building materials assessment for sustainable construction based on figure of merit as a concept

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International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 2, February 2017, pp. 203–217 Article ID: IJCIET_08_02_023 Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=2 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 © IAEME Publication Scopus Indexed

BUILDING MATERIALS ASSESSMENT FOR SUSTAINABLE CONSTRUCTION BASED ON

FIGURE OF MERIT AS A CONCEPT Ajit Sabnis

Corresponding Author, Department of Civil Engineering, School of Engineering and Technology, Jain University, Bangalore, India

M R Pranesh Department of Civil Engineering, School of Engineering and Technology,

Jain University, Bangalore, India

ABSTRACT Sustainability assessment and Engineering design in buildings call for effective decision

making in respect of material selection and construction methodology. A good sustainable solution involves choosing most suitable material and construction techniques that produce optimum results in terms of sustainability. Due to several choices available in material selection for construction, there is a need for a tool which can assist the designer in making the right choice of materials. Figure of Merit (FoM), as a tool is proposed here to meet this requirement. FoM is a unique dimensionless parameter derived by integrating two critical properties from Engineering and Economics. Engineering properties are Modulus of Elasticity and Density of materials. Economic factors are unit cost of material and construction cost per unit area. Concept of FoM was applied and study carried out on commonly used building materials and graphs drawn in comparison with embodied energy, embodied carbon and material density values. Outcome of the study indicated, “Lower the Figure of Merit; better is the suitability of building materials in sustainable construction.” As an illustration, FoM concept was also applied to one of the subsystems of a building namely formwork and found to be in consistency with the findings. Hence, it is suggested that Figure of Merit can be used as a quantitative tool for selection of materials. Key words: Figure of Merit, Building Materials, Material Selection, Sustainable Materials, Sustainable Construction. Cite this Article: Ajit Sabnis and M R Pranesh, Building Materials Assessment for Sustainable Construction Based on Figure of Merit as a Concept. International Journal of Civil Engineering and Technology, 8(2), 2017, pp. 203–217. http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=2

1. INTRODUCTION Materials used in building construction consume enormous amount of energy from raw material extraction to production stage and have seen growing demand in the present global scenario,

Building Materials Assessment for Sustainable Construction Based on Figure of Merit as a Concept


especially in developing nations like India. Between 1970 and 2010, global material consumption has grown three fold from 22 billion tonnes to 70 billion tonnes and per capita has gone up from 7 tonnes to 10 tonnes [1]. Domestic extraction of raw materials has also grown worldwide. It is estimated that 30 billion tonnes of raw materials are required to produce 10 billion tonnes of finished products. Increase in demand for materials is primarily due to unprecedented growth in population which results in Green House Gas (GHG) emissions entailing global warming along with other serious environmental impacts. As observed by World Health Organisation [2], by 2030, 60-70% of the world population will be in urban areas, exerting pressure on infrastructure development causing sustainability imbalance. Simultaneously, technological advances in the field of material science and material engineering continue to provide new generation building materials with enhanced properties with traditional building materials still in use. With several material options available, selecting suitable energy efficient building materials pose significant challenge to all the stakeholders of construction industry. Further, environmental concerns associated with different life cycle stages of a product significantly harm the environment.

According to the report generated by Organisation for Economic cooperation and Development-OECD [3], global material consumption is in the order of 62 billion metric tonnes per year and expected to reach 100 billion tonnes by 2030. This growth is primarily due to increase in global demand for three major material groups namely, construction, energy and metal, accounting for about 80% of the total material extraction, impelling imbalance between material supply capacity and demand. India being the second most populous country in the world, has to meet its housing and infrastructure demands on a continuous basis. Considering the housing schemes like, ‘Housing for all by 2022’, Indian government has to construct about 20 million houses in the next 5 years for people belonging to economically weaker sections. This mega exercise is bound to exert enormous pressure on environment and material requirement. As per available data, India consumes 4.6 billion metric tonnes (about 7%) of the total global material extraction and expected to reach 14 and 27 billion metric tonnes by 2030 and 2050 respectively. Current average material consumption per capita per annum in India is about 4.2 tonnes and likely to touch 9.6 tonnes by 2030, which approximately is the present global average excluding developed nations [4].

