Infrastructure Engineering - Research Publications

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    Fifth-generation district heating and cooling: Opportunities and implementation challenges in a mild climate
    Gjoka, K ; Rismanchi, B ; Crawford, RH (Elsevier, 2024-01-01)
    Fifth-generation district heating and cooling (5GDHC) systems have the potential to provide simultaneous heating and cooling, allowing for energy exchange between users with different needs. However, their viability in mild climates with a higher share of cooling demand remains unclear. In this paper, we propose a framework for assessing the engineering, economic and environmental performance of a 5GDHC system compared to a state-of-the-art business-as-usual solution and demonstrate it through a practical case study for a university campus in Melbourne, Australia. When accessible heat sources and sinks are available, the 5GDHC system provides a cost-effective solution, with annual cost savings between 9 and 29 % and GHG emissions reduction between 25 and 58 % compared to an already advanced business-as-usual system. Additionally, by using peak off-peak tariffs and an hourly emission factor for the electricity consumed, we demonstrate the 5GDHC operational flexibility in pursuing different objectives, such as minimising cost or emissions, respectively. The results suggest that 5GDHC systems are an economically and environmentally viable solution in milder climates, and a successful implementation of 5GDHC in Australia can create new market opportunities and pave the way for its adoption in other countries with similar climatic conditions and no established history of district heating systems.
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    Comparative assessment of embodied energy of recycled aggregate concrete
    Wijayasundara, M ; Crawford, RH ; Mendis, P (Elsevier, 2017)
    Concrete waste can be recycled to produce an aggregate product; referred to as recycled concrete aggregate (RCA). While RCA is mainly used as a road base filler material, it has the potential to replace natural coarse aggregate (NA) in structural concrete. In determining the environmental performance of the resultant concrete product from this substitution, referred to as recycled aggregate concrete (RAC) against its counterpart, natural aggregate concrete (NAC), it is important to consider the effects of the entire life cycle including the upstream processes associated with each. This paper evaluates “cradle-to-gate” embodied energy (EE) of RAC received at a construction site, in comparison to NAC, using the input-output-based hybrid approach, using an Australian context. The paper constructs a model to evaluate EE of RAC and analyses the incremental energy of RAC as opposed to NAC, to identify what contribute to the difference out of four primary factors discussed in previous research. It was found that the EE of RAC is marginally different to that of NAC by +2.1 to −1.1%, and the variation was subject to the magnitude and direction of the four factors considered. The mix composition, primarily the binder composition, was found to have the highest contribution to the difference, significantly standing out from the direct energy difference between RCA and NA, difference of sourcing distance between RCA and NA and the difference of direct manufacturing energy between RAC and NAC.
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    Methodology for the integrated assessment on the use of recycled concrete aggregate replacing natural aggregate in structural concrete
    Wijayasundara, M ; Mendis, P ; Crawford, RH (Elsevier, 2017)
    Recycled concrete waste in the form of recycled concrete aggregate (RCA) is presently used mostly as a road base filler in Australia. However, instead of producing natural aggregate (NA) to manufacture natural aggregate concrete (NAC) to use in structural concrete, there is potential to use RCA to manufacture recycled aggregate concrete (RAC). While the material performance of RAC compared to NAC is analysed in the existing literature, it is not evident whether the use of RCA in structural concrete results in financial and environmental benefits. Previous literature analysing these aspects mostly focuses on a single area of investigation. This paper presents an integrated methodology for the assessment of the use of RCA replacing NA in structural concrete, considering technical, financial, environmental and social perspectives. Cost-benefit assessment (CBA) has been used to evaluate the internalised impacts as well as external costs concerning the use of both RAC and NAC. The scope of each discipline-focused assessment is presented demarcating the relevant scope for further study, and the specific tools and methodologies to be adopted are specified. Finally, amalgamating the different discipline-focused assessments, a unique approach for comparing a sustainable, alternative raw material for concrete, is presented in this paper.
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    Integrated assessment of the use of recycled concrete aggregate replacing natural aggregate in structural concrete
    Wijayasundara, M ; Mendis, P ; Crawford, RH (Elsevier, 2018)
    The use of recycled concrete aggregate (RCA) replacing natural aggregate (NA) to produce concrete named as recycled aggregate concrete (RAC) has gained increased importance in the last few decades. Despite many visible advantages associated with the initiative, RAC is not manufactured at commercial scale to replace natural aggregate concrete (NAC) used as structural concrete in Australia presently. To identify whether the production of RAC should be favoured against NAC, an integrated assessment combining multiple criteria is essential as the previous research findings provide mixed outcomes on financial viability, product performance and environmental performance. This paper uses an integrated assessment methodology employing cost-benefit analysis (CBA) which combines the financial, direct and indirect environmental, social outcomes associated with the initiative to evaluate its suitability. By combining several qualitative and quantitative studies published by the author/s, an integral result to compare the use of RCA replacing NA in structural applications is conducted in this study. Net present value (NPV) to society associated with a unit volume of RAC is evaluated as a representative indicator to compare RAC against NAC in this paper. The results state that a unit volume of RAC results in a positive NPV of 4.2–6.0% of the price of NAC for 30% replacement (and 16.3–22.6% for 100%), prior to being used in a building r. Simulation of application of the RAC to two case study buildings indicate that the average price of concrete used in the buildings is decreased by 4.1–6.1%. The results indicate that, if the external benefit associated with the production of RAC is internalised and passed on to the purchaser of the product, production of RAC in structural buildings result in a positive NPV and saving of building material costs to the contractor.
