Automation in Construction 37 (2014) 131–144

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Automation in Construction

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Economic and environmental assessment of deconstruction strategiesusing building information modeling

A. Akbarnezhad a,⁎, K.C.G. Ong b,⁎, L.R. Chandra b

a Department of Civil and Environmental Engineering, The University of New South Wales, CE209, H20, UNSW Kensington Campus, Sydney NSW2052, Australiab Department of Civil and Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, E1A 07-03, 117576, Singapore

⁎ Corresponding authors.E-mail addresses: a.akbarnezhad@unsw.edu.au (A. Ak

ceeongkc@nus.edu.sg (K.C.G. Ong).

0926-5805/$ – see front matter © 2013 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.autcon.2013.10.017

a b s t r a c t

a r t i c l e i n f o

Article history:Accepted 18 October 2013Available online 13 November 2013

Keywords:DeconstructionEnvironmental impactEconomic impactBuilding information modelingEmbodied energyCarbon footprint

Choosing themost sustainable deconstruction strategy requires assessment of the effects of various contributingfactors including prices and energy embodiment of thematerials and components, the travelling distances, ener-gy use and cost associated with the recycling processes, inflation rate, costs of designing the components forreuse-ability, costs of disassembly and re-assembly. Furthermore, a typical building comprises thousands of dif-ferent components with various characteristics whichmay affect their reusability and recyclability. These lead toan enormous amount of information that needs to be stored and made available for analysis prior to and duringthe deconstruction stage. The present study proposes a framework for evaluating and comparing the effects ofvarious alternative deconstruction strategies on cost, energy use and carbon footprint of construction using theinformation provided by a typical building information model. The results of a case study are presented to illus-trate the potential applications of the proposed method.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

The awareness among the owners, engineers and contractors aboutthe importance of sustainability in the construction industry as well asthe economic benefits achievable through deconstruction has increasedsignificantly over the past few decades. As a result, particular attentionhas been focused on replacing the traditional demolition and landfillingstrategy with more elaborate deconstruction strategies in which theenergy and capital invested in building components are fully or partiallyretrieved through reuse and recycling.

Recycling is one of the main and oldest strategies in C&D wastemanagement. Recycling reduces the demand for new resources bymaking use of waste that would be otherwise lost to the landfill sites.The environmental and economic benefits of recycling of C&D wasteshave beenwidely reviewed in available literature [1]. Numerous studieshave been conducted to investigate the possible applications for therecycled construction materials as well as to develop novel techniquesto improve the yield and efficiency of the recycling processes [2].Recycling is considered as a significantly more sustainable option com-pared to traditional demolition and landfilling because it reduces the

barnezhad),

ghts reserved.

cost and energy use incurred by landfilling and reduces the demandfor extraction of newmaterials bymaking available alternative recycledmaterials. However, onemajor problemassociatedwith recycling is thatthe recycled materials are normally used in a lower grade applicationcompared to the initial application for which the parent componentswere designed and fabricated [3]. Therefore, it makes sense to assumethat a great proportion of the initially invested energy used to fabricatethese components is lost. This is on top of the additional energy that isconsumed during the recycling process. For instance, concrete recyclinginvolves energy intensive crushing and sorting processeswhich togetherwith transportation to the recycling site may result in a significantamount of energy consumption and thus carbon emissions. Therefore,an accurate life cycle cost and energy analysis is required to assess thesuitability of a particular recycling strategy for a specific project.

Alternatively, if designed properly, at the end of the building servicelife, building components may be re-usable for the same or similarapplications as the original components. As a result of the consistentlygrowing cost of construction materials and construction services, reus-able components are likely to end up being of more value at the timeof deconstruction than the time of their initial fabrication. A great dealof research has been recently focused on investigating the possibilityof reusing the structural and non-structural components of a buildingat the end of the building's service life [4–7]. The technical andmanage-rial procedures developed to make the latter possible are normallyreferred to as “design for disassembly (DfD)” or “design for deconstruc-tion”. Disassembly and re-use of building components have several

132 A. Akbarnezhad et al. / Automation in Construction 37 (2014) 131–144

advantages over conventional demolition and/or recycling. First, unlikerecycling, reuse of building components preserves the invested embod-ied energy of the deconstructed building components by re-using themand extending their service life. Reuse of materials also reduces signifi-cantly the cost, energy use and carbon emissions resulting from demo-lition, processing for recycling, and transportation to landfill andrecycling facilities.

However, besides the technical difficulties in designing componentsfor disassembly and reuse-ability, another factor preventing the wide-spread use of disassemble-able components in current practice is theextra cost and energy that has to be borne to design the componentsfor re-usability. For instance, designing structural concrete elementsfor disassembly may require the use of additional embedded steelconnections to facilitate assembly and disassembly operations to avoiddamage. This may increase the initial costs, embodied energy andcarbon emissions associated with fabrication of the components.Besides, construction using DfD components necessitates a number ofnon-traditional services during the assembly and disassembly processessuch as selective removal of the cover concrete for access to connectionsas well as additional propping and lifting which may again have envi-ronmental and economic impacts.

As discussed, choosing a sustainable deconstruction strategyinvolves investigatingmany parameters contributing to the cost, energyuse and carbon emissions. In addition, a typical building comprisesthousands of different components with various characteristics whichmay affect their reusability and recyclability. These lead to an enormousamount of information that needs to be stored and made availablefor analysis prior to and during the deconstruction stage. Using thetraditional documentation techniques for this purpose would meanhundreds more detailing and instruction sheets that need to be storedfor a considerable length of time. However, the development of variousbuilding information modeling software as well as international dataexchange schemes such as IFC could facilitate the storage and easyaccess of information for processing. The present study proposes aframework for evaluating and comparing the effects of various alterna-tive deconstruction strategies on costs, energy use and carbon emissionsincurred in various stages of the building life cycle using the informationprovided by a typical building information model. The objective is toprovide decision makers with an easy to use method for selection ofthe most sustainable deconstruction strategy applicable to a particularbuilding. The proposed framework does not use the special featuresmade available by any particular BIM software nor does it proposenew technological advancements in the capabilities of the existingBIM software. The results of a case study are presented to illustratethe potential applications of the proposed method.