Engineering properties of construction materials play a vigorous role in assessing structural integrity of a building and more or less well defined in terms of worldwide acceptance, measurement and quantification. When it comes to measuring eco-properties of construction materials, there is no such well-established equipment or specified technique. Most energy impact assessment methods currently available for life cycle analysis consider embodied energy and embodied carbon as two critical eco-properties along with energy consumed during transportation, maintenance and decommissioning, as associated parameters. Embodied energy is associated with energy consumption under cradle to cradle system boundaries, whereas embodied carbon gets associated with GHG emissions into the atmosphere.

Energy, raw material extraction, product manufacturing and their impact on environment are intricately connected giving rise to three important interactions between a) materials and embodied energy (EE), b) EE, c) Global warming and materials. The synergic effect of three interactions results in complex interaction phenomena called Sustainability Development Index (SDI) as discussed by Ajit Sabnis et al. [5]. World Commission on Environment defines sustainable development as development which meets the needs of present generations without compromising the needs of future generations. According to Kibert [6], 40% of world’s energy flow and material are due to buildings. Total quantum of material extracted from non-renewable sources thus becomes a realistic indicator of environmental impact. This necessitates judicious usage of materials and minerals drawn from non-renewable resources. Hence, selection of suitable construction materials from sustainability perspective attains high importance.

Ajit Sabnis and M R Pranesh


This paper discusses selection methodology of building materials for sustainable construction using the concept of Figure of Merit (FoM) and an attempt made to provide a framework in assessing the impact of construction materials on environment. Material selection for sustainable construction involves in finding best match between design requirements based on function and material properties with least environmental impact. Figure of Merit used here is a non-dimension number derived using two engineering characteristics-modulus of elasticity and density and two cost stimulants-construction cost per unit area and unit cost of materials. FoM values obtained are graphically represented to quantitatively determine the sustainability quadrant and sustainability range within which materials fall by plotting against other critical material parameters.

Sustainability assessment and Engineering design in buildings call for strategic economic decision making in respect of selecting suitable construction materials and construction techniques that produce optimum results in terms of sustainability. As suggested by Cabeza et al. [7], in addition to reducing the embodied energy of materials, it is equally important to consider recycling potential of building materials. Hence, there is a need for developing a tool which can assist the designer in adopting better choice of materials with lower embodied energy and higher structural integrity.

2. AN OVERVIEW OF FIGURE OF MERIT (FOM) Figures of Merit (FoM) have varying definitions depending on a context and are being extensively used in several engineering fields to rank the most suitable alternative amongst the available options. FoM in engineering designs is used to find out material suitability, compare utility, applicability and design options. In commercial sectors, FoM helps to decide upon the dependability of a particular brand.

Studies carried out by Kima et al. [8] in the field of thermoelectric materials adopt principle of Figure of Merit to predict the efficiency of thermoelectric materials. Jeffrey O. Grady, in his book System Management: Planning, Enterprise Identity, and Deployment, Second Edition, classifies risks as low, medium and high, based on the Figure of Merit values. Studies reveal many such examples of FoM applications and formulations using engineering parameters. Varun et al. [9], Prakash et al. [10] proposed a sustainability index based on Figure of Merit for renewable energy sector with renewable energy options. Prioritization of sustainable electricity generation methods considered two critical parameters, net energy and carbon dioxide emissions. Based on FoM rankings, they concluded that electricity generated by the wind power is most sustainable.

Filetin and Galinec [11] proposed use of FoM in material selection processes and observe that Figure of Merit to be a mathematical expression where inputs are some of the important engineering characteristics of a material and the output data validating these characteristics. Thus by comparing the Figures of Merit of different materials, assessment can be made as to which material is better suited for a given condition. Several combinations of characteristics are suggested by Filetin and Galinec considering important characteristics of materials. Suggested combinations by Filetin and Galinec, contained two critical parameters, elasticity modulus and density of material, playing predominant roles.

