concrete basicss for gem

CONCRETE CONCRETE BASICSBASICS

A Guide to Concrete PracticeA Guide to Concrete PracticePrepared by Eng Abdelrahman Prepared by Eng Abdelrahman

ZayedZayedConcrete Expert Orascomci Concrete Expert Orascomci

December 2013 GEM December 2013 GEM

December 17December 17thth 2013 2013

22

THE “QUALITY” ZED AND THE COST OF QUALITY

BOQ RATE FOR WHAT WE DO

COST PROFIT

ZeroDefect

s

If an error is made,The COST to produceA correct product is:1 + 1 ¼ + 1 = 3 ¼ WHAT ABOUT OUR

PROFIT???

1

1

1 ¼

Concrete MaterialsConcrete Materials

33

Concrete is basically a mixture of Concrete is basically a mixture of cement, water/air, and aggregates cement, water/air, and aggregates (percentages are by volume (percentages are by volume


CEMENTCEMENT WATERWATER COARSE AND FINE COARSE AND FINE

AGGREGATESAGGREGATES ADMIXTURES (if ADMIXTURES (if

required).required).

55

Concrete MaterialsConcrete MaterialsWhat is the benefit of cement ?What is the benefit of cement ?

The cement powder, The cement powder, when mixed with when mixed with water,water,

Forms a paste.Forms a paste. This paste acts l ike This paste acts l ike

glue and holds or glue and holds or bonds the aggregates bonds the aggregates togethertogether ..

CEMENTCEMENT

October 27th, 2010October 27th, 2010 66

Concrete MaterialsConcrete MaterialsWhat is the type of What is the type of aggregate ?aggregate ?

Aggregates are of two Aggregates are of two basic types:basic types:

COARSE: crushed rock, COARSE: crushed rock, gravel or screenings.gravel or screenings.

FINE: fine and coarse FINE: fine and coarse sands and crusher fines.sands and crusher fines.

Sand should be Sand should be concreting sand and not concreting sand and not bricks sand or plasterers bricks sand or plasterers sandsand

AGGREGATESAGGREGATES


Concrete MaterialsConcrete MaterialsWhat is the l ightweight What is the l ightweight

aggregate ? aggregate ?

ExpandedExpanded– ShaleShale– ClayClay– SlagSlag

Lightweight Lightweight AggregateAggregate


Concrete MaterialsConcrete MaterialsWhat is the Quality of What is the Quality of

aggregate ? aggregate ?

Aggregates should be : Aggregates should be : STRONGSTRONG and and HARDHARD A stronger, harder aggregate A stronger, harder aggregate will give a stronger finalwill give a stronger final

concrete. Never use a crumble or concrete. Never use a crumble or flakey rock like sandstone.flakey rock like sandstone.

DURABLE to stand up to wear and DURABLE to stand up to wear and tear and weathering.tear and weathering.

CHEMICALLY INACTIVE so the CHEMICALLY INACTIVE so the aggregates don’t react with the aggregates don’t react with the cement.cement.

CLEAN Dirt or clay sticking to the CLEAN Dirt or clay sticking to the aggregates will weaken the bond aggregates will weaken the bond between paste and aggregates.between paste and aggregates.

Aggregate SizeAggregate Size


•GRADED Aggregates should range in size so that they fit together well.•This gives a stronger and denser concrete.•Rounded aggregates give a more workable mix. •Angular aggregates make concrete harder to place, work and compact, but can make concrete stronger.


What is the water proprties?What is the water proprties? Water is mixed with the cement Water is mixed with the cement

powder to form a paste which holds powder to form a paste which holds the aggregates together like glue.the aggregates together like glue.

Water must be clean, fresh and free Water must be clean, fresh and free from any dirt, unwanted chemicals from any dirt, unwanted chemicals or rubbish that may affect concrete.or rubbish that may affect concrete.

Many concrete plants now use Many concrete plants now use recycled water. recycled water.

Always check bore water before Always check bore water before use.use.

