混凝土方面毕业论文外文翻译--回顾英国公路管理处理硫酸盐硅灰石膏侵害的经验-公路隧道

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1、AreviewoftheexperienceofthaumasitesulfateattackbytheUKHighwaysAgencyNeilLoudonHighwaysAgency,SSRCESDMDivision,HeronHouse,49-53GoldingtonRoad,BedfordMK403LL,UKAbstractThepapersummarisesandreviewstheUKHighwaysAgencyexperienceofthaumasitesulfateattack.ThaumasitesulfateattackwasfoundinFebruary1998inanum

2、berofbridgefoundationsandburiedcolumnsontheM5MotorwayinGloucestershire.Thepaperwillhighlighttheinvestigationofthesestructures,andassesstheimplicationsoftheresultsoftheextensivetestingundertakenatthesesites,forotherstructures.SubsequenttothediscoveryofthaumasiteinGloucestershiretheHighwaysAgencyparti

3、cipatedintheThaumasiteExpertGroupsetupbytheMinisterforConstruction.ThereportproducedbythegroupinfluencedthedevelopmentoftheAgenciesownguidance.Investigationswereundertakennationallyusingriskbasedcriteria,todeterminewhethertheoccurrenceofthaumasitewasalocalphenomenon,orofmorewidespreadconcern.Concurr

4、entlyguidancewasalsoissuedformanagingandminimisingtherisksofthaumasiteinnewconstruction,andthisculminatedinthedevelopmentofanewspecificationforburiedconcrete.Therearealsoimplicationsforgroundinvestigations,andthesewillbediscussed.ThepaperwillalsohighlightthecasestudyoftheA1MallyGillBridgeinCountyDur

5、ham,whereamarkedlydifferentsetofcircumstancesgaverisetothaumasitesulfateattackinafoundation.TheHighwaysAgencyhasbeeninvolvedwiththedevelopmentofimprovedguidance,asaresultoftheExpertGroupReport,toensurethatthatthereisaconsistencyofapproachacrosstheconstructionindustry.Thepaperwillacknowledgethatthere

6、arestillmanyunknowns,particularlythemechanismgoverningtheoccurrenceofthaumasiteandthespeedofthaumasiteproduction.AparticularaspectofconcerntotheHighwaysAgencyistheongoingmanagementofstructuresthatareknowntobeormaybeaffectedbythaumasite.Whatarethemethodsforinvestigationandtestingandaretheresuitableme

7、thodsforremotedetection?Doweneedtointroducenewinspectionregimes?Whataretherequirementsfortherepairofthaumasiteaffectedstructures?Mentionwillbemadeofsomeoftheresearchinthisarea,particularlythetrialofrepairedconcreteatMoretonValence.Thepaperwillsummarisethelessonslearntsofarfromthethaumasiteexperience

8、,theimplicationsforthefuturemanagementofstructuresinpotentiallyhigherriskareas,andidentifyresearchneeds.CrownCopyright_2003PublishedbyElsevierLtd.Allrightsreserved.Keywords:Thaumasite;Structures;HighwaysAgency1. BackgroundInearly1998,inthecourseofothermaintenanceandbridgestrengtheningworks,unusualco

9、ncretedeteriorationwasfoundtohaveoccurredinthefoundationsandburiedcolumnsonacoupleofbridgesontheM5MotorwayinGloucestershire.Subsequentinvestigationsprovedthattheobserveddefectsweretheresultofthaumasitesulfateattack,andtheHighwaysAgencywerefacedwithanumberofimmediatequestions.Howseriouswastheattack?W

10、eretherestructuralimplications?Howmanybridgeswereaffected?Wasitalocalproblem,ornational?Whatwerethecosts?Howdoweundertakerepairsorotherremedialaction?Werethereanyfaultsintheoriginaldesignandconstruction?Werethereimplicationsfornewconstruction?WhatweretheimplicationsbeyondtheHighwaysAgencyinterests?D