Bleek [12] presented the concept of ‘Material Intensity Per Service Unit (MIPS)’ and evolved an indicator based on the utilization of natural resources for their consumption in a finished form at the end of a supply chain. MIPS-was defined by as inverse of resource productivity and the proposed equation comprised ecological rucksacks of all input materials and number of utilities the finished product offers. Mancini et al. [13] successfully applied MIPS concept for evaluating the sustainability of diets based on the use of natural resources along the supply chain in thirteen European countries. Roldán and Valdés [14] outlined a methodology of developing a Figure of Merit for evaluating sustainable development using social, environmental and economic indicators and applied it to different regions of Mexico without taking into account any of the engineering characteristics of materials.



Dixit et al. [15] in their review paper on embodied energy computation methods observe variation in methods being adopted for data collection of energy inputs and product manufacturing processes leading to incompleteness and inaccuracies of these methods. Most modern building materials available in the market today tend to become energy intensive due to processes and long distance transports, as observed by Reddy [16]. Dixit et al. [17] suggests embodied energy of construction materials depend on product’s manufacturing processes and identifies ten different system boundaries for embodied energy computation.

Ajit Sabnis and Pranesh [18] used Figure of Merit (FoM) in material selection including cost function and further integrated it with other energy indicators in developing a new Sustainability Development Index (SDI), a tool that helps assessing sustainability levels of buildings in percentage. Nguyen et al. [19] developed a sustainability development indicator called TPSI for tall buildings above twenty floors. ‘Tall-Building Projects Sustainability Indicator-TPSI’ drew a threshold line for twenty floors or sixty meters height. Their findings showed beyond 20 stories, the eco-efficiency of buildings reduce dramatically in terms of structural and economics aspects. Pilon et al. [20] presented a methodology using the concept of FoM to screen the composite materials containing phase change materials (PHM) for energy efficient buildings with crack resistant concretes. Schrader and Rickman [21] refer to particle type, particle size, particle shape, and density as four types of measurements required for constructing a FoM equation.

3. FORMULATION OF FOM EQUATION There are no stipulated guidelines available in construction industry for deriving the FoM equations. FoM, in the present discussion, is constructed using two critical reference engineering properties and two construction industry cost stimulants as described in section 1. These four parameters in the FoM equation are intricately connected and influence material selection. Jiao et al. [22] developed modified Input-output based analysis to compute EE of materials and systems by relating cost data and demonstrated strong correlation between EE and cost of materials. In construction, though high material strength and low material density are preferred, they need not be always the most suitable selection criteria. Cost of materials and cost of implementation also play a vital role. For completing the sustainability assessment of a building, FoM has to be further integrated with other critical eco parameters. This is in consistency with the suggestion made by Ashby [23] to consider Mass, Embodied Energy and Embodied carbon in the selection strategy of materials.

FoM is a non-dimensional parameter and designated as ZFOM

3.1. FoM Objective Objective of developing the ZFOM for various construction materials is to effectively integrate them with cost parameters and validate them with other parameters namely embodied energy, embodied carbon and density. It is a well-established fact that cost of materials increase due to various process involved during the life cycle of a product starting from energy consumed during raw material extraction, transporting the raw material to the factory, processes involved in processing and refining of raw materials, manufacturing of a product, packing and lastly its transport to the construction site. Further, higher material density entails higher transportation cost which in turn results increased greenhouse gas emissions

3.2. Constructing FoM Equation Figure of Merit (ZFOM) for various construction materials is derived using the following equation.

