Anticipating urban mining

Abstract

Inrecentyearstherehasbeengrowinginterestinurbanminingfromvariousenvironmentaland

economicperspectives.Materialshiddeninbuildingsareattractivealternativestorawones,while

buildingactivitiesareresponsibleforalargeshareofwaste.Thepaperisasummaryoffindingsfrom

ananalysisofpossibilitiesforurbanmininginAmsterdam,focusingonprospectingformetalsin

residentialbuildings.BothgloballiteratureandinterviewswithDutchdemolitionexpertssuggest

thatperformanceinmetalrecoveryfrombuildingsisashighasitcanget.However,estimationof

metalcontentinbuildingsandofwasteprocessingratesisfarfromreliable,accurateandprecise

enoughtosupportsuchclaimsoridentifypossibilitiesforfurtherimprovement,especiallyinrelation

toprocessesofurbanandreal-estateredevelopmentandrejuvenation.Toimproveunderstanding

andembeddingofurbanminingintheseprocesses,wepropose(a)aBIM-basedinformation

infrastructurethatconnectstomunicipalandownerinformationprocesses,soastoprogressively

collectallrelevantinformation,allowforvalidation,verificationandlocalizationofvaluable

resources,aswellasidentifyopportunemomentsfortheirextraction,and(b)policiesthat

overcomethefragmentedinstitutionalcharacterofthebuildingsector,makinginformationsharing

aconsequenceofnetworkingbasedontrustandsharedvalues,drivenbybothdemandandsoft

incentivesrelatingtocircularity.

Keywords

Urbanmining;constructionanddemolitionwaste;buildinginformationmodelling(BIM);policy

formation;renovation;redevelopment;prospecting.

Urban mining

Importance for Amsterdam

ThepaperdepartsfromafeasibilitystudyforfurbanmininginAmsterdam,inparticularformetalsin

residentialbuildings.Recoveringresourcesfromtheanthroposphereinadenselypopulatedcityisa

complextask,whichisneverthelessjustifiedbythejointimperativeofreducingunprocessedwaste

andextractingvaluefromexistingstock.Moreover,citiesseemtobetherightplaceforit,asthe

largerthesizeofacommunity,thehigherthebuildinganddemolitionactivity[1],andalsobecause

higherwastegenerationrates(WGR)forconstructionanddemolitionwaste(C&DW)havebeen

observedincountrieswithhigherpopulationdensities[2].Theunderlyingreasonsforbothinclude

highereconomicactivity,populationmobility,higherlivingstandardsandstricterenvironmental

regulations:allcharacteristicofoldyetstilldynamicurbancentreslikeAmsterdam.

Thefocusonmetalswasopportunistic:giventhehighdemandonmetals,oneshouldexpectthat

thereissubstantialinterestintheirrecovery,resultingintoeitheradvancedexistingpracticesor

emergingopportunities.Therestrictiontoresidentialbuildings,ontheotherhand,directedresearch

towardsthearguablymostdifficultcaseamongbuildingstock.Residentialpropertieshavesmaller

sizes,distributedownershipandalongerlifethanothertypesofbuildings,aswellashigherdiversity

intheirconstructionandmaterials.Whenitcomestometalrecovery,theycannotbeconsideredthe

easiestproposition,sotheresultsofthisresearchcouldbegeneralizedtoalltypesofbuildingstock

withmorereliabilitythaniftheresearchconsidered,forexample,industrialbuildings.

Approach

Obtaininganoverviewoftheworldwidestateoftheartintherecoveryofmetalsfromthebuildings

wasbasedonexploratoryliteraturereview,startingwithjournalpapersinScopusbutnotrestricted

toit.Particularattentionwasgiventopapersthatincludedactualcasesassourceofquantitative

information,soastoestablishareliablepictureofwhatisavailableandhowitiscurrently

processed.Thefindingswerecorroboratedbysemi-structuredinterviewswithDutchexpertsin

buildingdemolitionandwastemanagement.Theserevealedlocalpractices,experiencesand

performance,whichwereconsideredagainsttheoverviewofpossibilitiesfromtheliteraturereview,

soastoidentifyrelevantfactorsandpossibleimprovementsthatwouldstimulateurbanminingin

Amsterdam.Suchfactorsandimprovementswereassumedtorelatetostakeholderprocesses,for

example,plannedrenovationprojectsofhousingcorporations,whichcouldprovidestructural

opportunitiesforresourcerecovery.

Literature review

C&DW

Constructionanddemolition(C&D)arewidelyacknowledgedasoneofthemostimportantsources

ofwaste.C&DWintheNetherlandsin2010(aleanyearforthebuildingindustry)amountedto

24Mt,whileindustryproduced15Mtandconsumers9Mt[3].C&DWisgenerallydividedinto

wastegeneratedfromnewconstruction,renovationanddemolition.Demolitioncontributesupto

70%ofC&DWinsomecontexts[4].Inothersitiscalculatedat55%,withrenovationproducing29%

andnewconstruction16%,whiledemolitionis8%ofthetotalbuildingandconstructionactivity,

renovation40%andnewconstruction52%[5].Wastegenerationpergrossfloorarea(WGA)at

demolitionisreportedasbeingtwentytimesmore[5]orevenfiftytimesmorethannew

construction[4].RenovationWGAisestimatedatfivetimesmorethannewconstruction[5].

