WATERWATER

Water requirement in concreteWater requirement in concrete

Minimum water required for hydration Minimum water required for hydration reaction - reaction - 23%23% ( by wt of cement) ( by wt of cement) Further requirement for continued hydration- Further requirement for continued hydration-

15%15% (by wt. Of cement) (by wt. Of cement)

Total requirement thus = Total requirement thus = 38%38% Any excess causes Any excess causes ‘CAPILLARY ‘CAPILLARY

FORMATION’ FORMATION’ and results intoand results into

Less strengthLess strengthLess durability Less durability

                                                                                                     

              

                                                                                                     

              

WaterWater

It should be clean &free from It should be clean &free from oils,acids,alkalis,salts,sugar,organioils,acids,alkalis,salts,sugar,organic materials etc.c materials etc.

The pH value not less than 6.The pH value not less than 6. If water is satisfactory for mixing, If water is satisfactory for mixing,

it is safe for curing.it is safe for curing. No strain on curingNo strain on curing

LimitsLimits Chlorides Chlorides shouldn’t be more than shouldn’t be more than 10,000 ppm 10,000 ppm Sulphates Sulphates shouldn’t be more than shouldn’t be more than 3,000 ppm 3,000 ppm Turbidity Turbidity shouldn’t be more than shouldn’t be more than 2,000 ppm 2,000 ppm Carbonate & bi Carbonate Carbonate & bi Carbonate if more than if more than

2,000 ppm tests for setting time & 2,000 ppm tests for setting time & strength be conductedstrength be conducted

(causes quick setting )(causes quick setting )

MixingMixing

MIXING MIXING

Mixing should ensure that mass becomesMixing should ensure that mass becomes– HomogeneousHomogeneous– Uniform in colourUniform in colour– Uniform in consistencyUniform in consistency

Types of mixing Types of mixing – Hand mixing (generally not recommended. Hand mixing (generally not recommended.

If used then 10% extra cement to be usedIf used then 10% extra cement to be used but but not to the advantage of contractor)not to the advantage of contractor)

– Machine mixing – efficient and economicalMachine mixing – efficient and economical

MIXING (contd - ii)MIXING (contd - ii)

MACHINE MIXINGMACHINE MIXINGBatch mixerBatch mixerContinuousContinuous

Batch Mixers Batch Mixers – Pan typePan type

– Drum typeDrum type» Tilting Tilting » Non tiltingNon tilting» Reversing or forced actionReversing or forced action

P1500

                                                                                               

MIXING (contd - iii)MIXING (contd - iii)

Designation of mixers (As per IS : Designation of mixers (As per IS : 1791 – 1968)1791 – 1968)

Tilting – 85T, 100T, 140T, 200TTilting – 85T, 100T, 140T, 200T Non Tilting – 200 NT, 280 NT, 340 Non Tilting – 200 NT, 280 NT, 340

NT, 400 NT, 800 NTNT, 400 NT, 800 NT Reversing – 200R, 280 R, 340R, 400R.Reversing – 200R, 280 R, 340R, 400R.

Figures – capacity in litres.Figures – capacity in litres.

MIXING (contd -vi)MIXING (contd -vi)

MIXING TIMEMIXING TIME 25 to 30 revolution @ 15-20 rpm 25 to 30 revolution @ 15-20 rpm

is minimum required for proper is minimum required for proper mixing. Therefore 2 minute mixing is mixing. Therefore 2 minute mixing is desirable. desirable.

Mixing is faster in natural aggregatesMixing is faster in natural aggregates

WORKABILITYWORKABILITY

WorkabilityWorkability

CompactibilityCompactibility- or ease with which - or ease with which concrete can be compactedconcrete can be compacted

MobilityMobility- or ease with which concrete - or ease with which concrete can flow into formwork & around can flow into formwork & around reinforcement.reinforcement.

StabilityStability- or ability of concrete to - or ability of concrete to remain stable, cohesive and remain stable, cohesive and homogeneous mass while handling, homogeneous mass while handling, vibrating without segregationvibrating without segregation

Categories of WorkabilityCategories of Workability

CategoryCategory CFCF Slump Slump mmmm

Vee Bee Vee Bee secsec

Extremely Extremely lowlow

0.680.68 00 > 20> 20

V. LowV. Low 0.780.78 0-100-10 7-207-20

LowLow 0.850.85 10-2510-25 5-105-10

MediumMedium 0.920.92 25-5025-50 3-53-5

HighHigh 0.950.95 50-12550-125 2-32-3

V. HighV. High 0.970.97 125-200125-200 0-20-2

SLUMP TESTSLUMP TEST

Vessel shape – frustum of cone of 30 cm ht. Vessel shape – frustum of cone of 30 cm ht. 10 cm. dia at top & 20 cm at bottom10 cm. dia at top & 20 cm at bottom

Concrete filled in four layers each Concrete filled in four layers each compacted with 25 strokes of bullet points compacted with 25 strokes of bullet points 16 mm dia, 60 cm long, steel rod. 16 mm dia, 60 cm long, steel rod.