ZFOM = E/ρ x Cm x 1/Ca (1) Where; E = Elasticity modulus in GPa,



ρ = Material density in kg/m3, Cm = Material cost in INR / m3and

Ca = Cost of construction in INR/m2 On substitution, FoM emerges as a non-dimensional numerical value. Cost in the present

discussion is taken in INR for illustration. FoM equation can be applied to any location and applicable currency be deployed. ZFOM values for some critical construction materials in Indian scenario are computed and tabulated in Table 1. Computation of ZFOM takes into account, range of E-values from standard data tables, cost of construction materials and cost of construction prevailing in one of the Indian metros, Bangalore. Cost of construction per unit area of a ‘ready to occupy’ building is found to be in the range of INR 20000-65000 (US $ 350 – 1100) per square meter.

Table 1 FoM (ZFoM) Values of Construction Materials

4. EMBODIED ENERGY (EE)-CONSTRUCTION MATERIALS Assessing energy impact of building materials on environment based on embodied energy (EE) has been the focus of study for the past several decades. Useful relationship between building materials, construction processes, and their environmental impacts has also been established. As observed by Langston and Langston [24] the process involved in the actual assessment of EE is a complex process and involves numerous data from various sources. EE is typically measured as a quantity of nonrenewable energy consumed per unit of material or a subsystem constituting a building system. Though EE measurement is considered as a reasonable impact indicator, it should be weighed along with durability and performance characteristics of materials. Further, as suggested by several researchers, there is no specific widely accepted EE computing methodology accurately and hence

Density

Kg/m3 L H L H1 Aluminium 2700 68.00 82.00 22.15 87.28 54.712 Brass 8500 110.00 120.00 60.42 215.40 137.913 Low Carbon steel 7800 200.00 215.00 12.49 43.87 28.18

4 Stainless steel 8000 189.00 210.00 64.25 233.30 148.78

5 Polypropyline 910 0.90 1.55 0.21 1.19 0.70

6 Polyethelene(HDPE) 960 0.62 0.86 0.12 0.53 0.32

7 Polycarbonate 1210 2.00 2.44 1.06 4.23 2.648 PVC 1580 2.14 4.14 0.53 3.38 1.96

9 Epoxy 1400 2.35 3.08 2.93 12.56 7.75

10 Ceramic Tiles Dry 2000 350.00 400.00 17.62 65.81 41.7211 Bricks in Clay 1st Qlty 2080 10.00 50.00 0.04 0.74 0.3912 Stabilised mud bricks 1850 0.70 1.00 0.00 0.01 0.0013 Stone (Hard) 2880 35.00 50.00 0.04 0.20 0.1214 Granite (Polished) 2880 50.00 60.00 2.91 11.43 7.1715 Sand stone 2200 25.00 40.00 3.34 17.45 10.3916 Marble 2500 60.00 80.00 5.03 21.94 13.4917 Concrete 2400 15.00 25.00 0.05 0.27 0.1620 Cement Mortar wet 1900 2.00 3.00 0.05 0.27 0.1621 Glass(Soda-lime) 2500 68.00 72.00 5.71 19.74 12.7221 Hard Wood 940 20.60 25.20 0.62 2.46 1.5422 Soft Wood(sawn) 550 8.40 10.30 0.36 1.43 0.8923 Plywood 700 6.90 13.00 0.53 3.28 1.9124 MDF 500 2.00 4.00 0.13 0.85 0.49

25 Gypsum Plaster Boards 800 1.50 3.50 0.10 0.74 0.42

Ceramics

Hybrids

MaterialSl

No

ZFOM x 106

FoME (MOE)

Range GPa

MetalsPolymers

Mean FoM



variations in EE values are unavoidable [25, 26, 27, 28,]. Embedded in the measure of EE, are the associated ramifications of greenhouse gasses, resource depletion, global warming and biodiversity reduction.

From sustainability point of view, construction materials can be defined as those materials which have low ecological impacts, which minimize resource use, impart no health risks and do not compromise durability aspects. These materials in their finished form consume enormous energy before they reach the point of implementation. Energy consumed during several processes involved in transforming raw materials into finished products, is directly proportional to greenhouse gas emissions leading to Global warming. Buildings contribute almost 40% of CO2 emissions and are major contributors to the greenhouse gas (GHG) emissions.