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    Net incremental indirect external benefit of manufacturing recycled aggregate concrete
    Wijayasundara, M ; Mendis, P ; Crawford, RH (Elsevier, 2018-08-01)
    Concrete waste (CW) either reaches landfill with mixed waste or crushed to produce crushed concrete (CC) used as a road-base product in Australia. The coarse portion of CC, referred to as recycled concrete aggregate (RCA) has the potential to be used as an aggregate in structural concrete replacing natural aggregate (NA). The environmental performance of RAC has been studied in comparison to NAC, in terms of direct environmental implications (DEI) concerning the processes in the production chain of these products. However, when replacement at industry level is considered, the implications go beyond the DEI, and affect a series of other products/processes within a system boundary, referred to as indirect environmental implications (IEI). This paper quantifies the key IEI associated with the use of RCA in structural concrete and evaluates the external costs and benefits associated with it using economic evaluation methods. The net benefit associated with the avoidance of landfill of CW, extraction of NA, and transportation of waste and by-products are the major externalities identified and quantified in this paper. Evaluation of these suggest that there is a significant net benefit ranging from 9% to 28% of the price of natural aggregate concrete (NAC) with the production of recycled aggregate concrete (RAC), for RCA replacement rates between 30% and 100%.
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    Template schools: Measuring indoor environmental quality
    Crawford, RH ; Jensen, CA ; Chan, TK ; Hes, D ; Aye, L (The University of Sydney, 2011)
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    A holistic model for designing and optimising sustainable prefabricated modular buildings
    Gunawardena, DS ; Ngo, TD ; Mendis, PA ; Aye, L ; Crawford, RH ; Alfano, JA (University of Moratuwa, 2012)
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    Time-efficient post-disaster housing reconstruction with prefabricated modular structures
    Gunawardena, T ; Tuan, N ; Mendis, P ; Aye, L ; Crawford, RH (Open House International Association, 2014-09-01)
    With many natural disasters such as earthquakes, cyclones, bushfires and tsunamis destroying human habitats around the world, post-disaster housing reconstruction has become a critical topic. The current practice of post-disaster recon- struction consists of various approaches that carry affected homeowners from temporary shelters to permanent hous- ing. While temporary shelters may be provided within a matter of days as immediate disaster relief, permanent hous- ing can take years to complete. However, time is critical, as affected communities will need to restore their livelihoods as soon as possible. Prefabricated modular construction has the potential to drastically improve the time taken to pro- vide permanent housing. Due to this time-efficiency, which is an inherent characteristic of modular construction, it can be a desirable strategy for post-disaster housing reconstruction. This paper discusses how prefabricated modular struc- tures can provide a more time-efficient solution by analysing several present-day examples taken from published post- disaster housing reconstruction processes that have been carried out in different parts of the world. It also evaluates how other features of modular construction, such as ease of decommissioning and reusability, can add value to post- disaster reconstruction processes and organisations that contribute to the planning, design and construction stages of the reconstruction process. The suitability of modular construction will also be discussed in the context of the guidelines and best practice guides for post-disaster housing reconstruction published by international organisations. Through this analysis and discussion, it is concluded that prefabricated modular structures are a highly desirable time-efficient solu- tion to post-disaster housing reconstruction.
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    Time efficient post-disaster housing reconstruction with prefabricated modular structures
    Gunawardena, Tharaka ; Ngo, Tuan ; Mendis, Priyan ; Aye, Lu ; Crawford, Robert (The Urban International Press, 2014-09-01)
    With many natural disasters such as earthquakes, cyclones, bushfires and tsunamis destroying human habitats around the world, post-disaster housing reconstruction has become a critical topic. The current practice of post-disaster reconstruction consists of various approaches that carry affected homeowners from temporary shelters to permanent housing. While temporary shelters may be provided within a matter of days as immediate disaster relief, permanent housing can take years to complete. However, time is critical, as affected communities will need to restore their livelihoods as soon as possible. Prefabricated modular construction has the potential to drastically improve the time taken to provide permanent housing. Due to this time-efficiency, which is an inherent characteristic of modular construction, it can be a desirable strategy for post-disaster housing reconstruction. This paper discusses how prefabricated modular structures can provide a more time-efficient solution by analysing several present-day examples taken from published postdisaster housing reconstruction processes that have been carried out in different parts of the world. It also evaluates how other features of modular construction, such as ease of decommissioning and reusability, can add value to postdisaster reconstruction processes and organisations that contribute to the planning, design and construction stages of the reconstruction process. The suitability of modular construction will also be discussed in the context of the guidelines and best practice guides for post-disaster housing reconstruction published by international organisations. Through this analysis and discussion, it is concluded that prefabricated modular structures are a highly desirable time-efficient solution to post-disaster housing reconstruction.