Abcs of Concrete

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1 ABC ABC’ s OF CONCRETE s OF CONCRETE A General Overview of Concrete A General Overview of Concrete Concrete Components Concrete Components Aggregates (coarse and fine) = 60% to 75% of Aggregates (coarse and fine) = 60% to 75% of a concrete mix a concrete mix Paste = 25% to 40% of a concrete mix Paste = 25% to 40% of a concrete mix Cement (cementitious materials) = 7% to Cement (cementitious materials) = 7% to 15% of a concrete mix 15% of a concrete mix Water = 14% to 21% of a concrete mix Water = 14% to 21% of a concrete mix Air = 4% to 8% of a concrete mix Air = 4% to 8% of a concrete mix Admixtures Admixtures The quality of a concrete mix depends The quality of a concrete mix depends upon the quality of the paste and the upon the quality of the paste and the aggregate, and the bond between the aggregate, and the bond between the two. two. In properly made concrete, all aggregate In properly made concrete, all aggregate particles are completely coated with particles are completely coated with paste, and all of the spaces between the paste, and all of the spaces between the aggregate particles are filled with paste. aggregate particles are filled with paste. Coarse Aggregates Coarse Aggregates River Gravel / Crushed Stone River Gravel / Crushed Stone Rounded / Angular Rounded / Angular Coarse Aggregate - Rounded Gravel Coarse Aggregate – Crushed Limestone

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Abcs of Concrete

Transcript of Abcs of Concrete

  • 1ABCABCs OF CONCRETEs OF CONCRETEA General Overview of ConcreteA General Overview of Concrete

    Concrete ComponentsConcrete Components

    Aggregates (coarse and fine) = 60% to 75% of Aggregates (coarse and fine) = 60% to 75% of a concrete mixa concrete mix

    Paste = 25% to 40% of a concrete mixPaste = 25% to 40% of a concrete mix Cement (cementitious materials) = 7% to Cement (cementitious materials) = 7% to

    15% of a concrete mix15% of a concrete mix Water = 14% to 21% of a concrete mixWater = 14% to 21% of a concrete mix Air = 4% to 8% of a concrete mixAir = 4% to 8% of a concrete mix

    AdmixturesAdmixtures

    The quality of a concrete mix depends The quality of a concrete mix depends upon the quality of the paste and the upon the quality of the paste and the aggregate, and the bond between the aggregate, and the bond between the two.two.

    In properly made concrete, all aggregate In properly made concrete, all aggregate particles are completely coated with particles are completely coated with paste, and all of the spaces between the paste, and all of the spaces between the aggregate particles are filled with paste. aggregate particles are filled with paste.

    Coarse AggregatesCoarse AggregatesRiver Gravel / Crushed StoneRiver Gravel / Crushed Stone

    Rounded / AngularRounded / Angular

    Coarse Aggregate - Rounded Gravel Coarse Aggregate Crushed Limestone

  • 2Fine AggregatesFine Aggregates Natural SandRounded Particle Shape

    Manufactured Sand Angular Particle Shape

    Gradation Advantages Disadvantages

    CementCement

    Types of Cement: I NormalII Moderate Sulfate ResistanceIII High Early StrengthIV Low Heat of HydrationV High Sulfate Resistance

    Cement MillCement Mill

    KILN

    CLINKER SILO

    GRINDING MILL

    GYPSUM SILO

    RAW MATERIAL PROPRTIONED

    RAW MATERIALS BLENDED

    RAW MATERIAL STORAGE

    RAW MATERIAL STORAGE

    ROLLER MILL

    Cement Truck Concrete Truck

    Supplementary Cementitious Supplementary Cementitious Materials / Mineral AdmixturesMaterials / Mineral Admixtures

    Fly AshFly Ash Ground Granulated Blast Furnace Slag Ground Granulated Blast Furnace Slag

    (GGBFS)(GGBFS) Silica Fume (Microsilica)Silica Fume (Microsilica) Natural PozzolansNatural Pozzolans

    Supplementary Cementitious Supplementary Cementitious Materials / Mineral AdmixturesMaterials / Mineral Admixtures

    Added to the concrete as part of the total Added to the concrete as part of the total cementitious system.cementitious system.

    May be used in addition to or as a partial May be used in addition to or as a partial replacement for cementreplacement for cement

    Used to improve a particular concrete Used to improve a particular concrete propertyproperty

    Most are byproducts of other industrial Most are byproducts of other industrial processesprocesses

    Economic benefits Economic benefits

  • 3Mixing Water For Concrete Harmful Impurities in WaterHarmful Impurities in Water

    Alkali Carbonate & BicarbonateAlkali Carbonate & Bicarbonate High Chloride Content High Chloride Content High Sulfate ContentHigh Sulfate Content Other Salts (manganese, tin, zinc, copper)Other Salts (manganese, tin, zinc, copper) Acid or Alkaline WatersAcid or Alkaline Waters Organic Impurities & AlgaeOrganic Impurities & Algae SugarSugar SiltSilt OilsOils

    WaterWater--Cement Ratio (w/c) Cement Ratio (w/c) LawLaw

    For given materials, the strength of the For given materials, the strength of the concrete (so long as we have a plastic concrete (so long as we have a plastic mix) depends solely on the relative mix) depends solely on the relative quantity of water as compared with the quantity of water as compared with the cement, regardless of mix or size and cement, regardless of mix or size and grading of aggregate.grading of aggregate.

