Embodied Energy

Embodied energy defined as the amount of energy to produce a material.

From: Waste and Supplementary Cementitious Materials in Concrete, 2018

Chapters and Articles

Carbon and biofuel footprinting of global production of biofuels

Deep Gupta, Sudhir Kumar Gaur, in Biomass, Biopolymer-Based Materials, and Bioenergy, 2019

19.3.3.4 Embodied energy

The energy embodied in the structural materials of, and energy used in, the construction of each biofuel production plant (or biorefinery) is called “embodied energy[29]. The footprint for embodied energy footprint per liter of biofuel was then calculated via [15]:

Embodiedenergyfootprintcomponent(gha/Lofbiofuel)=embodiedenergy(GJ/Lofbiofuel)*conversionfactor(gha/GJ)

It was presumed here that the origin of embodied energy was associated with fossil fuels. The conversion factor was hence computed from primary energy sources and the conversion factors adopted by Alderson et al. [42].

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Sustainable Built Environment & Sustainable Manufacturing

K.I. Praseeda, ... Monto Mani, in Encyclopedia of Sustainable Technologies, 2017

EE in Building Materials

EE of material is the sum of energy consumed for the main processes involved in production of the material (direct energy input) and the energy spent for procurement of raw materials and other resources required for the main production processes (indirect energy inputs). It is the total primary energy required for extraction of resources, transportation, manufacture, assembly, disassembly, and end of life disposal of a product (Monahan and Powell, 2011). Existing compilation on EE values for building materials include mainly open-access institutional, industrial, commercial, and individual databases (Menzies et al., 2008). Table 1 summarizes the details of the above databases with regard to data characteristics. EE values for building materials from available sources have been compared in Table 2.

Table 1. Embodied energy data from institutional databases

Sl. No.Institutional databasesData source and characteristics
1Inventory for Carbon and Energy (ICE) developed by University of Bath, UK
(Hammond and Jones, 2008)
Embodied energy data collected from journal articles, conference articles, books, life cycle studies, etc.
2Database from Centre for Building Performance Research, New Zealand (NZ)
(Alcorn, 2003)
Estimated embodied energy data using process-based hybrid analysis method
3United States Life Cycle Inventory database by National Renewable Energy Laboratory (NREL) (USLCI, 2012)Database compiled from various sources
4ATHENA Sustainable Materials Institute building material inventory, CanadaLife cycle data estimated using process analysis method

Table 2. Comparison of embodied energy of common building materials from few data sources

Building materialsInstitutional databaseIndividual studies
ICE Database (Hammond and Jones, 2008)New Zealand Database (Baird et al. 1997)Kofoworola and Gheewala (2009)Langston and Langston (2008)Dias and Pooliyadda (2004)Scheuer et al. (2003)Reddy and Jagadish (2003)Debnath et al. (1995)Empty Cell
Location of data sourceUKNZThailandAustraliaSrilankaUSNot specificIndiaNZ
UnitMJ/kgMJ/kgMJ/kgMJ/kgMJ/kgMJ/kgMJ/kgMJ/kgMJ/kg
Aggregate (gravel)0.10.10.21.140.29
Aluminum virgin218191216.5250207236.8130
Recycled28.8
Bricks32.51.8632.71.421.7
Cement4.67.83.6204.23.75.859.298.98
Ceramic tile92.52.214.875.5
Clay tile6.5
Hollow or solid concrete blocks0.670.942.130.7
Glass1515.917.1130.56.825.811.06*31.5
General insulation4553.7
Lime5.35.6317.6410.39
Paint6890.481.560.281.8
Gypsum plaster1.84.53.310.9
Natural sand0.10.10.10.330.60.04
Steel virgin35.33222.17032.6830.64220.6234.9
Recycled9.514.1
Stone slabs granite0.1–13.90.70.1
Limestone0.30.1
Marble2
Timber3.06*
Glue laminated124.6
Medium density fiber (MDF) boards1111.9
Particle board9.58
Plywood1510.48.5
Vinyl flooring65.6479.1
PVC67.57060.796

EE values compiled in Table 2 show wide range for EE of any specific construction material. Variations in EE value of a material across different countries/databases can be attributed to several reasons such as difference in production technologies, method of EE assessment, difference in data characteristics, etc. Studies show significant variation in EE of materials for different time periods and across different regions highlighting the importance of periodic updating of the EE values (Debnath et al., 1995; Cole and Rousseau, 1992).

