Concrete technology and durability design - Cowi

Concrete technology and durability design

COWI and concreteBeirut Seafront and Marinas, LebanonCOWI – the companyCOWI is internationally recognisedas a major consultant in several areasfrom energy and waste to economics,but in particular known forits leading position in major bridge,road, airport, marine structures andtunnel projects throughout theworld. Concrete is a key materialfor these modern structures andCOWI has therefore created a strongconcrete design and research environmentwithin the company toprovide specialist services in thisarea.Concrete – the materialThe structural design, suitable specificationsfor the concrete and thereinforcement, the placing and theproper curing are all important parametersto achieve the desired results.COWI’s concrete technology expertisecovers standards and specificationsboth in Europe andinternationally. Suitable specificationscan be prepared to ensure thatthe customer receives the concretesolution that is optimal for the intendedservice life requirements andthe exposure conditions.COWI participates in R&D networksand projects with universities,government institutions as wellas private partners in several countries.COWI’s concrete technologistsand designers participate in nationaland international standard organisations,through CEN-groups, Danishand European standardisation work,FIB model codes, RILEM, etc. Theyare often invited speakers or keynote lecturers at international conferenceson concrete technology andthis is reflected in the large numberof COWI publications and referencesin the concrete field.COWI seeks to include innovativeideas as part of large and smallprojects in order to create value fortheir customers through savings toprovide durable and sustainablesolutions.Concrete technology anddurability design• Durability and service life design• Specifications and constructionmonitoring• Materials technology• Special design solutionsSeeb International Airport, OmanGreen Heart Tunnel, The NetherlandsChedi Hotel, Oman

Sutong Bridge, China3

4Durability andservice life designVillamar at the Harbour Development Project, BahrainCOWI’s durability design services• Assistance in defining the owner’sservice life requirement, e.g. endof design life, level of reliability andfrequency of maintenance• Elaboration and evaluation ofdifferent durability design optionsincluding appropriate structuraldetailing• Assessment of macro and microexposure conditions• Modelling of deteriorationmechanisms for materials andenvironmental actions• Service life modelling and designusing the DuraCrete approach• Development of appropriatespecifications for materials throughdurability modelling• Conversion of specificationsto concrete mix designs andcompliance testing• Back analysis of service life uponcompletion of construction• Quality assurance programmes• Life cycle costing• The Birth CertificateProbabilistic service life designNowadays, civil engineering structures,such as bridges, tunnels, marinestructures and other infrastructureprojects, are designed for aservice life of 100, 120 or even 200years. This surpasses the assumeddesign service life of most codes andstandards substantially.The operational approach to designfor durability is to define durabilityas a service life requirement.In this way, the non-factual andrather subjective concept of ‘durability’is transformed into a factualrequirement of a number of yearsduring which the structure performssatisfactorily without unforeseenhigh costs for maintenance. In thisway, the time factor is introduced asa design parameter. Service life designbased on these functional requirementsis carried out in a similarway to the load and resistance factordesign concept used for structuraldesign.COWI’s leading position within durabilitydesign is based on morethan 40 years of worldwide experiencein design, operation and maintenanceof reinforced concrete structures.COWI, spearheading the internationaldevelopment of rational servicelife designs, provides a modernfully probabilistic design methodologyfor durable concrete structures,i.e. the DuraCrete approach. COWIimplements this state-of-the-art approachin new designs and in the reevaluationof existing structures. Ithas been adopted by national authoritiesand individual clients allover the world as well as by internationalassociations, e.g. fib.The DuraCrete approach can effectivelycombat chloride and carbonationinduced reinforcementcorrosion. All uncertainties regardingenvironmental exposure, materialproperties and deterioration aretaken into account.AssumptionsTerms of definitionsOther administrative provisionsPrinciples of service lifeDesign criteriaFull probabilisticapproachProbabilistic models:- Resistances- Load/exposure- GeometryPartial factor designDesign values:- Characteristic values- Partial safety factors- Combination factorsLimit states Design equations Design provisions Design provisionsDesign/verificationsProject specification for material selection and executionMaintenance planInspection/monitoring planQuality plan for execution(optional)Deemed to satisfy designExposure classesAvoidance ofdeteriorationExposure classesIn case of non-confirmity with the performance criteria, thestructure becomes either obsolete or subject to a redesignService life design flow chartafter fib: “Model Code forService Life Design”MaintenanceInspection of executionCondition control during service life