2. Building information modeling

Building information modeling (BIM)may be defined as the processof generating andmanaging building information during the service lifeof a building. A typical building informationmodel contains informationsuch as building geometry, spatial relationships, geographic informa-tion, quantities and properties of the building components and thematerials used as well as any other customized information added bydesigners, owners and contractors. Building information models arenormally generated using three-dimensional, real-time and dynamicsoftware [8].

The use of building information modeling in architecture and struc-tural design and detailing, especially in modular construction, has beenwidely adopted both by industry and academia [8–11]. These applica-tions take advantage of the capabilities of BIM in 3D visualization aswell as in simultaneous planning and management of the various con-struction sectors including the structural, architectural and mechanicaland electrical sectors. In addition, another aspect that has recentlyattracted a great deal of attention is the possibility of using such com-prehensive databases provided by the building information models to

design, construct, manage, demolish and re-use building componentsto address sustainability and environment issues [8]. The most empha-sized applications of BIM in sustainable design include selection of theoptimized orientation of a building to reduce the energy costs, buildingmassing to analyze the building form and optimize the building enve-lope, daylight analysis, water harvesting to reduce water needs in abuilding, energy modeling to reduce the energy needs and analyzingrenewable energy options, and site and logisticsmanagement to reducewaste and carbon footprint [8,9,12,13]. These applications are usuallymade possible by linking the BIM software to a secondary softwaresuited for sustainability analysis. All the abovementioned analyses areperformed mainly during the design stage. For instance, the newAutodesk Ecotect 2010 analysis software permits various sustainabilityanalyses of data imported in the gbXML format fromRevit Artictechture,ArchiCAD and Bentley Architecture [14]. These analyses include theshading design, solar analysis, lighting design, photovoltaic array sizingand load matching, acoustic analysis, thermal analysis, ventilation andair flow analysis, etc. In addition, the Autodesk Green Building Studiocan be used in conjunction with Ecotect 2010 to evaluate the energyuse and carbon footprint of the various design alternatives [14]. Suchanalyses may also be conducted using other available software withsimilar capabilities such as the Graphisoft Ecodesigner integratedwith Graphisoft ArchiCAD and Virtual Environment by IES which hasPlug-ins for Revit and SketchUp.

However, although a great deal of attention has been placed onsustainable design and construction using BIM, significantly less efforthas beenput on investigating the possibility of using the comprehensivedatabase available through BIM in the deconstruction stage of abuilding. The present paper proposes a potential application of BIM foruse at the deconstruction stage of the buildings. A conceptual frame-work is developed for identifying the best deconstruction strategiesin term of economic and environmental impacts, among a set ofpredefined or automatically generated strategies, using the informationstored in the building information model.

3. BIM-based deconstruct-ability analysis framework

The importance of developing a comprehensive scheme for evalua-tion of deconstruction strategies was briefly explained in Sections 1and 2. It is inevitable that not all building components can be designedto be reused or recycled and optimum sustainable deconstruction mayrequire a well-managed strategy that combines recycling, re-use andlandfilling. Such a strategy should be designed to achieve a balancebetween the environmental and economic impacts.

The main objective of the present paper is to provide a systematicapproach for identifying themost economic and environmental friendlydeconstruction strategy applicable to a particular building throughevaluating and comparing the economic and environmental impactsof the various alternative deconstruction strategies using the informa-tion provided by a typical building information model. Fig. 1 showsthe general steps involved in the proposed method. As shown, theprocedure starts with the creation of a comprehensive building infor-mation model containing a set of deconstruction related attributesusing the information input by the designers, components fabricatorsand contractors at various stages of building design, construction andservice life (Stage I). In computing, an attribute is defined as a specifica-tion that defines a property of an object, element or file. Attributes canbe defined in various levels including element,model, and system levelsto assign various properties to the elements, the model and all models(every model developed using the software), respectively. The decon-struction relevant information is a set of information determining thevarious deconstruction options applicable to an individual componentin the model. This information may be entered manually by individualusers or imported automatically from available component libraries.The methodology for inclusion of this information in the BIM softwareand that for using this information is discussed in Section 4.1. At the

Construction Materials Life Cycle

Stage III: Analysis

Stage II: Data Transfer

Waste Dumping in Landfills

Deconstruction Selection of the Most

Sustainable Deconstruction Strategy

Economic and Environmental Assessment of various

Deconstruction Strategies

Identifying the Recyclable and Disassemble-able Components

BIM Database

Extraction of Natural Resources

Processing into Construction

Materials

Fabrication of Building

Components

Assembly into Building

Building Service

Materials Properties

Mix Proportions

Structural Capacities

Lifting and Transport information

Assembly Sequence

Assembly Details

As-Built Joint Locations

As-built Geometrical and Topological Data

Addition and Removal of Components

Modifications Processing and Sorting of Data

Stage I: Formation of BIM Database

Reuse through DfD

Recycling

Fig. 1. The main steps involved in BIM-assisted economic and environmental assessment of deconstruction strategies.

133A. Akbarnezhad et al. / Automation in Construction 37 (2014) 131–144

next stage (Stage II), a data transfer scheme is used to transfer the infor-mation stored in the BIM database to a secondary processor which sortsout the selected information into a specific data structure required forfurther analysis. Finally, at Stage III, a computer processor is used to

perform the economic and environmental evaluation of variousdeconstruction strategies using the data made available in Stages I andII. The methodology used in each of the above stages is presented inthe following sections.

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4. BIM-based economic and environmental analysis framework

The methodology presented in the following is general and shouldbe applied to other BIM models generated by currently available BIMsoftware. For validation of the proposed framework, the present paperreports on implementation examples using a typical building informa-tion model generated using Tekla Structures software. The Tekla Struc-tures components library includes only structural building components;however in our opinion the concepts and methodology proposed maybe easily extended to other types of components, e.g. non-structuralcomponents, etc.

4.1. Addition of customized deconstruction-related attributes

Contrary to conventional structural and architectural modeling andvisualization software which use mainly a combination of lines (with-out any attributes attached) to visualize a building, in object-orientedmodels created using BIM software, each entity represents an actualbuilding component. In other words, components modeled using theBIM software are represented as generic or product specific objectswith their own geometry, relations and attributes. For instance, besidesthe usual geometry and topological relations, the commonly used attri-butes for structural components include material properties, profileshape, structural capacities, etc.