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Environmental Life Cycle Analysis of Water Desalination Processes

Habib Cherif, Jamel Belhadj, in Sustainable Desalination Handbook, 2018

15.4.3 Embodied Energy

Embodied Energy (EE) represents the nonrenewable energy consumed in the acquisition of raw materials, their processing, manufacturing, transportation to site, and construction throughout the whole life cycle. LCA tool is applied during a life cycle period of 20 years in order to investigate the embodied energy of a typical reverse osmosis desalination plants (water pumping, water storage and an RO desalination unit) as shown in Fig. 15.14 [68].

Fig. 15.14.

Fig. 15.14. Typical reverse osmosis desalination plant.

The typical reverse osmosis desalination plant includes three motor pumps (submerged pump P1, desalination pump P2, and storage pump P3) with different functions, RO desalination unit, and three water tanks (T1, T2, and T3). Water tower T3 is used as hydraulic storage [69].

The amount of materials used in the typical RO desalination plant for 1 m3 of permeate flow as the components of an RO module, piping, tanks, motor pumps are listed in Table 15.8. The types of materials used in RO module are fiberglass-reinforced plastic, Cotton fabric, Polypropylene, and Cellulose acetate. Also, many types of materials used in motor pumps as Stainless steel, Copper, Iron, Cast iron, etc. Therefore, each material used in the typical RO desalination plant has its embodied energy, which depends on the amount of the materials.

Table 15.8. Amount of materials used in the hydraulic process

ComponentsQuantityMaterials
Pressure vessels (RO Module) 1 m3/d
RO module casing11.28 kg100% fiberglass-reinforced plastic
Permeate spacer3.36 kg100% Cotton fabric
Feed spacer3.68 kg100% Polypropylene
Membrane1.12 kg100% Cellulose acetate
Piping (PEHD) kg/m
Piping for HP applications6.71 kg/m (d = 160 mm, NP16)10% Stainless steel, 90% polyethylene resins
Piping for LP applications3.05 kg/m (d = 160 mm, NP6)100% polyethylene resins
Permeate piping3.05 kg/m (d = 160 mm, NP6)100% polyethylene resins
Reservoirs kg/m3
Brackish water tank4.2 kg /m380% PVC, 20% fiber reinforced plastic
Permeate tank4.2 kg/m380% PVC, 20% fiber reinforced plastic
Water tower350 kg/m390% concrete, 10% Iron
Motor pumps
Immersed motor pump1 (3.5 kW)28.4 kg90% Stainless steel, 5% Copper, 5% Iron
Motor pump2 (7.5 kW)130 kg85% Stainless steel, 5% Cast iron, 5% Copper, 5% Iron
Motor pump3 (2 kW)32 kg75% Stainless steel, 15% Cast iron, 5% Copper, 5% Iron

Global embodied energy of the typical RO desalination plant during a life cycle period of 20 years for 1 m3/day of permeate flow is summarized in Table 15.9. Global embodied energy integrates balance-of-system (BOS) such as cables, connectors, and protections, the exchange of each component as RO membrane and Static Converter (SCV).

Table 15.9. Embodied energy for a typical RO desalination plant components

Materials RO Module (MJ/m3)1536.7
Materials RO Module after 5 years (MJ/m3)1383
Materials RO Module after 10 years (MJ/m3)1229.3
Materials RO Module after 15 years (MJ/m3)1075.7
Piping (MJ/m)1375.8
Tanks (MJ/m3)2263.23
Motor pump P1 (MJ/kW)283.35
Motor pump P2 (MJ/kW)684.87
Motor pump P3 (MJ/kW)679.20
BOS (MJ/m3)100
SCV (MJ/kW)1260
SCV after 10 years (MJ/kW)940

Embodied energy breakdown for a typical reverse osmosis desalination plant during a life cycle of 20 years is presented in Fig. 15.15. It can be observed that RO membrane and water tower represent the major parts of embodied energy consumed due to regular exchange of RO membrane (every 5 years) and the amount of materials used in water tower (90% concrete, 10% Iron). In Ref. [68], the authors show that the embodied energy for a 20-year lifetime of 1 m3 of fresh water (embodied energy of only hydraulic process) is around 2.2 MJ/m3 (0.61 kWh/m3).

