1 Concrete ppt

Slide 1

Tuesday, July 28, 2015Prof. V.M.Agrawal1

Construction Methods and Techniques1Tuesday, July 28, 2015Prof. V.M.Agrawal2Concrete TechnologyConcrete batchingMixingTransportingPlacingCompactingCuringfinishing

2Tuesday, July 28, 2015Prof. V.M.Agrawal3What is ConcreteConcrete is one of the most commonly used building materials.Concrete is a composite material made from several readily available constituents (fine and coarse aggregates, cement, water), and admixtures (when required).3Tuesday, July 28, 2015Prof. V.M.Agrawal4What is ConcreteOrdinarily concrete is made by mixing an inorganic material known as cement with water together with natural sand or stone dusts and natural stones which may be uncrushed or crushed.

Concrete is a versatile material that can easily be mixed to meet a variety of special needs and formed to virtually any shape.4Tuesday, July 28, 2015Prof. V.M.Agrawal5Advantages of concreteAbility to be castEconomical DurableFire resistantEnergy efficientOn-site fabrication

5Tuesday, July 28, 2015Prof. V.M.Agrawal6Disadvantages of concreteLow tensile strengthLow ductilityVolume instabilityLow strength to weight ratio

6Tuesday, July 28, 2015Prof. V.M.Agrawal7Constituents of concreteCementWater Fine AggregateCoarse AggregateAdmixtures

7Tuesday, July 28, 2015Prof. V.M.Agrawal8CementMost commonly used cement is called Portland Cement patented in 1824 in England, when mixed with water, hardens, hence hydraulic cement . Basic raw materials used in the manufacture of cement are calcium carbonate found in lime Stone or chalk, and silica, alumina and iron oxide found in clay or shale. 8Tuesday, July 28, 2015Prof. V.M.Agrawal9Aggregate

Cement sand mortarCoarse aggregateAggregates forms the skeleton matrix 60-75% by volume. 25-40% Paste & 1-2% Voids.

Aggregate shall be inert and strong.

9Tuesday, July 28, 2015Prof. V.M.Agrawal10AdmixturesChemical Admixture: Used for specific Property/performance enhancement.Mineral Admixture: Used for improvement of long term strength and durability performance.Using above admixtures together, high Strength and high performance concrete Materials can be designed.

10Tuesday, July 28, 2015Prof. V.M.Agrawal11Designation Of Normal Strength ConcreteConcrete is designated through 28 day Standard cube compressive strength.

In Indian Standard Code of practice (IS 456) a concrete is designated by its characteristic cube compressive strength at 28 days, the cube being cast, cured and tested in a standard manner.

11Tuesday, July 28, 2015Prof. V.M.Agrawal12Performance Of ConcreteNormal strength concrete: 60MPaHigh strength concrete: 60f C120MPa.Ultra High strength concrete: 120MPa.

Performance at fresh state: Self CompactingLong term durability performance.12Tuesday, July 28, 2015Prof. V.M.Agrawal13Concrete Process

13Tuesday, July 28, 2015Prof. V.M.Agrawal14Batching of concreteThe measurement of materials for making concrete is known as batching.The two methods of batching are:Volume batchingPoor method of proportioning materials.Used for small scale workUsed for unimportant concretingWeight batching (IS456:2000)Correct and good method of proportioning materialsUsed for all work (mandatory for all large scale work)14Tuesday, July 28, 2015Prof. V.M.Agrawal15Volume batchingTypical gauge box is used to measure volume of materials50 kg of cement = 35 litresWater can be measured in litres or in kg. Bulking of sand makes the proportioning inaccurate.

15Tuesday, July 28, 2015Prof. V.M.Agrawal16Volume of various gauge boxesItemWidth (cm)Height (cm)Depth (cm)Volume (litres)A33.33302020B33.33302525C33.33303030D33.33303535E33.33304040F33.33304545G33.3330505033.33 cm = 13 inch30.00 cm = 12 inch

16Tuesday, July 28, 2015Prof. V.M.Agrawal17Batch volume of materials for various mixesGrade of concreteCement (kg)Water (litres)Fine agg. (litres)Coarse agg. (litres)1:5:10 (M5)50351753501:4:8 (M7.5)50351402801:3:8 (M10)50351052101:2:4 (M15)5035701401:1.5:3 (M20)503552.51051:1:2 (M25)5035357017Tuesday, July 28, 2015Prof. V.M.Agrawal18Weight batchingAccurate method of proportioningWeight balance are used for weighting the materials (generally attached with the mixer )1 bag of cement = 50 kgWater can me measured in kg or in liters.