Metals from anthropocentric stock

Giventhehighpricesformetalsintherecentpast,interestinrecyclingmetalsfromwasteishardly

surprising.30%ofcopperconsumedinEuropeand50%ofironintheUSAoriginatesfromsecondary

sources[6],whileinAustralia65%ofsteelisrecycled,includingupscalingofoldcastiron[7].

Ambitionsforthefutureremainhigh:inChina,copper,iron,aluminiumandleadsubstitutionrates

in(replacementofprimarymetalsourcesbysecondaryones)throughurbanminingcanbeupto

50%by2030[8,9].Recyclingofmetalsisalsosignificantwithinthewasteindustryitself,asit

significantlyreducesitsnetcarbonfootprint[10].

Withtheworldwidepopularityofreinforcedconcreteasbuildingmaterialandtheincreasing

quantitiesofwiringandpipinginbuildings,itisevenlesssurprisingthatbuildingscontain50%or

possiblymoreofallmetalsinuse[11].ThismakesC&DWimportantincomparisontootherwaste

sources.Forcopperrecoveryitisoneofthemostpromisingsources,togetherwithelectricaland

electronicequipment(theclearleader)andend-of-lifevehicles,especiallyintermsofmassflow,

whereitcompeteswithindustrialandmunicipalsolidwaste[2].Metalsingenerallyrepresent3%of

allC&DWaccordingtomostsources[2,12],althoughsomeestimatesgoupto13,5%[13]–

somethingthatcanbeattributednotonlytoregionaldifferencesandvarietyinconstructiontypes

butalsotohowwastegenerationisestimated(discussedfurtherbelow).Distinctionbetweentypes

ofC&Disimportanthere,too.InNorwayitisestimatedthatrenovationproduceseighttimesmore

metalwastethannewconstruction,whiledemolitiongoesuptoeightytimesmore[5].

Residential buildings

Indemolition,non-residentialbuildingsdominateintermsoffloorareainmostEuropeancountries.

Furthermore,thedemolishednon-residentialbuildingsaremuchlargerandnewerthanresidential

ones[1].IntermsofWGA,therearerelativelysmalldifferencesbetweenresidentialandnon-

residentialbuildings,exceptforrenovation,wherenon-residentialbuildingproducefourtimesmore

C&DW[14].

Current performance

Thecombinationofhighmetalprices,thetheoretical100%recyclabilityofmetals,theirpotentially

endlesslifecycleandtheirhighefficiencyofseparationfromotherwaste,aswellasmeasureslike

landfillbansforrecyclablewaste,expectationsarehigh:100%recyclingofmetalsisakeygoalinthe

globalC&DWindustry[10].Ofmetalsembeddedinconcrete,90%isexpectedtoberecoveredand

recycled[9].

SuchexpectationsarenotoutoftonewithgeneralrecyclingperformanceinC&D:annually94%of

C&DWintheNetherlandsissuccessfullyrecycled[3],albeitmostlyindowngradedforms,e.g.as

materialsforroadbuilding[15].Bycomparison,thetargetsetbytheEuropeanCommissionin2008

is70%recyclingofC&DWby2020[16].Metalrecyclingisamajorcontributortothissuccess:it

performssowellthatassessmentsofC&DWmanagementsuggestthatfurtherimprovementisnot

expectedtohaveaneffectonoverallperformance[13,17].

Estimation approaches

Therearetwofundamentalapproachestoestimatingthequantitiesandcompositionofmetalsin

use[18]:

1. Topdown:estimationsfromthebalancebetweentheamountofmetalsenteringuseand

theamountofmetalsexitinguseinend-of-lifeproductsorotherwaste.Thisapproach

requiresreliabledataoverseveraldecades.

2. Bottomup:estimationsbasedoninventoriesofallmetalproductsinuseandtheapplication

ofproxyindicatorstocovergapsandsimplifycounting.Thisapproachispopularbecauseof

theavailabilityofdataonproxyindicatorslikebuildingsormotorvehicles[11].Themain

problemliesinthereliabilityofestimatingthemetalcompositionofsuchindicators[19].

Estimatingthemetalcontentofabuildingcanbedoneinanumberofcomplementarymanners,

rangingfromconstructioninformationinconjunctionwithsitevisitstolifetimeanalyses(top-down

approach)toend-of-lifeinvestigationsthroughinspectionspriortodemolitionandgeneralization

fromprecedents[20,21].Typically,combinationsoftheaboveareappliedtoarriveatreliable

results.However,whatholdsforonebuildingmaynotapplytoanother:withbuildingsitismore

difficulttogeneralizethanwithe.g.motorvehiclesbecausebuildingsareseldommassproducedin

anindustrializedmanner[22].Still,commoncharacteristicsandcomponentsleadtotherecognition

offairlystandardizedtypesatsomeabstractionlevel.Atsuchlevelswearetemptedtoapplyrulesof

thumbliketheonesfoundintechnicaltextbooksonconstructiontoarriveatsomebasicestimates

acrossarangeofbuildings.Asaresult,C&DWliteratureaboundswithgenericcategorieslike

residentialversusnon-residentialorsmallversuslargebuildings.Themostusefulcategorizations

involvebasicfeatureslikethetypeofload-bearingstructure(steelframe,reinforcedconcrete,wood

frameetc.),whichhavebearingonthematerialcompositionofabuilding.Asaresult,literature

containsawiderangeofvariousestimatesforthemetalcontentofbuildings:

• 14-75kg/m2ofsteelinChineseresidentialbuildings,dependingontheperiodandtypeof

construction[23]

• 606kg/cofironinresidentialbuildingsinNewHaven,CT;forcopperinthesame

municipalitywehaveamoreanalyticalbreakdown[18]:

o 28kg/cinplumbing(asopposedto32onaverageintheUSA)

o 25kg/cinwiring(28intheUSA)

o 3.1kg/cinairconditioningandrefrigeration(16intheUSA)

• 195kgofcopperpersinglefamilyhouseinAustraliaor110kgpersharedlivingcomplexand

• 290kgofzincpersinglefamilyhouseinAustraliaor188kgpersharedlivingcomplex[11]

• 80kg/cofcopperinSwitzerland(40%intheroofand30%inpowersystems),witha

comparable60kg/cinStockholm,whileinCapeTownits5-10%ofEuropeancities,outof

whichonethirdisinsanitationandtwothirdsinpowersystems[24]

Probablythebestillustrationofthefuzzinesscanbefoundinacomparisonbetweenestimationsof

astudyonanumberofGermanbuildingswiththeresultsofprecedentresearch[20]:

• steel:study0,1-8,6kg/m3–others2,08-37

• aluminium:study0,03-0,5kg/m3–others0,013

• copper:study0,002-0,5kg/m3–others0,05-0,24

IntermsofC&DW,similarvariationcanbeobserved:

• MetalwasteinFlorida[12]:

o Residentialconstructionorextension:0,30kg/m2(woodframe)or1,5(concrete)

o Residentialdemolition:10kg/m2(woodframe)or15(concrete)

o Residentialalterations:0,75kg/m2–butroofreplacement:6,8

• Metalwasteinresidentialrenovation:0,4-6,8kg/m2[14]

• SteelC&DW[25]:

o ConstructionwasteinChina:4kg/m2but5,1accordingtotransportationrecords,

whileinotherresearchithasbeenreportedas6kg/m2

o IntheUSA:0,9kg/m2

o InNorway:0,48kg/m2

o InKorea4,53kg/m2

Interview results

InterviewswithDutchexpertsfromsmallandlargedemolitionandwasteprocessingfirmssupport

thefindingsfromtheliteraturereview.AccordingtotheDutchAssociationofWasteCompanies

[26],basedonresearchofStatisticsNetherlands(CBS),EurostatandRijkswaterstaat(theDutch

Agencyfornationalinfrastructureconstructionandmaintenance),about40%ofwasteinthe

NetherlandsisgeneratedbytheC&Dindustry.C&DWisthelargestcontributortothewaste

productionofthecountry.C&DWconsistofmultiplewastetypes.90%ofthetotalweightis

concrete,brickorasphalt.Theother10%containsplastics,woodandmetals[27].

Motivatedbyeaseofextraction,value,regulationsandsocialinvolvement,metalsappeartobeina

closed-loopwastesystem.Asavaluablecommodity,theyreceiveparticularattention,evenin

residentialbuildings,eventhoughtheconcentrationofwiringandpipingislowerthaninnon-

residentialbuildingslikefactoriesandoffices,whichmoreoveremployhigherquantitiesofmetalsin

theirconstructionandouterenvelope.Estimatesfrominterviewedspecialistsvaryfrom5m3ofiron

(primarilyheatingservicesandconstructionsteel)and1,5m3ofallothermetals(excludingiron)to

150kgofferrousmetalspersingle-familyhouse.Aluminiumisnotwidelyusedforwindowframesin

residentialbuildings;theestimationsgivenwere5to10%ofallwindowframesinresidential

buildings.

Concerningperformance,interviewssuggestthatmetalsarepracticallyalwaysrecoveredatsome

pointintheprocessingchainandmostlyrecycled.Indemolitionprojects,themetalspresentare

identifiedbyvisualinspectionsbeforehand,mostlybasedonexperienceratherthandocumentation.

Demolitionexpertscanbeconsideredexpertsonvaluerecognition,too.Theyarequiteawareofthe

potentialvalueofmaterialsingeneralandinmanycasesofthevalueofparticularmaterialsand

componentstospecificpotentialbuyers.Demolitionfirmsarewellconnectedandcapableof

recognizingorevenanticipatingmarketdemandformaterialsfromsecondarysources.

Mostoftheeasytoremovemetalsneedtobeextractedquicklybydemolitionworkers,beforepetty

criminalsgettothem.Dependingonthetimeframeoftheproject,theexperienceofthedemolition

firmandcurrentdemand,thehardertoreachmetalsmayalsoextractedonsite.Whentimeor

experienceislimitedordemandlagsbehind,mixedwasteisdeliveredtowasteprocessingfacilities

andmetalsareextractedoffsite.

Wasteseparationatthesource,asrequiredbyDutchnationalbuildingregulations[28],mainly

concernshazardoussubstancesbutC&DWfirmsappearwillingtogobeyondtheirlegalobligations.

