High Strength Concrete And Modulus Of Elasticity .

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High Strength Concreteand Modulus ofElasticity: AddressingIncreasingly ComplexProjectsFebruary 1, 2018

Overview Introduction What is high strength concrete? Performance requirements Commonly Used Constituents Production and Delivery Quality Control and Testing Modulus of Elasticity2

High Strength Concrete:An Introduction

What is high strength concrete?Wanda VistaDesignCurrent View4

What is high strength concrete?35th Street Bridge Chicago5

A vast range ACI defines high strengthconcrete as a mix with aspecified compressivestrength over 8000psi Throughout much of theUnited States, concreteproducers in urban areas arecapable of producing 14000psi mixes A few projects havesuccessfully placed mixesspecified to achieve 19000psi6

The unanswerable question High Strength concrete is a relative term Locally available materials Construction practices Stakeholders determine thedefinition of High StrengthConcrete “The reason for suchdiversity is twofold: needand ability need to the typeof construction and theinitiative of the designer,and the commitment of theconcrete producer andquality of locally availablematerials.”(Albinger, 1988)7

Performance RequirementsThe more subtle requirements Even after determining a specified strength,high strength concrete must often meet manyother requirements to satisfy stakeholders Design Constructability Modulus of Elasticity Durability Set Time Early Strength Consistency Workability retention Placeability Finishability Form Stripping Post-tensioning High strength concrete differs fromconventional concrete in that a high strengthbonding system is weaker aggregate filler8

Communication The importance of good communication between allparties cannot be stressed enough for high strengthconcrete jobs9

Constituents

Cementitious materials Unlike traditional concrete, the paste for highstrength concrete is the strongest portion of the mix The following material are normally used to produce arobust paste: Cement (Type I/II) Fly Ash (C or F) Slag (Grade 100 or 120) Silica Fume11

Particle Packing Arguably, the most important factor to achieving highstrength concrete is development of a dense, multicomponent paste12

Selection of Cementitious Materials High Strength concrete can be produced with nearlylimitless combinations of cementitious materials Thermal Concerns Minimize cement Maximize slag (50 %) Pumpability Increase fly ash Addition of silicafume Low Permeability Silica fume 5 – 20%13

Testing of Cementitious MaterialsDesign Phase Evaluate cementitiousmaterials beforeselection Mill certifications ASTM C618-12a ASR and SulfateResistanceProduction Phas Monitor performanceduring product Loss on ignition Foam index Mortar cubes (ASTM C109 and 989)14

Aggregate SelectionCoarse Aggregate Key differences from conventional concrete Smaller aggregate often preferred More surface area Crushing eliminates weak zones Shape and face Cubical shape Rough texture Well graded material May require blending Increased density Higher specific gravities15

Aggregate SelectionFine Aggregate Key differences from conventional concrete Coarse sands Decrease surface area Finishability Not prioritized commonly Fineness Modulus FM of 3.0 optimal Manufactured sand is often preferred16

Aggregate Testing Constant evaluation of aggregates is needed toprevent performance changes Aggregates used in high strength concrete are subject toweekly gradations Monitor the specific gravity and Mohr’s hardness of coarseaggregate Aggregate moisture should be carefully tracked to protectdesign W/CM ratio17

Admixture Selection The creation and widespread use of chemicaladmixtures have allowed for the development of highstrength concrete High Range Water Reducers – modern polycarboxylates Allow for W/CM ratios within .35 - .20 and workability Hydration Stabilizers Maintain control over set times and increase long-term strength Viscosity Modifying Admixtures Reduce segregation Reduce bleeding Reduce friction and pressure in pump Air Detraining Admixtures Provides low air contents to maintain design strength andpermeability18

Production and Delivery

Design and Proportions ACI 211.1 (proportioning normal weight concrete) isstill applicable in designing high strength mixes1.2.3.4.5.6.Identify relevant requirementsSelected desired consistency (slump or spread)Select nominal max aggregate sizeEstimate water content based on constituentsEstimate W/CM ratio based on requirementsEstimate amount and proportions of cementitious based on watercontent and W/CM ratio7. Estimate admixture dosage rates8. Estimate coarse aggregate volume9. Estimate fine aggregate volume10. Conduct lab trials11. Conduct field trials Make necessary adjustments20

