inferences with existing ERP systems. The third SaaS layer meets the demands of
multiple stakeholders with as-needed knowledge-based process management and quality
assurance applications. Figure 3(b) summarizes the type, evidence process, media, and
external interactions of the three layers. BIBP employs a clear data-information-knowledge
(DIK) paradigm to map the evidence from practice to blockchain BIM to users (and existing
software systems).

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(a) system architecture

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(b) evidences and external interactions involved in system architecture
Figure 3. Overview of blockchain-enabled IoT-BIM platform

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5.2.1 Infrastructure as a Service (IaaS)
IaaS of the BIBP includes two modules, namely IoT and user interface. The edge
infrastructure supports the IoT module, which contains IoT-enabled production resources,
protocols, gateway nodes, broker nodes, and computing unit nodes. In this study, OPM-MC
resources and processes are linked with their virtual twins through RFID, and protocols are
used to regulate the synchronization of data-information-knowledge in OPM-MC. Thus,
RFID with existing protocols can capture OPM-MC data from regular operations to
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blockchain BIM. Gateway nodes act as an interface to preprocess the data collected from
RFID and feed the data to the subsequent nodes. Broker nodes are responsible for allocating
computing unit nodes to handle time-sensitive tasks or transferring challenging tasks to the
cloud. By relying on smart contracts, blockchain IoT interfaces can provide users with
effective operational control. For instance, once a window is produced for a module, the
operator can scan the RFID tag affixed on it and publish this transaction proposal to the
blockchain, and when the proposed transaction reaches a consensus in the decentralized
network, the smart contract can send a task completion notification to the production manager
and other stakeholders. Different combinations of IoT configurations can be provided for
various future tasks. For instance, one can use GPS sensors with low energy consumption for
future logistics tasks.

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The user interface module supports user interaction in the platform. For example, the client
can view the inspection results of the material, 2D panels, and 3D modules through the user
interface. In addition, the developed user interfaces are connected to a web-based operating
platform, allowing users to view the real-time progress of production preparation, production,
and inspection through the imported BIM.

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5.2.2 Blockchain BIM as a Service (BaaS)
BaaS of the BIBP includes two major modules to interoperate information, semantics, and
inferences. The first module is the open blockchain BIM interface, extending the existing
open BIM standard IFC (ISO 16739-1:2018). The second module is the blockchain BIM
system, which includes BIBP network, ledger, and a set of smart contracts.

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The first module (open blockchain BIM standard) is capable of handling more functions than
the conventional IFC standard. The new extension involves two parts. The first part is a SDT
model for blockchain computability. BIMs are usually massive in size, and the blockchain is
not good at handling massive data due to the network capability. In addition, as shared by
multiple stakeholders, BIM is subject to simultaneous changes by different parties at the same
time. The research conducted by Xue and Lu (2020) shows that SDT can manage real-time,
simultaneous changes as IFC change consensuses. The other extension to IFC is the IoT
properties, which used to be non-existed in the IFC properties. Examples include production
lines, production preparations, and defects. These new properties are attached to the IFC
standard directly.

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Figure 4 shows an example illustrating how the new open blockchain BIM standard works on
an object’s geometry modification in a BIM. A window on a wall (see Figure 4(a)) was
changed to a larger width in Figure 4(b). Figure 4(c) shows the corresponding change record,
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where the two lines indicate the unique identification of the window and the pair of original
and changed properties. The changes are associated with the IFC objects by a multi-level
decomposition of the building hierarchy. The change record is short – which is not available
in IFC without SDT – enough for blockchain. Besides, by swapping the value pair of original
and changed properties, the time arrow of the changes can be reversed so that the rewind and
tracing operations are available – which are not available in IFC – from the new blockchain
BIM standard. With the new blockchain BIM standard, even a massive BIM can be stored on
the blockchain.

