Mass Concrete How Big - American Concrete Institute .

5/26/2017Mass ConcreteHow big isbig?Bob HowellMay 19 , 2017American Concrete Institute is a Registered Provider with The AmericanInstitute of Architects Continuing Education Systems (AIA/CES).Credit(s) earned on completion of this program will be reported to AIA/CESfor AIA members. Certificates of Completion for both AIA members and nonAIA members are available upon request.This program is registered with AIA/CES for continuing professionaleducation. As such, it does not include content that may be deemed orconstrued to be an approval or endorsement by the AIA of any material ofconstruction or any method or manner of handling, using, distributing, ordealing in any material or product.Questions related to specific materials, methods, and services will beaddressed at the conclusion of this presentation.The American Institute of Architects has approved this course for1 AIA/CES LU Learning Unit.The American Institute of Architects has approvedthis course for 1 AIA/CES LU learning unit.ACI is an AIA/CES registered provider.21

5/26/2017Learning Objectives Understand the ACI definition of mass concrete Discuss factors affecting concrete temperaturein mass concrete Learn how to control concrete temperaturethrough mixture proportioning and constructionpractices Understand ACI specification requirements formass concrete (ACI 301 section 8)3 let’s get back to our presentationMass ConcreteHow big isbig?2

5/26/2017Outline What is mass concrete? Concrete temperature Factors affecting mass concrete- Materials- Size- Construction Submittals (ACI 301) ACI documents on mass concrete5What is mass concrete?Pre 1900’s concrete Cement more coarse Slow delivery methodsCrystal Springs Dam (completed in 1890) – located in San Mateo County, California – courtesy of nwcultural.com63

5/26/2017What is mass concrete?Hoover Dam (1931-1936) – near Boulder City, Nevada – courtesy of the U.S. Bureau of Reclamation7What is mass concrete?D 10ftPiers for the San Francisco-Oakland Bay Bridge, courtesy of John Gajda, CTLGroup84

5/26/2017What is mass concrete?Mat foundation, courtesy of Carrasquillo Associates9What is mass concrete?Dictionary definition of Mass:- A coherent, typically large body of matter with no definite shape- Bulk, size, expanse, or massivenessMassConcreteSizeCorrect but incomplete105

5/26/2017What is mass concrete?Definition (ACI)Any volume of structural concrete in which a combination of: dimensions of the member being cast, the boundary conditions, the characteristics of the concrete mixture, and the ambient conditionscan lead to: undesirable thermal stresses, cracking, deleterious chemicalreactions, or reduction in the long-term strengthas a result of: elevated concrete temperature due to heat of hydration.11Interpreting the Definition of Mass zeConstruction(Environmental)126

5/26/2017Specification Requirements (ACI 301-16) Section 8 of ACI 301-16 coversmass concrete. Sections 1-5 are also applicable:-General requirementsFormwork and formwork accessoriesReinforcement and reinforcementsupportConcrete mixturesHandling placing and constructing13Concrete Temperature: ACI 301-16 Maximum temperature in concrete after placement shallnot exceed 160ºF Reason for limit: Delayed Ettringite Formation (DEF)which is a form of internal sulfate attack Expansion and formation of gaps around aggregateT 160ºFparticlesDEF, courtesy of CTLGroupconcrete pier cross-section (mid-height)147

5/26/2017Concrete Temperature: ACI 301-16 Maximum temperature difference between center andsurface of placement shall not exceed 35ºF ( T 35ºF) Thermal gradient creates thermal stresses. Thermal stress concrete tensile strength crackingΔT 35ºFCracked bridge pier, courtesy of TxDOTconcrete pier cross-section (mid-height)15Thermal Deformation – Mechanism8

5/26/2017Concrete Temperature: ACI 301-16 Mass concrete temperature must be monitored Place 1 sensor and a backup at:1) The center of the largest portion of placement2) 2 in. from center of nearest exterior surface3) Shaded location to monitor ambient temperature Monitor temperatures hourly Compare temperatures with limits21Shadedlocation3temperature sensor, courtesy of www.FLIR.com.mid-height of pier17Concrete Temperature: ACI 301-16average dailyambient temp231mid-height of pier: should not exceed 160ºFTemperaturelimits2 : should not exceed 35ºF3 : is less than 35ºF stop temperature control11–1–Contractor must submit a thermal control plan189

