2.1 Sustainability in the Construction Industry

Sustainability includes social, environmental, and economic goals which have been named as its dimensions, social aim works for people to co-exist on Earth over a long period of time; environmental dimension emphases on maximizing the profit or minimizing the costs in a system; finally, Environment Sustainability can be expressed as the responsible activity with the environment to prevent depletion or debasement of the natural resources and save them for the long-term environment quality [37]. However, definitions of this term are disputed and have varied with literature, context, and time [38]. Many definitions emphasize the environmental dimension [39] which includes addressing major environmental issues, such as climate change and biodiversity loss. The idea of sustainability can be about decisions at the global, national, organizational, and individual levels [40]. UNESCO distinguishes the two like this: “Sustainability is often thought of as a long-term goal (i.e., a more sustainable world), while sustainable development refers to the many processes and pathways to achieve it” [41].

For long-term economic success, researchers around the world have emphasized the importance of integrating sustainability into construction project management [42]. In today's world, the construction industry has a significant effect on all three aspects of sustainability: economic, environmental, and social. Industry and academia have recognized sustainability in construction projects as a key concern [43]. Evidence shows that rising incomes, growing consumerism culture, rapid population growth, and rampant urban development contribute to the negative environmental impacts of the building sector [44]. Despite all the challenges, some studies show that it is possible to achieve environmental, economic, and social goals in a stable macroeconomic environment [45].

As applied to the microeconomics of construction project management, sustainability ensures that a built environment is adequately maintained throughout the useful life of the asset while being environmentally friendly [46]. The findings of recent studies on the environmental impact of construction activities have attracted the attention of international industry players (including governments, construction professionals, scientific communities, traders, and customers) [45]. As this sector contributes to and benefits from the production and consumption of raw materials and finished items in the supply chain, it has a significant disproportionate impact on the environment [47].

Waste generated during the construction process accounts for approximately 30%–35% of construction costs [25], and this sector employs more than 111 million people worldwide [47]. In addition, the construction industry is accountable for roughly 40% of the pollution in potable water while creating 50% of landfill trash. It pollutes the air by ∼23%, consumes 40% of the world's energy, and emits a significant quantity of greenhouse gases [48].

Sustainable construction practices are strongly correlated with a profitable and competitive construction industry, improved client satisfaction, and efficient use of resources [49]. Sustainable construction is a high priority for governments in developed countries, while in underdeveloped countries, economic growth is still a higher priority. The increasing importance of economic growth to achieve social equality has pushed environmental problems to the background because the necessity of construction in emerging countries has increased [50]. However, sustainability has not yet been fully integrated or adopted in the construction industry [51].

According to some researchers, the main barriers to sustainability adoption stem from low awareness of sustainability [52], lack of government support [53], high initial investment costs, customer attitudes [54], lack of knowledge and standards, financial constraints, and poor design practices [51].

Babalola and Nishani [55] believe that a policy for sustainable construction should be developed and important stakeholders such as government, financiers, end-users, and professionals should be involved in specific processes. Moreover, a proper model for sustainable development in the construction sector has not existed in the past years and for this reason, the industry has been criticized [56].

These days, most companies use a three-dimensional performance measurement system (environmental, social, and economic performance) to assess their sustainability performance [57]. This three-dimensional analysis can measure the global impact of corporate activities and determine the level of sustainability, showing that sustainability is not just a management tool [58].

According to Liu et al. [59], sustainable construction should be assessed in economic, social, and environmental systems. Some other researchers also point out that the social, economic, and environmental dimensions of sustainability for sustainable development should be coordinated and balanced [60, 61].

Social sustainability is achieved by establishing social standards in the construction industry, increasing the quality of life, and carrying out social projects. The aim of this dimension is to ensure close cooperation between customers, employees, suppliers, and other resources to increase customer satisfaction [57].

A significant portion of previous studies has assessed construction projects in terms of social sustainability [62-66]. According to Taherkhani [67], there is no comprehensive social sustainability framework to identify and measure social factors in buildings. Therefore, socio-environmental, socio-economic, socio-political, socio-cultural, and socio-institutional systems should be designed to create this framework.