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Figure 4. Illustrative example of the semantic differential transaction record of a design
change: (a) example wall; (b) window size changed; (c) differential record (0.36KB) of the
design change
The second module, blockchain BIM system, is implemented on Hyperledger Fabric (a
permissioned blockchain platform), containing the services of the BIBP network, ledger, and
chaincode (in Hyperledger Fabric, smart contracts are packaged as chaincode). The details of
each service is explained as follows.
(i) BIBP network: The BIBP network is a two-channel structure that provides ledgers (L1,
L2) and chaincode (S1, S2) to facilitate data-information-knowledge-driven OPM-MC (see
Figure 5(a)). Each dimension (physical space, data space, information space, knowledge
space, and service space) of the data-information-knowledge model can serve as an
organization (𝐷𝐷𝑃𝑃𝑃𝑃 , 𝐷𝐷𝐷𝐷𝐷𝐷 , 𝐷𝐷𝐼𝐼𝐼𝐼 , 𝐷𝐷𝐾𝐾𝐾𝐾 , 𝐷𝐷𝑆𝑆𝑆𝑆 ) to join the network, in which the participants of
organizations must obtain certificates from the corresponding certificate authority
(𝐶𝐶𝐶𝐶𝑃𝑃𝑃𝑃 , 𝐶𝐶𝐶𝐶𝐷𝐷𝑆𝑆 , 𝐶𝐶𝐶𝐶𝐼𝐼𝐼𝐼 , 𝐶𝐶𝐶𝐶𝐾𝐾𝐾𝐾 , 𝐶𝐶𝐶𝐶𝑆𝑆𝑆𝑆 ). For instance, the certificate authority 𝐶𝐶𝐶𝐶𝑆𝑆𝑆𝑆 can distribute
certificates to the client, contractor, manufacturer, and inspector affiliated with 𝐷𝐷𝑆𝑆𝑆𝑆 to
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approve their identities. 𝐷𝐷𝐷𝐷𝐷𝐷 and 𝐷𝐷𝐼𝐼𝐼𝐼 manage the network by defining policy rules in the
network configuration (NC). They also designate members as administration points (𝑂𝑂𝐼𝐼𝐼𝐼 and
𝑂𝑂𝑆𝑆𝑆𝑆 ) for ordering services. 𝐷𝐷𝐼𝐼𝐼𝐼 , 𝐷𝐷𝐾𝐾𝐾𝐾 , and 𝐷𝐷𝑆𝑆𝑆𝑆 establish a consortium for knowledge-based
OPM-MC services on Channel 1, where configuration CC1 lists involved organizations’
definitions and policies. Also, 𝐷𝐷𝑆𝑆𝑆𝑆 , 𝐷𝐷𝐾𝐾𝐾𝐾 , and 𝐷𝐷𝐼𝐼𝐼𝐼 will join peers, named 𝑃𝑃𝑆𝑆𝑆𝑆 (stakeholder
peers), 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 (process management and quality assurance peers), and 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 (BIM peers), to

Channel 1. Decentralized applications (DApps) such as 𝐴𝐴𝑆𝑆𝑆𝑆 (stakeholder communication),
𝐴𝐴𝐼𝐼𝐼𝐼𝐼𝐼 (intelligent process management and quality assurance), 𝐴𝐴𝐵𝐵𝐵𝐵𝐵𝐵 (BIM application) can be
connected to Channel 1 by using certificates from the corresponding CAs. S1 is installed on
𝑃𝑃𝑆𝑆𝑆𝑆 , 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 , and 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 to process business services, knowledge, and information level
transactions from DApps, and then these transactions are packaged into blocks by 𝑂𝑂𝐼𝐼𝐼𝐼 and
𝑂𝑂𝑆𝑆𝑆𝑆 . Endorsed transactions will be passed to the peers in Channel 1 and recorded in their
immutable ledger copies L1.

Figure 5. Blockchain BIM system: (a) network; (b) ledger

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Similarly, 𝐷𝐷𝑃𝑃𝑃𝑃 , 𝐷𝐷𝐷𝐷𝐷𝐷 , and 𝐷𝐷𝐼𝐼𝐼𝐼 can establish a consortium for data and information-based
OPM-MC services on Channel 2. CC2 lists the participated organizations’ definitions and
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policy rules. 𝐷𝐷𝐷𝐷𝐷𝐷 and 𝐷𝐷𝐼𝐼𝐼𝐼 will join peers, named 𝑃𝑃𝐵𝐵𝐵𝐵 (broker nodes), 𝑃𝑃𝐶𝐶𝐶𝐶𝐶𝐶 (computing unit
nodes) and 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 , to Channel 2. DApps such as 𝐴𝐴𝐵𝐵𝐵𝐵𝐵𝐵 and 𝐴𝐴𝑆𝑆𝑆𝑆𝑆𝑆 (RFID-enabled construction
resources) can be connected to Channel 1 by using certificates from the corresponding CAs.
S2 is installed on 𝑃𝑃𝐶𝐶𝐶𝐶𝐶𝐶 , 𝑃𝑃𝐵𝐵𝐵𝐵 , and 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 to process data level transactions from DApps, and
then these transactions are packaged into blocks by 𝑂𝑂𝐼𝐼𝐼𝐼 and 𝑂𝑂𝑆𝑆𝑆𝑆 . Endorsed transactions will
be passed to the peers in Channel 2 and recorded in their immutable ledger copies L2.
(ii) Distributed ledgers: In the network, each peer retains a copy of the ledger. The ledger is
used to record factual information about OPM-MC objects. For example, in channel 1, BIMbased process management and quality assurance can be recorded on L1, while in channel 2,
RFID transactions can be recorded on L2. Each ledger consists of two parts: a world state and
a blockchain, as shown in Figure 5(b). The world state shows the current value of an object’s
attributes as an individual ledger state. The second part, blockchain, is an immutable
historical record of how objects arrived at their current states. In a blockchain, blocks are
interconnected in sequence, and each block is composed of a block header, block data, and
block metadata. A block header includes a block number, a current block hash, and a
previous block hash. Block data contains a set of transactions, and each transaction represents
a query or update to the world state. When 𝑂𝑂𝐼𝐼𝐼𝐼 and 𝑂𝑂𝑆𝑆𝑆𝑆 pack the block in the ordering service,
these transactions will be recorded. Block metadata contains a timestamp, certificate, public
key, and signature of the block creator.

