Key success factors towards circular economy in public-private partnership projects Open Access

There is a continuous trend of academic publications and release of industrial reports in the last few decades about measures to achieve environmental sustainability, social equity and economic prosperity. These global measures are situated within the United Nations Sustainable Development agenda. For the environment, the cardinal objectives include the attainment of clean energy, clean and healthy environment through proper waste management, and reach zero carbon emission standards to address climate crisis (White, 2018; Babayemi et al., 2016). The remaining cardinal focus are the alleviation of poverty, economic empowerment, and social diversity and inclusion programs for communities (Mihai et al., 2021). However, these measures have faced substantial economic setbacks due to the outbreak of coronavirus, trade wars and economic recessions resulting in significant financial difficulties for governments and contracting authorities to sponsor the programs. According to Akomea-Frimpong et al. (2023a), the rippling effects of these difficulties are affecting the delivery and operation of sustainable projects in transport, water, energy and healthcare within the public-private partnership (PPP) agreements. Further, Sridharan et al. (2025) mentioned that PPP projects faced significant corruption challenges with improper accountability of operational expenditure. These challenges place a limit on the sustainability of PPP projects and put a huge burden on the public budget by increasing the debt stock of nations. One of the preferred models to address these challenges is circular economy (CE). The CE model promotes the optimal use of natural resources, recycles already used materials, and the elimination of construction wastes (Ginga et al., 2020). Additionally, CE focuses on the principles of sustainability, encompassing the imperative to safeguard the environment and mitigate climate change (Schöggl et al., 2020). The CE is instrumental in the emission reduction strategies aimed at advocating for recycling practices that effectively minimize environmental and resource-related consequences (Ruzive et al., 2023). Velenturf et al. (2019) and Kirchherr et al. (2017) argued that CE is essential in providing solutions to the world’s pressing pollution (emission) challenges from mega infrastructure projects. It facilitates efficient emission and energy resource management systems in projects (Lindahl, 2024). Furthermore, Genovese et al. (2017) asserted that incorporating CE principles yields obvious environmental benefits including innovation, competitiveness and cost-saving.

It is not clear how these benefits of CE have been realized in PPP projects. The more than century old PPP model for projects development is heavily reliant on traditional linear economy approach (Strasser et al., 2021). This approach in the execution of PPP projects facilitate take, use and discard resources which is adversarial to the environment and public budgets and sustainable development (Li and Wang, 2023; Ghorbany et al., 2024). The utilization of the linear approach in PPP projects also embraces a significant consumption of fossil fuel products and resource depletion which results in tons of construction wastes and carbon emissions fueling climate crisis (Marinina et al., 2022; Geisendorf and Pietrulla, 2018). Due to these challenges, there is an inclination towards the advocacy and measures to incorporate CE framework into PPP project to effectively tackle the aforementioned problems (Wuni and Shen, 2022; Bogovac et al., 2021). Despite the increased advocacy, benefits and growing application of CE, very few studies were identified on PPP projects in the construction and engineering management literature. A search in scholarly databases such as Scopus, Google Scholar and Web of Science demonstrate little studies directly address CE in PPP projects. For instance, Memari et al. (2025) article is limited to success factors on circular supply chains in PPP infrastructures, and Tahir et al. (2024)’s research was only centered on energy and recycling of waste projects. Akomea-Frimpong et al. (2024b) presented comprehensive critical success factors for CE application for PPP projects but the article is a literature review paper with no empirical support. Therefore, the purpose of this paper is to analyze the success factors facilitating circular PPP project delivery using empirical data sourced from practitioners in the PPP sector. The result identified key determinants for effective integration of CE principles into PPP projects. The current study also provides essential information for researchers and policymakers on the major success factors on CE in PPP project management. Literature review section comes next to this section comprising of the explanations of CE, PPP projects and the interrelationships between the two concepts. The methodological steps in conducting this study are found in Section 3. The findings and interpretations of the data are shown in Section 4 and 5 respectively. Section 6 demonstrates the implications of this study while Section 7 and 8 present the conclusions, limitations and recommendations for further studies.