Currently available BIM software have provided users with theability to add new attributes (variables) to the objects. These attributesmay be either in the form of numbers or strings. In the present study, anumber of new deconstruction related attributes are proposed to facil-itate the automatic assessment of the various deconstruction strategies.These attributes are listed as follows.

1— Recyclability attribute: This attribute determineswhether or not thematerials used to fabricate a component are suitable for recycling.The suitability of a material for recycling may be determined auto-matically using various pre-defined data libraries containing infor-mation on the availability of the technology for recycling of therelevantmaterials and the availability of amarket for the respectiverecycled products. In addition, another factor determining the recy-clability of a material is the availability of recycling facilities locally.In the present study, a binary attribute, taking 0 and 1 valuesfor non-recyclable and recyclable components, respectively, wasused to indicate the recyclability of materials. A data library ofthe materials with recycling technology currently available inSingapore was used to automatically assign the recyclability attri-bute specific to a particular component.

2 — Reusability Attribute: This attribute determines whether or not acomponent has been designed as a reusable component. Reusabil-ity may be determined based on the designed service life of thecomponent, existence of disassemble-able connections in compo-nent and availability of disassembly and re-assembly equipment.In the present study a binary attribute, taking 0 and 1 values fornon-reusable and reusable components, respectively, was used toindicate reusability of the components. Reusability is determinedautomatically in two steps. First the component is tagged asbeing suitable for reusability if the remaining service life is equalor greater than the service life of the new building in which thecomponent is to be reused. In the next step, connection-type attri-butes are checked against a list of the pre-defined approveddisassemble-able connections. The components with suitabledisassemble connections are tagged as re-usable. The connection-type attributes are stored in BIM as user input during the designstage. If the connection is selected from predefined connectiontypes (available in the component library) during modeling, theattributes associated with the connection are automaticallyadded to the BIM. The remaining service life of the existing build-ing is estimated by subtracting the elapsed service period from

the estimated service life of the building component. The estimat-ed service life of component is stored in BIM as a design input. Theelapsed service period is calculated using the proposed date of newconstruction and the date of first construction. The predictedservice life of the new building is a user input during the analysis.

3— Structural Attributes: This category of attributes is used to store theoriginal design capacities such as maximum moment and shearcapacities of a structural comportment. Furthermore, if there areany variations in the designed capacities along the structuralelement, appropriate structural attributes should be used to storesuch variations. The structural capacities requiredmay be assignedto the respective attributes by users manually or imported fromcompatible structural analysis software. A number of BIM softwaresuch as Tekla Structures are capable of communicatingwith a num-ber of structural analysis engines. The structural attributes may bevery useful in determining whether or not the components can bere-used in thenew structurewith a layout different from that of theoriginal building. Thismay be simply determined by comparing themaximummoment and/or shear capacities of the available compo-nents with that required of the components when used in the newbuilding.

4 — Handling, Installation and Disassembly Attributes: This category ofattributes may be used to provide information on the handling,installation and disassembly procedures required of a reusablecomponent to minimize possible damage during the disassembly,lifting, transportation and re-assembly. Typical disassembly attri-butes may include information on the thickness of the cover con-crete of an embedded steel connection to be removed as well asthe required fixing points to be provided for disassembly of theconnection.

5 — Geographic Coordinates Attributes: These attributes may be used tolocate automatically the nearest recycling and re-use facilities andcapture the traveling distances between the construction site andsuch facilities. The information provided by these attributes isnecessary for assessing the economic and environmental impactsof alternative deconstruction strategies available. The values asso-ciated with such attributes may be simply acquired through com-municating between the BIM software and local GPS systems orother customized databases containing information such as thelocation of available industrial recycling plants, prefabricationplants, and component storage yards as well as the location of thenew construction site inwhich the components are to be deployed.In the present study, a database of the geographical coordinates ofall major recycling and prefabrication facilities in Singapore wasdeveloped and used to estimate the transportation distancesrequired.

6 — Condition-Related Attributes: These attributes may be used to storethe results of various condition assessment tests including non-destructive tests and visual inspections that may be used inassessing reusability of components, vis-à-vis structural integrityand remaining service life.

For illustration purposes, Fig. 2 shows the property window of aconcrete columnmodeled in Tekla Structures. As can be seen, to accom-modate the proposed customized deconstruction-related attributes, anadditional property tab named “deconstruction” was added to theuser-defined properties defined in the Tekla Structures software.

4.2. Data processor

The processor is essentially a functional unit in the framework thatparses the input data acquired from the report files (IFC files or anyother data file formats generated by the BIM software) and creates aninternal data structure to provide easy data access for its receptor, theEconomic and Environmental Impact Analyzer (EEIA) unit. In the pres-ent study, a data processor was developed using VBA programing under

Fig. 2. The deconstruction property tab created in Tekla Structures software to input deconstruction-related information.

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Microsoft Excel. The data processor automatically opens the report filegenerated by the BIM software and imports all the required data forthe selected components to a spreadsheet. The processor then sortsout the data based on the cast unit defined through numbering ofcomponents. The final data structure includes information on the castunit number, component type, component profile, number of the simi-lar objects in the model, material, length, weight, volume, recyclabilityand reuse-ability.

4.3. Economic and environmental impact analyzer unit

The economic and environmental impact analyzer unit is a computerprogram that uses the structured information provided by the processorto perform various economic and environmental analyses. In the presetstudy, a VBA program under Microsoft Excel was developed to evaluatethe cost and environmental impact associated with various pre-defieddeconstruction strategies. Various components of the VBA programdeveloped as well as the methodology used for economic and environ-mental assessment are described in the following.