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Two types of world states, namely W1 and W2, are defined in L1 and L2. W1 has three key𝑄𝑄𝑄𝑄

value pairs: 〈𝐾𝐾𝑖𝑖𝑃𝑃𝑃𝑃 , 𝑉𝑉𝑖𝑖𝑃𝑃𝑃𝑃 〉, 〈𝐾𝐾𝑙𝑙 , 𝑉𝑉𝑙𝑙

𝑄𝑄𝐴𝐴

𝐵𝐵𝐵𝐵𝐵𝐵
〉 and 〈𝐾𝐾𝑚𝑚
, 𝑉𝑉𝑚𝑚𝐵𝐵𝐵𝐵𝐵𝐵 〉. These key-value pairs show the latest

knowledge states of the ith project management, lth quality assurance and the mth BIM
𝑄𝑄𝑄𝑄

changes, respectively. Specifically, 𝐾𝐾𝑖𝑖𝑃𝑃𝑃𝑃 and 𝐾𝐾𝑙𝑙

processes and inspection procedures. 𝑉𝑉𝑖𝑖𝑃𝑃𝑃𝑃 and 𝑉𝑉𝑙𝑙

present the sequence number of OPM-MC

𝑄𝑄𝑄𝑄

𝑄𝑄𝑄𝑄

show the knowledge of 𝐾𝐾𝑖𝑖𝑃𝑃𝑃𝑃 and 𝐾𝐾𝑙𝑙 ,

such as project management and quality assurance optimization, simulation and prediction
𝐵𝐵𝐵𝐵𝐵𝐵
results. 𝐾𝐾𝑚𝑚
indicates the identifier of BIM changes, and 𝑉𝑉𝑚𝑚𝐵𝐵𝐵𝐵𝐵𝐵 shows the properties of BIM
changes, such as geometric, semantic, and topological information. The second type of world
state W2 〈𝐾𝐾𝑗𝑗𝑆𝑆𝑆𝑆𝑆𝑆 , 𝑉𝑉𝑗𝑗𝑆𝑆𝑆𝑆𝑆𝑆 〉 shows the latest data states of the jth SCO. 𝐾𝐾𝑗𝑗𝑆𝑆𝑆𝑆𝑆𝑆 presents the identity
of IoT-enabled construction resources, and 𝑉𝑉𝑗𝑗𝑆𝑆𝑆𝑆𝑆𝑆 shows the detailed data about resources,

such as states and location. Simply put, every endorsed transaction will cause the key-value
pair to change, which is then updated in ledgers.

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(iii) Chaincode: In BaaS, chaincode S1 and S2 are installed on the peers in Channel 1 and 2,
respectively. S1 contains seven smart contracts for value assessment, capacity assessment,
availability assessment, process optimization, quality control, BIM modification, and
decision support. When a stakeholder proposes a transaction, the value assessment contract,
capacity assessment contract, and availability assessment contract will help evaluate the
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transaction’s business value and the capacity and availability of off-site production resources
and processes. Next, these smart contracts will determine whether to validate the transaction
based on peers’ responses. After approval, 𝐴𝐴𝐼𝐼𝐼𝐼𝐼𝐼 creates a proposal to Channel 1, in which the
process optimization contract and the quality control contract first use the knowledge model
to optimize and simulate the proposal and then provide a suitable plan. Then, 𝐴𝐴𝐵𝐵𝐵𝐵𝐵𝐵 can use
the BIM modification contract to record the BIM modifications caused by the transaction.
When consensus is reached, the optimized process management and quality assurance plan
can be imported from BIM to Channel 2 by executing the decision support contract.