Fig. 15.15.

Fig. 15.15. Embodied energy distribution of a typical RO desalination plant.

From the LCA investigation of a typical RO desalination plant, embodied energy for various industrial motor pumps from Grundfos manufacturer data as CRN 3–10, CRN 20–16 SF, SP 8A-5, SP 30–5, CRTE 2–7 is presented in Fig. 15.16, while Fig. 15.17 presents the evaluation of embodied energy for different industrial RO membranes.

Fig. 15.16.

Fig. 15.16. Global EE of various motor pumps.

Fig. 15.17.

Fig. 15.17. Global EE of various RO membranes.

Global embodied energy model of motor pump is given by

(15.6)EEMP=5.52×WMP1.47

where EEMP is the embodied energy model of motor pump expressed as a function of weight motor pump (WMP).

Global embodied energy model of desalination RO membrane is given by

(15.7)EERO=6443.5×Ac0.94

where EERO is the embodied energy model of an RO membrane expressed as a function of Active area (Ac).

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Sustainability of using recycled plastic fiber in concrete

Rabin Tuladhar, Shi Yin, in Use of Recycled Plastics in Eco-efficient Concrete, 2019

21.2.1 Embodied energy

Embodied energy is the energy associated with the manufacturing of a product or services. This includes energy used for extracting and processing of raw materials, manufacturing of construction materials, transportation and distribution, and assembly and construction. Cradle-to-grave approach in calculating embodied energy also includes energy required for refurbishing and maintaining infrastructures during their service life and for demolition and waste management at end of life. Embodied energies (expressed as MJ/kg) for commonly used construction materials are shown in Fig. 21.3. Embodied energy concept can be used to evaluate sustainability of various construction materials by comparing the energy required to produce them. Embodied energy of a structure is significantly influenced by the type of construction materials used, manufacturing efficiency, transportation distance, durability of the materials, and construction methods implemented. Durable materials last longer and reduce the overall embodied energy used over the lifetime of the product. Recycled materials also have significantly lower embodied energy compared to its virgin counterparts as it eliminates the energy required for extraction and processing of raw materials. For instance, production of PP fibers from virgin plastics requires extraction of crude oil, coal, or natural gas; transportation and processing in refineries; polymerization and production of plastic pellets and granules. However, using recycled plastic feedstock to produce PP granules eliminates extraction and processing of fossil fuel and remarkably reduces embodied energy of recycled plastic products. As seen in Fig. 21.3, recycled PP with 70% recycled component is around 25 MJ/kg less than one-third of the embodied energy of virgin PP. It is important to note that collection, transportation, and processing of recycled materials also consumes energy. Nevertheless, energy required to produce recycled PP is much lower compared to the energy required for extraction and processing of fossil feedstock.

Figure 21.3. Embodied energy for different construction materials (Tectonica, 2018; Hammond and Jones, 2008).

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Life Cycle Energy Consumption of Buildings; Embodied + Operational

Rahman Azari, in Sustainable Construction Technologies, 2019

5.2.1 Embodied Energy

Embodied energy is used differently in the literature based on the stages of building life cycle that are included in its definition. Most literature approach embodied energy from a cradle-to-gate perspective and estimate it as the summation of the energy that is consumed directly or indirectly for production of construction materials used in a building (Dixit et al., 2010). This approach to embodied energy only incorporates the preconstruction stage (i.e., extraction of materials, manufacturing of products, components, and systems) of building life cycle. Some other literatures expand this definition to cradle-to-site, and incorporate both preconstruction and construction stages of the life cycle, and the associated transportation (Hammond and Jones, 2008). A more comprehensive definition of embodied energy is based on cradle-to-grave scope, which includes not only preconstruction and construction stages but also maintenance, demolition, and disposal stages of the building life cycle. This cradle-to-grave approach to embodied energy defines it as the total energy used in the entire life cycle of a building, excluding the energy that is used for the operation of building. Based on this approach, embodied energy is the summation of initial, recurring, and demolition embodied energies (Yohanis and Norton, 2002). Initial embodied energy is the total energy that is consumed to extract raw materials, manufacture and transport products and components, and construct a building. Recurring embodied energy is the energy that is required to maintain a building and repair or replace its materials and components.