Almahmoud and Doloi [68] believe that social sustainability can be created in a neighborhood community that is shaped by new construction thanks to social functions such as health, physical comfort, economy, access, integration, and participation. Bashir et al. [62] believe that social sustainability in construction includes resource management and project planning; health, safety, and well-being; employee conditions and rights; ethics and integrity; diversity, inclusion, and social participation; and knowledge and skills development. Kordi et al. [64] also categorized the characteristics of social sustainability into nine main components: (1) safety and health; (2) impact assessment; (3) employment; (4) stakeholder participation; (5) satisfaction; (6) quality education; (7) social procurement; (8) design/ownership protection; and (9) human rights.

Construction has been cited as a factor in many environmental problems, including the excessive consumption of global resources and environmental pollution. Nowadays, research on green building design and the use of environmentally friendly building materials has increased to reduce negative environmental impacts [56]. Some researchers have investigated BIM [23, 69], green building technologies [70], and the use of waste material techniques [71] to achieve environmental sustainability in the construction industry.

Economic sustainability in the construction industry has diverse implementation opportunities. However, it has not yet been as widely considered as other sustainability techniques [72]. Alaloul et al. [72] assessed economic sustainability in the construction industries of the United States, China, and the United Kingdom. The study showed that the construction sector can be sustainable by investing in labor intensity. According to Alaloul et al. [72], labor intensity is the only way to have energy and resource-efficient processes, make optimal use of resource reserves, and ensure optimal workflow.

2.2 Sustainable Delivery of Construction Projects

In order to construction projects to be sustainable, they must serve many often-conflicting goals, including environmental protection, social improvement, and advancing the strategic interests and financial well-being of construction companies [73]. This means that sustainable practices will be included in every stage of project development and implementation [74]. With this in mind, the current body of research on sustainability may be divided into several distinct groups. Standards, sustainable resources, environmental design, and corporate responsibility are just some of the topics that have been researched in the field of construction [75]. Stakeholder management [76], life cycle management [77], and sustainability assessment are all examples of relevant issues that arise during the delivery phase of a project [78]. Sustainable project organizations, sustainable project practices, and sustainable project management have also been the subject of research. Developing countries where tend to be sustainable often use western techniques [75].

The triple bottom line (TBL) is a widely used framework for understanding sustainable development that takes into account not only economic considerations, but also social and environmental (or ecological) (or financial) aspects (People, Planet, and Profit are sometimes called the 3Ps). As defined by Willard [79], these three elements form the foundation of sustainable development. Organizations in the construction sector have been driven to accept the concept of sustainability in construction projects due to the growing trend towards clean production, green products, and increasing awareness of climate change [75].

The conflict between social and environmental progress and the strategic interests of the construction company makes it difficult to achieve sustainability in construction projects [73]. Adopting this approach requires incorporating sustainability ideas into project actions from start to finish. Therefore, there are several groups into which the existing body of sustainability research can be classified [75]. Standardization research [80], sustainable materials research [74], environmental design research, and CSR (corporate social responsibility) research are all examples of the construction sector [73]. Stakeholder management, life cycle management, and sustainability assessment are three examples of these groups that are involved in the actual delivery of projects [75].

Furthermore, studies in the field of sustainable project management [81], sustainable project organizations [82], sustainable project practices [83], and sustainable decision making [82] have been done. What is more, countries in the developing world that strive for sustainability often model their policies and practices after more industrialized countries [83]. However, criteria that determine the sustainability of construction projects are highly context-specific, and methods used in developed countries may not be applicable in less developed countries [83]. Until now, there has been less academic research on how sustainability principles can relate to building initiatives. Much of the work that has been done so far has taken an exploratory approach and focused on specific subfields of sustainability. Although the results are limited, they indicate delivery problems in underdeveloped countries [75].

Environmentally friendly and resource efficient “sustainable buildings” have been used in the literature [84]. For example, Kineber and Hamed [75] studied the sustainable delivery of construction projects in developing countries using the structural equations approach. To accomplish this, they used existing literature to inform the development of an end-of-package questionnaire, and their results showed that the factors that strongly influence sustainable delivery are preparation-related factors. Moradi and Sormunen [85] presented a conceptual model for lean and sustainable project delivery in building construction. They developed a conceptual framework for project delivery that combines and integrates sustainability, lean construction, and building information modeling in terms of principles, practices, tools, and techniques. Ahmed and El-Sayegh [16] identified the criteria for delivery methods selection for sustainable construction projects using the structural equations approach. The results showed that the criteria of integration level, green team, green contract, green responsibility, and technology are significant for choosing the project delivery method in sustainable construction.