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Chaincode S2 contains four smart contracts for managing data-oriented services across
physical, data, and information spaces. These contracts are state validation contract, state
computing contract, state evaluation contract, and state update contract. In DApps, 𝐴𝐴𝑆𝑆𝑆𝑆𝑆𝑆
observes the states of production resources and processes to comprehend the interference in
existing process management and quality assurance. Also, these states can be submitted as
transaction proposals to Channel 2. When having a new proposal, state validation contract,
state computing contract, state evaluation contract can check, compute, and evaluate the data
in the proposal, and if they all produce a positive response, the states will be approved. In the
process management and quality assurance, the state update contract can give the updated
states to the 𝐴𝐴𝐵𝐵𝐵𝐵𝐵𝐵 . Additionally, 𝐴𝐴𝐵𝐵𝐵𝐵𝐵𝐵 can subscribe to past states and interferences to study
the performance of process management and quality assurance, thereby improving future
performance through knowledge models.

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5.2.3 Software as a Service (SaaS)
SaaS of BIBP includes a consensus mechanism. The consensus mechanism adopted by 𝑂𝑂𝐼𝐼𝐼𝐼
and 𝑂𝑂𝑆𝑆𝑆𝑆 can help peers ensure the correctness and order of transactions. BIBP uses CFT
consensus mechanism to control the transaction flow. In BIBP, 𝐴𝐴𝑆𝑆𝑆𝑆 , 𝐴𝐴𝐼𝐼𝐼𝐼𝐼𝐼 , 𝐴𝐴𝐵𝐵𝐵𝐵𝐵𝐵 , and 𝐴𝐴𝑆𝑆𝑆𝑆𝑆𝑆 are
the specific services to perform consensus transaction flow.

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Users can first use 𝐴𝐴𝑆𝑆𝑆𝑆 to propose a transaction T1 with proposal P (e.g., the transaction
details) to initiate production communication, as shown in Figure 6(a). Then, 𝐴𝐴𝑆𝑆𝑆𝑆 should
invoke the certificate from the CA to verify its identity and authority to join channel 1
through the gateway. Next, 𝐴𝐴𝑆𝑆𝑆𝑆 sends P to the peers involved in channel 1 for initial
endorsement. In this case, 𝑃𝑃𝑆𝑆𝑆𝑆 assesses the business value of P by using the value assessment
contract in S1, provides a response R1, and offers an endorsement E1 with a digital signature.
𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 and 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 evaluate the state, capacity, and availability of processes and resources using
the capacity assessment contract, availability assessment contract, and BIM. After evaluation,
𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 and 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 provide R2 and E2 and R3 and E3, respectively. As a result, 𝐴𝐴𝑆𝑆𝑆𝑆 receives all
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the responses and decides whether to proceed further or terminate T1. After reaching a
consensus, 𝑂𝑂𝐼𝐼𝐼𝐼 and 𝑂𝑂𝑆𝑆𝑆𝑆 can order T1 into a block and deliver it to the peers involved in
channel 1. The peers can endorse the block and append the block to the L1 after their
endorsement is positive. Then, peers will notify the user of the DApps that T1 has been
executed. Afterward, 𝐴𝐴𝐼𝐼𝐼𝐼𝐼𝐼 uses the transaction that has been ordered and notified to 𝐴𝐴𝑆𝑆𝑆𝑆 to

make an initial plan as transaction T2 with proposal P and send it to 𝑃𝑃𝑆𝑆𝑆𝑆 , 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 , and 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 .

Considering constraints, risks, and uncertainties, 𝑃𝑃𝑆𝑆𝑆𝑆 , 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 , and 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 simulate and optimize
the plan by calling the process optimization contract and quality control contract, and then
provide R1 and E1, R2 and E2, R3 and E3. 𝐴𝐴𝐵𝐵𝐵𝐵𝐵𝐵 records the BIM modification caused by the
plan as transaction T3 with proposal P and sends it to 𝑃𝑃𝑆𝑆𝑆𝑆 , 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 , and 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 for
endorsement. 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 and 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 will invoke the BIM update contract to review BIM changes
and IFC objects and then provide R2 and E2 and R3 and E3. Using the decision support
contract, 𝑃𝑃𝑆𝑆𝑆𝑆 can endorse the modified BIM through a consensus and provide R1 and E1.