18Tuesday, July 28, 2015Prof. V.M.Agrawal19Mixing of concreteThrough mixing of the materials is essential for the production of uniform concrete.Mixing facilitates concrete to become homogenous, uniform in colour and consistency.The two methods of mixing concrete are:Hand mixingUsed for small scale work.Used for unimportant concreting10-20 % extra cement should be added to cater the inferior concrete quality.Machine mixingAccurate method of mixingUsed for all scale of works.Mandatory requirement for RCC work.Economical if quantity is large.19Tuesday, July 28, 2015Prof. V.M.Agrawal20Machine mixing20Tuesday, July 28, 2015Prof. V.M.Agrawal21Drum type mixer

21Tuesday, July 28, 2015Prof. V.M.Agrawal22Non-tilting type mixer The non-tilting drum mixer implies that the orientation of the drum is fixed. The materials are added at one end and discharged at the other

22Tuesday, July 28, 2015Prof. V.M.Agrawal23Non-tilting type mixer Slow rate of discharge.SegregationHopper or chute is used to charge the ingredients.

23Tuesday, July 28, 2015Prof. V.M.Agrawal24Non-tilting type mixer

24Tuesday, July 28, 2015Prof. V.M.Agrawal25Tilting type mixer The tilting drum mixer allows the inclination to drum.Drum axis usually is 15 degree from horizontal during mixing.

25Tuesday, July 28, 2015Prof. V.M.Agrawal26Tilting type mixer Conical or bowl shaped drum with vanes.Discharge is rapid and segregation is less.

26Tuesday, July 28, 2015Prof. V.M.Agrawal27Tilting type mixer

27Tuesday, July 28, 2015Prof. V.M.Agrawal28Reversing type mixer The reversing drum is similar to the non-tilting mixer except that the same opening is used to add the constituents and to discharge concrete. The drum rotates in one direction for mixing and in the opposite direction for discharging the concrete.Two sets of blades are arranged spirally to obtain the desired effect for discharge and mixing

28Tuesday, July 28, 2015Prof. V.M.Agrawal29Pan type mixer

It is forced action mixer unlike drum type.Circular pan rotating about a vertical axis.Vanes or scraper is provided, it ensures through mixing of ingredients.29Tuesday, July 28, 2015Prof. V.M.Agrawal30Pan type mixer

30Tuesday, July 28, 2015Prof. V.M.Agrawal31Continuous type mixer Materials are continuously fed into the mixer at the same rate as the concrete is discharged. Usually used are non-tilting drums with screw-type blades rotating in the middle of the drum. These mixers are used for applications that require a short working time, long unloading time, remote sites (not suitable for ready-mix) and/or small deliveries.Due to the short mixing time, the air content is not easily controlled even with the addition of air entraining admixtures.31Tuesday, July 28, 2015Prof. V.M.Agrawal32Batching PlantComponents of a Batching Plant

1. Aggregate bins for various types of aggregates.2. Feeding mechanisms such as scrappers, conveyors or hoists etc. to transfer aggregate to scales (balances).3. Balance and measuring system.

32Tuesday, July 28, 2015Prof. V.M.Agrawal33Batching PlantComponents of a Batching Plant

4.Cement silos and a conveyor screw or bucket conveyor.5.The storage tank for water and water measuring system.6.Dispenser for chemical (liquid) admixture.33Tuesday, July 28, 2015Prof. V.M.Agrawal34Batching Plant

34Tuesday, July 28, 2015Prof. V.M.Agrawal35Ready Mix Concrete (RMC)

35Tuesday, July 28, 2015Prof. V.M.Agrawal36Batching plant typePlant Type can be cyclic or continuous. Plant Type can be automatic or manual.Accuracy: Recommendation of IS 456 is 2% for the quantity of cement measured and 3% for the quantity of aggregate, water and admixture being measured. 36Tuesday, July 28, 2015Prof. V.M.Agrawal37Plant CapacityCapacity depends on 1) size of the job; 2) required production rate; and 3) required standard of batching performance.