The research and practice on embodied energy are gaining more interest in recent years, especially because the share of embodied energy in life cycle energy use is increasing as more high-performance energy efficient buildings are being built. However, there is no consensus yet amongst the scholarly community about the relative significance of embodied energy in life cycle energy use of buildings or the absolute embodied energy consumption levels per unit of floor area. Indeed, the significance of embodied energy can vary as a function of building’s level of operational energy efficiency, as illustrated in Fig. 5.3. Ramesh et al. (2010) report a share of 10%–20% for embodied energy, based on an article review effort that involves 73 conventional residential and office buildings. In another effort, Sartori and Hestnes (2007) examine the data on 60 conventional and low-energy buildings studied by the extant literature on energy use in buildings and conclude that embodied energy constitutes 2%–38% of total energy use in conventional buildings and 9%–46% in low-energy buildings. In a recent study, Chastas et al. (2016) study 90 cases of residential buildings and report embodied energy’s share as being 6%–20% in conventional buildings, 11%–33% in passive buildings, 26%–57% in low-energy buildings, and 74–100% in net-zero energy buildings.

Figure 5.3. Share of embodied energy in life cycle energy use of residential buildings with various levels of operational energy efficiency.

Source: Data from Chastas, P., Theodosiou, Th., Bikas, D., 2016. Embodied energy in residential buildings—towards the nearly zero energy building: a literature review. Build. Environ. 105, 267–282.

Based on a review of previous articles, Ding (2004) suggests that the embodied energy use in buildings ranges from 3.6 to 8.76 Giga Joule (GJ) per square meter of gross floor area (with a mean of 5.506 GJ/m2) in residential buildings and from 3.4 to 19 GJ/m2 of gross floor area (with a mean of 9.19 GJ/m2) in commercial buildings. In another review study, Aktas and Bilec (2012) use more recent information and suggest an initial embodied energy (i.e., associated with preuse phase) range of 1.7–7.3 GJ/m2 (with a mean of 4.0 GJ/m2) for conventional residential buildings and 4.3–7.7 GJ/m2 (with a mean of 6.2 GJ/m2) for low-energy residential buildings. According to them, the higher initial embodied energy in low-energy buildings is due to thicker building skins and extensive use of insulation. Aktas and Bilec (2012) also show that the embodied energy of demolition phase ranges between 0.1% and 1% of total energy use in a residential building.

The variations in shares and absolute values of embodied energy use reported by the literature also occur due to differences in system boundaries, analytical methods, geographical locations, and data source and quality (age, completeness, representativeness, etc.) (Dixit et al., 2010).

At urban scale, compact cities with high-density downtown areas as compared with low-density urban sprawl offer lesser car dependency, better public transit services, lower building and transportation energy use, and lesser waste of electricity that is generated by power plants. Therefore, both embodied and operational energy of buildings can vary with the urban density too. Norman et al. (2006) conduct a life cycle assessment (LCA) analysis on two case-study residential buildings in Toronto; one being a high-density multistory compact condominium in the downtown area and the other one a low-density two story dwelling in suburban areas. Their findings suggest a 40% share of embodied energy in the low-density building’s total energy use and 30% in the high-density building’s. They also show that brick, windows, drywall, and concrete are the biggest contributors to embodied energy in both the cases, with a total of 60%–70% contribution (Norman et al., 2006).

Because embodied energy of buildings varies based on the choice as well as the quantity of construction materials, low embodied energy buildings are generally lightweight buildings constructed out of materials with lesser energy intensity. In addition, using locally produced materials reduces transportation and, therefore, lowers the embodied energy through lesser fuel quantity needed for transportation. Design for durability, reusing, and recycling too is critical in increasing efficiency for embodied energy.