Incaseofmetals,thereisaclearfinancialdrivebutcorporateresponsibility,including

environmentalawareness,isalsobecomingafactor.Somedemolitionfirmsinitiatefar-reaching

agreementswithmanufacturerssoastoreducetheneedformaterialsfromprimarysources,e.g.on

howtosupplyC&DWfordirectre-entryinproductionprocesses.

Theoverallchainseemshighlyvariableanddependentontime,opportunityandpersonal

preferencesbutintermsofrecoveryintervieweesthoughttherewaslittleimprovementpossible.

Theindustryappearsawareofopportunities,skilledandknowledgeable.Whatseemsvariableand

adhoccouldalsobeviewedasadaptabilitytosituationsandconditions,allowingtotakeinto

accountfinancial,timeandotherconstraints.

Demolitionandwasteprocessingexpertsalsoappearsawareofdangers,inparticularconcerning

pollutantsthatmayrenderC&DWrecyclingunfeasible.IntheNetherlands,thisprimarilyrefersto

asbestos,whichcanbepresentinpiping,plating(especiallyaroundheatingboilers),façade

elementsand,mostdisturbinglyformetalrecovery,pastesandsealants.Proximitytoasbestos

meansthatmetalcomponentsarecurrentlyexcludedfromfurtherprocessing,atleastuntil

decontamination.

The state of the art: findings and directions

Estimation

Anacknowledgedprobleminliteratureisthatgrossestimatesinvolvingabstractproxiescannotbe

easilyvalidatedduetoregional,typologicandothervariations[19].BuildingsinSwitzerlandand

SwedenmaybesimilarbutthoseinCapeTownhaveflatroofsandnoheating,resultinginto

differentmetalcontent[24].Equallyimportanttoenvironmentalandtypologicfactorsandfeatures

arethedynamicsofbuildings,whichmakeestimationsratherhard,e.g.throughrenovationsthat

resultintohibernatingmetalstocklikeoldpiping[20]orunreportedorpoorlydocumentedchanges

likedetailsmodifiedbycontractorsduringconstruction[15].

ConcerningC&DW,weoftenlackactualdataandopportunitiesforverification[21].Whileweknow

thatmetalsarepresent,confidenceinestimationstendstobeweak,sowiderangesareappliedto

compensateforthelowreliability[14].Furthermore,thereisvariationduetothetypeofC&D

activity:newconstructionprojectsmaybepreciselyreported,whilerenovationanddemolitionare

generallyinsufficientlydocumented[5].Intheend,allwehaveisestimatesthatareusefulinthe

absenceofpreciseandaccuratedata,primarilyforhighabstractionlevelsthatpaintavaguepicture

ofpotentialratherthansupportforpolicy,planning,designormanagement.Itistherefore

questionablewhetheritmakessensetocontinuewiththerefinementofsuchindicativeestimations.

Fromamethodologicalviewpoint,theunitsappliedtoC&DWmeasurementareamatterfor

concern[29].Forwaste,mass(kg)seemsasafechoice,certainlyformetaltoberecycled.Forthe

sourcesofthewaste,leavinggrandtotalsandestimationspercapitaaside,thereistoomuch

emphasisonthegrossfloorareaofbuildings(m2),whichseemsapoorproxy,asitbearsan

uncertainrelationtothe‘solids’ofarchitecture:thewalls,floors,roofsetc.thatcontainthemetals

thatinterestthisstudy.Itseemsthatestimationmethodsarebasedontheavailabilityratherthan

therelevanceofdata.

Validation, verification and localization

Abstractprojectionsmakeurbanmininginitiallyquiteattractivebutcloserinspectionofexisting

practicesandpossibilitiessuggeststhatexpectationsmayhavetobeloweredbecauseof

uncertainty.Realopportunitiesrequirepreciseandcomprehensiveprocessesofdatacollection,

estimation,validationandverification.ThesecanbebeneficialtoC&DWmanagement,atboth

projectandpolicylevel,providedtheygobeyondstaticestimationstotakeintoaccountthelifecycle

dynamicsofabuildingandprovideapermanentlyup-to-datepictureoftruepossibilities.The

problemisthatinformationonthestructureandmaterialcontentofbuildingsisphysically

widespread,i.e.inhandsofvariousstakeholdersandinvariousforms,includingdifferentversionsof

thesamedocuments.Especiallyduringuse,abuildingmaybemodifiedandrefurbishedmanytimes,

withoutadequatedocumentationfortheplanningorregistrationofthechanges.

Manyowners(particularlyinstitutionalones)andlocalauthoritieshavebeenpropagatingtheneed

tocollectandorganizeexistinginformationtowardsacomplete,coherentandconsistent

informationsystemthatdescribesthebuildingdynamically(i.e.includingitshistory).Tocollect

existinginformationinanefficientandeffectivemanner,oneneedstwothings.Thefirstis

connectionstoexistinginformationprocesses,fromdesignandfacilitiesmanagementtoweather

dataandbuildingpermitapplications.Suchconnectionsprovideaccesstovaluableinformation,

suchasprecisedescriptionsofzincorleadontheroofofaprotectedmonument.Theyalsoallow

stakeholderstoexplicitlyincluderecoveryofmaterialsintheirpoliciesandactivities,e.g.inthe

demolitionplanofabuilding.