Capacity of the material handling system, bin size, batcher size and; mixture size and number controls the capacity Q=min(Q1, Q2, Q3, Q4..) 37Tuesday, July 28, 2015Prof. V.M.Agrawal38Instrumentation and MeasurementsMechanical lever system, load cells etc for measurements of mass.Controlling the discharge from storage and weigh hoppers is through gates operated by compressed air cylinders.Presetting of desired batch weights can be done by devices such as punched cards, digit switches or rotating dials and computers. 38Tuesday, July 28, 2015Prof. V.M.Agrawal39Instrumentation and MeasurementsElectrical or microwave moisture gauges can be used as aggregate moisture meters . Water is most commonly measured through flow meters, although in some plants water is also weighed .With the need of adequate calibration, frequent regulatory routine and specialists checks of weighing process are required.39Tuesday, July 28, 2015Prof. V.M.Agrawal40Tolerance Individual batch IS 4526:2004

40Tuesday, July 28, 2015Prof. V.M.Agrawal41Tolerance Individual batch IS 4526:2004Tolerances applies to:Minimum weight (kg) =[0.3scale capacity (kg)] /Weigh tolerance (%) (as in table)Uniform concrete exhibits less variation.Variation depends on variation in proportions-e.g., higher C and W, (the errors in cement & water measurements) will result in higher variation in strength.Proper Batching ensures better quality





Non agitating trucks are used with central batch plants45Tuesday, July 28, 2015Prof. V.M.Agrawal46Ready Mix Concrete (RMC) Non agitating trucks are used with central batch plants

Truck Agitators46Tuesday, July 28, 2015Prof. V.M.Agrawal47Ready Mix Concrete (RMC)


48Tuesday, July 28, 2015Prof. V.M.Agrawal49Types of Mixers as per Code IS 1791:1985Tilting Mixer85 T100 T140 T200 TNon Tilting Mixer200 NT280 NT375 NT500 NT1000 NTReversible Mixer100 R280 R375 R500 R1000 RT = TiltingNT = Non Tilting R = ReversibleThe value denotes the capacity of drum in liters.

Margin: Mixers, when operating, shall be capable of holding and mixing an actual mixing batch 10 percent in excess of the nominal mixed batch capacity49Tuesday, July 28, 2015Prof. V.M.Agrawal50Mixing time Mixing time should be sufficient to produce a uniform concrete. The time of mixing depends on the type of mixer and also to some properties of fresh concrete.Concrete mixers are designed to run at a speed of 15 to 20 rpm. For proper mixing, 25 to 30 revolutions are necessary.Hence, 1.5 to 2 minutes of mixing ensures the homogeneity.Strength of concrete increases with mixing time, but with mixing time beyond 2 min does not make any significant change in compressive strength of concrete.Undermixing non-homogeneityOvermixing danger of water loss, brekage of aggregate particles50Tuesday, July 28, 2015Prof. V.M.Agrawal51Mixing time IS 4925-1968 mixing time for each batch of materials, except the full amount of water, provided that all the mixing water shall be introduced before one-fourth the mixing time elapsed shall be 1, 2 and 2minutes respectively for mixer capacity up to 2 m3, 3 m3 and 4 m3 respectively.IS 456 : 2000 guidelines specifies a overall minimum mixing time of 2 minutes.51Tuesday, July 28, 2015Prof. V.M.Agrawal52Mixing time Increasing mixing time may result in more uniform distribution of hydration product resulting in higher compressive strength.Prolonging the mixing process too long may not increase the strength proportionally and may result in a decrease in some cases.Over grinding of the material and in some cases may increase the proportion of fines.Quite often excessive mixing leads to segregation in case of leaner concretes. 52Tuesday, July 28, 2015Prof. V.M.Agrawal53Mixing time

53Tuesday, July 28, 2015Prof. V.M.Agrawal54Mixing time IS 4925:2004

54Tuesday, July 28, 2015Prof. V.M.Agrawal55Some specific requirements Specimen enquiry format IS 4925:2004 , Annex A

Material Testing RequirementsIS 4926:2003 , Annex B

Concrete Mix Information IS 4926:2003 , Annex D

55Tuesday, July 28, 2015Prof. V.M.Agrawal56Ready Mix ConcreteReady mixed concrete production is a process, where by, mixing and transportation of concrete can be combined together and the product is delivered to the site, at times right in the mould straight away.

IS-4926:, the definition of Ready mixed concrete is: Concrete delivered at site or in to the purchasers vehicle in a plastic condition and requiring no further treatment before being placed in position in which it is to set and harden.