Don’t use sea water as it may rust Don’t use sea water as it may rust the steel reinforcement in the the steel reinforcement in the concrete.concrete.

waterwater

DateDate 1010

Concrete MaterialsConcrete MaterialsADMIXTURE TYPEDADMIXTURE TYPED Air-entraining admixturesAir-entraining admixtures Water-reducing admixturesWater-reducing admixtures Plasticizers Plasticizers Accelerating admixturesAccelerating admixtures Retarding admixturesRetarding admixtures Hydration-control admixturesHydration-control admixtures Corrosion inhibitorsCorrosion inhibitors Shrinkage reducersShrinkage reducers ASR inhibitorsASR inhibitors Coloring admixturesColoring admixtures Miscellaneous admixturesMiscellaneous admixtures

ADMIXTURESADMIXTURES


Admixtures are mixed into the concrete to change or alter its properties, i.e.

The time concrete takes to set and harden, or its workability.

Concrete MaterialsConcrete MaterialsADMIXTURE TYPEDADMIXTURE TYPED

Type A: water-reducingType A: water-reducing••Type B: retardingType B: retarding••Type C: acceleratingType C: accelerating••Type D: water-reducing and Type D: water-reducing and

retardingretarding••Type E: water-reducing and Type E: water-reducing and

acceleratingaccelerating••Type F: high-range water-Type F: high-range water-

reducingreducing••Type G: high-range and Type G: high-range and

retardingretarding

ADMIXTURESADMIXTURES



Concrete Materials

ADMIXTURES

Ready Mix PlantReady Mix Plant 1-Coming Materials

2-Mixing 3-Out going product

Concrete PropertiesConcrete Properties

Fresh concrete = workableFresh concrete = workable

Workabil i ty = transport + place + compact + f inish = 2-3hrs

Consistance = stiffness =

Concrete PropertiesConcrete Properties

DateDate 1616

The Properties of Concrete are its characteristics or basic qualities.

The four main properties of concrete are:WORKABILITY

COHESIVENESSSTRENGTH

andDURABILITY

Concrete has three different states:PLASTICSETTING

HARDENINGIn each state it has different properties.

Concrete STATESConcrete STATESPlastic State When the Plastic State When the concrete is f irst mixed i t concrete is f irst mixed i t is l ike 'bread dough‘.It is l ike 'bread dough‘.It is soft and can be is soft and can be worked or moulded into worked or moulded into different shapes. In this different shapes. In this state concrete is called state concrete is called PLASTICPLASTIC . Concrete is . Concrete is plastic during placing plastic during placing and compaction.and compaction.The most important The most important properties of plastic properties of plastic concrete are workabil i ty concrete are workabil i ty and cohesiveness.and cohesiveness.A worker wil l sink into A worker wil l sink into plastic concreteplastic concreteDateDate 1717

Slump TestSlump Test Process of measuring the slump of fresh concrete.Process of measuring the slump of fresh concrete.

Here are some examples of different measures of slumpHere are some examples of different measures of slump::

Fresh Concrete Plastic Fresh Concrete Plastic STATESTATECohesivenessCohesiveness

Mobility

Compactibility

Bleed waterPlastic shrinkage cracking

Concrete STATES

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Concrete STATESConcrete STATESWhat is the Sett ing What is the Sett ing State?State? Setting StateSetting State

DateDate 2121

•Setting State Concrete then begins to stiffen. The stiffening of concrete, when it is no longer soft, is called SETTING. Setting takes place after compaction and during finishing.

•Concrete that is sloppy or wet may be easy to place but will be more difficult to finish.

•A worker leaves footprints in setting concrete.

Early Age Concerte – Early Age Concerte – Setting StateSetting State

Green Concrete = initial set = weak = easily damagedGreen Concrete = initial set = weak = easily damaged

Concrete STATES

Concrete STATESConcrete STATESWhat is the hardening What is the hardening

State?State?

Hardening State : Hardening State : After concrete has After concrete has set it begins to gain set it begins to gain strength and harden. strength and harden. The propert ies of The propert ies of hardened concrete hardened concrete are strength and are strength and durabil i ty.durabil i ty.