4.3.1. User interface for defining various deconstruction strategiesA user interface was developed to allow users to define a set of

feasible deconstruction strategies for evaluation and comparison. Inaddition, the analyzer unit developed in present study considers fourpre-defined strategies representing the most commonly used decon-struction strategies in practice. It should be noted that for deconstruc-tion of a particular building component to be possible, it must nothave reached the end of its service life. At the time of deconstruction,it would have completed one cycle of service life and the next cycle ofservice life would begin when it is reconstructed as part of the newbuilding to be built. Taking this into consideration, all the pre-definedstrategies are assessed over a minimum period of two life cycles. Theduration of the life cycles of the existing and new building is input bythe user through the user interface provided. The estimated life cyclesof buildings may vary during the life cycle of the project due to changesin the long term investment plans and organizational goals of the inves-tor organization. The variations in the life cycle duration significantlyaffect the results of the analysis. Therefore, in the case of considerablevariations in the planned life cycle of the buildings, the economic andenvironmental analysis should be repeated to investigate the effects ofthe change on the economic and environmental impacts of the

deconstruction strategies. The four predefined strategies considered inthe present study are as follows:

1. Strategy I (CC-L): This strategy is considered as the reference strategyrepresenting conventional demolition and landfilling. The wholebuilding is assumed to be constructed conventionally (using non-DfD elements) and then demolished. Debris is assumed to belandfilled.

2. Strategy II (CC-R): The whole building is assumed to be constructedconventionally (using non-DfD elements) and then demolished. Allrecyclable concrete and steel scraps are assumed to be recycled.

3. Strategy III (DfD-L): In this strategy, all building components withthe disassemble-ability attribute of 1 (i.e. with appropriate DfDconnections and required assembly/disassembly technology avail-able) are designed and fabricated with embedded disassemble-ableconnections. The re-usable building components are assumed to befully re-used in a new structure at the end of first cycle of servicelife. At the end of the second cycle of service life, however, the build-ing is demolished conventionally and debris is landfilled.

4. Strategy IV (DfD-R): This strategy is similar to strategy III, exceptthat at the end of the second cycle of service life, the building isdemolished and all the recyclable concrete and steel scraps arerecycled.

As can be seen, the third and fourth pre-defined strategies assumethat all structural building elements can be designed for disassemblyand thus may be fully reused in a new building to be built. As will bemore broadly discussed in Section 5.1, design and fabrication ofdisassemble-able structural elements are usually accompanied by anincrease in the initial fabrication cost as well as in the embodied energyand embodied carbon of the components. Therefore, careful assessmentduring the design stage is required to assess economic and environmen-tal impacts, positive or otherwise,when designing building componentsfor disassembly.

4.3.2. Data library with user interfaceThe data library is one of the most important units of the processor.

The data library provides information on the unit cost, energy consump-tion and greenhouse gas emissions of the various constructionmaterialsand construction and deconstruction activities. The deconstructionactivities include concrete demolition, concrete hacking, breaking ofconcrete into smaller pieces, removal of reinforcing bars and embedded

Table 1Cost, energy use and carbon emissions of selected construction and deconstruction activities used in the present study.

Cost/pricea Energy use Carbon emission

Value Unit Ref Value Unit Ref Value Unit Ref

Installation of reinforced concrete components 80 $/m3 [L] 317.50 MJ/m3 [L] 46.00 kgC/m3 [L]Manual assembly/disassembly of DfD connections 7.5 $/Joint [L] [NA] [NA] [NA] [NA] [NA] [NA]Selective demolition of cover concrete 645 $/m3 [L] 3745 MJ/m3 [C] 279.38 kgC/m3 [C]Mass demolition of concrete 125 $/m3 [L] 908 MJ/m3 [C] 27.58 kgC/m3 [C]Road transportation 5.2 $/

(hr. ton)[L] 2.65 kJ/

kg.km[15] 0.32 kgC/t.km [15]

Concrete recycling 6.7 $/ton [16] 18.20 MJ/ton [17] 1.69 kgC/ton [18]Steel recycling [NR] [NR] [NR] 5.6 MJ/kg [19] 570 kgC/ton [19]

Note: [L]= local source; [NA]= not applicable to the case study; [C]= from the equipment catalog; [NR]=not required: the economic effect is considered in calculations in terms of theselling benefits from steel scraps.

a Prices are in Singapore dollar (SGD ≈ 0.8 USD).

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steel components, transportation of debris to steel and concreterecycling plants, the steel recycling process and the concrete recyclingprocess. In the present study, a comprehensive database of the cost,energy use and carbon emissions associated with the above activitieswas developed using information gathered from available literatureand feedback from local construction and demolition contractors aswell as machinery suppliers and manufacturers.

In addition, the data library includes information on the location ofthe various concrete pre-fabrication, concrete recycling, steel recycling,component storage and other facilities related to building constructionand deconstruction. This information may be either entered manuallyor imported into the data library from a database containing thegeographical coordinates of the recycling and prefabrication facilitiesavailable locally. The analyzer unit developed in the present studymakes use of this information and the coordinates of the buildingimported from BIM to calculate traveling distances automatically andthereby the embodied energy, carbon emission and the costs associatedwith transportation of concrete components and construction debris.

Table 1 summarizes the default values for the energy use, carbonemissions and the costs associated with a number of the commondeconstruction activities as assumed in the data library developed.Data library was developed using a combination of data from variousreliable local and international sources. However, it should be notedthat when possible, all data should be obtained from reliable localsources to reflect the costs, energy consumption and carbon emissionsassociated with the specific procedures and equipment used locally.The estimated market prices and the embodied energy and carbon ofa number of the commonly used construction materials used in thepresent study are summarized in Table 2.

4.3.3. Economic and environmental analysesOne of the most common approaches for quantifying the environ-

mental impact of a construction project is to estimate the energy useand associated carbon emissions. The energy use and associated carbonemissions occur in various stages of a building life cycle (Fig. 3). The

Table 2Cost, embodied energy and embodied carbon of selected construction materials used in the pr

Cost/price Emb

Value Unit Ref Valu

Coarse crushed aggregates 23.4 $/ton [L] 81Natural sand 26 $/ton [L] 17Coarse recycled agg.a 16.3 $/ton [L] [NAFine recycledConcrete aggregatesa

15.8 $/ton [L] [NA

Steel rebarb 1.7–2.4 $/kg [L] 21.6Customized steel sections 3.4–5.4 $/kg [L] 25.3

a In calculation of energy use and carbon emissions compensated through recycling, the emnatural materials (aggregates) that should have been otherwise produced.

b Price varies based on the diameter.