11、oweneedtocarryoutanyresearch?0958-9465/$-seefrontmatterCrownCopyright_2003PublishedbyElsevierLtd.Allrightsreserved.doi:10.1016/S0958-9465(03)00146-XCement&ConcreteComposites25(2003)Thispapercoverstheresponsestosomeofthesequestions,andsummarisesthecurrentsituation,andidentifiesotherissuesforthefuture

12、.2. Tredington-AshchurchBridgeThaumasitesulfateattackwasfirstobservedinearly1998onaHighwaysAgencystructureinthesubstructureoftheTredington-AshchurchBridge,anoverbridgecarryingalocalroadovertheM5MotorwaysituatedbetweenJunctions9and10inGloucestershire.Ataboutthesametimesimilar,butlessseveredefects,wer

13、ealsofoundinGroveLaneBridgefoundations,alsoontheM5,butfurthersouth,betweenJunctions12and13.Tredington-Ashchurchisafourspanoverbridgewithareinforcedconcretedeck.Supportingcolumnsaresitedinthecentralreserveandverges,andextendthroughplacedfillforabout5mtoreinforcedconcretespreadfootings.Thebridgewasbui

14、ltabout30yearsago,totheapplicablecontemporaryMinistryofTransportstandardsandspecifications.Regularstructuralinspectionsandtestingoftheconcreteelementsabovegroundhavenotindicatedanyobservablesignsofdistresstothebridgeintheinterveningperiod.Plannedstrengtheningworktothecolumnsofthebridgenecessitatedex

15、cavationofsomeofthebackfillsurroundingtheconcretesupports,andinthecourseofthisworksitestaffobservedsomeunusualdeteriorationintheexposedconcrete.Thisindicatedthatsomeoftheconcretesurfaceshadturnedtoa_mushyconsistency,andof_wartyappearancewithevidenceofexpansionoftheresidualmaterial.Thiswasunexpectedt

16、othesaytheleast,andpotentiallyextremelyserious.DiagnosiswasfirstmadebyourMaintenanceAgents,GloucestershireCountyCouncil/HalcrowandlaterconfirmedbytheBuildingResearchEstablishment(BRE)asthaumasitesulfateattack,afterinitialconcretesampleshadbeenanalysed.Furtherexcavationofthebackfillensuedtocompletely

17、exposetheburiedcolumnsandthetopsurfaceofthefoundations,entailingextensivetemporaryworkstoprovidethenecessarysupport.Alargeprogrammeofinvestigationwasinitiated,includingextensiveconcretesampling,andsoilandgroundwatertesting,backedupbyathoroughlaboratorytestingregime,andanalyticalworktocorrelatesoilco

18、nditionswithconcretedefects.Theobjectivewastodeterminetheprecisecausesofthedeterioration,andtoseeifparameterscouldbefoundthatwouldassistfutureidentificationofaffectedstructuresandtheirinvestigation.OtherpapersattheconferencewilldealwiththeTredington-Ashchurchcasestudyinmuchmoredetail,howeversufficet

19、osaythatittranspiredthatanumberofcriticalfactorsincombinationhadoccurred(listedbelow),whichweresignificantintermsofthedeteriorationthatoccurred,andparticularlyinrelationtotheseverityofthethaumasitesulfateattack:(a) useoflimestoneaggregatesintheconcrete;(b) useofsulfateandsulfidebearingmaterialsforba

20、ckfillingaroundthefoundationsandburiedcolumns(thesoilexcavatedtoconstructthefoundationscontainedironpyrites(sulfides)whichstartedtooxidiseafterexposuretotheatmosphere,andaddedtothereservoirofavailablesulfates);(c) groundwatermovements;(d) physicaldispositionofthestructure(deepfoundationsandslenderco

21、ncreteelements);(e) constructionregime,particularlytheexcavationofalargeholethroughundisturbedgroundwhichwassubsequentlybackfilledwiththeexcavatedmaterialsandcreateda_sumparoundtheburiedcolumns;(f)leakingmotorwaydrainage;(g)relativelycoldconditions.ThesefactorsareillustratedinFig.1.Whenthedeteriorat