Hardened concrete Hardened concrete wil l have no wil l have no footprints on it i f footprints on it i f walked on.walked on.

Hardening stateHardening state


Hardened Hardened ConcreteConcrete

Compressive Compressive strengthstrength

deformation

elastic creep

Concrete STATES

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Working Safely with Working Safely with ConcreteConcrete

Protect:Protect:

Your EyesYour Eyes

Your BackYour Back

Your SkinYour SkinPlacing and Finishing Placing and Finishing

ConcreteConcrete

Working the Lafarge Working the Lafarge WayWay

DateDate 2626

Transpor ting and Transpor ting and HandlingHandling


PlanningPlanning

vs

Weather condit ionsWeather condit ions

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Plastic Shrinkage Plastic Shrinkage CracksCracks Most common form of cracking in concreteMost common form of cracking in concrete

Result when high evaporation rates cause the surface of fresh concrete Result when high evaporation rates cause the surface of fresh concrete to dry outto dry out

Do not compromise structural integrity of concreteDo not compromise structural integrity of concrete

Plastic shrinkage cracks are unsightly and can, over time, cause concrete Plastic shrinkage cracks are unsightly and can, over time, cause concrete to degradeto degrade

Evaporation RateEvaporation Rate

Wind speed in excess of 5 mph Low Relative Humidity High ambient temperature Time of Day

Annex D. CSA A23.1-09

There are four main factors that contribute to the rate of evaporation in concrete:

How can time the time of day contribute to evaporation rates?

Temperature, humidity, and wind speeds will fluctuate throughout the day

These fluctuations will increase evaporation rates

As such, pours at different times during the day will yield different results with the same concrete

Using the Evaporation Using the Evaporation Rate ChartRate Chart

Annex D. CSA A23.1-09

Air temperature

Humidity

Concrete Temperature

Wind Speed

Consider the Following Example:

Air Temperature = 25°C

Humidity = 40%

Concrete Temperature = 25°C

Wind Speed = 25km/h

Evaporation Rate = 1 kg/(m2·h)

To use the Evaporation Rate Chart input current:

Evaporation Evaporation of Sur face of Sur face Moisture Moisture from from ConcreteConcrete

Hot-Weather ConcretingHot-Weather ConcretingMetricMetric

Curing Program mitric.mht

Slump Slump TestTest

Control Tests for Control Tests for ConcreteConcrete

Frequency of Testing — Frequency of Testing — SlumpSlump

First batch of concrete each dayFirst batch of concrete each day Whenever the consistency of Whenever the consistency of

concrete appears to varyconcrete appears to vary Whenever strength-test cylinders Whenever strength-test cylinders

are made at jobsiteare made at jobsite


Temperature Temperature MeasurementMeasurement

ASTM C 1064ASTM C 1064(AASHTO T 309) (AASHTO T 309)

Temperature of Temperature of Freshly Mixed Freshly Mixed Portland Cement Portland Cement ConcreteConcrete


Densit y (Unit Weight) and Densit y (Unit Weight) and YieldYield


ASTM C 138(AASHTO T 121)

Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete

ASTM C 1040 (AASHTO T 271)

Density of Unhardened and Hardened Concrete in Place By Nuclear Methods

Air ContentAir Content Pressure Pressure

methodmethodASTM C 231 ASTM C 231 (AASHTO T 152)(AASHTO T 152)

Volumetric Volumetric methodmethod ASTM C ASTM C 173 (AASHTO T 196)173 (AASHTO T 196)

Gravimetric Gravimetric methodmethod ASTM C ASTM C 138 (AASHTO T 121)138 (AASHTO T 121)

Air indicator Air indicator method method AASHTO T AASHTO T 199199


Placing and CompactingPlacing and Compacting

CONSOLIDATING CONSOLIDATING CONCRETECONCRETE

Inadequate consolidation Inadequate consolidation can result in:can result in:– HoneycombHoneycomb

Inadequate consolidation Inadequate consolidation can result in :-can result in :- Sand streaksSand streaks

Inadequate consolidation Inadequate consolidation can result in :-can result in :-

– Excessive amount of entrapped air voids Excessive amount of entrapped air voids (bugholes)(bugholes)

Inadequate consolidation Inadequate consolidation can result in :-can result in :- Placement linesPlacement lines ..