Thesecondthingistointegratethisinformationinacomprehensivehierarchicalrepresentationthat

coversallnecessaryabstractionlevels,soastonotonlyfacilitatecorrespondinglevelsofdecision

making(frompolicydevelopmenttositeplanning)butalsodealwithquestionsofincompleteness

anduncertainty.Oneshouldexpectthatinitiallyinformationwillbelacking,vagueorconflictingbut

evenatlaterstagesitisoftennotpossibletoascertaincriticaldetailswithoutdestructiveresearch

intotheactualbuilding.Allowingformissingandvagueinformationintherepresentationis

thereforeapragmaticnecessity,whichcanbecounterbalancedbythehierarchicalstructureand

mechanismsofinheritance,parameterizationandconstraintpropagationitsupports.

Acomprehensiverepresentationthatcanaccommodatedetailsofthebuildingwhenrelevantisalso

usefulforthelocalizationofmetals.Knowingwithgrowingprecisionandaccuracywherespecific

metalcomponentscanbefoundinabuildingsupportsbetterplanningindemolitionactivitiesand

helpsidentifypossibilitiesforthebuildingstockofacityingeneral.Currentestimatesbasedon

proxiesfailtoaddressissuesoflocalizationsandhencealsoofe.g.selectivedemolition.

Opportunities for urban mining

Thereisalsoaquestionofscopeforurbanmining:ifbothliteratureandtheinterviewsagreethat

metalrecoveryfromC&DWisashighasitcanbe,whatcanprospectingformetalsinAmsterdam

addintermsofefficiencyorperformance?Isthereroomforurbanminingformetalsnexttowhat

alreadyhappensinthedemolitionandwasteprocessingchain?Historycanbehelpfulinthis

respect,asenthusiasmforurbanminingisnotnew;itisarecurringthemeintimesofextremeneed

likewar.Analysesofwartimeurbanminingsuggestthatthereareinherentlimitationsthatcannot

beignored.Forexample,duringthefirstworldwarinAustria,upto80%ofcopperforthemunitions

industrycamefromsecondarysourcesbutperhapsaslittleas10%ofthetotalamountofcopperin

usewasamenabletoextractionduetoreasonslikehighcostorsignificanceforothercriticaluses

[6].Moreover,theinitialdriveandperformanceappeartohavewanedafterthefirstyear,perhaps

becausethelow-hangingfruithadbeenalreadypicked.Onecouldthereforeputforwardthaturban

miningtodaycouldbecomeasimilarlyshort-livedbandwagonunlessstructurallyembeddedin

urbanandreal-estatere-developmentandrenovationprocesses,whereitseconomiccontribution,

howeversmallcannotbenegligible.

Renovation and refurbishment

ConnectivitytoAECOprocessesisthereforeimportantforsustainingandpossiblyamplifyingurban

miningwithinexistingAECOprocesses.Currentinterestinmetalrecoveryisclearlylinkedtodemand

andthehighpricesitcauses.However,evenafterademandpeak,theaccumulatedamountsof

urbansecondaryresourcesremainamajorenvironmentalandeconomicissue[23].Thereductionof

newconstructionactivityincombinationwiththepreservationtendencyinarchitecture[1]is

makingdemolitionandrenovationincreasinglyimportantinAECO.Inmanycases,renovationis

alreadyoutweighinginvaluenewconstructionwork[17],evenforresidentialbuildings[9],where

somerenovationtypeshaveaWGRnearingthatofthedemolition[12].

Renovationandrefurbishmentareattractivetargetsformetalrecoveryinawaythatcontrastswith

thefrequentemphasisonnovelwaysofdesigningandconstructingbuildingssothattheyfacilitate

recoveryandcircularity.Withoutdetractingfromthevalueoftheseattemptsatinnovation,one

shouldacknowledgethatanyresultstobeexpectedfromthemwillbeinafewdecadesfromnow–

andeventhentheywillrepresentasmallpercentageoftheproblemsandpotentialofthebuilt

environment:thevastmajorityofthecurrentbuildingstockwillstillbepresent,stillinthevast

majority.Ifwefailtoaddresstheissuesoftoday’sstock,theseissueswillpersistdespiteany

improvementstonewbuildings.

Arelatedissueisthatapproachestonewwaysofdesigningandconstructingbuildingstendto

advocatesummarylabellingofelements(“passports”)concerningtheabilitytoremove,replaceor

otherwiseprocessthem.Judgingfromtheexperiencesmentionedintheinterviews,oneshouldnot

presumethatsuchstraightforwardsolutionscouldcovertherichnessandcomplexityofrealityand

thedatathatdescribeit.Relationswithotherelementsandmaterials,weatheranduse,andother

contextualmattersformsignificant,dynamicaffectingfactorsthatcannotbecapturedbystatic

properties.Suchfactorsareoftenkeydeterminantsoftechnicalfeasibilityoreconomicviabilityin

recoveryandshouldthereforenotbeneglected.