    -- Duff A. AbramsDuff A. AbramsMay, 1918 May, 1918

    WaterWater--Cement Ratio = (w/c)Cement Ratio = (w/c)

    w/c = weight of water w/c = weight of water weight of cementweight of cement

    500 lbs. water in a mix500 lbs. water in a mix1000 lbs. of cement1000 lbs. of cement

    w/c = 500 lbs w/c = 500 lbs 1000 lbs. = 0.501000 lbs. = 0.50

    Effect Of Water Content On Effect Of Water Content On Compressive StrengthCompressive Strength

    1000

    2000

    3000

    4000

    5000

    6000

    0.3 0.4 0.5 0.6 0.7 0.8Water-cement ratio

    Com

    pres

    sive

    stre

    ngth

    , psi

    Non-air-entrained concreteAir-entrained concrete

  • 4Advantages of Reducing Water ContentAdvantages of Reducing Water Content

    Increased compressive & flexural strengthIncreased compressive & flexural strength Lower permeability, lower absorption, & Lower permeability, lower absorption, &

    increased watertightnessincreased watertightness Increased resistance to weatheringIncreased resistance to weathering Better bond between concrete & Better bond between concrete &

    reinforcementreinforcement Reduced drying shrinkage & crackingReduced drying shrinkage & cracking Less volume change from wetting & dryingLess volume change from wetting & drying

    Effect of too Much Water on ConcreteEffect of too Much Water on Concrete

    NonNon--cohesivecohesive SegregatingSegregating BleedingBleeding Poor finishabilityPoor finishability High permeabilityHigh permeability Reduced strengthReduced strength Low durabilityLow durability Increased Increased

    shrinkageshrinkage

    Air-Entraining AdmixturesType A Water-ReducingType C AcceleratingType D Water-Reducing & RetardingType E Water-Reducing & AcceleratingType F Water-Reducing, High-Range (plasticizers)Type G Water-Reducing, High-Range & Retarding

    AdmixturesThose ingredients in concrete other than

    cement, supplementary cementitious materials, water, & aggregates that are added to the mixture immediately before or during mixing. - PCA

    Admixture Storage Tanks

    Admixture DispensersAirAir--Entraining AdmixturesEntraining Admixtures

    Used to purposely introduce and stabilize Used to purposely introduce and stabilize microscopic air bubbles in concretemicroscopic air bubbles in concrete

    AirAir--entrainment dramatically improves the entrainment dramatically improves the durability of concrete which is exposed to durability of concrete which is exposed to freezing and thawingfreezing and thawing

  • 5Why do we need AirWhy do we need Air--Entrainment?Entrainment?

    .. Primarily to protect against freezing and .. Primarily to protect against freezing and thawing cycles.thawing cycles.

    Non AirNon Air--entrainedentrained

    32 32 ooFF

    Mechanism of Frost Mechanism of Frost Damage in ConcreteDamage in Concrete

    courtesy of M. Thomas

    Non AirNon Air--entrainedentrained

    32 32 ooFF

    Mechanism of Frost Mechanism of Frost Damage in ConcreteDamage in Concrete

    23 23 ooFF

    courtesy of M. ThomasWater Water Expands Expands

    Upon FreezingUpon Freezing

    Non AirNon Air--entrainedentrained

    32 32 ooFF

    Mechanism of Frost Mechanism of Frost Damage in ConcreteDamage in Concrete

    23 23 ooFF

    courtesy of M. Thomas

    Scaling DistressScaling Distress

    photo courtesy of M. Thomas

    AirAir--entrainedentrainedMechanism of Protection Mechanism of Protection

    by Air Voidsby Air Voids

    23 23 ooFF

    32 32 ooFF

    courtesy of M. Thomas

  • 6courtesy of M. Thomas

    AirAir--entrainedentrainedMechanism of Protection Mechanism of Protection

    by Air Voidsby Air Voids

    23 23 ooFF

    32 32 ooFF

    courtesy of M. Thomas

    AirAir--entrainedentrainedMechanism of Protection Mechanism of Protection

    by Air Voidsby Air Voids

    23 23 ooFF

    32 32 ooFF

    courtesy of M. Thomas

    AirAir--entrainedentrainedMechanism of Mechanism of

    Protection by Air VoidsProtection by Air Voids

    23 23 ooFF

    32 32 ooFF

    Water ReducersWater Reducers

    Used to:Used to: Reduce the quantity of mixing water required Reduce the quantity of mixing water required

    to produce concrete of a certain slumpto produce concrete of a certain slump Reduce w/cReduce w/c Reduce cement contentReduce cement content Increase slumpIncrease slump