22、ionwasfirstobserved,adecisionwastakentoclosethelocalroadcarriedbythebridge,onsafetygrounds,untilsuchtimeastheextentandnatureoftheproblemcouldbedetermined.Subsequentlythedefectswerefoundtobesurfaceeffects,withasoundcentralcoreofconcreteremaining.Assessmentofthestructureshowedthattheroadcouldbesafelyr

23、eopenedwhilsttheinvestigationscontinued.Basedontheinformationavailableatthetime,andtheneedtoundertaketheplannedstrengtheningworkonthecolumnsagainstvehicularimpact,itwasdecidedthatthecolumnsshouldberemoved.Thisdecisionwasreachedafterconsiderabledeliberation,andassessmentofcostedoptions,butwasinfluenc

24、edbythelackofavailableinformationonhowtorepairstructuralelementsaffectedbythaumasite.Therewasalsouncertaintyastowhethertheconcretedeteriorationhad_stabilisedorwascontinuing.Intheeventthemosteffectivestrategywasthecompleteremovalofthebridgecolumns.Asystemoftemporaryproppingwasintroducedtoallowthecolu

25、mnstobecutupandremoved,andanewfoundationandsupportscastontopoftheexistingfoundation.Alongsidethecontinuingsiteinvestigationwork,recordsofthestructurewereinspected,andalsoavailablegeotechnicalinformation.Itwasevidentthatthedesignof30yearsagohadbeenundertakeninaccordancewiththestandardsandspecificatio

26、nsofthetime,basedonthecontemporarysoilsurvey.Thishaddulytakenaccountoftheprevailingsoilconditionsinregardtotheoccurrenceofsulfates.Howeveratthattimetherewasnorequirementtoconsidersulfides,andsoincomparisontotherulesdevelopedin1999inresponsetothediscoveryofthaumasite,mayhaveunderestimatedtheinfluence

27、ofsulfatesby23classes(basedonBREDi-1052N.Loudon/Cement&ConcreteComposites25(2003)10511058gest3631).Clearlythiswasverysignificant,butnofaultcouldbeattachedtothedesignorconstructionprocessof30yearsago.WhilstworkwastakingplaceatTredington-AshchurchBridge,afurthermaintenancecontractatGroveLaneBridgefurt

28、hersouthontheM5Motorway,revealedsimilarsignsofthaumasitedeteriorationinburiedconcrete,althoughevidentlynotassevereoraswidespread.Inthiscaseafterinitialinvestigation,conventionalconcreterepairswereconducted,afterremovalofthecontaminatedconcrete.3. DETRExpertGroupWhentheconcretedeteriorationwasfirstdi

29、scoveredinthemotorwaybridges,itwasimmediatelyapparentthatthethaumasiteattackwasveryserious,andtherewerepotentialimplicationsforallnewconstructionaswellasexistingbuildingsandcivilengineeringstructures.TheHighwaysAgencybriefedtheDepartmentoftheEnvironmentTransportandtheRegions(DETR)andGovernmentMinist

30、ers.ItalsotranspiredthatBRE,throughDr.NorahCrammondandothercolleagues,hadbeeninvestigatingthaumasiterelatedconcretedeteriorationfornearly10years,thoughtheresultsofthisresearchhadnotbeenpublished,andthecurrenteditionofBREDigest3631,madeonlypassingreference.AdecisionwastakenatMinisterialleveltosetupaN

31、ationalExpertGroupunderthechairmanshipofProfessorLesClarkeofUniversityofBirmingham,witharemittoinvestigatethaumasiteandreportbackwithinsixmonths.Thiswasaverytightconstraint,butitwasdecidedthatitwasessentialtoprovideauthoritativeguidanceattheearliestopportunitytoallaypublicandindustryconcerns.TheExpe

32、rtGroupwasderivedfromawidecrosssectionofindustryandtheauthorwasalsosecondedtorepresenttheHighwaysAgency.Afterconsiderablediscussionanddeliberationareportentitled“TheThaumasiteFormofSulfateAttack:Risks,Diagnosis,RemedialWorksandGuidanceonNewConstruction“2wasproducedandpublishedinJanuary1999.Assuch,it