Towards an inclusive framework

Theproposedsolutionisnotafiniteonebutaframeworkthatbringstogetherdifferentpartsofa

sustainablefutureforurbanminingwithinpragmatictolerances.Thisframeworkisbuilton

acceptanceofthecomplexityoftheexistingsituationratherthanreductionistattemptsat

simplification.Itisthereforeinclusive:itattachesvaluetoallstakeholdersandactors,andtotheir

information.Theorganizationofsuchinformationintoacomprehensiveandcoherentdata

infrastructureisoneofthetwomaincomponentsoftheframework.Nexttothistechnical

component,asocialoneconnectsthedecisionmakingbyAECOpartiestopublicpolicymakers.

Publicpolicyandregulatorygovernancerepresentsocialandculturalaspectsthatoverlapwithand

enrichtheworkingofmarketforces;inconjunctionwithAECOprivateinitiatives,theydefine

possibleC&DWprocessingapproachesandperformance.

Information processing design

Materialresourcesinbuildingsrelatetotheinterestsofanumberofstakeholders:real-estate

owners,designers,engineers,managers,demolitionfirms,wasteprocessingenterprises,building

contractors,localauthoritiesandcitizens.Eachoftheseisaproducer,consumerorcustodianof

relevantinformation.Itcouldbearguedthatthenumberofstakeholderscanbereducedthrough

delegation:localauthoritiescanbeassumedtorepresenttheinterestsofcitizens,demolitionfirms

couldbeseenasthefrontendofaC&DWprocessingchainthatincorporateswasteprocessing

enterprisesetc.However,therelationbetweenauthoritiesandcitizensissignificantintermsof

transparencyinpolicymakingandgovernance,andcitizenscanbeanimportantsourceof

informationonthebackgroundsofpolicy,includingquestionsofintangiblevalue,whichcanhave

directinfluenceonC&DWtreatmentchoices.Similarly,therelationbetweendemolitionandwaste

processingshouldbemadeastransparentaspossiblebothforeconomicreasonsandbecauseit

contributestotechnicalandoperationalaspects,includingthechoicebetweenre-use,

remanufacturing,recyclingetc.Followingtheprincipleofinclusivenessandforsuchtransparency

reasons,thenetworkshouldcoverallstakeholdersandshouldremainalsoopeninthisrespect.The

mainconsequenceisthatitmakesinformationgatheringquiteextensive,beyondtheusualscopeof

e.g.ademolitionproject.

BuildingInformationModelling(BIM)isthecurrentlypreferredchoiceconcerninginformation

integrationinAECO.BIMpromisesaunifiedmodelasbasisforallactors,actionsandtransactionsin

adesignorconstructionprocess,aswellasadynamicenvironmentforinformationprocessing

throughoutthelifecycleofabuilding,withsignificantbenefitstoownersandoperators[30].In

urbanminingstudies,BIMhasalreadybeenidentifiedasanappropriateframeworkforinformation

management.ExistingattemptshaveextendedBIMwithwastemanagementfacilitiesthatcanbe

usedtoimprovebuildingdesignandmakewastepredictions[17,31],aswellasthroughtheaddition

ofRFIDandstresssensordatathatfacilitatebetterestimationofstresspropertiesovertheworking

life,disassembly,take-backandre-useofstructuralsteelcomponents[7].

BIMcanintegrateallinformationfromrelevantdocuments,includingtheconstruction

documentationandon-siteinvestigationsthatareessentialformetalextraction[20],aswellas

documentationfromAECOprocessesthatoccurinthelifecycleofabuilding(e.g.buildingpermitfor

aloftconversion).Theendresultisacomprehensive,coherentandconsistentmodelthatmakes

extensiveuseofthepotentialofcomputerizationforwastemanagement[21]andservesavarietyof

purposesforowners,occupants,authoritiesandAECOprofessionals,allowingthemtoaccessthe

informationtheyneed.

Theproposedapproachistobuildthehierarchicalrepresentationdiscussedaboveusingvariable

abstraction,dependingontheavailabilityofinformationandcorrespondingtodifferentproxies.

Whenthereislittleifanyinformationonabuilding,itcanberepresentedbyanabstractvolumetric

description–evenasymbolicone(asinamap)–denotingagenericcommodity.Suchabstract

descriptionsinheritinformationfromgeneraltypes,e.g.residential,officeorindustrialbuildings;

wood,metalorconcretestructures;high,middleorlowrisebuildings,etc.

Intermediatelevelsinthehierarchicalrepresentationareoccupiedbybuildingelementslike

reinforcedconcretecolumnsandbeams:intermediateproxies,whicharemoreeffectiveasbasisfor

decisionsandpolicies[22].Theseelementscanalsobeabstractorsymbolic,evengeneratedby

probabilisticreasoning:atypicallow-riseAmsterdamrowhousenormallyhaspartywallsthat

separateitfromadjacentbuildings,exteriorwallsandapitchedroof.Ifrelevantdocumentationis

available,theelementscanbecomespecific,withaparticularformandstructure.

Whetherabstractorspecific,suchelementsactasplaceholdersofre-usablematerialslikerebar,

wiringandpiping(includinghibernatingstock),againderivedfromprobabilisticandtypologic

processesorfromdocumentation.Ifthedocumentationsuffices,itispossibletodevelopthelower

levelsoftherepresentation,theonescontainingspecificmanufacturedcomponents,usuallywitha

preciseformandmaterialcomposition.Suchcomponentscanthereforeprovideaccurateand

preciseinformationthateliminatestheneedforproxies,facilitateslocalizationofresourcesand

henceplanningofextraction,andpavesthewayforadvancedextractionandprocessingapproaches

andtechnologieslikeRFIDtagging.