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Figure 6. Transaction flows in blockchain-enabled IoT-BIM platform: (a) channel 1; (b)
channel 2

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The transaction flow of OPM-CM process management and quality assurance in channel 2 is
demonstrated in Figure 6(b). After generating T2 in channel 1, 𝐴𝐴𝐵𝐵𝐵𝐵𝐵𝐵 can conduct crosschannel communications and convert the optimal plan into actual operations in channel 2 (as
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T1 and P) to guide production process management and quality assurance operations in
physical space. The state computing contract and state evaluation contract will be invoked to
help 𝑃𝑃𝐶𝐶𝐶𝐶𝐶𝐶 and 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 investigate operations while considering the states of production
resources and processes. Besides, 𝐴𝐴𝑆𝑆𝑆𝑆𝑆𝑆 can submit the real-time states as T2 and P to 𝑃𝑃𝐵𝐵𝐵𝐵 .
𝑃𝑃𝐵𝐵𝐵𝐵 can judge whether there is an abnormality in T2 through the state validation contract. If
there is an abnormality in R1, 𝑃𝑃𝐵𝐵𝐵𝐵 will use the state update contract to help pass the state to
𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 for further analysis through the knowledge model and provide R2 and E2. On the
contrary, if no abnormality is detected, 𝑃𝑃𝐵𝐵𝐵𝐵 will use the state computing contract to pass the
state to 𝑃𝑃𝐶𝐶𝐶𝐶𝐶𝐶 for processing, and provide R1 and E1. In addition, 𝐴𝐴𝐵𝐵𝐵𝐵𝐵𝐵 can subscribe to the
states submitted by 𝐴𝐴𝑆𝑆𝑆𝑆𝑆𝑆 to evaluate the existing states and improve future performance by
using the state evaluation contract with learning and predictive capabilities. Similarly, 𝑂𝑂𝐼𝐼𝐼𝐼
and 𝑂𝑂𝑆𝑆𝑆𝑆 order the transactions into a new block and append it to L2.

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6. Implementation and Evaluation

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6.1 Implementation

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Based on the proposed system architecture, a BIBP is developed as a shadow platform
parallel to the existing platform to illustrate its advantages. The research team chose the offsite mock-up production (OMP) phase of a modular construction project as the pilot scenario
for developing and implementing the platform.

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6.1.1 IoT Module and User Interface for the IaaS Layer
Firstly, the IoT module and user interfaces are implemented for the IaaS layer of BIBP. In
this study, passive RFID is adopted as the IoT plan, and RFID tags are affixed on material
packages, prefabricated components, and prefinished modules to monitor the process states of
OPM-MC, as shown in Figure 7. The set of comprehensive protocols fulfills the need for
mapping and integrating the data in existing means and systems to the BIBP. Also, broker
nodes are configured to allocate computing unit nodes to handle time-sensitive tasks or
transfer challenging tasks to the cloud. Besides, the gateway nodes act as a data converter in
the factory. Thus, the RFID actions are captured by 𝐴𝐴𝑆𝑆𝑆𝑆𝑆𝑆 , computed by the computing unit
node, endorsed by the peers in channel 2, and recorded on L2.

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Figure 7. IoT module

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The user interfaces are created through the development of the front-end. Figure 8(a) shows
the client’s interface for inquiring about past transactions. For example, the client can click
“Details” to view the inspection results of transactions. By clicking the “View” button, one
can also view the real-time off-site production progress in the web-based operating platform
through the imported BIM, as shown in Figure 8(b). The buffer capacity of the holding yard
can also be viewed in BIM. Such visualization helps project stakeholders identify any delays
in OPM-MC to understand the current situation and make relevant decisions collaboratively
on BIBP.

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Figure 8. BIBP user interfaces: (a) project client’s interface for inquiring about past
transactions; (b) function for production progress visualization

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6.1.2 Open Blockchain BIM Interface and Blockchain BIM System for the BaaS Layer
Secondly, the open blockchain BIM interface and blockchain BIM system are implemented
for the BaaS layer. To develop the open blockchain BIM interface, the existing open BIM
standard IFC needs to be extended. Thus, an SDT model for blockchain computability is
included to bridge the fundamental gap between the IFC and blockchain. The SDT model, as
shown in Figure 9(a), can manage the real-time, simultaneous changes as IFC change
consensuses. The other extension to IFC is the IoT properties, as shown in Figure 9(b). The
extended standard can handle more functions than the original IFC standard. For example,

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with the schematic definitions in the IFC standard, production analyses can be utilized, such
as code checking, progress analysis, and cost estimation.