Placement lines are dark lines on the Placement lines are dark lines on the formed surface at the boundary formed surface at the boundary between adjacent batches of concrete. between adjacent batches of concrete. Generally, they indicate that the vibrator Generally, they indicate that the vibrator was not lowered far enough to penetrate was not lowered far enough to penetrate the layer below the one being vibrated.the layer below the one being vibrated.


Cold joints Cold joints ——Delays in concreting can result in cold Delays in concreting can result in cold joints. To avoid cold joints, placing should be joints. To avoid cold joints, placing should be resumedsubstantially before the time of initial set. For resumedsubstantially before the time of initial set. For unusually long delays during concreting, the concrete unusually long delays during concreting, the concrete should be kept live by periodically revibrating it. Concrete should be kept live by periodically revibrating it. Concrete should be vibrated at approximately 15 minute intervals or should be vibrated at approximately 15 minute intervals or less, depending upon job conditions. Concrete should not less, depending upon job conditions. Concrete should not be over vibrated to the point of causing segregation. be over vibrated to the point of causing segregation. Furthermore, should the concrete approach time of initial Furthermore, should the concrete approach time of initial setting, vibration should be discontinued and the concrete setting, vibration should be discontinued and the concrete should be allowed to harden. A cold joint will result, and should be allowed to harden. A cold joint will result, and suitable surface preparation measures should be appliedsuitable surface preparation measures should be applied ....

VIBRATION OF VIBRATION OF CONCRETECONCRETE

The process of compacting concrete The process of compacting concrete consists essentially of the elimination of consists essentially of the elimination of entrapped air. This can be achieved by:entrapped air. This can be achieved by:

– Tamping or rodding the concreteTamping or rodding the concrete– Use of vibrators Use of vibrators

Freshly placed, uncompact Freshly placed, uncompact concrete is usually ful l of concrete is usually ful l of entrapped air bubbles. entrapped air bubbles.

Concrete wil l only achieve a Concrete wil l only achieve a high compressive strength and high compressive strength and density with minimum air content density with minimum air content through the use of mechanical through the use of mechanical means, i. e. the introduction of means, i. e. the introduction of high-frequency (fast, repetit ive) high-frequency (fast, repetit ive) vibrations. vibrations.

Only in this way can concrete Only in this way can concrete meet today’s requirements in meet today’s requirements in terms of strength and densityterms of strength and density . .

The high-frequency vibrations The high-frequency vibrations generated by the vibrator are generated by the vibrator are transmitted to the components of transmitted to the components of the fresh concrete. the fresh concrete.

Frict ional forces between Frict ional forces between individual part icles are individual part icles are substantial ly reduced. substantial ly reduced.

A flow process is created. A f low process is created. Air bubbles, excess water and Air bubbles, excess water and

paste entrapped through capil lary paste entrapped through capil lary action and surface tensions are action and surface tensions are released and escape to the released and escape to the surface. surface.

Greater density and homogeneity Greater density and homogeneity

Greater compressive strength Greater compressive strength Greater durabil i ty (e. g. de-icing salt) Greater durabil i ty (e. g. de-icing salt)

Better bond with rebar, particularly in Better bond with rebar, particularly in densely reinforced sections densely reinforced sections

Better bond between the individually Better bond between the individually “ “wet” on “wet” placed layers wet” on “wet” placed layers

Improved quality exposed (fair-faced) Improved quality exposed (fair-faced) surfaces surfaces

Makes possible use of drier mixtures, Makes possible use of drier mixtures, thus requiring less cementthus requiring less cement

VIBRATORSVIBRATORS

Internal vibratorInternal vibrator:: The poker is immersed The poker is immersed into concrete to compact it. The poker is into concrete to compact it. The poker is easily removed from point to point.easily removed from point to point.