energy use and the carbon emissions caused by an activity or a chainof activities required to manufacture a particular product are usuallysummed up and expressed respectively as the embodied energy andembodied carbon of the respective product. The total embodied energyof a finished building component is basically the total amount of energyconsumed in the extraction and processing of the raw material,manufacturing of the component, transportation of the component tothe construction site and installation. Similarly, the total embodiedcarbon of afinished building component is the carbondioxide emissionsassociated with the various stages considered in calculating energyembodiment. The embodied energy and embodied carbon of variousvirgin constructionmaterials have beenwidely investigated in availableliterature [21]. In addition, the average embodied energy, embodiedcarbon and production costs of a number of recycled constructionmaterials have been recently investigated [18]. Comparison betweenthe energy use and the resulting carbon emissions is normally usedto compare the environmental impacts of various constructionprojects. In such cases, the overall energy use and carbon emission asso-ciated with a particular project are estimated by summing up therespective values for fabrication, transportation and installation of theindividual components. However, to assess the environmental impactof deconstruction strategies, the contribution of a number of otherdeconstruction-related parameters toward the overall cost, embodiedenergy and embodied carbon of the building needs to be taken intoaccount (Fig. 3). A number of deconstruction related parameters con-tributing to additional costs and embodied energy and carbon in suchconstruction projects include:

1— Required Modifications in Component FabricationMethods: Choice ofa deconstruction strategy may require the use of especial fabrica-tion methods and materials that may affect the overall economicand environmental impacts of the project. For instance, the re-useof structural building elements may require adding on the designand fabrication of disassemble-able connections for the respectivestructural elements (Fig. 4).

esent study.

odied energy Embodied carbon

e Unit Ref Value Unit Ref

MJ/ton [20] 6.56 kgC/t [20]MJ/ton [20] 1.38 kgC/t [20]

] [NA] [NA] [NA] [NA] [NA]] [NA] [NA] [NA] [NA] [NA]

MJ/kg [21] 1.86 kgC/kg [21]MJ/kg [21] 1.95 kgC/kg [21]

bodied energy and carbon of recycled materials were assumed to be equal to that of the

Fig. 3. Contribution of various construction and deconstruction activities in the overall embodied energy and embodied carbon of building components.

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2 — Installation (Assembly and Disassembly) Procedure: Non-traditionaldeconstruction strategies such as design for disassembly andreuse (DfD) may require especial installation and disassemblyprocesses that should be taken into account in estimating the

Fig. 4. A representative beam-column (minor axis) DfD connection.

economic and environmental impacts. For instance, disassemblyof a disassemble-able beam element comprising embedded steelconnections requires removal of the cover concrete to expose thebolts (Fig. 4). Moreover, additional propping and lifting measuresmay be necessary for assembly and disassembly operations.

3— Transportation: Transportation contributes significantly to both theeconomic and environmental impacts of deconstruction projects.Therefore, it is important to account for the variations in thevolume of the materials to be transported as well as the travelingdistances required. For instance conventional landfilling mayrequire the transport of a significant amount of construction debristo remote landfill sites. On the other hand, the disassembly andreuse of components in a nearby construction project can lead tosignificant reductions in the transportation distance.

4 — Testing, Repair and Additional Processing: Deconstruction strategiestypically involve additional evaluation, repair and processingstages to ensure that the deconstructed materials/componentsare fit for use in the new structure. For instance, the concreterecycling process involves a sequence of crushing, conveying, andsorting procedures to turn concrete debris into recycled aggre-gates. The reuse of components may require additional testing,evaluation and repair to ensure fitness for use of the componentsin next cycle of service life in the new structure. In addition, itmay be necessary to store the components until they are readyfor deployment in the new building. These additional processesnormally contribute as additional costs, energy use and carbonemissions and thus need to be taken into account.

5 — Savings and Income: Besides the additional costs and energy useincurred, adopting a more sustainable deconstruction strategysuch as reuse and recycling may also result in considerable

138 A. Akbarnezhad et al. / Automation in Construction 37 (2014) 131–144

economic and energy savings by eliminating the need for conven-tional demolition and landfilling of debris. In addition, the reusableand recycled products reclaimed through deconstruction result ineconomic and environmental compensations either indirectly byeliminating the need for the purchase of or production of newraw materials and/or components or directly through the sale ofthe latter to external parties.

By accounting for the above contributing parameters, the economicand environmental impacts of various strategies may be estimatedusing the quantities obtained from BIM model. The cost associatedwith the materials used is estimated by multiplying the volumesinvolved by the respective unit price, using information importedfrom BIM database. Moreover, the cost of executing construction anddeconstruction, including installation, demolition, assembly, disassem-bly, transportation, etc., involved in a projectmay be estimated by calcu-lating the size of the work required, determined using the attributeswhich assign the respective activity to the components, andmultiplyingit by the unit cost entered manually by the user or imported from rele-vant data libraries. In the analyzer program developed in the present

Identify the recyclable and reusable c

If the component is both reusable and recyclable, chastrategy under in

Estimate the energy, carbon emissions and cost associaby multiplying the volumes calculated using the mat

Analyzer Unit

Start

Input data

Data Processor (e.g. IFC Processor,

Spreadsheet)

D

Data Input Unit

Model Database

Building Information

Model

IFC, CSVand/or gbXML

files

Export the selected recycling attributes back to thdeconstruction attribute for each

Estimate the cost, energy and carbon emissions due to by matching the deconstruction strategy attributes (assi

components and materials) with the component type aquantities and multiplying them by the

Calculate the selected sustainability indicators (DSIEC, and carbon associated with various indivi

Compare various deconstruction strategies and select thecriteria set by owners and/or constru

Fig. 5. The overall framework for environmental and e

study, the costs, including cost of materials and costs of execution ofconstruction and deconstruction, incurred throughout the whole lifecycle of the building were taken into the account. The cost analysisalgorithm is presented in Fig. 5. In order to obtain a relative measurefor comparing the cost effectiveness of various deconstruction strate-gies, the following parameter was defined as the Economic Indicatorof Deconstruction Sustainability (DSICO):

DSICO ¼Xn

i¼1PRPi þ CDL−ACCi−CTi−CDi−CRiXn

j¼1CCi

� 100

where, i is the number associated with a particular component, n is thetotal number of the building components, CCi is the cost incurred duringproduction, transportation and installation of a particular buildingcomponent (initial construction cost) conventionally (non-DfD con-struction), ACCi is the additional cost required formodifying the originalcomponent to imbue it with the relevant properties appropriate for theexecution of the proposed deconstruction strategy, PRPi is the price ofthe recycled component if it was produced from natural raw materials,

omponents using the predefined attributes

nge the predominant attribute according to the vestigation

ted with the material and component fabrication erial type attribute by the respective unit values

ata Libraries/ User Inputs

Locations: Component Manufacturers, Recycling

Facilities, etc.