The CE concept has a long historical root (Širá et al., 2022). According to Bruel et al. (2019), CE originated from economics particularly environmental economics. It is interlocked with philosophical positions in environmental science with roots from eco-industrial revolution. However, several experts argue that the origin of CE is attributed to the weaknesses of linear models (Sariatli, 2017; Gubeladze and Pavliashvili, 2020). MacArthur (2013) explained linear model as a “take-make-dispose” model where materials are discarded after use. The CE offers viable alternative to this approach through efficient resource consumption and production (Merli et al., 2018; Korhonen et al., 2018). The CE model reuse recycled resources to manufacture goods and reintroduced them into the economy (Guohui and Yunfeng, 2012). Several definitions of CE have been used over time by different industries and academic organizations; nevertheless, there is currently no distinct and well-accepted definition that is exclusive to PPP projects (Malabi Eberhardt et al., 2020). In this study, CE is explained as a model that eliminates financial and non-financial waste, promotes social inclusion, climate neutrality and long-term sustainability of PPP projects through recycling, reusing and optimized resource utilization strategies. The CE model is one of the sustainable solutions for PPP projects to meet Sustainable Development Goals (SDGs) (Rizos et al., 2017). The model provides positive environmental and climate impacts of resource use in PPP projects (Zink and Geyer, 2017; Velenturf et al., 2019). Furthermore, this model provides remedies for material and energy consumption through recycling, refilling and rethinking of the use of PPP construction resources (Ryen et al., 2022).

Private investment in public developmental projects has been prevalent in Europe since the 18th century (De Vries, 2013). In 1992, private finance initiative (the forerunner of PPPs) was introduced to champion the contributions of the private sector into public projects. According to Hodge et al. (2017), the application of PPP to deliver projects has risen since 1992 with wide usage in the European Union countries, Australia, China, United States and Canada. In the PPP arrangements, private entities partner with the state institutions to plan, finance, build, operate and deliver public utilities and infrastructures (Grimsey and Lewis, 2007; Tshombe and Molokwane, 2016). In this study PPP projects are explained as public projects (infrastructures or services) executed by governmental agencies and institutions together with private entities. The PPP projects are characterized by two principal partners namely the public sector (the national government, municipal authorities and local councils) and the private entities such as financial institutions, investors, private contractors and suppliers (Bogovac et al., 2021). These partners bring together resources (financial and non-financial) to construct and manage projects. The PPP contracts are long-term in nature spanning many years with concessionary periods (Cui et al., 2018). The burden of risks and benefits are shared by the partners according to the PPP contract agreements. Hodge et al. (2017) revealed that PPP adoption is increasing in many developing countries as a viable instrument to attract foreign direct investments. For instance, Liang and Hu (2018) found that foreign investors, not native Chinese private institutions, have participated in completing many PPP projects in China. Notably, different forms of PPPs exist such as build-operate-transfer, and design-finance-build-operate at local councils and state governments in these developing countries (Li and Akintoye, 2003; Tang et al., 2010).

The PPP is beneficial due to its track-record of successes in funding and risk management of projects (Mofokeng, 2019; Akomea-Frimpong et al., 2022). It has also maintained an enviable position as one of the best project delivery models in the global infrastructure sector (Bayliss and Van Waeyenberge, 2018). PPP possesses better delivery qualities than conventional methods of procurement because it utilizes resources from multiple partners (Cui et al., 2018). It is a tool for support sustainable infrastructure projects, which is crucial in sustainable development of less developed nations (Cui et al., 2018). PPP arrangements are also important in reducing public financial burdens, and it played a significant role in delivering vaccines during the coronavirus outbreak (Castelblanco et al., 2022). The PPPs are capable of managing multiple stakeholder interests (Sarmento and Renneboog, 2016).It has been widely used to execute social projects in transport, water, energy and public health which enhance social cohesion and development (Wang and Ma, 2021). Research outputs also indicate PPP as a mechanism for local councils and nations to achieve the 17 SDGs (Cui et al., 2018; Akomea-Frimpong et al., 2022). This is due to the potentials of PPP arrangement to incorporate social, economic and ecological values into developmental agendas (Bello, 2025). Nonetheless, PPP models have many challenges while delivering projects. For example, the majority of PPP projects demonstrate harmful environment practices (Arzo and Hong, 2024). Akomea-Frimpong et al. (2022) mentioned that PPP projects follow the linear economy model: extract resource, use the resources to construct and operate projects, and dispose resources off at the close phase of the projects. This leaves little or no room for reuse of resources and long-term sustainable practices included.