5Busan-Geoje Fixed Link, South KoreaLife cycle costingLife cycle cost optimisation, e.g.formulated as an optimisation of thenet present value of a structure, hasbecome an integral part of COWI’sservice life design philosophy. Withoutthis, a rational evaluation offuture costs in a comparable mannerto rate alternative solutions, preferablyas a life cycle costing (LCC),the service life design will not bepossible. This is mainly because anyserious savings in future maintenancecosts will not be adequatelyconsidered to compensate for anyincreased initial construction costs,although such future savings may bevery substantial. COWI’s LCC servicesinclude:• Recognition of potential savingsin whole-life costs through builtindurability, e.g. selective use ofstainless steel• Evaluation of life-cycle costingand cost optionsThe Birth CertificateA valuable means to increase theknowledge of the expected performanceand service life is to establish abaseline study of the finally achievedquality of the in-situ structure. Thiscould conveniently be done and reportedas part of the handing-overof the structure from the contractorto the owner. Therefore, COWI hasestablished the concept of the BirthCertificate, which includes a firstforecast of the service life based onfactual data, e.g. the actual coverthicknesses and the actual chloridediffusion coefficients, from the existingstructure. At later inspectionsthis data can be updated and usedto revise the expected residual servicelife resulting in an ever-increasingaccuracy of the remaining servicelife forecast. This powerfuldecision tool provides the ownerwith valuable information on futuremaintenance and repair needs. Influence of concrete cover on service lifeGuidelines for service life designDuraCrete:General guidelines fordurability design andredesignfib:Model code forservice life designFinancial Harbour, 53-storey tower, BahrainStonecutters Bridge, Hong Kong, China

6Specifications and construction monitoringThe Pearl Development Project, QatarQA at precasting yard, Busan-GeojeFixed Link, South KoreaQA at immersed tunnel site, Busan-Geoje Fixed Link, South KoreaSpecificationsCOWI has many years experience inassisting both clients and contractorsin the preparation and/or reviewof specifications for major internationalprojects, including immersed andbored tunnels, all types of bridges,marine structures, airports and infrastructureschemes all over theworld. Irrespective of the type ofcontract COWI can provide specialistassistance to fulfil particular needs.COWI’s expertise is based on athorough understanding of the relevantinternational standards complementedby an extensive knowledgeof concrete and materials technologyin combination with experience in amultiplicity of construction techniques.Consequently, COWI hasthe ability to interpret any specialdemands, be they structural, environmentalor financial, in order toprovide specific requirements forparticular parts of a project.Quality assurance andconstruction monitoringIn order for a concrete structure tofunction as foreseen by the design,the construction process must becontrolled by a suitably framedquality assurance (QA) scheme.COWI has the knowledge to establishsuitable QA schemes in linewith the preparation of project specifications.In addition, COWI hasexperienced concrete specialists,who can review/audit constructionmaterials, mix designs, functionalrequirements, method statementsand inspection and test plans, etc.,against specified requirements andproject objectives.Consequently, the same personnelhave the ability to assess the acceptabilityof non-conformances if andwhen they arise and the suitabilityof associated corrective actions, remedialworks, etc., to ensure thatthe project objectives are met.QA at segment factory, HallandsåsTunnel, Sweden

7Customised formwork, Hallandsås Tunnel, SwedenCooling pipes for control of heatdevelopment during curingArchitectural finishesArchitectural finishes is another areaof importance as the achievement ofan acceptable surface finish to theconcrete is often in conflict with thedurability requirements of a structure.This is particularly importantwhere prestigious and/or innovativestructures are exposed to harsh environments,e.g. the Middle East.COWI has special experience andinterest in this area and can adviceon appropriate solutions to achievethe overall architectural objectivesof the project.Architect’s model for underground station,Copenhagen Metro, DenmarkCuring technologyIn order to secure the long term durabilityof a concrete structure a wellthought-out curing programmeshould be specified and the curingproperly monitored during construction.COWI’s main areas of curingtechnology expertise include:• Control of early age cracking dueto thermal movements, earlyshrinkage, creep and settlements• Evaporation control to avoid thedamaging effects of drying outwhich can lead to cracking andreduction in surface quality• Hot weather concreting, particularlyrelevant to the Middle East andother high temperature environments• Cold weather concreting to ensureearly protection from damage dueto freezing conditions• Limitation of maximum temperatureto avoid the deterioration effect ofdelayed ettringite formation (DEF)Most of the above curing conditionsare interconnected and cannot beconsidered in isolation.COWI has experienced personneland specialist tools, e.g. 2/3-D finiteelement method (FEM) programmesfor temperature and stress simulationto design appropriate integratedcuring systems and/or review proposedsystems against specified requirements.3-D FEM simulations of heatdevelopment during curing. Basedon R&D collaboration with IPL,DTU, Lyngby, Denmark