Data Libraries

Cost, Energy and Carbon Emission Info:

construction materials and activities from the related

databases

e BIM modelas the optimized component

End

various construction and deconstruction activities gning various required activities to certain type of ttributes followed by calculating the respective

unit values from the data library.

DSIENand DSICAindices)as well as cost, energy, dual activities and overall strategies.

most desirable one according to the ction authorities

conomic assessment of deconstruction strategies.

Fig. 6. The structural layout of the case project.

139A. Akbarnezhad et al. / Automation in Construction 37 (2014) 131–144

CTi is the transportation cost during deconstruction (to storage site, newconstruction site or recycling facility), CDi is the cost incurred fordemolition or disassembly, CRi is cost of the recycling process and CDLis the savings in the deconstruction cost due to elimination of need forconventional demolition and landfilling. In general, the economicdeconstruction sustainability indicator is the ratio between the eco-nomic benefits attained or the economic savings achieved by replacingconventional demolition and landfilling with deconstruction and thetotal cost of the conventional construction. Similar parameters may bealso defined for comparing the energy use and carbon footprint ofvarious deconstruction strategies. In the present study, DSIEN andDSICA indicators are defined to assess respectively the relative energyuse and carbon emissions associated with the various deconstructionstrategies considered.

DSIEN ¼Xn

i¼1ERPi þ EDL−AEEi−ETi−EDi−ERiXn

j¼1EECi

� 100

DSICA ¼Xn

i¼1CRPi þ CADL−AECi−CTi−CDi−CRiXn

j¼1EECi

� 100

where, EECi and ECCi are respectively the energy use and carbon emis-sions due to production, transportation and installation of the buildingcomponents conventionally, AEEi and AECi are respectively the addi-tional energy use and equivalent carbon emissions caused bymodifyingthe original component according to the requirements set by theproposed deconstruction strategy, ERPi and CRPi are respectively theembodied energy and carbon of the recycled products if they wereproduced conventionally, ETi and CTi are respectively the energy andcarbon embodiment due to the transportation during deconstruction

Table 3General information obtained from BIM model of the case study.

Total number beam elements 910Total number columns 294Total number slab panels 532Total number wall panels 98Total volume of concrete (m3) 852.11Total weight of steel rebar used (tons) 137.60Total weight of DfD connections (tons) 50.77

(to storage, new construction site or recycling facility), EDi and CDi arerespectively the energy and carbon embodiment as a result of decon-struction (demolition or disassembly), ERi and CRi are respectively theenergy use and carbon emissions caused by the recycling process andEDL and CADL are respectively the savings in energy usage and carbonemissions due to elimination of need for conventional demolition andlandfilling. The above sustainability indicators are generally the ratiobetween the energy (or carbon) embodiment retrieved or saved byreplacing conventional demolition and landfilling with deconstructionto the total energy consumed (or the carbon emitted) in conventionalconstruction only.

Besides the sustainability indicators defined in the present study, theprocessor developed enables the users to define other sustainabilityindicators if necessary. The indicators may be especially defined toaccommodate rating systems, such as LEED, BREEAM or Green Globes,as well as other priorities set by owners and designers.

4.3.4. Modifying the BIM to comply with the selected strategyOnce the best deconstruction strategy has been determined by

comparing the results obtained using the EENA processor, the BIMmodel should be updated according to the requirements of the selectedstrategy. In the present study an attribute termed “recommended

Fig. 7. Representative beam to column (major axis) and slab to beam DfD connectionsmodeled in BIM.

140 A. Akbarnezhad et al. / Automation in Construction 37 (2014) 131–144

deconstruction method” was assigned to each component. This attri-bute stores the recommended deconstruction method (includingreuse, recycling and landfilling) for dealing with the respective compo-nent based on the results of the deconstruction analysis. In addition,other deconstruction related attributes of the components wereprogrammed to comply automatically with changes as required by therespective strategy selected. Additional attributes were defined tostore the embodied energy and embodied carbon as well as the fabrica-tion and transportation costs estimated for the respective component.An additional interface was also developed, at the model level, to storeinformation on the overall economic and environmental impacts ofthe entire project. The most important benefit of updating the informa-tion on the BIM software is that the updated BIM model can serve as asingle comprehensive database to manage the whole building lifecycle from the design stage to the deconstruction stage. Creating adynamic linkage between the BIM software and processor can be easilyachieved as outlined in Section 4.2 in the reverse order.

5. Case study

The case study presented serves to validate the economic and envi-ronmental assessment algorithm described. Due to the lack of dataavailable on the cost, energy use and carbon emissions associated withprocessing (especially recycling process and DfD related operations) ofnon-structural components and due to the limitations of the BIMsoftware used in this study, only structural components and associatedmaterials were considered. However, the principles explained above aregeneral and may be readily extended to other materials and buildingcomponents if reliable data is available. The objective of this casestudy is to illustrate the application of the proposed methodology inevaluating the economic and environmental impacts of the commonlyadopted deconstruction strategies. The case study does not intend torecommend a particular deconstruction strategy as the most sustain-able strategy. As discussed in the introduction section, the economicand environmental impacts of deconstruction strategies are influencedsignificantly by many project-specific parameters and thus decisionmaking about the selection of most sustainable deconstruction strategyapplicable to a particular building requires detailed evaluation of theeconomic and environmental impacts of the alternative strategiesavailable by accounting for the project-specific conditions.

5.1. Case description

The case study presented herein is based on part of an actual housingproject in Singapore. The building considered comprises 14 stories withtwo apartment units at each level. The structural layout is summarizedin Fig. 6. The building is construed as a fully precast concrete system. Thequantity of various structural elements and the materials used asextracted from the BIM model are listed in Table 3. All the structural

Table 4The cost, embodied energy and embodied carbon of DfD connections.