The core tenets of CE from Ellen MacArthur Foundation (2015) and Cramer (2017) reports include waste reduction, separating economic growth from environmental damage, and creating value. The reports and existing empirical literature provide the defining enabling key success factors (KSFs) of CE. These KSFs are explained in this paper as activities which are essential in influencing the application of CE in PPP projects. The KSFs also represent terminologies such as promoting factors, enabling factors, drivers, driving factors, influencing factors, success factors and critical success factors. These terms are applied interchangeably and have the same meaning, and they are linked to PPP projects (Figure 1). A key enabling factor of CE is to minimize resource consumption in the development of PPP projects (Allam and Jones, 2018). This means practitioners need to adopt CE practices that diminish dependence on virgin materials and foster greater circularity (Kandpal et al., 2024). Another success factor is the promotion of green economy, which seeks to integrate diverse industries into a sustainable chain where the waste of one industry functions as an input for another (Ghisellini et al., 2016). Ultimately, CE enhances green economy through production, environmental impact assessments and the optimization of energy consumption (Ghisellini et al., 2016). Consequently, it can be asserted that CE reduces waste generation, and facilitates synergy among industries, the environment and people in the green economy development (Goyal et al., 2022; Yang et al., 2023). Moreover, the CE model’s success factor is mitigation of resource leakages and facilitation of financial prudence in PPP projects (Folhas, 2020). There is a growing interests in factors promoting CE in PPP research and practice (Alkhuzaim et al., 2021). For example, Bogovac et al. (2021) and De Silva et al. (2025) emphasized the enabling factor of assimilation of circular and low-carbon resources and material for PPP projects. Akomea-Frimpong et al. (2024b) explained critical success factors of CE including resource and environmental efficiency management for PPP infrastructures. Effective leadership, contract management, regulations and technological innovations have been identified as key factors in ensuring sustainable PPP projects (Fatimah et al., 2020). These enabling factors have considerable advantages to ensure successful execution of PPP projects as shown in Figure 1 (Ghisellini et al., 2016).

This section constituted the searching and retrieving of literature using keywords: KSFs, CE and PPP projects. The search happened in prominent databases such as Scopus, Google Scholar, EBSCOhost and Web of Science (Kukah et al., 2021). The documents that were retrieved from the search were two hundred and forty-three (243) comprising of journal articles, books, theses, reports, conference papers and institutional documents. Three inclusion criteria were applied to select relevant literature out of the documents. First, the availability and accessibility of the document. Literature should be easily accessible in academic databases. Second, the document should have been written in English. Documents composed in other languages such as Spanish, Arabic, Chinese and others were excluded. Third, the document should comprehensively cover CE and projects under the PPP contracts. Documents that just mentioned either CE or PPP projects without linking the two concepts were removed from the document list. The content analysis of the remaining sixty-nine (69) documents helped in identifying thirty-four (34) factors promoting CE for PPP projects (Owojori and Okoro, 2022).

From the review of past studies, the factors identified were inserted into a questionnaire within the Microsoft Word. In addition to the factors, the questionnaire had another section dedicated to the profile of the respondents. In detail, the profile questions included the location of the respondents, their work experience, project type and the number of PPP projects associated with them. It also included the education and job status of the respondents (Hwang et al., 2013). While the questions on the profiles of the respondents were a mixture of closed and open-ended statements, the questions about the factors were closed ended. The closed ended statements relating to the factors enhancing CE principles in PPP projects were measured on the five point Likert scale (Zou et al., 2014). With measurement scale of strongly agree (5) to strongly disagree (11). To support the reasons for the use of Likert Scale as the measurement scale in this article, PPP studies such as Toriola-Coker et al. (2023) and Chou and Pramudawardhani (2015) argued for this tool as the ideal rating scale on success factors. Validation of the questionnaire was undertaken through a pilot study where seventeen PPP academic and industry experts were contacted to review the questionnaire. The comments from the pilot study helped in making changes to the questionnaire where experts suggested either the removal or combination of some of the 34 factors from Section 3.1. Table 1 contains the final list of items for the study. The questionnaire was submitted to an ethics committee as part of a doctoral thesis. The committee reviewed and approved the questionnaire together with a list of potential participants to check the study did not breach any ethical principles such as trust, privacy, respect for autonomy and anonymity.