Construction materials display wide range of embodied energy variations and emit GHGs with varying magnitudes in their life cycle. Appropriate selection of construction materials play a vital role in cutting down carbon dioxide emissions and make buildings more sustainable. Studies carried out based on embodied energy and embodied carbon for impact assessment have their own limitations due to varying geographic locations and local climatic conditions.

Alcorn and Baird [29] modified energy coefficients using hybrid analysis while applying to New Zealand to avoid inaccuracies and limitations embedded in energy values. Buchanan and Honey [30], while investigating the total energy consumption by a building and its impact on global warming, used energy coefficients suggested by Baird and Chan (1983). Noteworthy contributions have been made by several researchers including Adalberth [31] [32], Pullen [33], Crawford and Treloar [34] and Lenzen et al. [35] in the past for assessing the impact of built environment on natural environment taking into consideration the embodied energy and carbon emissions.

Table 2 shows embodied energy, embodied carbon, density and mean FoM values for construction materials.

Table 2 EE, EC, FoM Values for Construction materials

MATERIAL EE MJ/kg

EC kgCO2/kg

Density kg/m3

Mean FoM

Aluminium 218.00 8.24 2700 54.71Brass 80.00 4.39 8500 137.91Low Carbon steel 20.10 1.37 7800 28.18

Stainless steel 56.70 6.15 8000 148.78

Polypropyline 115.10 3.93 910 0.70

Polythelene(HDPE) 76.70 1.57 960 0.32

Polycarbonate 112.90 6.03 1210 2.64

PVC 77.20 2.61 1580 1.96

Epoxy 139.00 5.91 1400 7.75Ceramic Tiles 12.00 0.74 2000 41.72Clay Bricks 3.00 0.23 2080 0.39CSEB 0.83 0.084 1850 0.00Stone (Hard) 1.00 0.056 2880 0.12Granite 11.00 0.64 2880 7.17Sand stone 1.00 0.058 2200 10.39Marble 2.00 0.116 2500 13.49Concrete 0.75 0.1 2400 0.16Cement Mortar wet 1.10 0.171 1900 0.16Glass(Soda-lime) 15.00 0.86 2500 12.72Hard Wood 10.00 0.30 940 1.54

Soft Wood(sawn) 7.40 0.19 550 0.89Plywood 15.00 0.42 700 1.91MDF 11.00 0.37 500 0.49Gypsum Plaster Boards6.75 0.38 800 0.42

METALS

POLYMERS

CERAMICS

HYBRIDS



5. FOM APPLICATION IN MATERIAL SELECTION Material selection criteria in the present discussion are explained in the following paragraphs through FoM Charts developed using FoM, EE, EC and Density properties. FoM charts in principle are classified as FoM-Quadrant Charts, FoM-Range Charts and FoM-Eco Charts. Quadrant charts identify materials based on suitability and design; Range charts identify material range within the imposed limits of FoM and EE and, Eco charts identify materials from sustainability point of view.

5.1. FoM - EE Quadrants Hammond and Jones [36] [37], Alcorn and Baird [29], Reddy and Jagdish [38] have made notable contributions in terms of computing energy values for several construction materials and tabulating them. While most metals show higher embodied energy, building materials under polymer and ceramic classification show lower and mid-range values. In the present discussion, it is attempted to classify construction materials under four groups namely; 1) Most suitable, 2) Not Suitable, 3) Materials where FoM matters most and 4) Materials where EE matters most. FoM value of 30 and EE value of 30 MJ/kg are imposed as baseline values on the basis of best range energy data from ICE inventory [36], material profile. These limits are shown as horizontal and vertical lines demarking four quadrants. Concept of four quadrants is explained by taking materials under metal and ceramic classifications.