Producer Limitations High strength concrete is often limited bythe producers supply streams andequipment Determine if plant has adequate materialstorage systems Aggregate bins and stockpiles Cementitious siloes Admixture tanks and lines Central mix plants often produce moreconsistent concrete One drum, one operator Calibration and use of moisture probes Maintain consistency and reduce aggregatetesting burden Consistent maintenance of equipment Ensure adequate mixing action of all equipment21

Order taking and Dispatching Customer expectations and behavior may needmodification from sales staff Establish appropriate order window and consistency Ensure all materials are available Slump or spread Minimum loads size can help prevent excess variability Appropriate truck staging and delivery rate High strength concrete often requires more time to produce Instruct drivers on proper high strength concrete procedures Empty all water from drum prior to loadingStandardize wash time and volumeProvide minimum revolutions to driversEliminate water additions22

Mixing and Production ASTM C 94 outlines production ofconcrete and applies to high strength Ensure concrete is thoroughly mixed Superplasticizer Silica fume Try to avoid shrink mixing if using a centralmix plant Reduce batch size to accommodate increasedcementitious material 5-15% reduction Protect your W/CM ratio – ensure noadditional water is added! Drivers Customers23

Quality Control and Testing

High Strength Specimens and testing While high strength specimensfollow many of the same testingprocedures as conventionalconcrete, they are inherentlymore sensitive to poor testingpractices As material strength increases,specimens become increasingly brittle To ensure consistency, personnelmust have proper knowledge,performance, and equipment Communication betweenproducer, concrete contractor,and independent testing lab willhelp greatly25

Slump and Spread High strength concrete can have a consistencybetween conventional slump and self-consolidatingconcrete due to constructability requirements Rebar congestion Pumping distance This unique trait can lead to confusion over the typeof consistency measurement Align consistency measure for each high strength mix with allparties based on submitted design26

Specimen handling and storage Because of their size, high strength specimens are stronglyinfluenced by changes in temperature and moisture duringcuring periods Both initial and final curing should ensure the specimens do not losemoisture Saturated lime water storage Moist Room storage Insulated and heated storage boxes ensure ambient temperaturesminimally affect mix performance The use of elevated SCM proportions and hydration stabilizer canleave specimens more susceptible to early age transport damage27

Compressive Strength Testing AASHTO or CCRL accreditedlabs must be used forevaluation of high strengthconcrete specimens Specimen storage Preparation of specimens (cappingor grinding) Not all labs may have thenecessary equipment orcertification to process highstrength concrete specimens Compression machines may need600,000 lbs total load capacity Load rates consistent withconventional concrete of 20 to 50psi/sec (ASTM C 39)28

Modulus of Elasticity

Modulus of Elasticity Young’s Modulus: Measure of the stiffness of a solid material Defines the relationship between stress (force per unit area) andstrain (proportional deformation) in a material30

Modulus of Elasticity (Young’s Method) A solidmaterial willdeform when aload is appliedto it. If itreturns to itsoriginal shapeafter the loadis removed,this is elasticdeformation. In the rangewhere theratio betweenload anddeformationremainsconstant, thestress-straincurve is linear.31

Specimen PreparationEnd Grinding Samples over 12,000psi must be ground beforecompression and modulus testing (ASTM C1231)32

Specimen Prep Cont.Air voids and moisture Voids withinthe specimencan produceskewedresults Both mixdesign andspecimencastingpracticesimpact finalsurface Specimenmoisturemust be keptconstant33

Apparatus and SetupMoE RigRig with Cylinder34

Testing MoEYoung’s Modulus setupPoisson’s Ratio setup35

MoE Loading Curve ASTM C469 requires a specimen to be loaded to at least40% of its compressive strength and then unloaded in acontrolled manner three times36

MoE Report and Graph37

Specimen Evaluation Examine cutspecimens forvoids,segregation,or otherabnormalities38

High Strength Concrete References Design and Control of Concrete Mixtures – 16th Edition Published by PCA ACI 363R-10 Report on High-Strength Concrete Published by ACI High-Strength Concrete: A Practical Guide Michael A. Caldarone ACI 211.4R-08: Guide for Selecting Proportions forHigh-Strength Concrete Using Portland Cement &Other Cementitious Material Published by ACI39

Thank You40

ASTM C469 requires a specimen to be loaded to at least 40% of its compressive strength a

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