    Low range, mid range, & high rangeLow range, mid range, & high range Provide 5% Provide 5% -- 30% water reduction30% water reduction Mixes with high slumps and/or low w/c are Mixes with high slumps and/or low w/c are

    possible when these admixtures are usedpossible when these admixtures are used

    Different uses require different amounts of Different uses require different amounts of flowability/workabilityflowability/workability

    NO W/R

    HIGH RANGE W/R

    NORMALW/R

    MID RANGE W/R

  • 7Water-Reducing & Retarding Admixtures

    An admixture that causes a decrease in the rate of hydration of the hydraulic cement, and lengthens the time of setting.

    Hydration control admixtures (Delvo, Recover, etc.) are classified as water-reducing & retarding admixtures

    Accelerating Admixtures

    An admixture that causes an increase in An admixture that causes an increase in the rate of hydration of the hydraulic the rate of hydration of the hydraulic cement, and thus shortens the time of cement, and thus shortens the time of setting, or increases the rate of strength setting, or increases the rate of strength development, or both.development, or both.

    Properties of Freshly Mixed Properties of Freshly Mixed ConcreteConcrete

    MixingMixing WorkabilityWorkability Bleeding & SettlementBleeding & Settlement ConsolidationConsolidation Hydration, Setting Time, & HardeningHydration, Setting Time, & Hardening

    MixingMixing

    The sequence of adding materials into a mixer The sequence of adding materials into a mixer affects the uniformity of the mixaffects the uniformity of the mix

    Different batching sequences require Different batching sequences require adjustments in the time of water addition, the adjustments in the time of water addition, the total number of revolutions of the mixer drum, total number of revolutions of the mixer drum, and the speed of revolutionand the speed of revolution

    Batch size is important to mixing procedureBatch size is important to mixing procedure Design and condition of the mixer drum and Design and condition of the mixer drum and

    blades is an important factor in mixing blades is an important factor in mixing

    WorkabilityWorkability Workability is the ease of placing, consolidating, Workability is the ease of placing, consolidating,

    and finishing freshly mixed concrete and the and finishing freshly mixed concrete and the degree to which it resists segregationdegree to which it resists segregation

    Factors that influence workability are:Factors that influence workability are: Method & duration of transportationMethod & duration of transportation Quantity & characteristics of cementitious materialsQuantity & characteristics of cementitious materials Slump of the concreteSlump of the concrete Grading, shape, & texture of aggregatesGrading, shape, & texture of aggregates EntrainedEntrained--air contentair content Water contentWater content Concrete & air temperaturesConcrete & air temperatures AdmixturesAdmixtures

    Bleeding & SettlementBleeding & Settlement Bleeding is the development of a layer of water at the Bleeding is the development of a layer of water at the

    surface of freshly mixed concretesurface of freshly mixed concrete Caused by settlement of heavier particles and upward Caused by settlement of heavier particles and upward

    migration of watermigration of water Helps to control plastic shrinkage crackingHelps to control plastic shrinkage cracking Excessive bleeding causes a high w/c at the surfaceExcessive bleeding causes a high w/c at the surface Bleeding rate & amount of settlement due to bleeding Bleeding rate & amount of settlement due to bleeding

    increases with initial water contentincreases with initial water content A properly designed mix (wellA properly designed mix (well--graded aggregates, graded aggregates,

    certain admixtures, aircertain admixtures, air--entrainment, SCMentrainment, SCMs) reduces s) reduces bleeding bleeding

  • 8ConsolidationConsolidation

    Vibration sets into motion the particles in freshly Vibration sets into motion the particles in freshly mixed concrete, reducing the friction between mixed concrete, reducing the friction between themthem

    Concrete with optimally graded aggregates are Concrete with optimally graded aggregates are easier to consolidate and placeeasier to consolidate and place

    Poor consolidation results in honeycombing and Poor consolidation results in honeycombing and weak concreteweak concrete

    Mechanical vibration allows concrete with a Mechanical vibration allows concrete with a lower consistency to be usedlower consistency to be used

    Hydration, Setting Time & Hydration, Setting Time & HardeningHardening

    Hydration is the chemical reaction between cement and Hydration is the chemical reaction between cement and water. This gives cement paste its binding propertywater. This gives cement paste its binding property

    Calcium silicate hydrate (CSH), along with other Calcium silicate hydrate (CSH), along with other compounds, is formed when cement reacts with water.compounds, is formed when cement reacts with water.