The potential respondents were targeted all over the world to participate in the study. The decision to adopt this approach was motivated by the researcher’s intention to obtain responses from a wide range of participants from different understandings, cultures, geographical areas, and experiences about PPP projects since this model has been implemented in every country across the face of the earth. Moreover, the rationale for selecting this approach is previous studies have used same approach such as Darko et al. (2017) and Osei-Kyei and Chan (2017). These studies emphasized the need to reach out to respondents with diverse backgrounds which strengthens the generalizability of the study. Purposively, PPP practitioners were searched on LinkedIn, a social media platform known for its peculiar features to identify the profile of professionals on PPP projects. Professionals who replied to the messages invited other professionals who had vast knowledge and more than ten years’ experience on PPP projects. The potential respondent list was two hundred and fifty-six (256). Given the global scope of the study, an online questionnaire was distributed to eligible respondents using the “Google Forms” which facilitated the efficient transmission and collection of feedback (Kalesnikaite and Baker, 2024). The selection of the online administration of the questionnaire was also motivated by the efficiency in terms of time, cost-effectiveness, and its global reach (Fathi and Shrestha, 2023). A section of the online questionnaire contained a consent section which sought for the voluntary approval (or disapproval) of participants to be part of the study. The responses received were one hundred and eighty-seven (187). Representatively, this represents 73.05% response rate (see Table 2). As seen in Table 2, majority of the respondents have strong educational background, with half holding a master’s degree, as well as diverse perspectives, with a significant portion having mid to senior-level experience, potentially providing a balanced view of CE success factors. Geospatially, the findings show a growing interest or expertise in CE practices with PPP infrastructure in both developed and emerging economies. As a result, the current study’s assessment of KSFs incorporates a wide range of background experiences. Most respondents indicated practical experience on multiple projects in Table 2.

Initially, the internal consistency of the dataset to prove its reliability was tested with the Cronbach Alpha (CA). The test showed CA of 0.849 in agreement with the established of CA of 0.7 and above (Ekanayake et al., 2023). The normality distribution of the data was calculated with the Shapiro–Wilk test (SWT). The findings and implications of the SWT was that the data did not meet the normally distributed pattern at 5% significance level in Table 3 (Akomea-Frimpong et al., 2024a). The Kruskal–Wallis H-Test (KWHT) was conducted afterward due to its suitability for datasets which defies the principles of normality distribution. The goal of the test was to analyze the potential existence of variations in the rating of the success factors pertaining to circularity in PPP projects (Ali et al., 2023). The disparities in the two groups of respondents from the private and public sector using the KWHT show insignificant differences about their perspectives on issues concerning the CE for PPP projects as shown in Table 3. To assess the relative importance of the success factors (KSFs), the mean score ranking was undertaken in reference to previous studies such as Wuni and Shen (2022) and Agyekum et al. (2023). In addition, the principal factors from the data were assessed using factor analysis (Shrestha, 2021). The Bartlett’s test of sphericity (BTS) measured the correlating relationship between the success factors within the factor analysis (Williams et al., 2010). The Kaiser–Meyer–Olkin (KMO), another test that supports the factor analysis examined the adequacy of the data sample (Budaev, 2010). The outcomes of the two underlying tests show BTS at 0.000 (5% significance level) and KMO at 0.984, which are satisfactory. Finally, the fuzzy synthetic evaluation (FSE) was conducted to determine the critical factor groups following the factor analysis. The adoption of the FSE was deemed significant in addressing the issues of ambiguity and prejudice that arise in multi-faceted decisions involving diverse participants in a study (Ekanayake et al., 2023). This is particularly crucial given the emphasis placed on CE by governments and private institutions (Adabre and Chan, 2020). Furthermore, determining the order of the importance of the groups of KSFs is relevant for real-life (practical) decision-making by PPP practitioners. The fuzzy synthetic assessment methodology is essential to achieve this goal (Niazmandi et al., 2024). Several studies including Dulia et al. (2021), Temitope et al. (2023) and Akomea-Frimpong et al. (2024a) have extensively employed FSE. The four (4) principal groups extracted from the exploratory factor analysis (EFA) formed the foundation of the FSE. The assessment of the major factors utilizing the FSE was conducted using a three-step processes:

1. Step 1: Compute the weightings for the KSFs and categorized (principal) factors.

2. Step 2: Compute the membership function levels for the KSFs and categorized (principal) factors.

3. Step 3: Compute the significance index for categorized (principal) factors.

Table 3 presents the descriptive results on the success factors (KSFs) data. Following the studies of Wuni and Shen (2022), Jha and Iyer (2006) and Cheung et al. (2011), a threshold of ≥3.5 of the mean was set to determine the significant factors. KSFs which achieved a mean score of 3.5 or above were deemed significant, while those scoring below 3.5 were considered insignificant. Based on the mean, the top five KSFs for CE in PPP infrastructure projects were identified as optimization of zero carbon and recyclable resources (mean = 4.73), the need for environmental protection (mean = 4.69), legislation to promote circular models (mean = 4.62), circular supply chain expertise for public buildings (mean = 4.54), and effective leadership (mean = 4.46). These findings underscore the critical role of resource optimization, environmental protection, supportive legislation, specialized expertise, and strong leadership commitment in the success of CE initiatives within PPP projects (Oluleye et al., 2023). These results align with the research of Akomea-Frimpong et al. (2024b), who also identified these KSFs as the most critical factors for CE in PPP projects. While the mean provided insights into the relevance of the KSFs, the KWHT test assessed the variations of opinions of the respondents on the KSFs. In addition, the spectrum of importance of the factors was established as shown in Table 3 on the following scale: 4.2–5 (very important), 3.2–4.2 (important), 2.2–3.2 (somewhat important) and 0–2.2 (not important).

The EFA is a method utilized to ascertain the interrelationships between the KSFs (Shrestha, 2021). It served as a dimension reduction strategy to arrive at the principal groups of the KSFs (Chan et al., 2022). The principal component analysis and varimax rotation techniques were applied to extract the KSF groups to enhance clarity and interpretability. Four principal success factors (PSFs) came out from the EFA analysis, collectively accounting for 78.703% variances. These findings underscore the importance of the measures towards success of the CE implementation in PPP projects. The four (4) were subsequently labeled as PKSFs and shown in Table 4. PKSF 1 (Environmental Protection Initiatives) constituted 31.157% of the variances, and it comprises of seven (7) items. The second PSF (effective leadership and proficiency of the project team) constituted 24.128% of the variation with six essential success factors. The PKSF3 (effective stakeholder engagement and regulations) accounts for 15.785% of the variances and contains five (5) items. PKSF4 (Innovative technologies and data sharing) accounts for 7.633% of the variances with four items. In this EFA analysis, the KSFs were automatically included in the PKSFs (components) from the SPSS software algorithm, and common group names were given based on the characteristics of the KSFs in each group.

In this stage, the first step was to compute the weights of the KSFs and the four (4) groups of factors (PSFs) from Section 4.2. This computation was done to assess the contribution of each of the KSFs in the PSFs (Kukah et al., 2023). Therefore, the weighting was computed using equation (1) below. Imperatively, what makes computation of weighting important to FSE is that the results for the FSE are dependent on it (Omer et al., 2023). Equation (1) is:

where Wi = Weights of each KSFs or PSF;

Where Mn = mean values of key factors and

Where μi = summation of the mean values of all KSF.

Using Equation (1) and shown in Table 5, the Environmental Protection Initiatives (EP) contains five (5) KSFs, including KSF4, KSF3, KSF8, KSF12, KSF14, KSF9 and KSF13. For example, KSF3 has a mean score of 4.73, so the weight of KSF3 is:

Table 5 presents the weightings for the remaining KSFs utilizing the same Equation (1). The total mean values for Environmental Protection Initiatives (EP), Good leadership and competence of the project team (LC), Effective stakeholder engagements and regulations (SR) and Innovative technologies and data sharing (IT) are 26.96, 24.95, 18.79 and 14.48, respectively.

The same equation was applied to the groups (PSFs) to earn their weight. The weighting value of the Environmental Protection Initiatives (EP) group for example is:

The weighting for the other three (3) categorized PSFs followed the same computation approach (see Table 5).

Using grading alternatives (GA), the membership functions (MFs) of the five points on the Likert Scale set in Section 3.2 with 1 = strongly disagree to 5 = strongly agree.

Where:

• MF_PA is the member function (MF) of success factors.

Z = _1p (x = 1,2,3,4,5) is the GA, which is the linguistic grade, N_i is the sum of respondents who rated the GA on each KSF and $MFpa=ZXPANi$ is the MF. This is simplified in the equation as.

Therefore, the MF of KSF4 is obtained from ratings of strongly disagree (0.00%), disagree (10.70%), neutral (21.40%), agree (64.20%) and strongly agree (3.70%). From Equation (2), the MF is:

In Table 5, the MF for KSF4 is (0.001, 0.107, 0.214, 0.642, 0.037). The same approach was used to compute the reaming success factors, and the resulting values are presented in Table 5.

Afterward the MF of the principal factor components, PKSFs (F_i) was calculated using Equation (4), which involved multiplying the weightings (W_i) and MF of KSFs within each PSF in Equation (4):

Where:

• F_i = the fuzzy evaluation matrix

• W_i = the weights of the success factors in each of PSFs.

• • = represents the fuzzy composition operator.

• Q_i = MFs of the KSFs under each PSF, as shown in Table 5.