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Figure 9. New open blockchain BIM standard: (a) semantic differential transaction model for
blockchain BIM; (b) extension of IFC standard (ISO 16739-1:2018)

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The blockchain BIM system was configured with a network and two sets of chaincode.
Moreover, Channel 1 and 2 were configured for passing transactions related to OPM-MC
applications to distributed ledgers. Figure 10(a) shows the detailed information of the BIBP
network, which includes five-dimension organizations (𝐷𝐷𝑃𝑃𝑃𝑃 , 𝐷𝐷𝐷𝐷𝐷𝐷 , 𝐷𝐷𝐼𝐼𝐼𝐼 , 𝐷𝐷𝐾𝐾𝐾𝐾 , 𝐷𝐷𝑆𝑆𝑆𝑆 ), where 𝐷𝐷𝑆𝑆𝑆𝑆
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and 𝐷𝐷𝐼𝐼𝐼𝐼 also designate members as administration points (𝑂𝑂𝐼𝐼𝐼𝐼 and 𝑂𝑂𝑆𝑆𝑆𝑆 ) for ordering services.
Additionally, Figure 10(b) and (c) present channel 1 and 2 and their associated organizations,
respectively. Three peers (𝑃𝑃𝑆𝑆𝑆𝑆 , 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 , and 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 ) were added to channel 1 of the BIBP
network for intelligent process management and quality assurance in OPM-MC. 𝑃𝑃𝑆𝑆𝑆𝑆
comprises four peer nodes: client, main contractor, manufacturer, and inspector, while 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 ,
and 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 each has a peer node. Chaincode (S1) was installed on 𝑃𝑃𝑆𝑆𝑆𝑆 , 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 , and 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 in

channel 1 (see Figure 10 (d)). Similarly, 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 , 𝑃𝑃𝐵𝐵𝐵𝐵 and 𝑃𝑃𝐶𝐶𝐶𝐶𝐶𝐶 joined channel 2 to support
state monitoring and operations of process management and quality assurance in OPM-MC,
and each of them has one peer node. 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 was defined for cross-channel communications
between channel 1 and 2. Chaincode S2 was installed on 𝑃𝑃𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 , 𝑃𝑃𝐵𝐵𝐵𝐵 and 𝑃𝑃𝐶𝐶𝐶𝐶𝐶𝐶 in Channel 2.

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(a) network

(b) channel 1

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(c) channel 2

(d) Chaincode

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Figure 10. Blockchain BIM system

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6.1.3 Consensus Service for the SaaS Layer

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Thirdly, the genesis block of the BIBP network was configured to initialize the CFT
consensus mechanism for the SaaS layer, as shown in Figure 11. SaaS supports a pluggable
consensus mechanism that enables the platform to be more effectively customized to fit
particular use cases and trust models. For instance, a more traditional byzantine fault tolerant
consensus can be configured in a multi-party, decentralized use case.

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Figure 11. Initialization of the consensus mechanism

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6.2 Evaluation

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BIBP was tested in the OMP phase of a modular construction project, which involves the
production of 10 modules in Foshan, Mainland China. The research team observed and
recorded the usage and later compared BIBP with the existing IoT-enabled BIM system
developed by Li et al. (2018).

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6.2.1 Testing Scenario
The processes for testing with BIBP include production preparation, production, and
inspection, as shown in Figure 12. The test involves several typical scenarios, such as order
placement, IoT sensing, smart process management, quality assurance, and BIM state
updates. The transaction flow of each application scenario is described as follows. Firstly,
users can submit the transactions with the proposals from the DApps to peers through the
gateway node, and then peers can endorse them by invoking smart contracts and provide
corresponding responses. Secondly, peers send the endorsements and responses together with
their digital signatures back to the DApps. Thirdly, endorsed and valid transactions are
bundled into blocks through the ordering nodes and sent to peers through the defined
communication channels. Finally, peers verify the transactions in the newly received blocks,
and if these transactions are correct, they append the blocks to their ledgers and send
completion notifications to the DApps.

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Figure 12. Processes for testing with blockchain-enabled IoT-BIM platform

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As shown in Figure 12, the endorsed processes are displayed in four colors through 𝐴𝐴𝐵𝐵𝐵𝐵𝐵𝐵 : (i)
pink (production prepared); (ii) yellow (prefabricated components produced); (iii) blue
( prefinished modules entirely produced); (iv) green (modules inspected). State changes in
BIM (e.g., format: {‘ifcprocess’:{‘entirely produced’→ ‘inspected’}}) can be communicated
in channel 1. Besides, when modules are entirely produced, the differences between the asmanufactured BIM and the as-designed BIM can be determined by the knowledge model
used for quality assurance in 𝐴𝐴𝐼𝐼𝐼𝐼𝐼𝐼 .