    CSH forms dense bonds between crystalline phases of the CSH forms dense bonds between crystalline phases of the hydration reaction and other materials (unhydrated cement, hydration reaction and other materials (unhydrated cement, sand, coarse aggregate)sand, coarse aggregate)

    Heat is released as cement hydrates (heat of hydration)Heat is released as cement hydrates (heat of hydration) Rate of hydration determines the rate of hardeningRate of hydration determines the rate of hardening Cement fineness, admixtures, water content, & temperature Cement fineness, admixtures, water content, & temperature

    (of materials & ambient) affect the rate of hydration(of materials & ambient) affect the rate of hydration

    Cement Grains

    Dispersion obtained due to the presence of water

    Attractive forces between cement grains will cause flocculation with

    LOSS OF FLUIDITY

    Batch Water

    Traditional Water-Cement System

    Flocculation

    With Loss of Fluidity and Workability

    Hydration Products

    Cement HydrationCement Hydration

    Properties of Hardened Properties of Hardened ConcreteConcrete

    CuringCuring Drying RateDrying Rate StrengthStrength DensityDensity Permeability & WatertightnessPermeability & Watertightness Abrasion ResistanceAbrasion Resistance DurabilityDurability

    CuringCuring

    Concrete will continue to gain strength as Concrete will continue to gain strength as long as:long as: Unhydrated cement is presentUnhydrated cement is present The concrete remains moistThe concrete remains moist The temperature remains favorable The temperature remains favorable Sufficient space is available for hydration products Sufficient space is available for hydration products

    to formto form When relative humidity in the concrete is less When relative humidity in the concrete is less

    than 80%, or the temperature of the concrete than 80%, or the temperature of the concrete drops below freezing, hydration & strength drops below freezing, hydration & strength gain virtually stop gain virtually stop

    Moist curing concrete is the best way to cure Moist curing concrete is the best way to cure concreteconcrete

  • 9Drying RateDrying Rate

    Concrete doesnConcrete doesnt cure by drying (it t cure by drying (it needs moisture to hydrate)needs moisture to hydrate)

    When concrete dries out, it stops When concrete dries out, it stops gaining strength gaining strength

    Drying shrinkage is a primary cause of Drying shrinkage is a primary cause of crackingcracking

    Size & shape of a concrete member Size & shape of a concrete member affect the drying rateaffect the drying rate

    StrengthStrength

    Compressive strength is the resistance to axial loads (28Compressive strength is the resistance to axial loads (28--day strength)day strength)

    Compressive strength achieved by concrete results from:Compressive strength achieved by concrete results from: w/cw/c The extent of hydrationThe extent of hydration Curing conditionsCuring conditions Age of the concrete Age of the concrete

    Air content also affects strengthAir content also affects strength Compressive strength measured by testing cylindersCompressive strength measured by testing cylinders Flexural strength used to design pavements & slabsFlexural strength used to design pavements & slabs Other measures of strength include: tensile strength, Other measures of strength include: tensile strength,

    torsional strength, shear strength, & Modulus of Elasticity (E torsional strength, shear strength, & Modulus of Elasticity (E = ratio of stress to strain) = ratio of stress to strain)

    DensityDensity

    Weight per unit volume of concreteWeight per unit volume of concrete Normal concrete is usually 137 to 150 Normal concrete is usually 137 to 150

    lb/ftlb/ft33

    Varies depending on:Varies depending on: The amount and density of the aggregateThe amount and density of the aggregate Amount of entrained and entrapped airAmount of entrained and entrapped air Water & cement contentsWater & cement contents

    Reducing the paste content increases Reducing the paste content increases densitydensity

    Permeability & WatertightnessPermeability & Watertightness

    Permeability is the ability of concrete to resist Permeability is the ability of concrete to resist penetration by water of other substancespenetration by water of other substances

    Watertightness is the ability of concrete to hold back Watertightness is the ability of concrete to hold back or retain wateror retain water

    Permeability of concrete is a function of the Permeability of concrete is a function of the permeability of the paste & aggregatepermeability of the paste & aggregate

    Lower permeability improves concreteLower permeability improves concretes resistance to s resistance to freezing & thawing, resaturation, sulfate & chloride freezing & thawing, resaturation, sulfate & chloride ion penetration, and other chemical attackion penetration, and other chemical attack

    AirAir--entrainment aids in watertightness but has little entrainment aids in watertightness but has little effect on permeabilityeffect on permeability

    Permeability increases with dryingPermeability increases with drying Permeability often measured by the rapid chloride Permeability often measured by the rapid chloride

    permeability testpermeability test

    Abrasion ResistanceAbrasion Resistance

    Very important in floors, pavements, Very important in floors, pavements, bridge decks, & hydraulic structuresbridge decks, & hydraulic structures

    Abrasion resistance is closely related to Abrasion resistance is closely related to compressive strengthcompressive strength

    Type of aggregate and surface finish Type of aggregate and surface finish have a strong influence on abrasion have a strong influence on abrasion resistanceresistance

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    DurabilityDurability

    Durability is the ability of concrete to resist weathering actioDurability is the ability of concrete to resist weathering action, n, chemical attack, & abrasion while maintaining its desired chemical attack, & abrasion while maintaining its desired propertiesproperties