Figures 1 and 2 are scattered graphs showing FoM and Embodied energy values for materials under Metals and Ceramics category taken from Table 1 for illustration. In Figure 2, both X and Y axes are in log scale. Two dotted lines representing baseline values of FoM and EE, separating four quadrants are fixed at 30 and 30 MJ/kg respectively. FoM values up to 30 are considered to be Low-Range Values, 30 to 75 as Mid-Range and above 75 as High-Range. Similarly, Embodied Energy values of construction materials up to 30 MJ/Kg are considered as Low-Range, 30 to 60 MJ/kg as mid-Range and above 60 MJ/kg as high-Range. Normalizing the graph with the above characteristics, we have materials falling in four quadrants namely;

Figure 1 FoM-EE Acceptability Criteria for Metals

Q1: Lower FoM, Lower EE – Most suitable Q2: Lower FoM, Higher EE- Choice of materials if FoM matters the most Q3: Higher FoM, Lower EE – Choice of materials if EE matters the most. Q4: higher FoM, Higher EE- Not suitable



From Figure 1, it is observed that Steel falls in Q1 with low FoM value and low embodied energy and hence becomes most suitable. Its suitability enhances when recycled steel is used. Average embodied energy of virgin steel is about 12 to 15 % higher than 50% recycled steel [36]. Other three metals namely Stainless steel, Brass and Aluminium fall in quadrant 4 and hence not suitable as sustainable construction materials. However, Aluminum has a low FoM as compared to Brass and Stainless steel and virgin Aluminium has an embodied energy 15 times higher compared to predominantly recycled Aluminium [36]. Hence Aluminium, being closer to baseline separating Q1 and Q2, can be considered as suitable material. Selection criteria for aluminium is also viewed from recyclability, lightness, low maintenance, low energy and mid-range FoM parameters.

From Figure 2, it is observed that most construction materials under ceramic classification generally fall in Q1. For example, CSEB-Compressed Stabilized Earth Blocks with least embodied energy value of and least FoM become most suitable. Since Ceramic tiles in the market are available with several choices, it is possible to choose a ceramic tile which satisfies low FoM and low embodied energy criteria. In case of ceramic tiles or vitrified tiles, cost of material plays a vital role in determining FoM value.

Figure 2 FoM-EE Acceptability Criteria for Ceramics

5.2. FoM Range Values Figures 3, 4 and 5 show range values of FoM from Table 1 and graphically represented as floating columns. Values falling in low and mid-range are represented by yellow fields and those falling in high FoM range are represented by blue fields. It is observed from Figure 3 that Aluminium, Low carbon steel and Structural steel fall in the low and mid-range zones of FoM and embedded in yellow fields. Thus, with low FoM values, these materials become more suitable compared to Brass and Stainless steel with high FoM values embedded in blue fields. But it can also be interpreted that, Brass and Stainless steel with FoM values falling in the mid-range, can be used as suitable construction materials.



Figure 3 FoM Range Values for Metals

Referring to Figure 4, natural stone floor materials and concrete, falling in the yellow field with low to negligible FoM become more suitable flooring materials as compared to ceramic tiles falling in blue field. Figure 5, represents FoM values for three masonry materials commonly used in Indian construction industry as illustration. It is interpreted from the chart that, CSEBs, Concrete and Clay bricks falling in yellow field are more suitable as construction materials. Higher range values of FoM are for wire cut bricks which are nearly fourfold expensive than conventional 1st quality clay bricks and hence blue field.

Figure 4 FoM Range Flooring Materials Figure 5 FoM Range Masonry Materials

5.3. FOM-EE Comparison Embodied Energy and Embodied Carbon coefficients published by University of Bath [19], are used in the present discussion to assess energy impact of construction materials on global warming. It is now an established fact that greenhouse gasses such as Carbon dioxide and other detrimental pollutants are embedded within the materials. As observed by Hammond and Jones [37], in order to quantify the total embodied energy, assessment based on ‘Cradle to Site’ principle needs to be applied systematically including stages from raw material extraction to processing to transportation to delivery at construction site stages.