Table 1 presents the most relevant parameters determining sustainable delivery for construction projects based on past research.

2.3 Circular Economy in the Construction Industry

Economic sustainability in the construction industry is defined as a cyclical process that considers input and output factors. At the same time, it shows the evaluation of the long-term impact on economic activity [72]. The basic principles of economic sustainability in the construction industry are the ratio of maximum output to minimum input and the integration of short-term returns and long-term benefits of construction projects [23]. Sustainability in construction has three dimensions: (1) economic sustainability [91]; (2) sustainable building design includes the design of public spaces in the context of green infrastructure (this includes water and air purification, climate regulation, soil and nutrient cycling, natural waste decomposition, and habitat provision) and (3) services and benefits for society (including from health and socio-economic, such as sports conditions, housing quality, and healthy lifestyle) [92].

Understanding costs in the context of economic sustainability is complex and should primarily be viewed from the perspective of life cycle cost management. In another study, economic analysis and its indicators allow the evaluation and comprehensive decision-making process for the effectiveness of the proposed construction project in road transport [93]. Accurate calculation and evaluation of all cost components are important for making the right decision on economic return.

Understanding costs in the context of economic sustainability is complex and should be viewed primarily from the perspective of life cycle cost management, and it is important to consider accurate calculation and evaluation of all cost components while making correct decisions on economic efficiency [93]. In sustainable design, user perspective and user-centered design are important. In the digital age, contextual design is emphasized in the construction industry, which gives a new dimension to data modeling and building information. Past studies indicate a push to increase the use of CD and data modeling, primarily with regard to the psychological, architectural, environmental, and economic aspects of buildings [94-96].

Incorporating circular economy principles into construction project management offers opportunities to optimize resource use, minimize waste generation, and improve overall sustainability [97]. Available statistics indicate a high share of construction waste generation up to 10 billion tons worldwide [98] which is unsustainable in the long term, and the reason for this amount of waste may be the current approaches in several economies. Moreover, currently, the linear economy is an unsustainable model from the point of view of environmental effects, and this is due to the one-way flow from raw materials to waste [97].

There can be many challenges and obstacles for the sustainable design of buildings that take into account the principles of the circular economy. These obstacles include the need for standardized methods and the need for assessment tools [97]. This issue has been discussed in some countries such as Saudi Arabia; however, in general, it is a global problem in the construction industry [99]. Mandičák et al. [23] addressed sustainable design and BIM in construction project management through circular economy principles. Their goal was to analyze the impact of using building information modeling on sustainability indicators measured through costs. To achieve the research objectives, they defined the basic parameters of sustainability in the construction industry as the rate of recycling and waste and CO₂ emissions reduction. Furthermore, Pearson correlation analysis was used to evaluate the data, and their results showed that sustainable design can be achieved using building information modeling (BIM).

Sustainable construction and building information modeling, along with economic sustainability, were discussed in several studies (Table 2). In many cases, they focused on monitoring key performance indicators in construction projects. It should be noted that these results have always led to findings through the monitoring of significant indicators. However, they have not provided results on the impact of using building information modeling (BIM) for sustainable purposes in construction project management.

2.4 Building Information Modeling (BIM) and Sustainability

One of the oldest and still most common definitions of Building Information Modeling is the one given by the National BIM Standard-United States Project Committee (NBIMS-US). As defined in the original NBIMS document, BIM is a digital representation of the physical and functional characteristics of an object. It acts as a shared knowledge source for information about an object and forms a reliable basis for decision-making throughout its life cycle, from scratch. This definition highlights three very important stages: in the first stage, in a BIM-led investment process, a “source of knowledge and information” is created, which is used as wisdom and knowledge; second, this knowledge provides the basis for decision-making or at least reduces uncertainty and increases the understanding of a phenomenon. Third, the exchanged resource must accompany the building object throughout its life cycle from its first conception to its possible destruction. During this cycle, the shape and scope of the source changes, but it always inherently accompanies the building object as its digital twin. All three mentioned aspects are still of great interest and emphasis [107].

In the UK, the original definition of BIM is expressed slightly differently, with an emphasis on process. It emphasizes that BIM is not a technology but a process. They define it as follows: BIM is the process of designing, constructing, and operating a building or infrastructure using object-oriented electronic information [108]. An interesting definition of BIM is mentioned by the famous online BIM dictionary: Building Information Modeling (BIM) is a set of technologies, processes, and principles (standards) that enable several stakeholders to jointly design a facility in a Build and operate a design center in a virtual space [109].