    Resistance to freezing & thawingResistance to freezing & thawing Deterioration caused by expansion during repeated freezing & Deterioration caused by expansion during repeated freezing &

    thawing thawing AirAir--entrained concrete has higher freezeentrained concrete has higher freeze--thaw resistance than thaw resistance than

    non airnon air--entrained concreteentrained concrete Low w/c is beneficialLow w/c is beneficial Allowing concrete to dry before freezing is beneficialAllowing concrete to dry before freezing is beneficial

    AlkaliAlkali--aggregate reactivityaggregate reactivity Occurs when active minerals in some aggregates react with Occurs when active minerals in some aggregates react with

    alkali hydroxides in concretealkali hydroxides in concrete AlkaliAlkali--silica reaction (ASR)silica reaction (ASR) AlkaliAlkali--carbonate reaction (ACR)carbonate reaction (ACR)

    Chemical resistance, sulfate attack, carbonation, delayed Chemical resistance, sulfate attack, carbonation, delayed expansionexpansion

    Alkali-Silica Reaction (ASR) Requirements for Durable, Scale Requirements for Durable, Scale Resistant Concrete Resistant Concrete

    WaterWater--Cement Ratio (w/c): 0.50 or lessCement Ratio (w/c): 0.50 or less Adequate Cement ContentAdequate Cement Content Adequate StrengthAdequate Strength Adequate AirAdequate Air--Entraining System (6%)Entraining System (6%) Sound, Clean, WellSound, Clean, Well--Graded AggregatesGraded Aggregates Minimum Finishing (Well Timed)Minimum Finishing (Well Timed) Adequate Moist CuringAdequate Moist Curing Air Drying Before Exposure to Freezing Air Drying Before Exposure to Freezing

    WVDOH Classes of Structural WVDOH Classes of Structural ConcreteConcrete

    Class A (3,500 psi, 7.5% air) Class A (3,500 psi, 7.5% air) Railing, cribbing, precast shapes, filler, steel grid floorsRailing, cribbing, precast shapes, filler, steel grid floors

    Class K (4,000 psi, 7.0% air) Class K (4,000 psi, 7.0% air) Bridge superstructure (sidewalks, parapets, decks, & median barrBridge superstructure (sidewalks, parapets, decks, & median barriers)iers)

    Class B (3,000 psi, 7.0% air) Class B (3,000 psi, 7.0% air) Roadway applications (sidewalks, castRoadway applications (sidewalks, cast--inin--place inlets, manholes, & box place inlets, manholes, & box

    culverts) and bridge substructure (columns, piers, abutments, etculverts) and bridge substructure (columns, piers, abutments, etc.)c.) Class C (2,500 psi, 6.0% air) Class C (2,500 psi, 6.0% air)

    Massive footings, pedestals, & pier shafts (nonMassive footings, pedestals, & pier shafts (non--reinforced or lightly reinforced or lightly reinforced applications)reinforced applications)

    Class D (2,000 psi, 5.5% air) Class D (2,000 psi, 5.5% air) Unformed & nonUnformed & non--reinforced concrete for backfilling of excavated reinforced concrete for backfilling of excavated

    pockets or voids beneath footingspockets or voids beneath footings Class H (4,000 psi, 6.5% air) Class H (4,000 psi, 6.5% air)

    Bridge decks & other bridge elements when designated in the planBridge decks & other bridge elements when designated in the planss

    Other WVDOH Types of Concrete & Other WVDOH Types of Concrete & Related MaterialsRelated Materials

    Specialized concrete overlays (section Specialized concrete overlays (section 679) 679) Latex modified concrete (LMC)Latex modified concrete (LMC) Microsilica concreteMicrosilica concrete

    Pavement concrete (Section 501)Pavement concrete (Section 501) Low slump if slip form construction is usedLow slump if slip form construction is used

    Controlled lowControlled low--strength material (CLSM strength material (CLSM --flowable fill)flowable fill)

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    Flowable Fill (CLSM)Flowable Fill (CLSM)

    NonNon--compacted, cementitious material used primarily compacted, cementitious material used primarily as a backfill in lieu of a compacted materialas a backfill in lieu of a compacted material

    Mixes typically consist of a combination of:Mixes typically consist of a combination of: CementCement Fly ashFly ash Fine aggregateFine aggregate WaterWater AdmixturesAdmixtures

    Three types of CLSM in WVDOH specs:Three types of CLSM in WVDOH specs: Type A: 50 psi min./150 psi max.Type A: 50 psi min./150 psi max. Type B: 50 psi min.Type B: 50 psi min. Type C: 1000 psi min.Type C: 1000 psi min.