Cone is removed & concrete allowed to Cone is removed & concrete allowed to settle vertical settlement is ‘settle vertical settlement is ‘SLUMPSLUMP.’ .’

COMPACTION FACTOR TESTCOMPACTION FACTOR TEST

Here workability Here workability

is the amount of work required is the amount of work required

to place concrete and to compact it thoroughlyto place concrete and to compact it thoroughly Two hoppers are one above other and cylindrical Two hoppers are one above other and cylindrical

mould 30 cm. high, 15 cm dia at bottom to collect mould 30 cm. high, 15 cm dia at bottom to collect concrete. Wt. Of concrete collected in cylinder concrete. Wt. Of concrete collected in cylinder divided by theoretical wt. of concrete gives divided by theoretical wt. of concrete gives CFCF..

VEE BEE TESTVEE BEE TEST

Vibrating table 36 x 26 cm, with fixed Vibrating table 36 x 26 cm, with fixed cylindrical container & a transparent disc. cylindrical container & a transparent disc.

Ordinary slump test done by putting cone Ordinary slump test done by putting cone into the cylinder. Slump measured with into the cylinder. Slump measured with plastic disc. plastic disc.

Then vibration started with disc resting on Then vibration started with disc resting on concrete, concrete,

Time required for the concrete to take Time required for the concrete to take horizontal surface in sec. is Vee Bee degreehorizontal surface in sec. is Vee Bee degree . .

FACTORS AFFECTING WORKABILITYFACTORS AFFECTING WORKABILITY

WaterWater Size of particlesSize of particles CA/FA ratioCA/FA ratio Particle interference – gap grading helpsParticle interference – gap grading helps Shape of aggregatesShape of aggregates Admixtures – Air entraining agents, Admixtures – Air entraining agents,

pozzolanas.pozzolanas.

Effect of inadequate Effect of inadequate workability workability

Honey combingHoney combing Less strength Less strength Less durabilityLess durability

PLACEMENTPLACEMENT

Methods of transportationMethods of transportation

1.1. Mortar panMortar pan

2.2. Wheel barrow/hand cartWheel barrow/hand cart

3.3. Bucket & rope wayBucket & rope way

4.4. Truck mixer & dumperTruck mixer & dumper

5.5. Belt conveyorBelt conveyor

6.6. ChuteChute

7.7. Skip & hoistSkip & hoist

8.8. Pump & pipe line ( 8-70 cum concrete/ hr)Pump & pipe line ( 8-70 cum concrete/ hr)

8-20 cm pipe, mix should be truly plastic8-20 cm pipe, mix should be truly plastic

Spherical ball to clean the pipe called Spherical ball to clean the pipe called ‘GO DEVIL’‘GO DEVIL’

COMPACTIONCOMPACTION

Expulsion of entrapped airExpulsion of entrapped air

Each 1% entrapped air reduces Each 1% entrapped air reduces 6% strength6% strength

Methods of compactionMethods of compaction RoddingRodding RammingRamming TampingTamping Internal vibrationInternal vibration External vibrationExternal vibration Surface vibrationSurface vibration Platform or table vibrationPlatform or table vibration

Details of equipmentDetails of equipment

Frequency RangeFrequency Range- 100 Hz for 40 mm agg.- 100 Hz for 40 mm agg.-150 Hz for 20 mm agg.-150 Hz for 20 mm agg.- 200 Hz for 10 mm agg.- 200 Hz for 10 mm agg.

Needle DiameterNeedle Diameter-20 mm to 75 mm (length- 25 to 90 cm.)-20 mm to 75 mm (length- 25 to 90 cm.)