Based on different definitions, it can be claimed that the application of BIM can improve the sustainability performance of the project. The triple principle of sustainable development requires not only the focus of construction projects on economic benefits, but also environmental and social aspects to achieve sustainable economic and environmental development. Additionally, referring to Martens and Carvalho [110], sustainability performance covers three dimensions: economic, environmental, and social responsibility performance.

The BIM program improves the accuracy and timeliness of information acquisition throughout the project life cycle [111]. First of all, timely and accurate information can reduce rework by reducing design errors in the project development and management stages, which in turn improves economic performance [112]. Lee et al. [113] found out that using BIM to reduce project rework resulted in a return on investment of up to 15 times, where potential design defects with a serious impact on schedule can significantly affect the direct project cost.

Second, in the project management engineering phase, real-time quality control is an important way to control project schedule and overhead costs, and BIM can provide real-time on-site quality information collection and processing which helps identify potential construction defects. Therefore, it supports real-time quality control [114]. Finally, BIM has great potential in the project facility management phase, and these application areas include component location, real-time data access, and equipment maintenance [115]. On the other hand, construction management information platforms provide key services in data mining and information processing when shared adjustable computing resources and contribute to the economic performance of projects [116].

Zhang et al. [3] show that the BIM reduces the potential uncertainties associated with environmental management and has a positive effect on environmental performance. In the design phase, BIM application provides the possibility of simulating and analyzing natural light, natural ventilation, and the spatial pattern of the building, and the results are significant, that is, reducing resource consumption by more than 23% and carbon emissions by more than 17% percent per year [117]. In the construction phase, BIM is used as a link between building assembly and enterprise resource planning, combining large-scale prefab engineering manufacturing processes with on-site activities, and the benefits of this link have been shown in construction scheduling control, logistics, and transportation management [3].

Besides, by using digital technology to support sustainable design and construction, companies can accurately develop production schedules and control workflows to maximize resource efficiency and minimize resource wastage [118]. In the facility management phase, Zoghi and Kim [119] used system dynamics to analyze the positive impact of BIM on building demolition waste and found that BIM not only reduced construction waste but also reduced demolition costs by 57%. Additionally, BIM can be developed twice to increase its benefits. For example, Shi and Xu [120] developed a BIM-based information system for construction waste prediction and destruction, which increases recycling rates and reduces environmental pollution from landfills by identifying and controlling construction waste. Zhang et al. [3] showed that the application of BIM may improve social performance related to people's needs and housing population. Zoghi et al. [121] found that a high level of BIM application improves the social performance of a construction project by about 33%, which is manifested in saving resources, promoting preventive safety measures, and socio-environmental aspects.

Carbon emissions, which governments around the world are struggling with, are closely related to the construction industry, and BIM provides a new possibility to reduce carbon emissions in the context of sustainable project delivery [29, 30]. Carbon emissions from buildings include implicit carbon from the building materials production and operational carbon from energy consumption during daily operations [122]. Existing studies have shown that BIM reduce implicit carbon by optimizing the structural design of the building and selecting appropriate building materials in the initial design phase [123, 124].

BIM can be defined as a method to visualize the project and its spaces, structures, components, and materials with their essential information and characteristics [125]. BIM can also be defined as a set of technologies, processes, and policies that enable several stakeholders to jointly design, build, and operate a set of facilities in virtual space [126]. According to Herrera et al. [127], the application of BIM for the design and planning of construction projects includes cost estimation, 4D planning, site analysis, space planning, design review, sustainability assessment, 3D engineering analysis, and coordination (Table 3).

2.5 Building Information Modeling (BIM) and Circular Economy

Building Information Modeling (BIM) as an innovative technology plays a key role in implementing the principles of the circular economy in the construction industry. The circular economy emphasizes the optimal use of resources, reducing waste, increasing the lifespan of materials and their recyclability, and BIM as a digital tool can facilitate these processes [128]. One of the most important impacts of BIM on the circular economy is the creation of a comprehensive database of building information throughout its life cycle. In traditional systems, after the project is completed, information about the materials, design, and construction of the building is often lost or remains scattered and unusable. But with BIM, all this data is stored in a digital model and can be used in the future for analysis, maintenance, repairs, and even recycling of the building. This directly contributes to the principles of the circular economy, as it allows for the targeted recycling of materials and their reuse [129].