    Transporting Concrete

    Truck mixers Truck agitators Non-agitating trucks Mobile batch mixer

    Truck Mixers

    PlantPlant

    photophoto

    Central Mix Plant Discharging into Truck Mixer

    Information Plates on Truck Mixers

    PlantPlant

    photophoto

    Truck Agitators

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    Central Mix Plant Discharging into Non-Agitating Truck

    photophoto

    Mobile Mixers (Volumetric Batching)

    When Concrete Arrives at the Job When Concrete Arrives at the Job (what to look for)(what to look for)

    Maximum of 300 revolutions on the drumMaximum of 300 revolutions on the drum Concrete temperature (50Concrete temperature (50 F minimum, F minimum,

    9090 F maximum)F maximum) Need a concrete batch ticketNeed a concrete batch ticket Time limit of 1.5 hours from batching Time limit of 1.5 hours from batching

    (addition of cement to the aggregates) (addition of cement to the aggregates) until completion of dischargeuntil completion of discharge Reduced to 1 hour when concrete Reduced to 1 hour when concrete

    temperature is 85temperature is 85 F or aboveF or above

    Field Tests for ConcreteField Tests for Concrete(See MP 601.03.50 for Frequencies) (See MP 601.03.50 for Frequencies) Temperature TestTemperature Test Slump TestSlump Test Air Content TestAir Content Test

    Pressure MeterPressure Meter Volumetric Air Meter (RollVolumetric Air Meter (Roll--oo--Meter) Meter)

    Unit Weight & Yield TestUnit Weight & Yield Test Compressive Strength CylindersCompressive Strength Cylinders

    All acceptance testing must be performed by a certified All acceptance testing must be performed by a certified WVDOH Portland Cement Concrete (PCC) Inspector. WVDOH Portland Cement Concrete (PCC) Inspector. This applies to WVDOH personnel, Contractors, and This applies to WVDOH personnel, Contractors, and Consultants.Consultants.

    Slump Test Natural Slump vs. Chemical SlumpNatural Slump vs. Chemical SlumpNO W/R

    HIGH RANGE W/R

    NORMALW/R

    MID RANGE W/R

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    Recommended SlumpsRecommended Slumps

    Table 601.3.2 in WVDOH spec book lists the Table 601.3.2 in WVDOH spec book lists the optimum consistency (target slump) in different optimum consistency (target slump) in different situationssituations 11 for inclined surfaces, slip forming, etc.for inclined surfaces, slip forming, etc. 22 for reinforced structures which are accessiblefor reinforced structures which are accessible 33 for reinforced structures which arenfor reinforced structures which arent easily t easily

    accessibleaccessible

    WVDOH specifications allow an increase in the WVDOH specifications allow an increase in the target slump by 4target slump by 4 when superplasticizers are when superplasticizers are usedused Under no circumstances shall the slump exceed 8Under no circumstances shall the slump exceed 8

    Air Content Test Type B Pressure Meter

    Air Content Test Volumetric Method (Roll-o-Meter) Unit Weight & Yield Test

    Compressive Strength Cylinders Job Site Adjustments Job Site Adjustments (truck mixers only)(truck mixers only)

    Addition of water:Addition of water: Only allowed for slump adjustmentOnly allowed for slump adjustment Must turn the drum for 20 revolutions at mixing speed after Must turn the drum for 20 revolutions at mixing speed after

    water is addedwater is added No water may be added after discharge of the concrete has No water may be added after discharge of the concrete has

    startedstarted CanCant add more water than allowed by table 601.3.1 (limited t add more water than allowed by table 601.3.1 (limited

    number of gallons of water per bag of cement)number of gallons of water per bag of cement) Addition of air: Addition of air:

    Use same airUse same air--entraining agent that is in mix designentraining agent that is in mix design Mix with 2 gallons of waterMix with 2 gallons of water Turn the drum at least 30 revolutions at mixing speedTurn the drum at least 30 revolutions at mixing speed ReRe--test for slump & airtest for slump & air Only two adjustments are permitted per truckOnly two adjustments are permitted per truck

    Cylinders cannot be made until after all adjustments are Cylinders cannot be made until after all adjustments are completedcompleted

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    Depositing The ConcreteDepositing The Concrete

    Concrete should be placed continuously as near Concrete should be placed continuously as near as possible to its final positionas possible to its final position

    When more than one layer is needed, concrete When more than one layer is needed, concrete should be placed in layers of uniform thicknessshould be placed in layers of uniform thickness Consolidate each layer before placing the next layerConsolidate each layer before placing the next layer

    Time placement to eliminate cold joints (joint Time placement to eliminate cold joints (joint formed after previously placed concrete has formed after previously placed concrete has achieved its initial set)achieved its initial set)

    DonDont allow water to mix with the concretet allow water to mix with the concrete Limit concrete free fall (5 ft. maximum in Limit concrete free fall (5 ft. maximum in

    WVDOH specs.)WVDOH specs.)