5/26/2017Concrete Temperature: ACI 301-16 Mass concrete temperature must be controlled If limits are exceeded during construction,immediate actions have to be taken Do not place additional concrete until cause ofproblem is identified and corrected Temperature control measures must be maintaineduntil:(internal or core temp.) – (average daily ambient temp.) 35ºF19Monitoring Concrete TemperatureSource: John Gajda & Ed Alsamsam, “Engineering Mass Concrete Structures”2010

5/26/2017Factors Affecting Mass ConcreteConcrete TemperatureMaterialsSizeConstruction21Materials: Mixture Proportioning What is needed for mass concrete mixturedesigns?- Strength & durability- Workable design- Economical design- Low temperature rise Heat is generated by cementitious materials Adjust mixture ingredients to reduce heatgeneration (cement)2211

5/26/2017Materials: ACI 301-16 Meet general material requirements (see section4.2.1 of ACI 301-16)Use: Moderate to low heat of hydration cement (Type II) Cement Class F fly ash Cement slag Cement Class F fly ash slagDo not use: Type III or ASTM 1157 HE (High Early-Strength)23Materials: Cementitious Materials Use cementitious material that generates low heatSCMFly AshClass FFly AshClass CSlagCementSilicaFumeMetakaolinEffect on heatenergy Quantity and type of cementitious material affectheat generation Reduce mass of cement in a mixture2412

5/26/2017Materials: Determining Temperature Rise How do we determinetemperature rise?- Prediction (thermal)models- Test mixture proportions(trial blocks)- Or bothCourtesy of John Gajda, CTLGroup When should either be usedand why?Courtesy of Christopher Bobko25Simplistic Method for Determining Temperature RiseTemperature rise (Cement SCM x fSCM) x fcementEquivalent Cement ContentfSCMfcementClass F Fly ash0.5Slag (0-20%)1.0-1.1Class C Fly ash0.8Slag (20-45%)1Silica Fume1.2Slag (45-65%)0.9Metakaolin1.2Slag (65-80%)0.80.14 - 0.16All units are in UScustomary units(lb/yd3, ºF, etc )Adapted from John Gajda & Ed Alsamsam, “Engineering Mass Concrete Structures”2613

5/26/2017Simplistic Method for Determining Temperature RiseConcrete mixture contains: 550 lb/yd3 cementitious materials content 25% Class F fly ashfSCM Type II cement (low heat)Class F Fly ash0.5Equiv. cement 0.75 x 550 0.25 x 550 x 0.5 481 lb/yd3fcementTemperature rise 481 x 0.14 67ºF0.14 - 0.16Concrete Temp 80ºF 67ºF 147ºF27Simplistic Method for Determining Temperature RiseMixture 1Mixture 2Mixture 3Mixture 4550 lb/yd3;550 lb/yd3;550 lb/yd3;Type II cement; Type II cement;Type II cement;25% Class F fly70% slagno SCMashcementCementitiousMaterials Content650 lb/yd3;Type II cement;no SCMEquivalent CementContent650 lb/yd3550 lb/yd3481 lb/yd3473 lb/yd3Temperature Rise91ºF77ºF67ºF66ºFMaximum F2814

5/26/2017Materials: Determining Temperature Rise More advanced methods are available Chapter 4 of ACI 207.2R (Schmidt Method)- Predicts temperatures, temperaturedifferences, cooling rates, etc - Takes into account other factors such as thevolume-to-exposed surface ratio (V/S) Commercial Software29Cement Content & Temperature Control Time Reducing cement content reduces temperaturecontrol timeInternal (core) temp. – avg. daily ambient temp. 35ºFAverage daily ambient temperatureSource: John Gajda & Ed Alsamsam, “Engineering Mass Concrete Structures”3015