Another key aspect of BIM in the circular economy is optimizing the design of buildings to increase their lifespan and flexibility. In many traditional projects, buildings are designed without considering future changes, and if they need to be modified or changed, demolition and reconstruction are the main options, which lead to a waste of resources. However, BIM allows for the simulation of different scenarios so that buildings can be designed in a modular and flexible way, and in the future, they can be changed with minimal destruction and waste of materials. This not only helps reduce waste generation but also increases economic efficiency and reduces the costs of extensive renovations [24].

Additionally, BIM plays an important role in optimizing construction processes, which is directly related to the principles of the circular economy [23]. One of the common problems in the construction industry is the incorrect estimation of the required materials, resulting in the production of excess waste [23, 128]. By providing accurate models and advanced analytics, BIM allows for the accurate calculation of the number of materials required, which leads to reduced waste and increased resource efficiency [24]. In addition, BIM can optimize construction processes and select the most efficient option by simulating different execution methods. This capability reduces energy consumption, reduces execution time, and ultimately improves the overall productivity of the project [130].

From a demolition and recycling perspective, BIM could revolutionize construction waste management. In traditional methods, the demolition process is usually carried out without considering the possibility of separating and recycling materials, but BIM allows building components to be identified and categorized before demolition and planned for reuse or recycling. This can minimize construction waste and extend the life cycle of materials, which is a key goal of the circular economy [23, 24, 130].

Overall, BIM plays a significant role in realizing a circular economy in the construction industry by creating transparency in building information, increasing the recyclability of materials, optimizing design and construction processes, and improving demolition management. This technology not only helps reduce the environmental impact of buildings, but also reduces costs, increases efficiency, and improves resource management in this industry. Combining BIM with circular economy principles can lead the construction industry towards a more sustainable and efficient model. AlJaber et al. [129] showed that BIM has a considerable role in enhancing the management of a building's end-of-life while reducing the life cycle cost in the circular construction of buildings. Eftekhari et al. [24] believed that using a BIM-Based waste management framework significantly improve circularity in construction and resource efficiency.

de Lima et al. [131] claimed that the integration of BIM and design for deconstruction improves the circular economy of buildings. Behún and Behúnová [132] showed that it is thus possible to connect the concept of using modern information technologies to increase the potential of using non-energy recycled raw materials and materials to support the circular economy and sustainable development. Sudarsan and Gavali [133] studied the application of BIM in conjunction with circular economy principles for sustainable construction and showed that sustainable construction practices, such as low-cost and less carbon-emitting materials, reduced the overall cost by 25% and carbon emissions by 20%.

3.1 Research Method

From the point of view of the goal, this research is of an applied type, because the purpose of applied research is to use theoretical and practical knowledge in a specific field. This research can be used by professors, students, and researchers who research and study in the field of sustainable construction.

The type of data collection of this research is through a questionnaire and therefore this research is of a quantitative type. Also, this research is descriptive (non-experimental) research in terms of data and information collection and analysis method, which the researcher's effort is to give an appropriate answer to a problem that exists in the real world during a research process. In addition, considering that the current research is of a quantitative type and the data collection tool is a questionnaire, and the researcher has no involvement in the results of the research, therefore, this research is of a descriptive survey type.

3.2 Research Model and Hypotheses Development

3.2.3 Research Conceptual Model

As it was said, in the present research, the impact and role of BIM on the delivery methods of sustainable construction projects has been discussed with emphasis on the role of circular economy. In this article, structural equation modeling has been used to examine the topic of research and data analysis. The research variables are “BIM,” “Sustainable construction project delivery methods,” and “Circular economy.” The research variables are in the form of a conceptual model as shown in Figure 1.

3.3 Statistical Population, Statistical Sample, and Sampling Method

The statistical population of this research includes all full-time faculty members and experts in Iran's construction industry with a sustainable approach located in Isfahan city, whose number is equal to 210 people. In order to calculate the size of statistical population, we referred to an existing employment data base in Isfahan and to determine the sample size, Cochran's formula was used.

Since the statistical population of this research includes university faculty members and construction industry experts with various job experiences, it is heterogeneous. As a result, we used stratified random sampling. For this purpose, we divided the society into two main groups, academic and industry, and then in each group, we formed classes based on the amount of work experience of the people. Finally, we selected an almost equal number from each class as a statistical sample.