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Industrial Ecology

Amit Kapur, Thomas E. Graedel, in Encyclopedia of Energy, 2004

3.1 Energy Considerations in Material Choice

Embodied energy, or “embedded energy,” is a concept that includes the energy required to extract raw materials from nature, plus the energy utilized in the manufacturing activities. Inevitably, all products and goods have inherent embodied energy. The closer a material is to its natural state at the time of use, the lower is its embodied energy. Sand and gravel, for example, have lower embodied energy as compared to copper wire. It is necessary to include both renewable and nonrenewable sources of energy in an embodied energy analysis. The energy requirements for acquisition in usable form from virgin stocks of a number of common materials are shown in Fig. 7. From an industrial ecology perspective, a manufacturing sequence that uses both virgin and consumer-recycled material is usually less energy intensive than is primary production. The energy requirements for primary and secondary production of various metals are shown in Fig. 8. For one of the most commonly used industrial materials, aluminum, the energy requirement for secondary production of aluminum is approximately 90% less than the requirement for primary production using virgin resource. Therefore, an efficient recycling operation can lead to potential savings in energy consumption and associated environmental damage.

Figure 7. The primary energy consumption required to produce 1 kg of various materials. HD-PE, High-density polyethylene; PP, polypropylene; ABS, acrylonitrile butadiene styrene. Adapted from Schuckert et al. (1997).

Figure 8. Energy requirements for primary and secondary production of metals. Data from Chapman and Roberts (1983).

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Sustainability of gypsum products as a construction material

N. Lushnikova, L. Dvorkin, in Sustainability of Construction Materials (Second Edition), 2016

25.3.1 Embodied energy and carbon footprint of gypsum products

Embodied energy is the accumulative energy spent for a product’s total life cycle, from raw mining to disposal, and it is considered to be incorporated in the material itself. The estimation of a construction material’s from cradle-to-gate embodied energy is an estimation of the energy spent from the time of its extraction until the time it reaches the factory gate. Because of the wide range of manufacturing methods and the complexity of calculations, transportation distances and other variables for some building products, values of embodied energy vary from study to study (BEDB, 2009).

Carbon footprint value, which is estimated along with embodied energy, relates to the accumulated greenhouse gases caused by a product during its life cycle. According to research results presented by the University of Bath (United Kingdom), the embodied energy of gypsum plaster is about 1.8 MJ/kg, and its carbon footprint is 0.12 kg CO2 per 1 kg of product. This could be compatible with terrazzo tiles with corresponding values of 1.4 MJ/kg and 0.12 kg CO2 per 1 kg of product. In addition, gypsum plasterboard has an embodied energy of 6.75 MJ/kg and 0.38 kg CO2 per 1 kg of product, which is comparable to clay tile values of 6.5 MJ/kg and 0.45 kg CO2 per 1 kg of product (Hammond and Jones, 2006).

The embodied energy and carbon footprint of gypsum products for walling assemblies in the United States along with other relevant materials according to the data of the Buildings Energy Data Book (BEDB, 2009) are shown in Fig. 25.26. In general, a 60-year building life time was estimated. As can be seen, gypsum board partitions with wood studs have the lowest values of these parameters when compared to the other products.

Fig. 25.26. Embodied energy and CO2 for interior wall assemblies in the United States. 1 MMBtu = 1055 MJ, 1 sq ft = 0.093 sq m. 1 lbs = 0.454 kg.

Based on data from BEDB, 2009. Building Energy Data Book, 1.6.6 Embodied Energy of Interior Wall Assemblies in the U.S., pp. 1–37. Prepared for the Buildings Technologies Program. Energy Efficiency and Renewable Energy U.S. Department of Energy by D&R International, Ltd., 1.6.6 Embodied Energy of Interior Wall Assemblies in the U.S. Available at: http://static1.squarespace.com/static/513f072ae4b0a96a24469023/t/5410b01ae4b05f0d2fb6861d/1410379802995/docs_DataBooks_2009_BEDB_Updated.pdf, which is based on calculations of Athena EcoCalculator for Assemblies version 2.3, 2007.
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Earth-block versus sandcrete-block houses

H. Abanda, ... G. Elambo Nkeng, in Eco-Efficient Masonry Bricks and Blocks, 2015

22.12.4.1 Lean concrete

Volume of lean concrete.