DFD connection Type Weight(kg)

Fabrication cost ($)

Beam–beam Anchored steel box 15 84Beam–column(Major axis)

Bolted I section 47.5 256.5

Beam–column(minor axis)

Bolted I section 45.34 252.5

Column–column Spiral connector 55.3 188Slab–slab Bolted shear connector 4.56a 11.10a

Slab–beam Rebar laps 11.66b 28b

Wall–wall Wall shoe 36.40 200

a Per meter slab-slab interface.b Per meter slab-beam interface.

beams, columns, slabs and wall panels can be designed for disassemblyand reuse subjected to additional initial costs for embedding thenecessary disassemble-able steel connections in the respective concretecomponents and the cost of removal of the cover concrete to gain onaccess to the steel connections during disassembly operations (Fig. 7).The general information on the various steel connections required forreusability of structural components is summarized in Table 4. Thedesign of the embedded steel connections considered in this casestudy is based on the actual design of a series of DfD connectionswhich are currently under investigation experimentally at the NationalUniversity of Singapore. Although, the use of such steel connectionsimbues the property of reusability on the structural concrete compo-nents; it also has a significant impact on the costs aswell as the embodiedenergy and embodied carbon associated with the components (Table 4).Therefore, accurate cost, energy use and carbon footprint analyses areneeded to identify the economic and environmental justifications fordesigning the structural components for reuse-ability. In the following,the economic and environmental impacts of the four pre-defineddeconstruction strategies explained in Section 4.3.1 are investigatedfor the case study. The first and second cycles of service life of thebuilding are assumed to be 20 years. The other default assumptionsconsidered are summarized in Table 5. The user interface of theproposed program may be used to modify the default assumptions asnecessary.

5.2. Results and discussions

The following section presents and evaluates the results of aneconomic and environmental assessment of the various alternativedeconstruction strategies described in Section 4.3.1 for the case study.

5.2.1. Effects of deconstruction strategy on cost, energy use and carbonemissions in construction stage

The construction costs incurred by conventional construction andDfD construction methods during the first and second cycle of servicelife are compared in Fig. 8a. To account for the time value of money,all costs have been discounted to the base-date by considering adiscount rate of 4%. The discount rate should be determined based onthe earning power of money for the investor and the inflation rate. Inaddition, the respective energy use and carbon emissions incurredduring the construction stage (only) in the first and second cycle of ser-vice life are compared in Figs. 9a and 10a, respectively. The parametersconsidered in estimating the construction cost, energy use and carbonemissions in this study include production, processing and transporta-tion of construction materials, components fabrication, transportationof components to construction site and components installation.

As expected, the results showed that design for disassembly andreuse is accompanied by additional initial cost, energy use and carbonemissions during the design and fabrication of the components and

Embodied energy (MJ) Embodied carbon (kgC) Required concrete removalfor disassembly (m3)

380.86 29.35 0.0381201.75 92.63 0.038

1147.10 88.41 0.038

1399.09 107.83 0.15115.37a 8.90a 0.0015a

295b 22.74b 0.061b

921.00 71.00 0

Table 5The default assumptions considered by the economic and environmental analyzerprogram.

Other assumptions Unit Value

Distance from prefabrication plant to construction site km 50Distance from deconstruction site to concrete recycling plant km 50Distance from concrete recycling plant to steel recycling plant km 20Distance from the old building to the new building km 20Distance from deconstruction site to landfill km 50Reclamation rate of steel scraps from reinforcing bars and DfDconnections

% 88

Reclamation rate of coarse recycled concrete aggregate fromconcrete debris

% 50

Reclamation rate of fine recycled concrete aggregate fromconcrete debris

% 30

Price of steel scraps $/ton 351Cost of disposal of concrete debris in landfills $/ton 7.77Cost of disposal of concrete in recycling plants $/ton 4Inflation rate % 2.8Discount rate % 4

141A. Akbarnezhad et al. / Automation in Construction 37 (2014) 131–144

thus leads to a relatively higher construction cost and environmentalimpact during the first construction stage. As can be seen in Fig. 8a,because of theuse of relatively costly steel connections, the constructioncost for the case study seemed to increase by about 43% when the con-ventional components (Fig. 8a; denoted as CC: conventional construc-tion) were assumed to be replaced by disassemble-able alternatives(Fig. 8a; denoted as DfD: designed for disassembly). However, resultsshowed that despite this significant increase in the initial cost ofconstruction in the first cycle, DfD strategy led to about 79% reductionin the construction cost in the second cycle of service life and 11%reduction in the overall cumulative construction cost (over two cyclesof service life) when compared with the respective costs incurred inconventional construction.

Similar trends were also observed when comparing the energy useand carbon emissions associated with the DfD strategy with those asso-ciated with conventional deconstruction strategies. As can be seen inFigs. 9a and 10a, as a result of the considerably high embodied energyand embodied carbon of steel connections, the energy use and carbonemissions incurred by resorting to DfD construction for the first cycleof service life were respectively about 23% and 16% higher than thoseassociated with conventional construction. However, the reuse ofcomponent when the DfD strategy is adopted resulted in a significant

Fig. 8. The economic impact of various cons

reduction in the energy use and carbon footprint of construction inthe second cycle of service life. The embodied energy and embodiedcarbon of DfD construction in the second cycle of service life wereestimated to reach about only 7% and 9% of those associated withconventional construction. As a result, the overall (first service lifecycle + second service life cycle) energy use and carbon emissionsassociated with construction (only) using DfD strategy were estimatedto end up being lower by about 35% and 38%, respectively, than thoseassociated with conventional construction.

As can be seen, the results clearly demonstrated that the choice ofdeconstruction strategy can significantly affect the construction cost,energy use and carbon footprint. Therefore, the results highlight theimportance of considering the whole building life cycle when assessingthe environmental and economic impacts of various deconstructionstrategies.

5.2.2. Cost, energy use and carbon emissions in deconstruction stageFigs. 8b, 9b and 10b show respectively the cost, energy use and

carbon emissions in the deconstruction stage of the case studywhen adopting the various deconstruction strategies described inSection 4.3.1. Besides the cost, energy use and carbon emissionsincurred during disassembly and/or demolition, those associated withtransportation of the demolition debris to recycling facilities and bythe concrete and the steel recycling processes were also taken intoaccount.