33、wasasignificantachievementtopublishaverydetailedreportinsuchashorttimescale,andrepresentedacollaborativeandveryconstructiveapproachbyalltheparticipants,althoughitwasapparentthatthereweredifferingviewsonmanyaspects,andespeciallythedetailedandcomplexchemistryinvolvedinthaumasite.Itwasalsoapparentthatm

34、anyoftheconstructionindustryrepresentatives,hadunderstandableconcernsaboutthecommercialimplicationsfortheirownsectorofthemarket.Thereportdealtwiththenatureandriskofthaumasiteandsulfateattack,inspectionandtestingrequirements,structuralassessment,remedialworks,andaspecificationfornewworks,anditisparti

35、cularlywiththislastsectionIwasinvolved.Howeverthereportasawholeprovidedauthoritativeguidanceandrecommendationsforbothnewworks,andforclientsandpropertyownersmanagingstructuresandbuildings.Thereportitselfsetout_guidanceinareliamsitewdherereseoanrlcyhandcasestudieshadbeenundertaken,but_recommendationsw

36、heremorereliableandwelldocumentedinformationwasavailable.Itwasacknowledgedthatnotalltheanswerswereknown.Inparticulartherewasmuchdebatesurroundingthemechanismsforoccurrenceofthaumasite,andthetimescalesoverwhichitoccurred,andinthisareafurtherresearchwasessential.Consequentlysomecautionhadtobeexercised

37、inthedetailedrecommendations.Overallthereportacknowledgedthattherehadbeenrelativelylimitedoccurrenceofthaumasiteinpractice,althoughlaboratoryworkindicatedthatconditionsforthaumasitecouldberecreatedrelativelyeasily.Oneaspectofmajorimportance,particularlyasregardsnewconstruction,wastheneedtostrikethec

38、orrectbalancebetweentechnicalissuesandcommercialinterests.TodothistheReporthadtodealauthoritativelywiththetechnicalconcernswithoutunnecessarilyplacingrestrictionsontheuseoftheconstituentmaterialstoproduceconcrete.AtthetimeitwaspublishedtheReportacknowledgedthattheinformationwasofaninterimnatureandwo

39、uldneedtobeupdatedasmoreevidenceconcerningthaumasitebecomeavailable.Italsosoughtto_minimisetheriskoffutureoccurrence,ratherthantheintroductionofdraconianmeasurestocompletelyeliminatetherisks.KeyfacetstotheReportweretheidentificationofanumberofprimaryandsecondaryfactorsgoverningtheoccurrenceofsulfate

40、(thesearereferredtolaterinthepaper)andtheclassificationofthaumasiteinaffectedstructures:(a) _TSAforthaumasitesulfateattackwherethereissignificantdamagetothematrixoftheconcreteor(b) _TFforthaumasitemfoartionwherethaumasiteispresentinpre-existingvoidsintheconcrete,butthereisnodeteriorationevident(alat

41、entstageindevelopmentofTSA).TheReportalsocontainedpracticalinformationontherequirementsandmethodsforidentificationandtestingofconcreteandsoilsinexistingstructures,todetermineifthaumasiteispresent.Particularlyimportantwasthestrongmessagetoclientsanddesignersofnewstructurestoundertakeathoroughsoilsurv

42、eyaspartofthedesignprocess.Thishasalwaysbeenundertakenonroadbuildingprojectsandmajorcivilengineeringcontracts,butlesssoonsmallerworks,andinthedomesticpropertymarket.Chapter9oftheReportprovideddetailedspecificationrequirementsfornewconstructiontominimisetheriskofthaumasitesulfateattack,basedontheappr

43、oachalreadyadoptedinBREDigest3631,namelybyclassifyingthesulfateconditionsinthesoiladjacenttothedesignedconcrete,andbysettingaseriesofrestrictionsandoptionsfortheconcretemixesforeachclassification.Howeverthisapproachwasextendedtoadopta“package”ofmeasurestodealwithallgroundclassifications.Itsoughttole

