Infrastructure Engineering - Research Publications
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ItemComparative assessment of embodied energy of recycled aggregate concrete(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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ItemMethodology for the integrated assessment on the use of recycled concrete aggregate replacing natural aggregate in structural concrete(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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ItemIntegrated assessment of the use of recycled concrete aggregate replacing natural aggregate in structural concrete(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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ItemNet incremental indirect external benefit of manufacturing recycled aggregate concrete(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%.