• Contractors’ selection criteria for sustainable infrastructure delivery in Nigeria

      Ceranic, Boris; Dean, Angela; Arowosafe, Oluwumi I. (University of Derby, 2020)
      The research reported in this study developed and validated a framework for the pre-evaluation of contractors for sustainable infrastructure projects through Public-Private Partnership (PPP) in Nigeria. The proposed framework uses the Analytic Network Process (ANP) to select contractors for build-operate-transfer (BOT) contractors. Theoretically grounded on a system theory, a sustainable infrastructure delivery (SID) model is developed in this research. One of its important features is the ability to solve complex decision problems, typical of a decision-making process that involves selection of contractors for PPP projects. At the deductive phase of the proposed model is the integration of the ANP (multi-criteria decision-making technique) for data synthesis. An extensive literature review was conducted with regard to selection criteria for contractors. Furthermore, a web-based questionnaire survey was undertaken, aimed at capturing the perception of the Nigerian construction professionals regarding the importance of these criteria for pre-evaluation of contractors for public infrastructure procurement. A total of 143 questionnaires was received and their feedbacks were analysed with the IBM SPSS statistical package. The findings revealed a broad range of 55 relevant criteria that were linked to sustainable contractor selection. Through the application of factor analysis, the number of the criteria was reduced to 16, after multicollinearity issues in the data set had been resolved. The 16 factors were modelled to pairwise comparison matrices, transforming decision making process from linear to a systemic approach. A purposeful sampling methodology was then applied for the selection of decision-making panel (DM), who completed the pairwise comparison survey. The survey results were synthesised by ANP. The final solution derived order of significance of the two categories of contractors- multinational construction corporations (MCC) and local construction contractors (LCC) in respect to the delivery of a sustainable infrastructure. Sensitivity analysis of the research findings reveals that the 16 criteria have differential comparative advantages, which requires critical judgement during contractors’ pre-evaluation process. Although the overall priorities rank multinational construction corporations (MCC) higher than local construction companies (LCC), it is not absolute that MCC will deliver a better value for money on all tangible and intangible elements of sustainable infrastructure attributes. LCC outperform on some of the key criteria such as local employment creation and local material sourcing, which are essential pre-evaluation criteria. This research proposes a novel framework to harmonise sustainability indicators in contractor selection and offers a new theoretical insight into the approach to contractors’ selection criteria during pre-evaluation process, which contributes to the enhancement of PPP delivery in Nigeria. Overall, the proposed SID model has demonstrated the need for a shift in the modus operandi of the government’s ministries, department and agencies (MDAs) in Nigeria from unidirectional to systemic selection techniques. It clearly demonstrates the appropriateness of the ANP to predict the contractor that will deliver more sustainable infrastructure.
    • Effects of the graphene on the mechanical properties of fibre reinforced polymer - a numerical and experimental study

      Lu, Yiling; Dean, Angela; Pawlik, Marzena (University of Derby, 2019-11)
      Mechanical properties of carbon fibre reinforced polymer (CFRP) are greatly affected by interphase between fibre and matrix. Coating fibre with nanofillers, i.e. graphene nanoplatelets (GNPs) or carbon nanotubes (CNTs) has suggested improving the interphase properties. Although the interphase is of small thickness, it plays an important role. Quantitative characterisation of the interphase region using an experimental technique such as nanoindentation, dynamic mechanical mapping remains challenging. More recently, computational modelling has become an alternative way to study the effects of interphase on CFRP properties. Simulation work of CFRP reinforced with nanofillers mainly focuses on CNTs grown on the fibre surface called fuzzy fibre reinforced polymers. Modelling work on the effects of GNPs on CFRP properties is rather limited. This project aims to study numerically and experimentally the effects of the nano-reinforced interphase on mechanical properties of CFRP. A multiscale model was developed to study the effects of the GNPs reinforced interphase on the elastic properties of CFRP laminate. The effective material properties of the reinforced interphase were determined by considering transversely isotropic features of GNPs and various orientation. The presence of GNPs in the interphase enhances the elastic properties of CFRP lamina, and the enhancement depends on its volume fraction. The incorporation of randomly orientated GNPs in the interphase increased longitudinal and transverse lamina moduli by 5 and 12 % respectively. While aligned GNPs in the interphase yielded less improvement. The present multiscale modelling was able to reproduce experimental measurements for GNPs reinforced CFRP laminates well. The multiscale model was also proven successful in predicting fuzzy fibre reinforced polymer. Moreover, the interphase properties were inversely quantified by combining with the multiscale model with some standard material testing. A two-step optimisation process was proposed, which involved the microscale and macroscale modelling. Based on the experimental data on flexural modulus, the lamina properties were derived at macroscale modelling, which were later used to determine the interphase properties from the optimisation at the microscale. The GNPs reinforced interphase modulus was 129.1 GPa which is significantly higher than epoxy coated carbon fibre of 60.51 GPa. In the experiment, a simple spraying technique was proposed to introduce GNPs and CNTs into the CFRP. Carbon fibre prepreg was sprayed with a nanofillers-ethanol solution using an airbrush. The extremely low volume fraction of nanofillers introduced between prepreg plies caused a noticeable improvement in mechanical properties, i.e. 7% increase in strain energy release. For the first time, the GNPs-ethanol-epoxy solution was sprayed directly on the carbon fibre fabric. Resultant nano-reinforced interphase created on fibre surface showed moderate improvement in samples flexural properties. In conclusion, a multiscale modelling framework was developed and tested. The GNPs reinforced interphase improved the mechanical properties of CFRP. This enhancement depended on the orientation and volume fraction of GNPs in the interphase. Spraying was a cost-effective method to introduce nanofillers in CFRP and showed huge potential for the scale-up manufacturing process. In a combination of multiscale framework and optimisation process, the nanofillers reinforced interphase was for the first time determined. This framework could be used to optimise the development process of new fibre-reinforced composites.