44、aveasmanyoptionsopentodesigners,andparticularlytothecontractingandconcretesupplyindustries,andallsuchoptionsweredeemedtobeequallyeffective.Therewasalsoadesiretokeepallguidanceandrecommendationsassimpleaspossible,anduserfriendly.TheReportrecommendationsconsistedofdetailedmaterialsrequirementsforconcr

45、etemixesandthiswasalliedtoariskbasedstrategybasedondifferentstructuralperformancelevels,dependingontherequiredservicelifeandusageofthestructure.Therewasanoverarchingassumptionthatthesoil/groundwaterclassificationhadbeencorrectlyassessed,andtherecommendationsinchapter6oftheReporthadbeenfollowed,andso

46、consequentlytheconcreterequirementswereappropriatetotheexistingandanticipatedfuturegroundconditions.Therecommendedconcreteoptionsfollowedonfromthiscorrectsulfateclassificationofthesoils,withdueallowanceforanysulfidespresent.Otherrelatedguidanceinvolvedconsiderationoftheconstructionoperationsandthene

47、ed,whereappropriate,toprovideadditionaldrainagearoundstructures,toavoidcreatingsumps,andwherepossiblenottousereworkedsulfate/sulfidebearingbackfills.Theconcretematerialsrequirementsembodiedvariouscontrolsoncementcontent,andfreewater/cementratios,butadoptedanewclassificationofaggregatesbydefiningdiff

48、erentcarbonaterangesdependingontheamountofcarbonatepresentinthefineandcoarseaggregatefractions.Intermsofthestructuralperformancelevelthephilosophyadoptedwasonebasedonbandingofstructuresintohigh,normalandlowperformance,representingarangefromlongservicelifestructurestolowperformanceforshortservicelife

49、structures,andstructureswithmassiveburiedconcretefoundationsorthosewithslenderorcriticalburiedelements.Thisrecognizedthatthaumasiteattackinrealitywasassumedtobearelativelyslowprocess,andmaybeinsignificantforstructureswithonlyashortdesignlife.Morerestrictivemeasureswouldberequiredwhendealingwithlonge

50、rservicelivesforstructuresandcritical/sensitiveburiedelements,andconverselylesssevererequirementsimposedwherestructureshadshortanticipatedservicelives.Sincetherewereanumberofareaswherethedearthofresearchdatapreventedauthoritativerecommendationsformaterials,itwasagreedthatitwouldbeprudenttoadopta_mul

51、tlia-yeredprotectionapproach,wherebyanumberofadditionalprotectivemeasureswouldbeinstigated,inadditiontothematerialrequirements,inappropriatesituations.Theywouldrepresentanimportantfirstlineofdefenceandconsistedoftheadoptionofsurfaceprotectionanddrainagerequirements,aswellasthechoiceoflowercarbonater

52、angeaggregatesincertaincircumstances.OveralltheExpertGroupReportprovidedanumberofimportantmessages.Thenumberofstructurespotentiallyatriskwasnotthoughttobelarge,andthestructuralconsequencesnotgenerallyserious.Thedeteriorationwouldgenerallyprovideearlywarningsignsabovegroundwheresignificantthaumasites

53、ulfateattackwasoccurringbelowground.Therewasalsonotthoughttobeanysignificantproblemfordomesticproperties.TheReport,iffollowedwouldminimisetheriskofthaumasitesulfateattack,butalsopointedoutthatnotalltheanswerswereknownandthatfurtherresearchwasneeded.Italsoacknowledgedthattherewasaneedtoupdatevariousd

54、ocumentsandinparticularBS53283andBREDigest3631.4. HighwaysAgencyguidancefornewconstructionInparallelwiththeworkoftheThaumasiteExpertGrouptheHighwaysAgencysetdownitsownadvicefornewconstruction,basedontheExpertGrouprequirements.InterimAdviceNote254wasissued,whichlaiddownrequirementstobeadoptedforhighw

55、aystructures,tominimisetheriskofthaumasitesulfateattackinnewconstruction.Inparticularitassumedthatinmostcaseshighwaystructureswouldbedeemedtobehighperformancelevel,asbefittingtherequired120yearservicelife.TheAdviceNotealsoprovidedsomemorespecificguidanceondrainagearoundstructuralfoundationsandthetyp