    Direct PlacementDirect Placement

    Concrete Buggy or Wheelbarrow Truck Agitator

    Other Placement TechniquesOther Placement Techniques

    TremieTremie PumpPump BottomBottom--dump Bucketdump Bucket ConveyorsConveyors

    Tremie PlacementTremie Placement

  • 15

    Tremie PlacementTremie Placement Pump Truck PlacementPump Truck Placement

    Bucket PlacementBucket Placement Bucket PlacementBucket Placement

    Conveyor System Hopper

  • 16

    ConsolidationConsolidation Vibration (frequency of vibration expressed in Vibration (frequency of vibration expressed in

    vibrations per second vibrations per second Hertz)Hertz) Internal Vibration (spud vibrators)Internal Vibration (spud vibrators) Time of Internal vibration depends on the mixTime of Internal vibration depends on the mix OverOver--vibration results in nonvibration results in non--uniformityuniformity

    External Vibration (form vibrators, vibratory roller External Vibration (form vibrators, vibratory roller screeds, plate vibrators, etc.)screeds, plate vibrators, etc.)

    UnderUnder--vibration causes vibration causes honeycombs, bugholes, honeycombs, bugholes, streaks, cold joints (vibrating can keep concrete streaks, cold joints (vibrating can keep concrete alivealive) / lines, & subsidence cracking) / lines, & subsidence cracking

    Overvibration causes Overvibration causes segregation, streaks, loss of segregation, streaks, loss of entrainedentrained--air, form damage or failureair, form damage or failure

    Concrete SlabsConcrete Slabs

    Precautions should be taken to protect slabs Precautions should be taken to protect slabs from rain during placementfrom rain during placement

    Place concrete & level with rakes and shovelsPlace concrete & level with rakes and shovels Strikeoff (screed) the concrete. Straightedge Strikeoff (screed) the concrete. Straightedge

    often usedoften used Bullfloat the concrete (before bleedwater Bullfloat the concrete (before bleedwater

    accumulates)accumulates) Finishing operations (after the bleedwater has Finishing operations (after the bleedwater has

    evaporated) evaporated) edging, jointing, floating, edging, jointing, floating, troweling, & broomingtroweling, & brooming

    CuringCuring

    Finishing process drives out air and results in unsatisfactory air contents at the surface

    Affected depth of surface varies with finishing technique

    Satisfactory air content in interior of concrete

    Even with satisfactory interior air contents, unsatisfactory surface air contents may result due to the effect on air and paste from the finishing process

    Effect of Finishing Air-Entrained Concrete

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    Curing ConcreteCuring Concrete

    Curing is the maintenance of a Curing is the maintenance of a satisfactory moisture content and satisfactory moisture content and

    temperature in concrete for a temperature in concrete for a period of time immediately period of time immediately

    following placing and finishing so following placing and finishing so that the desired properties may that the desired properties may

    develop.develop.

    WVDOH Structural Concrete Curing WVDOH Structural Concrete Curing RequirementsRequirements

    All structural concrete (Classes A, K, B, C, & D) All structural concrete (Classes A, K, B, C, & D) shall be protected by one or more of the shall be protected by one or more of the following curing materials:following curing materials: Polyethylene coated burlapPolyethylene coated burlap Burlap clothBurlap cloth Waterproof paperWaterproof paper Curing compoundsCuring compounds White polyethylene sheetingWhite polyethylene sheeting

    All bridge decks shall be cured with burlap & All bridge decks shall be cured with burlap & waterwater

    WVDOH Structural Concrete Curing WVDOH Structural Concrete Curing RequirementsRequirements

    All structural concrete shall be moist cured All structural concrete shall be moist cured for 7 daysfor 7 days This time may be reduced if it is shown that This time may be reduced if it is shown that

    the concrete has reached 70% of the design the concrete has reached 70% of the design strengthstrength

    Under no circumstances shall the cure period Under no circumstances shall the cure period be less than 3 daysbe less than 3 days

    All bridge decks shall be moist cured for 7 All bridge decks shall be moist cured for 7 days regardless of strengthdays regardless of strength

    WVDOH Structural Concrete Curing WVDOH Structural Concrete Curing RequirementsRequirements

    When the air temperature is expected to fall below When the air temperature is expected to fall below 3030 F, measures shall be taken to maintain the F, measures shall be taken to maintain the concrete surface temperature between 50concrete surface temperature between 50 F and F and 9090 FF

    Days on which the surface temperature of the Days on which the surface temperature of the concrete falls below 50concrete falls below 50 F are not considered days F are not considered days of curingof curing

    Under no circumstances shall the concrete Under no circumstances shall the concrete temperature be allowed to fall below 35temperature be allowed to fall below 35 FF

    When protection (blankets, etc.) is removed from When protection (blankets, etc.) is removed from the concrete, the concrete temperature isnthe concrete, the concrete temperature isnt allowed t allowed to drop by more than 20to drop by more than 20 F per 24 hour period F per 24 hour period

    Effect of Curing on Compressive Strength

    Age, Days

    125

    100

    75

    50

    25

    0

    150

    3 7 28 90 180

    Moist-cured entire time

    In air after 7 days

    In air after 3 days

    In air entire time

    % o

    f 28

    com

    pres

    sive

    stren

    gth

    Curing Methods & MaterialsCuring Methods & Materials

    Concrete can be kept moist by three methods:Concrete can be kept moist by three methods: Maintain the mix water in the concrete during Maintain the mix water in the concrete during

    early hardening (wet cure early hardening (wet cure -- ponding, ponding, spraying, wet coverings, etc.)spraying, wet coverings, etc.)