V1=3m3

Therefore, the total mass of lean concrete (Ql) is given by

Q1=(22kN/m3)×3m3
Ql=6600kg

The embodied energy is defined by EEtp = Qtp × Ip(ee), where Ip(ee) is the embodied energy factor for concrete. In Bath ICE, the embodied energy and CO2 intensities of concrete dosed at 150 kg/m3 have not been provided. However, values for concrete dosed at 120 and 200 kg/m3 have been provided. From Bath ICE, the embodied energy intensities for concrete dosed at 120 and at 200 kg/m3 are 0.49 and 0.67 MJ whereas embodied carbon intensities are 0.06 and 0.091 kgCO2, respectively. Although using the lower or upper values would be an underestimation or overestimation, an average of both values is most probable, especially because these intensities are increasing functions.

On the basis of this assumption, the computed embodied energy and CO2 intensities for lean concrete dosed at 150 kg/m3 are 0.58 MJ {=(0.58 + 0.67)/2} and 0.0755 kgCO2 {=(0.06 + 0.091)/2}.

EEl=6600kg×(0.58MJ/kg)
EEl=3828MJ

The embodied CO2 ECl=Ql×Il(CO2), where Il(CO2) is the embodied CO2 factor for concrete:

ECl=6600kg×(0.0755kgCO2/kg)
ECl=498.3kgCO2
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Sustainability of glass in construction

M. Achintha, in Sustainability of Construction Materials (Second Edition), 2016

5.8.2 Embodied energy and carbon of common construction materials

The embodied energy/carbon of buildings has been somewhat neglected in government regulations as the current regulations mostly focus on the reduction of operational energy/carbon. According to Rawlinson and Weight (2007), the embodied energy of a typical complex commercial building in the United Kingdom may be equivalent to 30 times its annual operational energy use. Sturgis and Roberts (2010) estimated that embodied carbon can account for up to 45% of the total carbon impact of a building over its life cycle. Although an analysis of embodied energy/carbon is required in order to evaluate the total impact of a given building, a reliable investigation of the embodied energy/carbon is not trivial. For instance, transportation can affect the embodied energy—a material manufactured and used in London has an embodied energy impact different from the same material transported by road to Edinburgh. Recycled materials are sometimes used for the manufacturing of new products, and these products usually have a lesser carbon impact. It is also difficult to take into account the energy required for the maintenance, repair and refurbishment of a building over its life cycle.

Despite the difficulty of accurate analyses of the embodied energy/carbon impact of construction materials over the life cycle of a given building, few methods have been reported in the literature. One such method is the ‘University of Bath's inventory of carbon and energy database’ (Hammond and Jones, 2006), and this inventory provides an open-access database of energy/carbon impact of over 400 materials (Hammond and Jones, 2008). This database has been employed by various researchers and developers of carbon footprint calculators, including the UK's Environmental Agency's carbon calculator for construction (Hammond and Jones, 2008).

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Materials selection and substitution using aluminium alloys

M. Leary, in Fundamentals of Aluminium Metallurgy, 2011

25.7 Environmental consequence of material selection

Environmental impact is an increasingly important consideration for material selection decisions; however, the requisite analysis is complex, and many design metrics have been proposed (e.g. Schmidt and Taylor, 2006). Of these metrics, the method presented in this work will focus on the embodied energy and CO2 footprint; however, the method is compatible with other metrics of interest. The system boundary applied in this work will not include the retirement phase as it is considered to have a negligibly small contribution to the holistic life-cycle costs (Gibson, 2000). The following procedures will identify the environmental impact for the manufacturing phase. Methods for use-phase evaluation were discussed in Section 25.6.1.

25.7.1 Embodied energy

Embodied energy, Ee, is an estimate of the total energy required to produce one unit-mass of a particular material, including mining of raw materials, transportation and primary processing (Eq. 25.22).