8Materials technologyCOWI’s concrete and materials specialistshave broad internationalexperience from almost every regionaround the world and from almostevery type of civil engineering structure.COWI’s concrete and materialsgroup has more than 40 years experiencein materials and concrete investigationmethods, durability andtechnology and contribute regularlyto national and international conferences,books and magazines on concreteand reinforcement, from thedesign stage up to and including theas-built phase.Activities include all kinds of materialand construction topics, rangingfrom petrography and scanningelectron microscopy at nanometrelevel to large scale tunnelling, bridgeand pavement construction.COWI has an in-house, ISO 9001certified concrete laboratory specialisedin concrete investigations fromchemical analyses and petrographyto destructive as well as non-destructivemethods.With funding from the WorldBank and DANIDA, COWI has presentedinnovative solutions in roadconstruction with the use of alternativebinders and/or marginal aggregatesin road stabilisation. Besidesproviding passable roads all yearround in third world regions, suchsolutions are also environmentallyfriendly with regard to preservationof aggregate resources as well aslimiting CO 2 emissions.Concrete microstructureCOWI’s specialists have been involvedin many investigations concerningconcrete durability and deteriorationof various kinds ofconcrete structures worldwide; especiallywith several references fromthe Middle East known for its harshclimate.COWI’s materials and concrete specialistsare recognised in their separatefields as independent experts toperform investigations and evaluationsof new or deteriorated concreteand whenever a technical disputemay arise. This also includesexpert witness assistance in caseswhich may end up in court. Designtopics and expert knowledge onmaterials and standards from allover the world are also part ofCOWI’s knowledge base.Optical microscopyon thin sectionsConcrete block with severe cracking caused by DEF andtesting of cores by thin section microscopy and residualexpansion measurements

9Deterioration mechanismsCOWI’s main fields of expertise inmaterials technology include evaluationof concrete concerning:• Surface attack• Chloride ingress and risk of corrosion• Surface carbonation• Detection of causes of cracking• Determination of concrete compositionincluding water-cement ratio,type and content of cement aswell as aggregate, use of air entrainment,addition of fly ash,blast furnace slag, silica fume, etc.• Sulphate and seawater attack,delayed ettringite formation (DEF)and thaumasite formation• Soft water leaching, carbonic acidand aggressive CO 2 attack• Alkali-silica reactions (ASR) andresidual reactivity and expansionpotential. Experience with localaggregate types and test methods• Freeze-thaw durability, evaluationof quality of entrained air voidsystemsSuch evaluations, alone or combinedwith other advanced investigations,can solve almost any case of prematureconcrete deterioration. Investigationsof concrete exposed to chloridescan include determination ofchloride profiles and determinationof the chloride diffusion coefficientto quantify the future risk of reinforcementcorrosion.Modelling of the residual servicelifetime by the DuraCrete approachor other models is based on reliableresults obtained from advanced laboratoryinvestigations.Thin section microscopy showing alkali-silicareactive aggregate and gel in air voidInnovative, environmentally friendly andlow-cost road construction methods usingblast furnace slag or local pozzolans forstabilisation of secondary or marginalaggregate resources, TanzaniaScanning electron microscopyshowing ettringite in paste, cracksand voids of concrete exposed tosea water