Figure1.Indicativelevelsofabstractioninbuildingdocumentationandcorrespondinginformation(includingproxies)

Thehierarchicalstructureoftherepresentationallowsustotackleproblemsofuncertaintyand

incompletenessbysupportinginheritancebetweenwholeandpart,whilebuilt-inBIMconstraints

definenon-hierarchicalrelations,e.g.betweenadjacentelementsofdifferentkinds.Ifinformation

onpartsoraspectsofabuildingismissing,itispossibletouseproxieslikegenericdefaultproperties

fortheparticularpartoraspect,orpreferablydatafromprecedents:documentedbuildingsofthe

sameperiodortype.TheorganizedhousingdevelopmentoftheNetherlandsholdssignificant

advantageswithrespecttosuchreasoning.

Reversely,abstractingdetailedinformationintomorecompactestimatesbecomessignificantly

easier,transparentandreliable,aswellasrelevant:metalcontentcanbedescribedinamanner

appropriatetotheC&Dactivity,e.g.volumeofreinforcedconcreteelements,areaofaroof,wall

lengthinadwelling.Findingtheappropriateunit(buildingdwelling,kg/m2,kg/m3)foranactivity

(renovationofabathroomorkitchen,rewiringorreplacingthecentralheatingsystem)becomesan

explorationofeasy-to-generatealternativesfromthesamemodel.

Policy development

TheprospectinganalysisofurbanminingformetalsinresidentialbuildingsinAmsterdamreturned

twosignificantfindings:

• BothliteratureandinterviewssuggestedthatexistingAECOpracticesmanagetorecover

resourcestoadegreethatmaybehardtoimprove

• Estimationsofmetalcontentinbuildingsseemlessreliable,completeorprecisethan

requiredforvalidationandverification,orformakingexpensivedecisionstointensifyurban

mining

Thefirstfindingisinlinewithviewsthatconfineurbanminingtothehibernatingstocks,whichfor

somereasonarenotpartoftraditionalwastehandlingprocesses[32].Ananswertothelatteristhe

developmentofaninclusive,comprehensiveinformationinfrastructurethatbringstogetherthe

informationprocessesofallstakeholders(startingwithreal-estateownersandlocalauthorities).

Thisinfrastructurefacilitatessmoothtransitionfromexistingseparatepracticestoconnected,

collaborativeandyetdistributedprocessestowardscommonaims.

Together,thesefindingsraisethequestionconcerningpolicyrelevance.Towhatextentarethere

urban,hibernatingstocksofmetalandhowcantheybecomepartofthevaluechain?Andwhatis

theroleofpublicandprivatestakeholders,includingindividualbuildingownersandhomeowners,in

this?Preciseinformationiskeytothisdebate.Establishingtheproposedframeworkwillencounter

significantchallenges,likeanytransitionprocess,havingtodowithovercominglock-insofcurrent

institutionsstructuringdecision-making[33,34].

Anumberofchallengeshavealreadybeenreferredtointhisarticle,inlinewithobservationson

processesofchangeinotherarticles.Thesechallengeshavetheirorigininthefragmented

institutionalcharacterofAECO,operatinginmultiplemarketsandindistributedprojectteams[35].

Thesupplychainswithinconstructionarecharacterizedbymanysmallandmedium-sized

enterprises,whichlacktheresources,willingnessorcapacitytouseBIMfornovelapplications

requiringcollaboration[36,37].Likewise,therelevantinformationexchangeamongstanindefinite

numberofactors,publicandprivate,notjustinvolvesachallengeofdevelopinganinteroperable

platformtofacilitateinformationexchange,butalsopresupposesawillingnessofactorsto

collaborate,involvingtrustandreciprocity.Thedevelopmentandcaptureofjointvaluesthroughout

thechainfromalifecycleperspective,presupposesstandardizedinformationandprocedures[38].

However,relationsamongsttheactorsarecharacterizedasadversarial,shorttermandlackingin

trustandareconsiderednotstrongenoughtodevelopanetworkoforganizationsbasedontrust

andsharedvalues[38].Also,morecomplexsupplychainshavemoretiers,moreparticipantsand

moretransactionsbetweenthestakeholdersinthedifferenttiers.Thismakesthecreationofshared

valuesmoredifficult.Moreover,actorsaretemptedtopasstherisksandcostsofcontributingto

thesesharedvaluesontootheractorsupwardordownwardthechain,withpowerfulplayers

capturingthemarginswithinthechain[39].Thus,AECOlackstheincentivestobuildtrustanda

conceptionofsharedvaluesuchassustainability(thetopiconwhichmostofthestudiesintothe

valueofsupplychainmanagementisbased)orre-useofwaste,letalonetorecognizethepotential

valueofmininghibernatingstockofre-usablesandrecyclables.