Equation (4) is demonstrated in Environmental Protection Initiatives (EP) as the weighting multiplied by the MF:

W_i = (0.175, 0.174, 0.155, 0.133, 0.127, 0.122, 0.114) and

• = (0.011, 0.071, 0.173, 0.591, 0.153).

The approach towards getting the MFs for Good leadership and competence of the project team (LC), Effective stakeholder engagements and regulations (SR) and Innovative technologies and data sharing (IT) relied on the same process as environmental protection initiatives (see Table 5). Their results include:

• Q_LC = (0.008, 0.047, 0.220, 0.408, 0.318)

• Q_SR = (0.002, 0.022, 0.221, 0.434, 0.321)

• Q_IT = (0.000, 0.019, 0.088, 0.350, 0.543)

The significant indices of the PKSFs are the multiplication of the grade alternatives and the MFs of the individual PKSFs. The significant indices of the four (4) PKSFs from Equation (5) are:

Where:

• S = Significant Level of each PKSF

• W = Weighting of each PKSF

• Q = Membership function of PKSF

Using the L (GA) = Alternative linguistic grade in Section 4.3.2.

The significant indices of the PKSFs promoting CE in PPP projects are computed as follows:

The findings illustrated in Figure 2 demonstrate the order of importance of the factor groups on the KSFs. The factor group, PKSF4 recorded the first position which is about the application of technological models and sharing of data to ensure the successful implementation of CE. It is followed by effective stakeholder engagement and regulatory guidelines. The outcomes also show good leadership and equipping the project team with CE knowledge is important to realize circular PPP projects. The environmental initiatives (PKSF1) was the least scored factor group.

Environmental Protection Initiatives (PSF1) attained fourth position in the FSE analysis with an index of 3.804. Environmental and sustainability initiatives are influencing measures for CE in PPP projects. This component consists of seven (7) KSFs. The optimization of zero-carbon recyclable resources (KSFG3) has an average significant score of 4.73. According to Aithal and Aithal (2023), optimizing sustainable resources means maximizing renewable energy sources, reducing environmental impact and promoting sustainability. It supports the application of environmental criteria and performance indicators in project contracts, incentivizing zero-carbon friendly energies and CE principles throughout the planning, execution, and maintenance phases of projects (Ngan et al., 2019). Another relevant measure is environmental protection (KSF4), which has an average value of 4.69. This KSF suggests the prioritization of procedures and frameworks, as well as the integration of sustainable materials and technologies (Nisar et al., 2021). This is critical for mitigating the negative environmental impacts of PPP project activities. Green infrastructure practices (KSF12) are also an important consideration in this category. Grytsyshen et al. (2019) emphasized that green infrastructure practices in PPP are a critical success factor for the CE. This implies that PPP projects should be planned, designed, and coordinated to implement nature-based and environmentally friendly solutions for long-term environmental goals and protect the environment (Watkins et al., 2019). Rahman et al. (2021) mentioned that PPP projects using environmentally friendly materials benefit the sustainable ecosystems. Sha et al. (2021) also reiterated the essence of eco-friendly materials in environmentally friendly and durable project management.

Leadership and the level of competence of project managers and team (PKSF2) secured the third position with an FSE index of 3.980. One KSF within PKSF2 is the inclusion of circular supply chain experts for public buildings (KSF16), which underlines the necessity to recruit and train professionals to acquire knowledge and skills on CE procurement principles. Pieroni et al. (2021) argued for experienced practitioners who can offer strategic guidance and promote circular business models. Additionally, these competent CE professionals aid in the adoption of CE practices, spearhead consumer awareness campaigns, legislative measures, and product design for circularity (Khan et al., 2021). Given the intricate nature of PPP projects, effective leadership (KSF1) is indispensable for overcoming sustainable and climate neutral challenges, aligning the expectations of stakeholders to CE targets. Project leadership sets the project’s vision, fosters collaboration between partnering entities, and ensures the integration of futuristic and green practices throughout the project lifecycle (Saini and Agarwal, 2020; Villet, 2021).

Furthermore, engaging specialists in CE (KSF5) within PPP projects is crucial to achieve the objectives of CE (Afshari and Górecki, 2019). The involvement of the experts, particularly during the design phase, can catalyze CE business models and promote positive image of the projects to users (Knošková, 2020). Realignment of management training policies for practitioners towards circular contracts (KSF10) had a mean of 4.05 which is highly recognized as essential in the CE education programs. This ensures that practitioners possess the requisite skill set and understanding to implement CE principles to enhance project outcomes (Gerding et al., 2021; Lulaj et al., 2023). Hence, reinforcing project team CE competences and realigning leadership focus are imperative steps to achieve CE within PPP projects (Villet, 2021; Wuni and Shen, 2022).