External vibrators:External vibrators: External vibrators External vibrators clamp direct to the formwork requiring clamp direct to the formwork requiring strong, rigid formsstrong, rigid forms..

Know your effective compaction diameter: Know your effective compaction diameter: For practical purposes and as rule of thumb consider For practical purposes and as rule of thumb consider the operating diameter to be approx. 10 times the the operating diameter to be approx. 10 times the vibrator head housing diametervibrator head housing diameter ..

Internal VibrationInternal Vibration

Radius of Action

R

1½ R

Vibrator

Internal VibratorsInternal VibratorsDiameterDiameter

of head,of head,

(m(mmm))

Recommended Recommended frequency, frequency, ((vibvib././minmin.).)

Approximate Approximate radius of radius of

action, action, ((mmmm))

Rate of Rate of placement,placement,

((mm33/h/h))ApplicationApplication

20-4020-40 9000-15,0009000-15,000 80-15080-150 0.8-40.8-4Plastic and flowing Plastic and flowing concrete in thin concrete in thin members. Also used for members. Also used for lab test specimens.lab test specimens.

30-6030-60 8500-12,5008500-12,500 130-250130-250 2.3-82.3-8

Plastic concrete in thin Plastic concrete in thin walls, columns, beams, walls, columns, beams, precast piles, thin slabs, precast piles, thin slabs, and along construction and along construction joints. joints.

50-9050-90 8000-12,0008000-12,000 180-360180-360 4.6-154.6-15Stiff plastic concrete Stiff plastic concrete (less than 80-mm (less than 80-mm slump) in general slump) in general construction . construction .

Adapted from ACI 309

Systematic VibrationSystematic Vibration

CORRECTCORRECTVertical penetration a few inches into previous lift (which should not yet be rigid) of systematic regular intervals will give adequate consolidationINCORRECTINCORRECTHaphazard random penetration of the vibrator at all angles and spacings without sufficient depth will not assure intimate combination of the two layers

Placing Concrete in a Placing Concrete in a Sloping LiftSloping Lift

Placing and Finishing ConcretePlacing and Finishing Concrete

CORRECTCORRECTStart placing at bottom of slope so that compaction is increased by weight of newly added concrete. Vibration consolidates the concrete.INCORRECTINCORRECTWhen placing is begun at top of slope the upper concrete tends to pull apart especially when vibrated below as this starts flow and removes from concrete above.

To aid in the removal of trapped air the vibrator To aid in the removal of trapped air the vibrator head should be rapidly plunged into the mix head should be rapidly plunged into the mix and slowly moved up and downand slowly moved up and down..

Internal VibratorsInternal Vibrators

The actual completion The actual completion of vibration is judged by of vibration is judged by the appearance of the the appearance of the concrete surface which concrete surface which must be neither rough must be neither rough nor contain excess nor contain excess cement paste.cement paste.


Internal vibration isInternal vibration isdone with a mechanical done with a mechanical

vibrator or pokervibrator or pokervibrator. The POKER is vibrator. The POKER is

put into concrete andput into concrete andvibrates it from the vibrates it from the

inside.inside.


MethodMethodMake sure there are enough workers so some can compact Make sure there are enough workers so some can compact

while others continue to place.while others continue to place. Put the poker into the concrete QUICKLY. Take the poker Put the poker into the concrete QUICKLY. Take the poker

out very SLOWLY otherwise a hole, or weak spot, may be out very SLOWLY otherwise a hole, or weak spot, may be left in the concrete.left in the concrete.


The SIZE of the poker determines how much concrete is vibrated at one time.The SIZE of the poker determines how much concrete is vibrated at one time.The area vibrated at one time is called the RADIUS OF ACTION. This can The area vibrated at one time is called the RADIUS OF ACTION. This can be seen by over what radius air bubbles rise to the surface.be seen by over what radius air bubbles rise to the surface.The radius of action will be greater with a LARGER poker and more-workable The radius of action will be greater with a LARGER poker and more-workable concrete.concrete.Always compact in a definite pattern so the radius of action overlaps and covers the Always compact in a definite pattern so the radius of action overlaps and covers the whole area of the concrete.whole area of the concrete.