    Reduce the loss of mixing water from the Reduce the loss of mixing water from the surface (impervious paper, plastic, curing surface (impervious paper, plastic, curing compounds)compounds)

    Accelerated strength gain by supplying heat & Accelerated strength gain by supplying heat & moisture (live steam, heated forms & moisture (live steam, heated forms & blankets, etc.)blankets, etc.)

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    Bridge Deck CuringBridge Deck Curing

    Bridge Deck CuringBridge Deck Curing Curing with Plastic SheetingCuring with Plastic Sheeting

    Curing CompoundCuring CompoundCuring Time & TemperatureCuring Time & Temperature

    Period of time that concrete should be Period of time that concrete should be protected from freezing, high protected from freezing, high temperatures, & moisture loss depends temperatures, & moisture loss depends on:on: Type of cementitious materials usedType of cementitious materials used Mix proportionsMix proportions Required strengthRequired strength Size & shape of concrete memberSize & shape of concrete member Ambient weather conditionsAmbient weather conditions Future exposure conditionsFuture exposure conditions

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    Potential Problems for Freshly Potential Problems for Freshly Mixed Concrete in Hot WeatherMixed Concrete in Hot Weather

    Greater water demandGreater water demand Increased evaporation rateIncreased evaporation rate Increased rate of slump lossIncreased rate of slump loss Retempering at job siteRetempering at job site Potential for cold jointsPotential for cold joints Fast settingFast setting Plastic shrinkage crackingPlastic shrinkage cracking Difficulty in placing, consolidating, & finishingDifficulty in placing, consolidating, & finishing Control of airControl of air--entrainmententrainment

    BLEEDWATER

    EVAPORATION

    Plastic Shrinkage CrackingPlastic Shrinkage Cracking Plastic Shrinkage CrackingPlastic Shrinkage Cracking

    Practices for Hot Weather Concreting

    Use cool concrete (cool water and/or Use cool concrete (cool water and/or aggregates)aggregates)

    Protect against rapid moisture lossProtect against rapid moisture loss Transport, place, consolidate, & finish with Transport, place, consolidate, & finish with

    minimal delayminimal delay Schedule pours during cooler times of the Schedule pours during cooler times of the

    dayday

    Addition of Ice to a Truck Mixer

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    Objectives of Cold Weather Objectives of Cold Weather Concreting PracticesConcreting Practices

    Prevent damage to concrete due to freezing at Prevent damage to concrete due to freezing at early stagesearly stages

    Assure that the concrete develops the required Assure that the concrete develops the required strength for safe removal of formsstrength for safe removal of forms

    Maintain curing conditions that foster normal Maintain curing conditions that foster normal strength developmentstrength development

    Limit rapid temperature changesLimit rapid temperature changes Provide protection consistent with the intended Provide protection consistent with the intended

    serviceability of the structureserviceability of the structure

    Heated Curing BoxHeated Curing Box

    Effect of Freezing Fresh ConcreteEffect of Freezing Fresh Concrete

    Up to 50% reduction of strength if frozen Up to 50% reduction of strength if frozen before attaining 500 PSI compressive before attaining 500 PSI compressive strength.strength.

    Reduced durability of concretes exposed Reduced durability of concretes exposed to deicers.to deicers.

    Increased permeability (less watertight).Increased permeability (less watertight).

    Effect of Freezing on Concrete CylindersEffect of Freezing on Concrete Cylinders

    5000

    4000

    3000

    2000

    1000

    00 2 4 86 10 12 14 16

    Final set

    Initial setASTM C 403

    Penetration Resistance, psi

    Effect of cold temperature on rate of hardeningTime, hours

    73 Degrees

    50 Degrees

    Temporary EnclosuresTemporary Enclosures

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    Cold Weather Concreting Cold Weather Concreting Insulating MaterialsInsulating Materials

    Dry straw or hay (covered with tarpaulins, Dry straw or hay (covered with tarpaulins, polyethylene film or waterproof paper)polyethylene film or waterproof paper)

    Expanded polyurethaneExpanded polyurethane Expanded polystyreneExpanded polystyrene Curing blanketCuring blanket Mineral fiber, loose fill (rock, slag or glass)Mineral fiber, loose fill (rock, slag or glass)

    Dry Hay or StrawDry Hay or Straw Insulated FormsInsulated Forms

    Curing BlanketsCuring Blankets