3.4 Data Collection

One of the main parts of any research is collecting data. If this step is done regularly and correctly, the work of analyzing and drawing conclusions from the data will be done with speed and accuracy.

The questions of the questionnaire consist of three parts, which include specialized questions related to the research variables.

The present research questionnaire uses a 5-point Likert scale, which is one of the most common measurement scales. In the Likert scale, the basis of the work is based on the assumption that the questions are not balanced. In this way, scores are given to each question (e.g., from 1 to 5 for a 5-point Likert scale), and the sum of the scores each person gets from the questions will represent his or her orientation.

Table 4 shows the division of questions based on variables. The general form and scoring of this Likert scale for the questions is shown in Table 4.

To design the questionnaire, four questions for circular economy considering the last four components of Table 2 and eight questions for BIM based on eight components of Table 3 have been considered.

Apart from that, there are 23 questions related to the sustainable construction project delivery methods variable and which are based on the factors mentioned in Table 1. As it is shown in Section 2.2, the factors in this table are grouped into three main categories: “economic,” “environmental,” and “social” factors. Whereas, according to experts' opinions, we have made the questions related to this variable in “Evaluation,” “Preparation,” and “Usage” categories as follows in the Table 5.

3.5 Data Analysis Method

After data collection, the next step involves data analysis. In the analysis stage, the researcher must analyze the information and data in the direction of the research goal, answering the research questions and also evaluating the research hypotheses. In this article, Smart PLS software was used to obtain the final research model and examine its fit and ranking, and obtain the weights of the factors.

Structural equation modeling is a very general and powerful multivariate analysis technique from the multivariate regression family, and more precisely, an extension of the general linear model that allows the researcher to test a set of regression equations simultaneously. Structural equation modeling is a comprehensive approach to testing hypotheses about the relationships between observed and latent variables. Among all the multivariate analysis methods, the structural equation method is the only one that simultaneously uses both multiple regression analysis and factor analysis. What makes the structural equation method a powerful and widely used method among researchers is that in addition to its graphical appearance that facilitates interpretation, this method can simultaneously calculate a set of relationships between variables. None of the previous methods could simultaneously examine both the measurement model and calculate the causal relationships of the model. In general, the structural equation method reveals the internal relationships of variables through a set of equations similar to multiple regression of the structure [139, 140].

Structural equation modeling (SEM) was chosen because of its ability to simultaneously analyze the causal relationships between independent, dependent, and mediating variables [143]. This method allows us to examine the direct and indirect effects of BIM on sustainable project delivery methods by considering circular economy as a mediating variable. Other statistical methods such as multiple regression only analyze the direct effect of independent variables and cannot model indirect effects well. Also, path analysis is only applicable when the research variables are fully observed, while in this study, BIM and circular economy variables are modeled latently and multiple indicators are used to measure them. Therefore, the use of SEM allows for a more comprehensive analysis of complex relationships and leads to more accurate results in the field of construction sustainability.

4.1 Reliability of the Questionnaire

As mentioned, validity and reliability in structural equation modeling method include convergent validity, diagnostic validity, and structure reliability. In this research, the mentioned methods and Cronbach's alpha were used to calculate the internal consistency (reliability) of the questionnaire.

As can be seen in Table 6, the value of Cronbach's alpha for all three research variables is greater than 0.7, so the questions of the questionnaire for each of the mentioned variables have reliability from the point of view of the value of this index and can be used for Collected data and measured research variables.

AVE means average extracted variances and its value should be greater than 0.5. As can be seen in Table 6, the value of this index is greater than 0.5 for all three variables, and the collection tool from the perspective of this index is also valid.

The rho-A index is also used for diagnostic validity, which is equal to the amount of average variance extracted (AVE) and its value is greater than 0.5 and indicates the diagnostic validity of research variables.

Also, the CR index is used to check the composite reliability (structural reliability) and its value should be more than 0.7. As can be seen in Table 6, the structure has composite reliability according to the values of this index.

4.2 Testing Research Hypotheses

In the research methodology section, it was observed that two hypotheses were formulated in the current research to examine the relationship between research variables. In this research, in order to examine the research hypotheses, the method of structural equations was used in SMART PLS software.