The poker should be long The poker should be long enough to reach and enter enough to reach and enter into the layers of concrete into the layers of concrete under the one being under the one being compactedcompacted..

PRECAUTIONS Taking the poker out TOO QUICKLY will leave a hole in the concrete. To close the hole, vibrate near the hole and take the poker out VERY SLOWLY.


NEVERNEVER touch the form face with the poker as it can touch the form face with the poker as it can

damage the formwork and the concrete.damage the formwork and the concrete.


NEVERNEVER touch the reinforcement with the poker.touch the reinforcement with the poker.


NEVERNEVER spread or move concrete sideways spread or move concrete sideways with the poker, always use a shovel.with the poker, always use a shovel.

NEVERNEVER leave the poker running when not in use.leave the poker running when not in use.


HOW LONG TO COMPACT HOW LONG TO COMPACT For For concrete of average workability (ie slump of concrete of average workability (ie slump of 80 mm)80 mm)

with a poker size between 25–75 mm, with a poker size between 25–75 mm, concrete should usually be vibrated for concrete should usually be vibrated for betweenbetween

5 and 15 seconds. 5 and 15 seconds. It is worse to It is worse to UNDER-VIBRATEUNDER-VIBRATE than to than to

OVER-VIBRATEOVER-VIBRATE concrete. concrete.

Segregation Segregation refers to a separation of the components refers to a separation of the components of fresh concrete, resulting in a non-uniform mix of fresh concrete, resulting in a non-uniform mix

Sp.Gr. Size

Cement 3-3.15 5-80 µm

C.Agg. 2.4-2.8 5-40 mm

F.Agg. 2.4-2.8 < 5 mm

SEGREGATIONSEGREGATION

The primary causes of The primary causes of segregation are differences segregation are differences in specific gravity and size in specific gravity and size of constituents of concrete. of constituents of concrete. Moreover, improper mixing, Moreover, improper mixing, improper placing and improper placing and improper consolidation also improper consolidation also lead to segregation.lead to segregation.

Some of the factors affecting segregation:Some of the factors affecting segregation:– Larger maximum particle size (25mm) and Larger maximum particle size (25mm) and

proportion of the larger particles. proportion of the larger particles. – High specific gravity of coarse aggregate. High specific gravity of coarse aggregate. – Decrease in the amount of fine particles. Decrease in the amount of fine particles. – Particle shape and texture. Particle shape and texture. – Water/cement ratio.Water/cement ratio.

SEGREGATIONSEGREGATION

Bleeding is the tendency of water to rise to Bleeding is the tendency of water to rise to the surface of freshly placed concrete. the surface of freshly placed concrete.

BLEEDINGBLEEDING

It is caused by the It is caused by the inability of solid inability of solid constituents of the constituents of the mix to hold all of the mix to hold all of the mixing water as mixing water as they settle down.they settle down.

A special case of A special case of segregation.segregation.

Undesirable effects of bleeding areUndesirable effects of bleeding are::

BLEEDINGBLEEDING

Undesirable effects of bleeding are:Undesirable effects of bleeding are:

• With the movement of water towards the top, the top portion With the movement of water towards the top, the top portion becomes weak & porous (high w/c). Thus the resistance of becomes weak & porous (high w/c). Thus the resistance of concrete to freezing-thawing decreases.concrete to freezing-thawing decreases.

• Water rising to the surface carry fine particles of cement Water rising to the surface carry fine particles of cement which weaken the top portion and form laitance. This portion which weaken the top portion and form laitance. This portion is not resistant to abrasion.is not resistant to abrasion.

• Water may accumulate under the coarse agg. and Water may accumulate under the coarse agg. and reinforcement. These large voids under the particles may reinforcement. These large voids under the particles may lead to weak zones and reduce the bond between paste and lead to weak zones and reduce the bond between paste and agg. or paste and reinforcement. agg. or paste and reinforcement.

BLEEDINGBLEEDING


BLEEDINGBLEEDING

Cross section view of concrete illustrating bleed water accumulation along a coarse aggregate particle.