In addition, the estimated cost, energy use and carbon emissionsretrieved in the form of recycled products are presented in Figs. 8c, 9cand 10c, respectively. As can be seen, results showed that about 76%and 26% of the deconstruction cost incurred by adopting the CC-R andDfD-R strategies, respectively, can be compensated for through thesale of recycled concrete aggregates and the steel scraps (rebars andDfD connections). Furthermore, results showed that due to the highembodied energy and embodied carbon of the recycled steel rebarsand connections, the embodied energy and carbon retrieved throughrecycling, when adopting the DfD-R and CC-R strategies, outweigh (byabout 20% to 38%) those incurred during the deconstruction stage,highlighting recycling as an environmental friendly option. It shouldbe noted that the above assumes that the coarse and fine recycled con-crete aggregates produced are priced similar to that of new aggregates.Similar assumptions were also made with regard to embodied energyand carbon.

truction and deconstruction strategies.

Fig. 9. The energy consumed in various stages of building service life as a result of the deconstruction strategy adopted.

142 A. Akbarnezhad et al. / Automation in Construction 37 (2014) 131–144

5.2.3. Effects of deconstruction strategy on the overall cost, energy use andcarbon emissions

To arrive at the final decision on suitability of a particular decon-struction strategy, the overall (two cycles of service life) economic andenvironmental impacts of the respective strategy should be considered.Figs. 8d, 9d and 10d compare respectively the overall net cost, energyuse and carbon emissions incurred due to the various alternative decon-struction strategies presented. As can be seen in these figures, due to theespecially significant savings observed during the construction stageassociated with the second cycle of service life, the DfD based strategies(DfD-L and DfD-R) seemed to result in a considerably lower overall netcost, energy use and carbon emissions when compared to conventional

Fig. 10. The carbon emissions in various stages of building serv

deconstruction strategies (CC-L and CC-R). Results showed that theDfD-L and DfD-R strategies resulted respectively in about 9.4% and8.6% reduction in the overall (two cycles of service life) cost, 34% and37% reduction in energy use as well as 37% and 40% reduction in carbonemissions when compared to the CC-L and CC-R strategies. In addition,results showed that because of the concomitant savings in cost andenergy achieved through recycling of the C&D wastes generated, theDfD-R seemed to be the most economic as well as environmentalfriendly deconstruction strategy among the four alternative deconstruc-tion strategies considered for the case project. However, it should benoted that the economic and environmental impacts of deconstructionstrategies vary significantly with any variations in the project-specific

ice life as a result of the deconstruction strategy adopted.

Table 6The deconstruction sustainability indicators for various deconstruction strategies.

Deconstructionstrategy

Deconstruction sustainability indicator (DSI)

Economic (DSICO) Energy use (DSIEN) Carbon footprint (DSICA)

CC-L 0 0 0CC-R 2.55 17.14 15.07DfD-L 29.23 37.59 40.47DfD-R 37.19 53.17 53.85

143A. Akbarnezhad et al. / Automation in Construction 37 (2014) 131–144

parameters and the results of this case study may not be extended toother projects without detailed economic and environmental analyses.

Alternatively, the sustainability indicators defined in Section 4.3.3may also be used to compare the overall economic and environmentalimpacts of the various alternative deconstruction strategies. The DSICO,DSIEN and DSICA indicators for various deconstruction strategiesconsidered are listed in Table 6. As expected, all DSI indicators showeda minimum value of zero for the reference (CC-L) strategy. As can beseen, moving on to more sustainable deconstruction strategies (asdiscussed above) consistently results in an increase in the sustainabilityindicators, with the highest values belonging to DfD-R strategy whichwas shown be both the most economic and environmental friendlyalternative.

5.2.4. Sensitivity analysisThe above discussion clearly highlighted the extent of the economic

and environmental benefits achievable through identifying the mostappropriate deconstruction strategy applicable to a building throughevaluating and comparing the economic and environmental impactsof the various alternative strategies available. Besides this, automationin the assessment of deconstruction strategies may be also very usefulin providing a prompt assessment of the sensitivity of particulareconomic and environmental parameters. The latter may include avariation in the price, embodied energy and embodied carbon ofconstruction materials (such as aggregates, steel, etc.) as well as avariation in the cost and energy use of construction and deconstructionservices such as the component fabrication, component transportation,landfilling, recycling process, etc. For instance, the closure or relocationof existing recycling facilities and/or landfills may turn out to be criticalwhen assessing the overall impact of deconstruction strategies. For

Fig. 11. The variation in cost (a) and carbon (b) indicators o

illustration purposes, Fig. 11 shows the variation in the economic andcarbon DSI indicators with a variation in the traveling distance to thelandfill.

As can be seen in Fig. 11, an increase in the traveling distance tolandfill leads to a consistent increase in the DSICO and DSICA indicatorsof the DfD-R, CC-R and DfD-L strategies. In other words, an increase inthe distance to the landfill increases the economic and environmentaljustifications for recycling of debris as well as for implementing non-conventional deconstruction strategies such as design for disassembly.As can be seen, the highest rate of increase in the DSICO and DSIECAindicators with the distance to landfill seems to correspond to theCC-R strategy, indicating that recycling becomes more and more suit-able as distance to landfill increases.

6. Conclusions

Adopting a non-conventional deconstruction strategy necessitatesusually a number of changes in the design and planning of constructionprojects and therefore planning for deconstruction should start from thevery first stages of design and construction. This is especially importantwhen the deconstruction strategy requires changes in the design and fab-rication of the building components to imbue them with disassemble-ability which in turn affect the cost, embodied energy and embodiedcarbon of the respective components. Therefore, the assessment of theenvironmental and economic impacts of a particular deconstructionstrategy should be investigated over thewhole life cycle of the building.In the present paper, a general framework and methodology for the as-sessment of various deconstruction strategies applicable to a buildingusing a database of informationmade available via a typical building in-formation model was presented.

A case study was presented to illustrate the application of the pro-posed method in evaluating three common deconstruction strategies(landfilling, recycling and design for disassembly) applicable to thecase project. The proposed method could facilitate the decision makingprocess for selection of the most sustainable deconstruction strategyapplicable to a particular building by providing the decision makerswith a set of economic and environmental indicators using the informa-tion provided by building information models customized to include anumber of deconstruction-related attributes.

f deconstruction sustainability with distance to landfill.

144 A. Akbarnezhad et al. / Automation in Construction 37 (2014) 131–144

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