Effective stakeholder engagement and regulations (PSF3) was the second component from the FSE analysis with index of 4.051. Based on the findings, the most significant component within this category is legislation to promote circular models (KSF2), with mean value of 4.62. Since governments and state institutions are mostly responsible for regulating PPP project modalities in many jurisdictions, establishing a clear legal and regulatory framework concerning CE models in PPP projects will facilitate their implementation (Kukah et al., 2023). The next significant KSFs within KSF2 are land use and construction waste regulations (KSF7) and strong collaboration among stakeholders (KSF18), with averages of 3.71 and 3.64 respectively. These results are supported by the work of Padilla-Rivera et al. (2020) and Sofolahan et al. (2024), which indicated that the formation of a CE depends on stakeholders' understanding and support. However, there has been criticism from industry professionals and stakeholders regarding CE regulations s, leading to delays, cancellations, or reversals in their implementation, particularly in PPP projects (Akomea-Frimpong et al., 2023b). García-Quevedo et al. (2020) argued that a deficiency exists in establishing substantial collaboration guidelines among stakeholders regarding CE matters. This deficiency arises due to the perception held by certain experts that adopting CE practices will result in increased project costs (Kineber et al., 2024). To ensure the successful application of CE for projects within the PPP pacts, it is imperative to effectively address these perceptions and present inclusive CE financial solutions at the beginning of the projects.

Innovative technologies and data sharing (PSF4) was the first factor group from the FSE analysis, scoring an index point of 4.418. The index indicates the highest position of significance of the PKSF4 group and demonstrates the essence of innovative technologies and data sharing in the CE agenda in PPP projects. New and emerging smart technologies are capable of influencing the implementation outcomes of CE in projects (Sumra et al., 2025). PSF4 comprises of four factors, including comprehensive support from innovative technologies (KSF11), sharing of information on CE with trust (KSF21), usage of just-in-time IT delivery models (KSF20), and acceptance of innovative supply logistics for circular PPP projects (KSF22). The comprehensive support from innovative technologies is ensures digital construction models such as digital twins, wearable sensors and robotic cranes in project management. Kalogiannidis et al. (2022) identified a connection between digital technologies and the fast adoption of CE models. Similarly, Bressanelli et al. (2018) highlighted innovative onsite and offsite technologies in the advancement of CE principles in projects. Therefore, KSF11 can enhance the sharing of digital information on construction technologies in CE with trust (KSF21), ultimately leading to improved collaboration, transparency, and efficiency, resulting in sustainable development outcomes (Rejeb et al., 2022). Moreover, CE facilitates the usage of just-in-time IT delivery models (KSF21) by integrating real-time data analytics, agile development methodologies, and cloud-based solutions, leading to increased project efficiency, cost-effectiveness, and adaptability to changing requirements (Giorgi et al., 2022; Islam, 2024). The Just-in-Time (JIT) model in construction has been demonstrated to significantly reduce waste and improve productivity. For instance, Kong et al. (2018) found that JIT can reduce onsite wastes to the tune of 10.7%, while Hussein and Zayed (2021) demonstrated that JIT wastes can be quantified and eliminated to enhance construction productivity. Ajayi et al. (2017) added the prominence of JIT in circular supply chain and procurement heightens efficient project delivery systems. Integrating these initiatives influence the acceptance of innovative supply logistics for circular PPP projects (KSF20) (Zhang et al., 2022). The acceptance of innovative supply coordination and logistics also pose positive and significant additions to CE progress in projects. This corroborates with the assertions of Yang et al. (2023) and Hazen et al. (2020) that innovative supply logistics is crucial for circular optimization of resource of projects.