Figures 6 and 7 depict Embodied energy and Figure of Merit profiles interpreting suitability of construction materials in terms of sustainability. Mean FoM and embodied energy values for metals and ceramics are drawn from Table 2 and graphically represented as column charts for comparison between materials under respective categories. For example, from Figure 6, low carbon steel with embodied energy value of 20.10 MJ/kg and FoM value of 28.2 falls in the lower range of FoM and hence more sustainable. Stainless steel with high embodied energy and high FoM value is not sustainable as compared to low carbon steel. Similar analogy can be applied for materials under



ceramic category, Figure 7. Ceramic tile with high FoM value and high embodied energy though is not a great material from sustainability point of view but in lower ranges, it can be considered as a suitable material depending on the function it has to perform in the buildings.

Figure 6 FoM vs EE for Metals Figure 7 FoM vs EE for Ceramics

5.4. FoM-EC Comparison Carbon dioxide (CO2) is anthropogenic and available in plenty in the atmosphere. As one of the greenhouse gasses, it poses a great concern in mitigating global warming. Global warming results in the increase of average global temperature and affects macro and micro climates of eco-system. Embodied Carbon expressed in terms of per unit weight, gives an indication of its impact on global warming. Figures 8 and 9 show graphs for mean FoM and Embodied carbon values for ceramics and metals as illustration, taken from Table 2. It is gathered from these graphs, materials with lower FoM are more suitable in sustainable construction. For example, natural stones and concrete fall in lower range values of Figure of Merit and hence recommended as sustainable flooring materials as compared to ceramic or vitrified tiles (Fig 8). Stainless steel displays high Figure of Merit and high embodied carbon. Hence it cannot be considered as sustainable material (Fig 9).

Figure 8 FOM vs EC for Ceramics Figure 9 FOM vs EC for Metals

5.5. FOM-Density Comparison Mean FoM and material density for Metals and ceramics, drawn from Table 2 are plotted and represented in Figures 10 and 11 respectively. In metal category, brass and stainless steel display high density and high FoM characteristics and become unsuitable as construction materials. However, low carbon steel and aluminium fall in low and mid-range zone of FoM and hence become more suitable as construction materials (Fig 10). In case of materials falling under ceramics category, most materials except ceramic tiles fall below FoM baseline and are suitable as construction materials (Fig 11).



Uutilising ceramic tiles in buildings has to be reviewed along with other considerations (section 5.1) while decision making.

Figure 10 FOM vs Density for Metals Figure 11 FoM vs Density for Ceramics

6. FOM APPLICATION-SUBSYSTEM SELECTION

6.1. Formwork as a Subsystem Building as a system involves several subsystems as its components. Each subsystem encompasses many materials and processes like Foundation, Structural frame, Reinforcement, Structural Steel, Joinery, Flooring, Masonry, Plastering, Glazing, Formwork, Water proofing. The concept of Figure of Merit can be applied to any subsystem for its assessment. As an illustration, Formwork is analysed and assessed for its suitability. In Indian scenario, three types of formwork systems are in practice. Conventional formwork where the main sheathing is of steel floor plates and supporting shoring consists of adjustable steel props and spans. In ply formwork, sheathing material is replaced with plywood. In the third system, sheathing material made of aluminium floor plates.

Table 3 EE, EC and FOM Values for Formwork

Source: Ajit and Pranesh [2]

Table 3 shows values of Embodied Energy (EE), Embodied Carbon (EC) per unit area along with mean FoM (ZFOM) for all the three systems.

EE /m2 EC/m2

MJ kgCO2e

ConventionalFormwork with Timber joists, Adjustable steel props and spans, Steel floor plates for sheathing.

229 18.43 9.38

PlywoodAs above but resin coated Plywood as sheathing material.

234 18.81 19.37

Aluminium As in conventional formwork but with Aluminium floor plates for slabs.