TheproposedframeworkisthereforenotlogicallytobeexpectedtocomefromwithinAECO,

especiallysincethesectoralreadyperformsverywellintermsofresourceextractionandwilllacka

senseofurgency.Ademand-drivenapproachismorelikelytopushtheindustrytowardssuch

sharingofinformation.Regulatoryrequirementsandeconomicvalueofthemetalstobecaptured

arethefirmestexternalincentivesthatcanbringaboutchangeinthesector[34]thatisknownfor

itsresponsivenesstoexternalevents[38].However,regulatoryrequirementsrequireasolid

informationbasetogivetherightincentive,andpricesdonotincentivizeduetotheabsenceofa

recognizedmarketforthesehibernatingstocks.Moreover,addressingtheexistingbuildingstock,in

whichthehibernatingstockistobefound,isfarmorecomplicatedthandevelopingand

implementingambitionsfornewlydevelopedbuildings,eventhoughalsofornewbuildingsitisfar

fromcommontotakeend-of-lifestagesintermsofre-useandrecyclingintoaccount–usuallyend-

of-lifeattentionisdirectedatwastehandling.

Moreinternal,softincentivesarethereforeexpectedtobemoreeffective.Thepushfromlocal

governments,settingambitionswithregardstocirculareconomyandtheclosingofresourceloops,

isafirststep.IntheNetherlands,moreandmorecitieshaveembracedthecirculareconomy

conceptandhavedevelopedwhitepapersstatingambitions,sometimessupportedbythenational

government,isaplatformthroughwhichpublicandprivateforerunnersandknowledgeinstitutes

exchangeexperiencesandbestpracticeswithregardstocircularity[40].Theseinitiativesare

embeddedwithininternationalpolicyframeworksinwhichlocalgovernmentscollaborateandshare

knowledgeandbestpractices.Combinedwiththeconstructionindustry’sownsustainability

programmes,suchasthesustainabilitycertificationschemes,andthegeneralpushtowards

extendedproducerresponsibilityandcirculareconomy,thesemightgivetheincentivestostepby

stepcreateanichemarket,tobeupscaledandmainstreamedatalaterstage[34].Eventhoughthe

conceptsofcircularityandcirculareconomy,towhichre-useofmaterialsiskey,arestilldeveloping,

theseinitiativesandpolicyplansalreadyincentiveactorstothinkabouttheimplicationsofthis

conceptfortheirorganisation.Developers,contractorsandfinanciersallhavestartedpilotprojects

todevelop,tryandtestcircularconcepts,underliningtheneedforinnovation[41].

Thebottom-upwaysofdevelopingandtestingconceptsthatmaypossiblycontributetoacircular

economyareverypromising.Theyofferthebreedinggroundforthedevelopmentofsharedvalues,

andonaprojectbasis,theyemphasizetheneedfordataexchange.Moreover,theseprojectscreate

dedicatedambassadorsoftheconcept.Thepeoplewhohaveworkedontheseprojects,inthe

projectteams,starttospreadtheword,duetotheinvolvementofthehighestlevelinthe

organisationsinvolvedintheseshowcaseprojects.Suchambassadorshipisalsoconsideredtobe

oneofthekeyaspectsfornichedevelopment[33].Whenthesepoliciesarecontinuedandgradually

helptoshapeamoretangibleimageofurbanmining,thiswillsupportthecreationofawarenessfor

developingtheinformation-sharingframeworkassuggestedinthisarticle.Tomatchsupplyand

demandofconstructionmaterialsforre-useandrecycling,afine-grainedunderstandingofthe

potentialvalueofhibernatingstockisneeded.Inthisway,softpoliciesmayindeedcreateaneedfor

informationsharingessentialforprospectingtheurbanmine

Conclusions

• TheNetherlandsareontopoftheirgamewhenitcomestore-useandrecyclingofC&DW

waste,comparedtoothersectorsandcomparedtoEUtargets.Ingeneral,80%oftheDutch

wasteisrecycled,whereas94%ofC&DWisrecycled.Europeantargetsfor2020areseton70%

forC&DW.

• Metalsareinanalmostclosed-loopcycle.Theycanberecycledindefinitelywithoutlossof

performance.Furtherimprovementisnotexpectedtohaveaneffectongeneralrecycling

performance.OthertypesofC&DWaremoreoftenrecycledintodowngradedforms,e.g.as

materialsforroadbuilding.

• Althoughsomeinformationonquantitiesisrecovered,thedatahavealargevariationanddata

foundintheliteraturereviewarenotdirectlyapplicabletotheNetherlands.Moreresearchinto

thetracingofmetals,andpossiblyothermaterials,isneededtoimproveestimationson

quantities.

• Re-useandrecyclingofC&DWisdrivenbybothregulations,andfinancialandsocietal

motivations.Thisseemstobeafairlyhealthysituation.However,thereseemstobelittlestate

encouragementtodoevenbetter.Thankfully,thereareprivatedevelopmentsonsustainable

demolitionmanagementthatencouragere-useandrecycling.

• Atthispoint,giventheperformanceofrecyclinginC&D,thebuiltenvironmentisalreadyinuse

asanurbanmine.Thedifferencewitha‘true’mineisthefactthatthereis,sofar,noplanned

approachforexploitationinthelongerterm.Thismightnotbeadrawbackasthecurrent

systemisadaptableandextractedmaterialsseemtofindtheirwayeventually.Aconceivable

disadvantageontheotherhandisthatmaterialsaresometimesprocessedabroadresultingin

highercostsfortransportationandCO2emissions.

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