The current study has various implications for PPP policies, scholarly research and practices. At the project level, the information from this article will be helpful in lifecycle decision-making concerning costs of implementation, climate risk analysis, waste and environmental management. Concerning emissions from PPP projects such as roads and buildings will largely be addressed with adequate knowledge of the CE principles. From Section 4.3, the results demonstrate that the respondents rated the environmental initiatives component as the least important CE enabling factor. This finding could imply that practitioners have inadequate knowledge on the impact of the initiatives that protect the environment drive the achievement of CE targets in PPP projects. It may also imply practitioners have not implemented these environmental initiatives. Therefore, these outcomes could assist education, training and support programs among the practitioners and stakeholders to prioritize and apply environmental measures to ensure sustainable circular projects. Review and possible renegotiation of PPP contracts based on the information from this article could be valuable in resetting traditional projects into sustainable and circular project status. The study supports the arguments for amendments in current industry regulations for the easy acceptance of CE for PPP projects. The development and application of PPP-based project codes will facilitate the regulation of CE implementation as supported in Section 4.3 as the second most important factor groups. The identified KSFs are checklists for the development of CE implementation models. The findings also advance the literature by identifying the KSFs for CE that could be important constructs for conceptual and theoretical models. Currently, there is a lack of conceptual models and studies in scholarly literature on key CE such as procurement, contract management, stakeholder management and circular investment for PPP projects. This work (Figure 1) could serve as a reference to developing a more comprehensive conceptual model for PPP research.

This study has empirically analyzed and identified the KSFs for CE in PPP projects. A questionnaire survey distributed globally to practitioners in the PPP sector globally. The research employed mean and the KWHT to evaluate the significance of the 22 KSFs and the viewpoints of worldwide participants with many experiences. The mean analysis identified top five (5) KSFs for CE as follows: optimization of zero carbon and recyclable resources, the necessity for environmental protection, legislation to promote circular models, expertise in circular supply chains for public buildings, and effective leadership. Through EFA, four PKSFs were identified: Environmental Protection Initiatives (PKSF1), effective leadership and proficiency of the project team (PKSF2), effective stakeholder engagement and regulations (PKSF3), and innovative technologies and data sharing (PKSF4). The FSE analysis identified PKSF4 as the paramount success factor, succeeded by PKSF3, PKSF2, and PKSF1. It can be observed from the findings that leadership plays a very relevant role in the CE transition agenda for PPP projects. Leadership commitment from senior members of the project management team as well as effective involvement from political and community leaders are important to realize CE targets. PPP developmental projects are an integral part of local communities, so it is ideal that local authorities and custodians make and support decisions on CE adoption and implementation. Effective support from other stakeholders such as suppliers, subcontractors and banks is helpful in delivering circular projects. It is also evident from Table 4, that environmental initiatives, PKSF1 such as recycling and green project practices are key factors to attain circular PPP projects. This study has significant contributions for PPP practice. This is because it throws more light on the successful factors that promote the adoption of CE for PPP projects. The information on the KSFs could be a guide for PPP practitioners to understand relevant measures towards circularity of projects. The findings could also enhance the knowledge of practitioners and influence their decision-making to ensure long-term sustainable circular practices. The list of KSFs could be important in developing CE success factor frameworks to support PPP project management. The findings could have implications on project policies and industry standards. The results in PKSF3 point to the impacts of factors relating to construction codes, stakeholder engagement, risk, environmental and quality management standards circular transition measures for PPP projects …

This article recognizes the following limitations. Every respondent completed the survey based on their individual opinions and experiences which may differ from other participants. This approach to data collection is prone to bias and subjectivity. Future research may enhance survey data by incorporating more objective metrics, and use of secondary and econometric data to bolster the robustness of the findings. Also, to minimize the bias, a larger sample of data should be used for the data analysis. Second, further research should be invested in performance assessment of the KSFs and monitoring measures for sustainable CE application in PPP projects. Performance assessment models on the success factors should be developed and tested on several PPP initiatives such as transport, building, water and shopping centers. Third, it is not clear how contract arrangements as identified in KSF10 influence CE for the projects. Future studies should investigate CE-based contracts including procurements and other relevant agreements which influence transition to circular PPP projects. Fourth, KSF13 mentioned financial support for the application of CE but existing studies such as Akomea-Frimpong et al. (2024b) clearly mentioned transitioning to circular PPP projects is limited by financial challenges. Future studies should explore alternative financing models to facilitate the transformation of conventional PPP projects to CE status. Fifth, this study utilizes data from different geographical areas, but it is important further studies delve into the KSFs using country-specific data or analyze the factors separately. Moreover, project-specific database should be established to support the analysis of project-by-project analysis. Lastly, this study explored a limited number of factors (22 KSFs) on the integration of CE in PPP projects. It is suggested that further studies utilize research techniques such as interviews, focus group discussions and expert forums to identify additional success factors.

This paper is part of a research project investigating the circular economy in public-private partnership arrangements. Therefore, the authors are grateful to reviewers and editors who have contributed to improve the quality of this paper. We also thank our affiliated universities and anonymous participants for helping in the data collection process.