10Special designsolutionsCOWI’s durability and concretespecialists have a broad internationalexperience in tailored, specialconcrete and reinforcement designsolutions.Selected special design solutionsoffered by COWI include, but arenot limited to the following:• High performance concrete• Self-compacting concrete• Steel fibre reinforced concrete• Polypropylene fibre concrete• Green concrete• Membranes• Diaphragm walls and secant piles• Corrosion resistant reinforcementHigh performance concreteThe continuous demand for increasedstrength and improved durabilityof concrete structures hasled to the development of HPC. Thisdevelopment had three main objectives:• Protect the reinforcement againstcorrosion• Resist deterioration of the concreteitself• Provide adequate high strength tofulfil the structural requirementsHPCs for normal type structuresusually have a high cementitiousbinder content, a low water-cementratio and higher contents of plasticiserand superplasticiser. Such concretecan be used for bridges, tunnels,marine works, offshorestructures and high rise buildings,where the strength requirementsusually remain within a range of 50-80 MPa. A drawback of HPC is thatthe more refined the concrete mixesbecome, the higher is the sensitivityin relation to the actual handlingduring execution.SFRC foundations and slab for high-bay warehouse,Carlsberg Brewery, Fredericia, DenmarkHPC sets high demands on competenceand experience; competenceand experience that COWI can offer.Self-compacting concreteA concrete mix, where the placingand compaction has minimal dependenceon the available workmanshipon site, improves the truequality of the concrete in the finalstructure. This has been the maindriving force in recent years’ developmentof self-compacting concrete(SCC). With the aid of a range ofchemical admixtures and optimalgrading of the aggregates, concretewith a low water-cement ratio canbe made to flow through complicatedform geometry and around complexreinforcement without segregation.The form can be filled and auniform compaction without honeycombscan be achieved, also in thecover zone of the concrete. SCCexerts an increased pressure (attimes close to the hydrostatic pressure)on the formwork.COWI’s concrete specialists provideexpert knowledge on both mixdesign and execution includingformwork design for SCC.Constituents of a typical HPC mix,“cocktail concrete”Compressivestrength test ofHPC. Courtesyof BAM, Berlin,GermanySlump flow test with 4C-Rheometer todetermine the yield stress and plasticviscosity of SCC. Courtesy of DTI,Taastrup, Denmark

11Steel fibre reinforced concreteFor many applications steel fibrereinforced concrete (SFRC) is a verysuitable solution for structural members,which are not highly loaded inflexure or tension. Besides advantagesin terms of construction andcost, SFRC grants structural benefitsand superior durability propertiescompared to conventional reinforcedconcrete. The capacity of thefibres to reduce crack width anddeflection is often more importantthan the increase in tensile strengthof the concrete. Furthermore, theaddition of fibres enables bearingcapacities after cracking and allowsstress redistribution, which makesthe otherwise quasi-brittle behaviourof the concrete more ductile.COWI has manifold experienceand expert knowledge in all phasesof the design and the execution ofSFRC structures.Polypropylene fibre concreteThe provision of an adequate levelof fire protection is particularly importantfor tunnels as has been witnessedby the Great Belt and ChannelTunnel experience, but it canalso be relevant to other structureswhere the evacuation of personneland emergency services should beprotected.With regard to concrete structuresthe addition of a relatively smallamount of polypropylene fibres(PPF) to the concrete during themixing process can provide considerableimprovement in the fire resistanceof the finished structure. Arecent innovation has been to addPPF to shotcrete to improve the fireresistance of existing structures andunstable rock formations.COWI has considerable experiencein this area to provide assistancewith the following:• Concrete and shotcrete mix designs• Fixing systems for shotcrete• Fire testing• Acceptance criteriaGreen concreteGreen concrete is a synonym forresource-saving concrete. Use ofgreen concrete reduces the environmentalimpact of concrete structureswith regard to energy consumption,waste water and CO2 emissions.Green concrete can be less expensiveto produce, because waste productscan be used as a partial substitutefor cement, landfill taxes can beavoided and the energy consumptionin production can be lowered.COWI’s concrete specialists havebeen involved in related R&Dprojects and are experienced in specifyinggreen concrete.Tunnel fire test. Courtesy of SINTEF,Trondheim, NorwayConcrete slab without PPFs during firetest, Hallandsås Tunnel, SwedenFE simulation of principal stressdistribution from concentratedloading of TBM push rams forstructural design of SFRC liningsegments, District HeatingTunnel, Copenhagen, DenmarkSFRC lining segments, District HeatingTunnel, Copenhagen, Denmark