BLEEDINGBLEEDING


Imprint in concrete illustrating the collection of bleed water voids under a smooth steel bar held firmly in ahorizontal position during and after placement

The tendency of concrete to bleeding The tendency of concrete to bleeding depends largely on properties of depends largely on properties of cement.cement. It is decreased by:It is decreased by:

Increasing the fineness of cementIncreasing the fineness of cement Increasing the rate of hydration (CIncreasing the rate of hydration (C33S, CS, C33A and A and

alkalies)alkalies) Adding pozzolansAdding pozzolans Reducing water contentReducing water content Use more cement if paste content is low. Use more cement if paste content is low.

BLEEDINGBLEEDING

In general, the bleeding tendencies of concrete can beIn general, the bleeding tendencies of concrete can be reduced significantly by the following actions. Every reduced significantly by the following actions. Every reasonable effort should be made to take such measures reasonable effort should be made to take such measures when bleeding is a problem :-when bleeding is a problem :-1. Correct any aggregate gradation deficiency problem 1. Correct any aggregate gradation deficiency problem where materials of the required size gradations are where materials of the required size gradations are economically available. The use of gap-graded aggregates economically available. The use of gap-graded aggregates results in increased bleeding. Ideally, combined gradation of results in increased bleeding. Ideally, combined gradation of all aggregates should yield a percent retained on each sieve all aggregates should yield a percent retained on each sieve below the largest and above the No. 100 (150 μm) of below the largest and above the No. 100 (150 μm) of somewhere between 8 and 18%. The most common somewhere between 8 and 18%. The most common deficiency is in the 3/8 in., No. 4, 8, or 16 (9.5, 4.75, 2.36, or deficiency is in the 3/8 in., No. 4, 8, or 16 (9.5, 4.75, 2.36, or 1.18 mm) sieve sizes.1.18 mm) sieve sizes.

BLEEDINGBLEEDING

2- Increase the amount of fine aggregate passing the No. 2- Increase the amount of fine aggregate passing the No. 50,100, and 200 (300, 150, and 75 μm) sieves to near the50,100, and 200 (300, 150, and 75 μm) sieves to near the

maximum allowable amount. More water (and possiblymaximum allowable amount. More water (and possibly more cement) may be needed due to more paste beingmore cement) may be needed due to more paste being required; more shrinkage could result.required; more shrinkage could result.3 -Avoid admixtures that augment bleeding.3 -Avoid admixtures that augment bleeding.4 - Use concrete approaching the highest as-placed4 - Use concrete approaching the highest as-placed temperature permitted by the contract documents. (Note:temperature permitted by the contract documents. (Note: Except for bleeding, there are benefits to be derived fromExcept for bleeding, there are benefits to be derived from placing concrete at the lowest permissible temperature.)placing concrete at the lowest permissible temperature.) 5- Use dewatering techniques5- Use dewatering techniques

BLEEDINGBLEEDING

MIXING OF CONCRETEMIXING OF CONCRETE

The aim of mixing is to blend all of the The aim of mixing is to blend all of the ingredients of the concrete to form a ingredients of the concrete to form a uniform mass and to coat the surface of uniform mass and to coat the surface of aggregates with cement paste.aggregates with cement paste.

MIXING OF CONCRETEMIXING OF CONCRETE

Ready-Mix concrete: In this type Ready-Mix concrete: In this type ingredients are introduced into a mixer ingredients are introduced into a mixer truck and mixed during transportation to truck and mixed during transportation to the site. the site.

• Wet – Water added before transportationWet – Water added before transportation• Dry – Water added at siteDry – Water added at site

Mixing at the siteMixing at the site• Hand mixedHand mixed• Mixer mixedMixer mixed

Placing and CompactingPlacing and Compacting

Protection and CuringProtection and Curing

JointsJoints

construction

of ?

movement

Concrete ToppingsConcrete Toppings

of

4 x top size of aggregate (min recommended 50mm)

scrabble slurry

joint

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concrete basicss for gem

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