Thickness of layerThickness of layer- Not less than 100 mm, not more than 600mm- Not less than 100 mm, not more than 600mm

-preferably bet. 2/3 L to L of needle -preferably bet. 2/3 L to L of needle

Proper Internal VibrationProper Internal Vibration

Increase compressive strength & bondIncrease compressive strength & bond Decrease permeabilityDecrease permeability Decrease cold jointsDecrease cold joints Decrease honeycombingDecrease honeycombing Decrease excessive entrapped air Decrease excessive entrapped air Decrease segregationDecrease segregation

Spacing tipsSpacing tips

Overlapping field of actionOverlapping field of action Watch the concreteWatch the concrete High powered vibratorsHigh powered vibrators High slump concreteHigh slump concrete Field of action 8 times vibrators’ Field of action 8 times vibrators’

head diameterhead diameter

Stop vibration - whenStop vibration - when

Concrete surface- shining Concrete surface- shining appearanceappearance

Large air bubbles no longer escapeLarge air bubbles no longer escape Vibration change pitch or toneVibration change pitch or tone Over vibration is preferable to Over vibration is preferable to

under vibrationunder vibration

curingcuring

CURING OF CONCRETECURING OF CONCRETE

Curing is a procedure used for Curing is a procedure used for – Promoting the hydration of cementPromoting the hydration of cement– Control of temp and humidityControl of temp and humidity

As a result of curing As a result of curing – Strength is improvedStrength is improved– Durability is improved and permeability of Durability is improved and permeability of

concrete is reduced. concrete is reduced.

WHY CURING IS IMPORTANT ?WHY CURING IS IMPORTANT ?

Hydration progresses only when pores are Hydration progresses only when pores are saturated (80% relative humidity is reqd.)saturated (80% relative humidity is reqd.)

Initially the concrete has sufficient amount Initially the concrete has sufficient amount of water to begin with hydration. Water is of water to begin with hydration. Water is lost with time due to lost with time due to – EvaporationEvaporation

– Self desiccation (Relative humidity fallSelf desiccation (Relative humidity fall

below 80% due to hydration reaction)below 80% due to hydration reaction)

METHOD OF CURINGMETHOD OF CURING

Replenishing lost waterReplenishing lost water– ImmersionImmersion– PondingPonding– SprinklingSprinkling– Saturated covering i.e. Jute bagsSaturated covering i.e. Jute bags

Preventing moisture lossPreventing moisture loss– Curing compounds Curing compounds – Impermeable membrane covering. Impermeable membrane covering.

PERIOD OF CURINGPERIOD OF CURING

As per IS : 456 for OPC – 7 daysAs per IS : 456 for OPC – 7 days As per IRS : CBC for OPC – 14 daysAs per IRS : CBC for OPC – 14 days

Curing mainly depends uponCuring mainly depends upon– Type of cementType of cement

– Ambient atmospheric conditionAmbient atmospheric condition

– Mass to surface area ratio Mass to surface area ratio

CURING (cont..)CURING (cont..)

The process of curing shouldn’t be The process of curing shouldn’t be interrupted interrupted

Because Partial hydration makes Because Partial hydration makes capillaries discontinuous & on curing capillaries discontinuous & on curing again water may not enter the concreteagain water may not enter the concrete

High strength concrete should be cured High strength concrete should be cured at an early stageat an early stage. .

PRACTICAL ASPECTS IN PRACTICAL ASPECTS IN RELATION TO CURINGRELATION TO CURING

Widespread belief that humid climate Widespread belief that humid climate is sufficient for curingis sufficient for curing

Generally the person responsible for Generally the person responsible for curing is most unskilled. He doesn’t curing is most unskilled. He doesn’t appreciate the importance & therefore appreciate the importance & therefore doesn’t care much doesn’t care much

Curing is not a measurable item in the Curing is not a measurable item in the agreementagreement. .

CURING (cont..)CURING (cont..) It is better to It is better to

– Use curing compoundsUse curing compounds– Curing be kept as a separately payable item in bill of Curing be kept as a separately payable item in bill of

paymentpayment– Keep a set of cube in vicinity of structure & let it be Keep a set of cube in vicinity of structure & let it be

cured in the same way as the structure. Strength & cured in the same way as the structure. Strength & Permeability test on these cubes will reveal the Permeability test on these cubes will reveal the historyhistory

– Educate the person responsible for curing. Educate the person responsible for curing.

EFFECT OF CURING ON EFFECT OF CURING ON PERMEABILITY AND POROSITYPERMEABILITY AND POROSITY

Permeability (m/sec unit x 10Permeability (m/sec unit x 10-17-17)) Porosity (%)Porosity (%)

Curin Curin (days)/(days)/

W/CW/C

11 33 77 2828 9090 11 33 77 2828 9090

0.320.32 5.605.60 0.300.30 0.120.12 Very Very lowlow

Very Very lowlow

20.8020.80 19.719.7 14.414.4 9.809.80 5.905.90

0.400.40 18.7018.70 0.590.59 0.070.07 0.070.07 ”” 33.3033.30 28.628.6 20.920.9 16.8016.80 11.1011.10

0.500.50 214.0214.0 14.714.7 2.352.35 0.190.19 ”” 43.5043.50 37.837.8 32.232.2 20.8020.80 14.5014.50