[25.22]Ee=EstimatedenergyrequiredforprimaryproductionMassofprimarymaterialproduction

25.7.2 CO2 emissions

Of the proposed environmental impact metrics, CO2 emissions are of significant importance due to their contribution to climate change. The CO2 emission estimate applied in this work is based on the emissions associated with primary production, transport and feedstock manufacture (Eq. 25.23).

[25.23]Ec=MassofCO2arisingfromproductionMassofmaterialproduced

25.7.3 Environmental material selection curves

The material selection indices can be modified to accommodate environmental objectives such as minimal embodied energy and minimal CO2 emissions (Burvill et al., 2009) (Table 25.1). Based on these material selection indices, a series of material selection curves have been plotted for the identified materials (Fig. 25.18 and 25.19). Estimates of embodied energy and CO2 emission are obtained from industry average estimates obtained from the CES material selection system (Table 25.2). These measures are subject to significant uncertainties and are consequently reported for material types rather than specific alloys. To acknowledge these uncertainties, the reported environmental metrics include a tolerance bound; however, specific metrics in this work are calculated for mean values only for visual clarity.

25.18. Embodied energy for: tie (upper), beam (middle) and plate (lower) structural elements.

25.19. CO2 emissions for: tie (upper), beam (middle) and plate (lower) structural elements.

25.7.4 Secondary aluminium

The previous analyses presume the use of primary materials. Primary aluminium processing is energy intensive and results in significant environmental impact. These consequences can be mitigated by utilizing renewable or low-emissionpowersources, and by the application of secondary (recycled) aluminium. Secondary aluminium processing requires only five per cent of the energy consumption associated with primary aluminium (Section 3.2). Furthermore, aluminium is eminently recyclable and secondary and primary aluminium are structurally indistinguishable. To provide insight into the associated environmental merit, the CO2 emissions and embodied energy associated with secondary aluminium use are indicated in Fig. 25.20.

25.20. Embodied energy (upper) and CO2 emissions (lower) associated with secondary aluminium use.Note that all other materials are based on primary production attributes, as in Fig.25.18 and 25.19.

25.7.5 Summary of environmental material selection outcomes

The material selection curves aid decision-making through increased quantitative certainty of the environmental impact for a range of design scenarios. For the scenarios assessed in this work:

The environmental consequences associated with primary aluminium production are relatively high (Table 25.2). Consequently, the reference steel provides lower embodied energy and CO2 emissions for all k and N.

As k increases, the relative mass of the light alloy solution decreases; however, Ee and Ec remain constant. Consequently, scenarios with large k, for example plates and beams, minimise the environmental consequence of light alloy application.

Of the investigated light alloys, aluminium provides optimal environmental performance for all k and N.

Although aluminium provides the optimal environmental performance of the light alloys assessed, this analysis indicates that primary aluminium is not optimal for fatigue limited scenarios that attempt to minimise environmental impact. However, this outcome is highly dependant on the assumption of non-stationary applications, non-renewable energy sources and the use of primary material.

The use of secondary aluminium provides an opportunity to enhance environmental performance by virtue of the reduction in processing energy. For the scenarios investigated, secondary aluminium provides a significantly lower environmental impact than primary steel (Fig. 25.20).

Another opportunity to enhance environmental impact is the use of renewable or low-emission power sources, such as solar, tidal and wind energy. Low polluting technologies provide an opportunity to reduce the CO2 emissions associated with both primary and secondary processing.

It is apparent that aluminium provides a significant opportunity to achieve mass reduction over traditional materials (especially for high k values) but may incur an increased environmental impact. However, secondary aluminium incurs only five per cent of the environmental impact associated with primary processing, with no degradation of mechanical properties, and provides an opportunity to significantly enhance environmental performance. If scenarios are non-stationary, the environmental benefit of reduced mass acts to reduce use-phase emissions, which further offsets the impact associated with aluminium processing. The use of green energy provides another opportunity to reduce CO2 emissions. These factors result in many scenarios for which aluminium alloys provide a robust opportunity for environmentally optimal material selection.

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