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6.2.2 Evaluation Results
BIBP was evaluated by comparing with the existing IoT-enabled BIM system through five
performance indicators: storage cost, security, integrity, authentication, and authorization.
There are four settings made: (1) three batches of materials (structure, architecture, MEP) are
delivered to the factory; (2) an average of 4 transactions (one order from 𝐴𝐴𝑆𝑆𝑆𝑆 , one PM-QA
operation in 𝐴𝐴𝐼𝐼𝐼𝐼𝐼𝐼 , one state update in 𝐴𝐴𝐵𝐵𝐼𝐼𝐼𝐼 , one data collection by 𝐴𝐴𝑆𝑆𝑆𝑆𝑆𝑆 ) are produced per
material batch; (3) a total of 10 modules are produced and inspected in 35 days; (4) an
average of 21 transactions (one order from 𝐴𝐴𝑆𝑆𝑆𝑆 , six PM-QA operations in 𝐴𝐴𝐼𝐼𝐼𝐼𝐼𝐼 , seven state

updates in 𝐴𝐴𝐵𝐵𝐵𝐵𝐵𝐵 , seven data collections by 𝐴𝐴𝑆𝑆𝑆𝑆𝑆𝑆 ) are produced per module. A new block is
generated every 24 hours to record OPM-MC transactions. Therefore, each block bundles
about 7 transactions.

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(1) Storage Cost: To ensure the single point of truth for BIM, the BIM model needs to be
saved in the blockchain. However, it may lead to information redundancy in the blockchain
network. Thus, the storage cost was evaluated for this contribution. In this study, any BIM
state change is calculated as the minimum SDT in BIBP, thereby reducing the average size of
each transaction to 1 KB (Xue and Lu, 2020) and storing the detailed information in the local
database. The total occurred transactions during the test are 222 (4 × 3 + 21 × 10), and at the
maximum, 222 KB (222 × 1) may be produced in each ledger. In the IoT-enabled BIM
platform developed by Li et al. (2018), the BIM model (e.g., the model in Figure 9) is stored
in a webserver with the size of approximately 129 MB. Thus, BIBP system architecture can
lessen storage load, especially when critical data needs to be tracked in large BIM files.

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(2) Security: Another critical design philosophy in BIBP is to avoid a SPOF in IoT networks.
To this end, an evaluation was conducted to prove the security of BIBP in screening
malicious data. Before the final inspection, the research team deliberately set three of the ten
RFID tags as malicious tags (e.g., production completion as incompletion). The results prove
that BIBP can avoid a SPOF by rejecting the malicious IoT data through the consensus
mechanism. In the same situation, the inspector may directly read the RFID data and input it
directly into the IoT-enabled BIM platform, so that the malicious data is not easy to be
detected. According to Lu et al. (2021a), the security analysis of BIBP (particularly the IoT
network) can also be discussed through integrity, authentication, and authorization.

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(3) Integrity: In BIBP, the integrity of IoT data transaction can be ensured when it is
exchanged in Channels 1 and 2, because the hash algorithm of the blockchain can make them
tamper-proof. In contrast, IoT data collected for the IoT-BIM platform may be manipulated
by operators.

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(4) Authorization: BIBP uses a permissioned blockchain structure to provide pre-authorized

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users with certificates to join the network through membership services (see Figure 13(a)). The

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existing IoT-BIM platform also requires user registration and right permission.

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(5) Authentication: In BIBP, the authentication mechanism is realized through digital
signatures, which requires each peer to hold two keys (see Figure 13(b)). The public key is
used publicly and serve as identity verification anchor, and the private key is used to digitally
sign IoT data transactions. On the contrary, due to the lack of such a mechanism,
authentication cannot be guaranteed in the existing IoT-BIM platform.