The fitted model is shown in Figure 2; in this research, various indices were used to estimate the overall goodness of fit of the model with the observed data, which are shown in Table 6.

Diagram (2) shows the estimated model in SMART PLS software. There are latent and observed variables which are two fundamental concepts in statistical analysis, especially factor analysis and structural equation modeling. Moreover, latent variables, known as hidden variables, are variables that cannot be directly observed. In this research, latent variables are “circular economy,” “sustainable project delivery methods,” and “BIM.”

Observed variables are items or measures that are used to measure latent variables. In this research, “evaluation,” “preparation,” and “use” are applied to calculate “sustainable project delivery methods.” Apart from that “waste management,” “CO₂ emission,” “recycling,” and “rate of increase safety” are observed variables to measure “circular economy.” Finally, observed variables for measuring “BIM” are “3D coordination,” “4D planning,” “site analysis,” “space programming,” “sustainability evaluation,” “cost estimation,” “engineering analysis,” and “design review.”

Additionally, it can be seen in diagram (2) that the relationships between latent variables are shown with path coefficients and the relationships between latent and observable variables are shown with factor loading values. For example, among the dimensions of BIM, the factor loading of “engineering analysis” is 0.904, and this value for “3D Coordination” is 0.826. Therefore, it can be said that in the BIM process, the most attention and focus of experts and managers is on the engineering analysis factor. Apart from that, among the circular economy components, the highest factor loading value is given to CO₂ gas emissions with a weight of 0.893, and among the dependent variable components (sustainable project delivery methods), the dimension of preparation with a factor loading value of 0.934 has the highest importance.

As it is shown, all factor loading values for three latent variables are greater than 0.6, which indicates the importance of the relationship between latent and observed variables [139, 140].

What is more, the path coefficients are shown in Figure 2, which can be seen that the path coefficient of BIM-circular economy is equal to 0.925, the path coefficient of BIM-sustainable project delivery methods is equal to 0.452, and the path coefficient of circular economy-project delivery methods Stable is equal to 0.453. These values show the relationships between latent variables.

Apart from that, in Figure 2, the number 0.856 for the variable “circular economy” and the number 0.790 for the variable “sustainable project delivery methods” indicate the values of R², a measure that indicates the amount of change in each of the dependent variables of the model that is explained by the independent variables. The value of R² is presented only for the endogenous variables of the model and in the case of exogenous structures, its value is zero. In general, R² between 0.19 and 0.67 can be acceptable values for different research. Thus, in our research in which values of R² are greater than 0.67, we can claim that the independent variables are able to explain the dependent variables in an acceptable way.

After fitting the model, the goodness of fit of the model has been investigated based on the indicators available in the literature [144].

As it is shown in the Table 7, the calculated amount for all indices is in the acceptable range; thus, it can be said that the fitted model is reliable. Moreover, to prove the fitted data model and its significance, the p-value of the paths is shown in Figure 3.

In the Figure 3, the number written on paths (latent variable-latent variable and latent variable-observed variable) is T statistic. In examining the significance of the path coefficients and factor loadings, if the calculated values for each path are greater than 1.96, the coefficient in the model fit is significant at the 0.05 level, and if the values are greater than 2.58, the path coefficients and factor loadings are significant at the 0.01 level. As seen in Figure 3, all the calculated values are greater than 2.58, so it can be said that the path coefficients and factor loadings in the fitted model are significant at the 0.01 level (99%).

In the next step, to determine the extent of the influence of exogenous variables on endogenous variables, standardized regression coefficients related to the paths of each of the hypotheses were investigated. These coefficients express how much (percentage) the changes of the dependent variables are explained by the independent variables presented in the model. This level of influence can be seen in Figure 1 and Table 8.

As it is shown in Table 8, the value of T statistic calculated for each of the routes is greater than 2.58, and the coefficients of the routes are significant at the error level of 0.01. Therefore, the statistical null hypothesis that there is no significant relationship or the absence of meaningful influence among the variables of each path is rejected, and the statistical hypothesis that there is a significant influence or relationship between the variables of the sides in the path is accepted.

In the above relationship, a, b, and c are the coefficients of paths 2, 3, and 1, respectively. As can be seen, the resulting number is equal to 0.481; that is, about 50% of the total effect of BIM on sustainable project delivery methods is indirectly explained by the mediating variable of circular economy.

6.1 Theoretical Contribution

6.2 Practical Insights