56、eofprotectivecoatingsappropriateforapplicationtoburiedconcreteinhighwaystructures.5. HighwaysAgencystrategyforexistingstructuresHoweveraswellasdealingwithnewconstruction,theHighwaysAgencyalsoneededtoaddresstheissuesoftheoccurrenceofthaumasiteinexistingstructuresandparticularlywhetheritwasconfinedtot

57、heexistingareaofGloucestershireormorewidespread.Adecisionwastakentoembarkonanationalinvestigation.TheExpertGrouphadidentifiedanumberofprimaryandsecondaryfactorsthatmustcoexistorwouldinfluencetheoccurrenceorseverityoftheattack.Primaryfactors(a) presenceofsulfatesand/orsulfidesintheground;(b) presence

58、ofmobilegroundwater;(c) presenceofcarbonategenerallyincoarseand/orfineconcreteaggregates;(d) lowtemperatures.Secondaryfactors(a) typeandquantityofcementused;(b) qualityofconcretemixandcompaction;(c) changestogroundchemistryandwaterregimeresultingfromconstruction;(d) type,depthandgeometryofburiedconc

59、rete.InstructionswereissuedtoalltheMaintenanceAgentsinEnglandtocommenceaninvestigation.Thiswasdividedintotwoparts,initiallybasedonariskbaseddeskstudy,andfollowedupwherenecessarywithsiteinvestigationwork.Theaimofthedeskstudywastodeterminethecoexistentpresenceoftheprimaryfactors,andparticularlywhether

60、carbonatebearingaggregateshadbeenusedinburiedconcrete,andwhetherstructuralbackfilloradjacentgroundincludedsulfate/sulfides.Theassessmentwasalsorelatedtostructuralsignificanceandnetworkneeds,suchasplannedmaintenancework.Ofparticularinterestwerestructuressuchasthoseexhibitingsignsofdistressaboveground

61、,suchassettlementorothergroundmovementsorunexplainedcracking.Thisdeskstudyrequiredthecriticalexaminationofstructuresrecordsandsoilsurveyinformation.Insomecasestherewasinsufficientinformationavailable,andlimitedconfirmatorymaterialtestingwasrequired.Aspartofthedesktopassessment,structureswereprioriti

62、sedonthebasisofrisk.Followupinvestigationswerethenconductedonalimitednumberofthehigherprioritystructuresineacharea(ifnecessary),andwithjudgementmadeontheeaseofaccesstoburiedconcrete,soastominimisetheamountoftemporaryworksandtrafficmanagementrequired.Theaimoftheinvestigationwastodeterminewhetherthere

63、wereanyvisiblesignsofthaumasiteattackpresent.Iftherewas,thendetailedsamplingofthebackfill/soils,andconcretecoringwasundertaken,backedupbylaboratorytesting.Itwasimportanttoconfirmforthehighestprioritystructuresthatrecordinformationwascorrect.Ifallthecriticalfactorswerepresent,bothpositiveandnegativer

64、esultswereimportant.Theabsenceofthaumasite,wherecarbonateintheaggregatesandsulfates/sulfidesinthesoilswaspresent,wasjustasimportantasifthaumasitewasfound.SignificantresultsoftheinvestigationwerepassedbacktoBREtoassistwiththeirfutureresearch.Theresultsofthisinvestigationwereverymuchasexpected,andconf

65、irmedthefindingsoftheExpertGroupReport,andparticularlytheperceivedareasofgreatestrisk.ApartfromtheGloucestershire/Avonareawherefurthercasesemerged,theonlysignificantpositiveresultwasfromCountyDurham,andisreportedlaterinthispaper.Howevertheinvestigationwasinvaluable,asitalsoconfirmedthatnothaumasitewaspresentinthelowerriskareas.Somewordsofcautionaboutareasofriskarerequired,inparticularaboutthepresenceofcarbonatesinaggregates.Aggregatescanandoftenweretransportedsubstantialdistancesfromtheirquarrysourcetotheireventualplaceofuseandassumptionscannotbema