12Special design solutionsWaterproofing membrane installed inbored tunnel, Hallandsås Tunnel, SwedenSelective use of stainless steel reinforcement,Stonecutters Bridge, Hong Kong, ChinaSelective use of stainless steel reinforcement,Sheikh Zayed Bridge, Abu DhabiPhotomontage: HPRMembranesThe application of membranes forconcrete structures can be twofold:either to achieve a watertight concretestructure or to act as a protectivebarrier in case of concrete attack,e.g. high sulphate concentrationsin soil/groundwater.COWI has specialist experienceand can support clients and contractorswith selecting the most appropriatemembrane type depending onthe aggressivity of the environment,the geometric conditions of thestructure and the construction procedure.Diaphragm walls and secantpilesHistorically, diaphragm walls andsecant piles have been used withsuccess in relatively benign environments.However, in more hostile oraggressive environments, e.g. in theMiddle East, and with extendedservice life expectancy, special measuresare necessary to secure the requireddurability of the structure.COWI has specialist experience inthis area and can support clientsand contractors by providing innovativedurability design solutions, asspecial reinforcement solutions and/or concrete mix-design requirementsto mitigate the effects of chlorideinduced reinforcement corrosion.Corrosion resistantreinforcementThe implementation of corrosionresistant steel reinforcement is thesimplest and most effective methodto eliminate the risk of reinforcementcorrosion. This method doesnot only solve the corrosion problemin an infallible way even in themost corrosive chloride environments,but it also leaves the siteactivities nearly unchanged. Theselective use of stainless steel reinforcementin zones exposed to highchloride concentrations is a highlyreliable solution. This solution ensuresvery long problem-free servicelife in that part of the structure, providedthe concrete itself is made sufficientlyresistant to avoid othertypes of deterioration. Of particularimportance is the often overlookedfact, that SSR can be coupled withcarbon steel reinforcement withoutcausing galvanic corrosion. Anotherbenefit is the added value, whichfollows from the possibility of acceptingthe use of locally availablematerials even with chloride contaminationand the possible lack ofspecial qualifications of the localwork force.COWI has expert knowledge inspecifying appropriate reinforcementsolutions to attain the requiredservice life in all possible environments.COWI’s durability specialists canalso offer services concerning theassessment of alternative corrosioncountermeasures for concrete reinforcementand for the evaluation ofcorrosion protection of exposedstructural steel. This is supported bya continuous cooperation with universitiesand COWI’s involvement invarious related ongoing and futureR&D projects.Testing of reinforcementcorrosion countermeasures

13Tunnel shaft with secant piles andwaterproofing membrane, DistrictHeating Tunnel, Copenhagen, DenmarkPhoto: Henrik Pyndt Sørensen

Selected references15Villamar at the Harbour DevelopmentProject, Bahrain. Durability design forservice life of 50 years, 2007Hellmuth, Obata + Kassabaum (HOK)Offshore wind turbines, Sweden.Durability design of foundations forservice life of 25 years, 2005Metro Circle Line, Copenhagen, Denmark.Durability design for service life of 100years, 2007-2018Photo: Rene StrandbygaardLusail Development Project, Qatar.Durability design for service life of 50years, 2007District Heating Tunnel, Copenhagen,Denmark. Structural design of SFRC liningsegments and durability design of shafts forservice life of 100 years, 2004Photo: Henrik Pyndt SørensenNational Library, Qatar. Reassessment ofpiles and foundation, 2005-2006Al Reem Island Development Project, AbuDhabi. Durability design of foundationsfor service life of 50 years, 2007Busan-Geoje Fixed Link, South Korea.Durability design of bridge and immersedtunnel for service life of 100 years, 2005Messina Strait Bridge, Italy. Tenderdurability design for service life of 200years, 2005Great Belt Link, Denmark. Service lifeupdate from 100 to 150 years based onactual chloride profiles, 2001Photo: Jan Kofoed Winther Courtesy of ATI Impregilo S.p.AFinancial Harbour Development Project,Bahrain. Durability assessment includingBirth Certificate, 2006Sitra Bridges, Bahrain. Durability study ofdesign alternatives for replacement ofbridges, 2004Sutong Bridge, China. Durability designfor service life of 100 years, 2003Stonecutters Bridge, Hong Kong, China.Audit of durability design service life of100 years, 2005Photom.: Ove Arup & Partners

COWI officesInternational Projectswww.cowi.comCOWI is a leading northern Europeanconsulting group. We providestate-of-the-art services within thefields of engineering, environmentalscience and economics with dueconsideration for the environmentand society. COWI is a leader withinits fields because COWI’s 3500employees are leaders within theirs.Dr.-Ing.Carola EdvardsenSection ManagerConcrete Technologyand Durability Design+45 4597 2813cle@cowi.comHeadquarters:COWI A/SParallelvej 2DK-2800 Kongens LyngbyDenmarkTel.: +45 45 97 22 11Fax: +45 45 97 22 12E-mail: cowi@cowi.comInternet: www.cowi.comPhoto front page:Daniel Andersson andHenrik Pyndt Sørensen021-1700-031e-07aPrintet in Denmark by Kailow