Download - Abcs of Concrete
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Tremie PlacementTremie Placement Pump Truck PlacementPump Truck Placement
Bucket PlacementBucket Placement Bucket PlacementBucket Placement
Conveyor System Hopper
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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