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Figure 13. Authorization and authentication in blockchain-enabled IoT-BIM platform: (a)
certificate; (b) digital signature

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7. Discussion
This study makes three novel contributions to the existing body of knowledge. Firstly, our
research uses the advantages of blockchain to avoid a SPOF in IoT networks. The system
architecture lays the foundation for researchers to explore the IoT as blockchain oracles
(middleware agents that can capture and verify real-world information and feed it to the
blockchain) in construction supply chain management. Secondly, compared with the existing
IoT-BIM platform, this research proposes blockchain IoT-BIM as the infrastructure which
builds on a new open blockchain BIM standard extended from IFC. The novel open
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blockchain BIM standard provides a valuable reference for researchers to attach new IoT
attributes to BIBP to implement various functions easily. In practice, the new standard is also
conducive to public institutions (e.g., governmental supervision units that are unwilling to
force commercial software) to access and audit BIMs developed on commercial platforms.
Thirdly, our research links the permissioned blockchain to the IoT-BIM platform, which can
inherit the advantage of traceability of blockchain to record BIM modifications. The
information recorded in a blockchain is reduced mainly by capturing BIM modifications
instead of entire BIM files. In our OPM-MC pilot tests, the version history of BIM
modifications was captured and placed in a blockchain ledger with only around 222 KB,
adequately addressing the challenge of information redundancy in BIM and blockchain
integration.

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The limitations of this study provide opportunities for future research. Firstly, the algorithm
for the SDT model was still slow to process large BIMs, e.g., the 129 MB IFCXML case
would exceed the one-hour time limit. Future work can develop efficient IFCXML
computing modules and plug-ins for these commercial BIM platforms to promote the
integration of BIM and blockchain. Researchers can also explore other approaches such as
open BIM web service and the BIM Collaboration Format standard to minimize information
redundancy for BIM and blockchain integration. Secondly, only one pilot study was carried
out. Thus, the testing and the evaluation results can only be perceived as a proof of concept of
the BIBP, rather than a final version for benchmarking performance or proof of compatibility
to other production projects. Future works are recommended to fine-tune the platform and
test and evaluate it in the logistics and on-site installation phases of the surveyed modular
construction case and other construction projects. Thirdly, there is a lack of a systematic
framework for forecasting the costs of a production-scale, commercial BIBP. Thus, a detailed
cost assessment of the proposed BIBP is desired when better empirical data is available.

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Although these limitations can be addressed through future research, the barriers to using
BIBP in construction projects should not be underestimated. The Building Department in
Hong Kong has a series of concerns regarding technological (e.g., decentralization level),
organizational (e.g., top management support), and environmental (e.g., government support)
aspects to help construction organizations, ranging from large to small, to adopt blockchainbased solutions. As the construction industry is historically known for its slow adoption of
innovative solutions, the implementation of BIBP can be hindered by knowledge, attitudinal,
industry, financial, technical, process, and policy-related barriers. Therefore, researchers
should also study strategies to address each barrier and promote the adoption of BIBP.

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8. Conclusions
This research developed a blockchain-enabled IoT-BIM platform (BIBP) for off-site
production management in modular construction (OPM-MC) with a view to solving the
issues of a single point failure (SPOF) in IoT networks and the provenance of BIM
modifications. A design science research (DSR) method was adopted to develop a three-layer
BIBP system architecture. Firstly, Infrastructure as a Service (IaaS) was designed with an IoT
module and user interfaces to collect accurate data from daily production operations to
blockchain BIM and allow user interactivity. Secondly, Blockchain BIM as a Service (BaaS)
was developed by linking permissioned blockchain to BIM and extending the existing open
BIM standard. Thirdly, Software as a Service (SaaS) was configured with decentralized
applications to achieve knowledgeable processes with a consensus mechanism. The system
architecture was implemented and then compared with the existing IoT-enabled BIM
platform. It was found that BIBP can avoid a SPOF in IoT networks and ensure the
provenance of BIM modifications with reduced storage costs in OPM-MC.

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The limitations of this study provide chances for further investigation. First, the semantic
differential transaction (SDT) approach is imperfect as it is still slow to process large BIMs.
Researchers can explore other approaches such as open BIM web service, the BIM
Collaboration Format standard, and the “signature” of IFC objects to minimize information
redundancy for blockchain and BIM integration. Second, this research only applies the
developed platform to one pilot project for testing its effectiveness. Future research can
improve and extend the applicability of the platform to more practical projects to enhance its
effectiveness. Third, a detailed cost assessment was not included for the initial platform
establishment, deployment, storage, and ongoing maintenance. Thus, researchers should
develop a framework for assessing the costs of a production-scale, commercial BIBP. Fourth,
the complex nature of the barriers hindering the broader diffusion of BIBP in the construction
industry. Therefore, future investigations can focus on integrated strategies to address the
identified barriers.

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Acknowledgement
The work presented in this paper was financially supported by the Hong Kong Innovation and
Technology Commission (ITC) with the Innovation and Technology Fund (ITF) (No.
ITP/029/20LP). This funding source had no role in the design and conduction of this study.

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