5/26/2017Materials: Admixtures & AggregateAggregate: Use the largest maximumsize aggregate Optimize aggregate gradation(use denser gradations)Admixtures: Water-reducing admixtures Air-entraining admixtures Retarding admixturesReducescementitious contentand admixturesimprove workabilityReduces the likelihood ofcold joints31Materials: Aggregate Thermal stresses are a function of the coefficient ofthermal expansion of concrete The coefficient of thermal expansion of concrete isa function of the mineralogy of the aggregateCoefficient of thermal expansionof concrete(per millionths per ºF)Quartzite, Cherts6.6-7.1Sandstone5.6-6.6Granite and3.8-5.3GneissesLimestone3.1-5.13216

5/26/2017Factors Affecting Mass ConcreteConcrete TemperatureMaterialsSizeConstruction33Size – Placement Dimensions For placements with large minimum dimensions,internal heat cannot escape as rapidly as it isgeneratedACI 301-16 OptionalRequirements48 in. (4 ft)Commonly prescribed inspecifications36 in. (3 ft) Size alone is not sufficient to identify “mass concrete”3417

5/26/2017Size – Placement Dimensions 28 in. column Cement content 560 lb/yd328 in.35Size – Placement Dimensions 28 in. column Cement content 560 lb/yd328 in.T1 150ºFT2 125ºF Measured T1 & T2 160ºF limit T T1 - T2 25ºF 35ºF limitNot Mass Concrete3618

5/26/2017Size – Placement Dimensions 60 in. column Cement content 560 lb/yd360 in.37Size – Placement Dimensions 60 in. column Cement content 560 lb/yd360 in.T1 165ºFT2 125ºF T1 165ºF 160ºF limit T T1 - T2 40ºF 35ºF limitMass Concrete3819

5/26/2017Size – Placement Dimensions 28 in. column Cement content 560 700 lb/yd328 in.39Size – Placement Dimensions 28 in. column Cement content 560 700 lb/yd328 in.T1 170ºFT2 140ºF T1 170ºF 160ºF limit T T1 - T2 30ºF 35ºF limitMass Concrete4020

5/26/2017Placement Thickness vs. Equivalent Cement ContentNot mass concreteMass concreteSource: John Gajda, “When Should Mass Concrete Requirements Apply?”, Aspire Magazine, Summer 201541Factors Affecting Mass ConcreteConcrete TemperatureMaterialsSizeConstruction4221

5/26/2017Factors Affecting Mass ze Assume size and mixture proportions cannot bechanged Predicted temperatures exceed limits43Construction Batching, mixing, placing, andcuring Temperature control could beachieved through:- Construction Management- Insulation- Precooling- Postcooling4422

5/26/2017Construction Management Protecting the structure from excessive temperaturedifferentials by:- Placing concrete during cool weather or at night- Use of liftsCourtesy of John Gajda, CTLGroup45Insulation Used to control temperature differential Slows escape of heat at exposed surfaces Horizontal surfaces - blankets Formed surfaces:- Cover forms with blankets- Build insulated forms (foam insulation)4623

5/26/2017InsulationCourtesy of Carrasquillo AssociatesCourtesy of Mark Bloschock47InsulationCourtesy of John Gajda, CTLGroup4824

5/26/2017Precooling Involves reducing concretetemperature during batching &mixing Precooling aggregate bymisting or sprinkling waterCourtesy of Qanbar Ready Mix Using chilled water or crushedice Cooling concrete using liquidnitrogenCourtesy of Portland Cement Association49Postcooling: Cooling Pipes Consists of circulating a cool liquid through thinwalled pipes Accelerates heat removal:- Reduces peak temperature- Reduces temperature control time Cooling pipes are uniformly distributed Closer pipe spacing more rapidly remove heat5025

5/26/2017Postcooling: Cooling PipesCourtesy of John Gajda, CTLGroup51Postcooling: Cooling PipesCourtesy of Gerard M. Nieblas5226

5/26/2017Postcooling: Cooling PipesSource ofcold waterCourtesy of John Gajda, CTLGroup53Construction: Temperature Control Which temperature control method should be used? Cost and expected temperature rise are the mainfactors in determining choice of methodInsulationControls temperature differentialPrecoolingReduces concrete temperature before concrete isplaced (at the batch plant)PostcoolingActively reduces concrete temperature after theconcrete is placed Are there any ACI 301 (specifications) requirements?5427