15.6 2.5 1.01

Formwork System

ZFOMMaterial Specification



Figure 12 FoM vs EE for Formwork Figure 13 FoM vs EC for Formwork

EE and EC values for all the three systems are plotted against respective values of FoM and represented in Figures 12 and 13. FoM values for three formwork systems are computed using equation 1 separately adopting detailed process analysis of Life Cycle. Interpretation of graphs for suitability of a formwork system shows that Aluminium formwork with lowest Figure of Merit is most suitable from sustainability consideration as compared to other two systems. Aluminium floor plates allow high repeatability, recyclability and help us in avoiding plastering activity. Though capital investment on aluminium formwork is very high, considering 100 repetitions, aluminium formwork per repetition becomes highly economical. Plywood system with five repetitions and high FoM value is not preferred as sustainable system of formwork. There are many multi-story buildings where, aluminium and conventional formwork systems are applied in combination for optimization. From both EE and EC criteria, it is seen that lower FoM serves as an indicator of a better sustainable system.

7. DISCUSSION Concept of Figure of Merit (FoM) is applied in selecting building materials suitable for sustainable construction. Application of FoM is common in aeronautical, automobile and electronic industries where high strength materials with low density are preferred. Present discussion takes into account four critical parameters namely, Elasticity Modulus, Material Density, Cost of materials and Cost of construction per unit area. These are integrated to express a unique dimensionless value called Figure of Merit, designated as ZFOM. Selection of parameters for the evaluation of Figure of Merit is not a rigid decision. For different aspects, the parameterization shall vary to best suit the condition. Based on the requirements of the situation, the characteristics are selected so that a suitable Figure of Merit is obtained.

Values of ZFOM and EE of building materials are used to group building materials in four quadrants namely most sustainable, not sustainable, materials where FoM matters the most and materials where EE matters the most. These are graphically represented in Fig 1, 2. As an illustration, metals and ceramics are taken from the material chart and classification made. It is observed from the plots that most metals except steel fall in ‘not sustainable quadrant’ due to their high embodied energy and high ZFOM. In case of materials under ceramics, most of them come under ‘most suitable quadrant’ due to their low ZFOM and low EE. Four quadrants in Fig 1, 2 are separated by two base lines representing two base values of FoM and EE at 30 and 30 MJ/kg respectively.

Advantage of ascribing base values to FoM is to identify materials falling in different ranges with FoM perspective. FoM value between 0-30 considered as low range, 30-75 as mid-range and above 75 as high range. From FoM perspective, materials displaying lower ZFOM have better suitability in sustainable construction. Validation of proposed FoM concept is carried out by comparing and plotting FoM vs EE, FoM vs EC and FoM vs Density for metals and ceramics as illustration-Figures 6 to 11.



There are several formwork systems, water proofing systems; many envelop systems, plastering methodologies that can be adopted to complete a building. What is essential under these circumstances is a tool that addresses these variations and helps in selecting a suitable subsystem. FoM concept as applied to selection of a suitable subsystem is discussed using Formwork as example.Studies carried out by Reddy B.V.V and Jagdish, K.S [38] show that by using alternative sustainable construction materials and technologies, significant reduction in energy consumption, to the extent of about 30% can be achieved. The present study proposes use of Figure of Merit as a reasonable and practical tool to assess the suitability of construction materials leading to a sustainable solution.

8. CONCLUSION Based on the results presented, following conclusions are drawn:

Lower value of Figure of Merit represents higher suitability of building materials and systems in sustainable construction

Selection of materials cannot be done only with embodied energy, embodied carbon perspective but to be integrated with other critical engineering and cost characteristics of materials

Selection of materials for sustainable construction to be made taking recyclability, reuse parameters into consideration

Different alternative solutions can be identified using FoM tool.

It is possible to modify the building footprint with better sustainability level at the drawing board stage before commencement of actual construction.

9. ACKNOWLEDGEMENTS The authors acknowledge their gratification to the authorities of Jain University for extending cooperation in the present research.

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