As defined by ISO 14040
As defined by ISO 14040 an LCA analysis should consist of the phases illustrated in Figure above. A partial LCA framework is established for this study on the characteristics of construction materials and structural forms, including elements such as the study goal, the system boundary, scope definition, inventory analysis, impact assessment, and interpretation of results (Feifei Fu, 2014).
1.Goal and Scope Definition
The goal and scope definition of an LCA is the most important aspect of the process since they define the intended application and reasons for carrying out the study as well as the intended audience the results will be directed to. Particulars of the project comprise defining the functional units, the product system to be studied, system boundaries and outlining limitations and assumptions.
LCA is relatively a new system process with an iterative technique nature, hence clearly defined goals should be set for the clear distribution of results and for reaching justifiable conclusions. To answer the various questions arising from the scope defined of the assessment, a quantitative functional unit should ensure compatibility and comparability of LCA results.
Functional units are most important when multiple elements of products are compared such an example being a direct comparison of an 80m highway composite bridge with one span 15m footbridge could not be directly achieved for reasons of bridges different purposes of use and different size (ISO14040, 2006) (Feifei Fu, 2014).
The functional unit vastly accepted in practice is the normalised carbon (kgCO2e/m2) for carbon assessment of infrastructure (E.g. Buildings, bridges, etc.)
2.Life cycle inventory analysis (LCI)
This phase of the assessment includes the data collection and calculation procedures to quantify relevant inputs and outputs within the selected system boundaries (ISO14040, 2006). A number of data associated with the inputs and outputs datasets analysed can be obtained from publicly accessible inventory databases such as the Inventory of Carbon and Energy that contains materials embodied carbon factor (ECF) for modules A1-A3.
The LCI analysis inputs include data associated with raw material quantities, embodied carbon factors (ECF), transport emission factors (TEF) and waste generation per functional unit (e.g., kgCO2e/kg).
However, the data inputs range is largely affected by the material process technologies applied, regional or global conditions of the markets and the variations on data from different sources (DU, 2015). For example, an embodied carbon factor for reinforcement bar from UK-based producers could have an ECF of 0.684 kgCO2e/kg, whereas a UAE- produced bar with no recycled content could reach up to 2.13 kgCO2e/kg (O P & J J, 2020).
Furthermore, as seen in Figure below from (O P & J J, 2020), values of EPD (Environmental Product Declaration) data from 1500 specific concrete mixes were plotted showing the extensive range of carbon emissions of different concrete strength classes.
This can be justified since the amount of Portland Cement of concrete mixes, heavily influence the embodied carbon. A much lower embodied carbon can be achieved without compromising the desired strength and other project-specific requirements by using cement replacements such as Ground Granulated Blast Furnace Slag (GGBS), Pulverised Fuel Ash (PFA) and limestone (O P & J J, 2020).
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3.Life Cycle Impact Assessment (LCIA)
LCIA assessment is aimed at evaluating the significance of potential environmental impact categories, found from the LCI results of environmental releases (ISO14040, 2006). Such categories can be identified as global warming, acidification, abiotic depletion, urban air pollution and other (DU, 2015) (Kikuchi, 2016).
LCIA quantifies environmental impacts by multiplying the results of LCI with environmental impact factors (Kikuchi, 2016). A common category of choice is the impact category of global warming that has the indicative environmental impact factor of Global Warming Potential (GWP) in accordance with the GWPs gases used by the IPCC Fourth Assessment Report: Climate Change Act 2007 (IPPC, 2007) commonly referred to as carbon emissions.
To carry a consistent analysis, different gases are weighted by their GWP, so that greenhouse gas (GHG) emissions are reported on a consistent basis. To achieve an easy overall benchmark impact of the analysis, an equivalent unit of measurement, the carbon dioxide equivalent (kgCO2e) is used where different greenhouse gases can be compared on a like for like basis relative to one unit of CO2e (PAS2080, 2016) (BS15978, 2011).
GWP provides a common unit of measure, which allows the comprehensive compiling of data for comparison with aims of identifying reduction opportunities as well as a clear understanding of the data. For civil engineering projects most commonly measurements of embodied carbon from the material, construction and waste are analysed.
4.Life Cycle Interpretation
The final stage of an LCA per ISO 14040 is the interpretation and presentation of the results obtained from the LCI and LCIA. The sensitivity and uncertainty of analysis are performed to modify the results and conclusions are presented according to the defined goal and scope.
Analysis limitations, quality and uncertainties should be clearly and transparently explained and recommendations for further study should be made.
Useful References
Feifei Fu, H. L. H. Z. a. A. H., 2014. Development of a Carbon Emission Calculations System for Optimizing Building Plan Based on the LCA Framework. Hindawi Publishing Corporation Mathematical Problems in Engineering, 2014(Article ID 653849), p. 13.
ISO14040, 2006. Environmental management — Life cycle assessment — Principles and framework, Brussels: British Standard.
Kikuchi, Y., 2016. Life Cycle Assessment. [Online]
Available at: https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/life-cycle-impact-assessment
PAS2080, 2016. Carbon management in infrastructure, London: BSI.
BS15978, 2011. Sustainability of construction works — Assessment of environmental performance of buildings — Calculation method, s.l.: BSI.