56Tuesday, July 28, 2015Prof. V.M.Agrawal57Truck Mixer

57Tuesday, July 28, 2015Prof. V.M.Agrawal58Agitator truck

58Tuesday, July 28, 2015Prof. V.M.Agrawal59Agitator truck

59Tuesday, July 28, 2015Prof. V.M.Agrawal60Ready Mix ConcreteUniformity and loss of slump are two major issues.Time of haul is restricted to 1+ to 2 hours, also depends upon the ambient temperature, for higher ambient temperature the time of haul is lesser.The maximum number of revolutions of the mixing drum is limited to 300 revolutions at agitating speed and that at mixing speed is 100.60Tuesday, July 28, 2015Prof. V.M.Agrawal61Slump loss in RMC

61Tuesday, July 28, 2015Prof. V.M.Agrawal62Strength Loss In Remixing

62Tuesday, July 28, 2015Prof. V.M.Agrawal63Basis of supplyReady-mixed concrete shall be supplied having the quality and in the quantity in accordance with the requirements agreed with the purchaser or his agent.

All concrete will be supplied and invoiced in terms of cubic metres (full or part) of compacted fresh concrete. All proportioning is to be carried out by mass except water and admixture, which may be measured by volume.63Tuesday, July 28, 2015Prof. V.M.Agrawal64Transportation of concrete from RMCReady-mixed concrete shall be transported from the mixer to the point of placing as rapidly as practicable by methods that will maintain the required workability and will prevent segregation, loss of any constituents or ingress of foreign matter or water.

The concrete shall be placed as soon as possible after delivery, as close as is practicable to its final position to avoid rehandling or moving the concrete horizontally by vibration.64Tuesday, July 28, 2015Prof. V.M.Agrawal65Time in TransportThe general requirement is that concrete shall be discharged from the truck-mixer within 2 h of the time of loading.

However, a longer period may be permitted if retarding admixtures are used or in cool humid weather or when chilled concrete is produced.

The time of loading shall start from adding the mixing water to the dry mix of cement and aggregate or of adding the cement to the wet aggregate whichever is applicable.65Tuesday, July 28, 2015Prof. V.M.Agrawal66Transporting of concretePrecautions to avoid DelaysSegregationEarly Stiffening and drying out.

Means of transporting concreteMortar panWheel barrow, hand cartCrane bucket and ropewayTruck mixer and dumpersBelt conveyersChuteTransit mixerPump and pipe line

66Tuesday, July 28, 2015Prof. V.M.Agrawal67Transporting of concreteMortar panLabour intensive Small quantity transfer Early drying of upper surface while transporting, due to larger exposed surface area .Drying becomes a severe matter of concern in hot climatic conditionsWheel barrow and hand cartUsed for ground floor or for same floor concretingWhen used in uneven surface, due to vibration, concrete segregates.

67Tuesday, July 28, 2015Prof. V.M.Agrawal68Transporting of concreteCrane, Bucket and Rope wayBest way to transport concrete above ground floorHigh rise construction necessarily needs this systemFast and versatile to move in horizontal and vertical directionAllows placement of concrete at exact location (Eg. Column)Facilitates concreting in river bridges, valley, dam construction etc.Truck Mixer and DumpersUsed for Mass concreting in ground level, generally concrete pavementAgitators should be used to prevent segregation and stiffening68Tuesday, July 28, 2015Prof. V.M.Agrawal69Transporting of concreteBelt conveyersIt has limited applicationsConcrete segregates in conveyers due to steep inclines, transfer points, change of direction, points above rollers.Drying and stiffening problem due to long exposed surface for longer duration.Segregation due to vibration of belt.Used in places where access is limited.Good for the transporting large volume of concrete quickly.Whenever this method is used, the concrete should be remixed at the end of delivery before placing in final position.

69Tuesday, July 28, 2015Prof. V.M.Agrawal70Transporting of concreteChuteUsed to transfer concrete from a higher level to a lower level.Good for foundation concretingSegregation of concrete due to dumping effect.Skip and hoistUsed for vertical transportation of concrete in buildingsSegregation depends on vibration while travelling upward and condition of wheel rail assembly.If travelled for considerable height, slight remixing is advisible before placing.70Tuesday, July 28, 2015Prof. V.M.Agrawal71Transporting of concreteTransit mixersUsed to transport concrete from RMC Plants.Most popular and effective way for long distance transporting.These are truck mounted having a capacity of 4 to 7 cubic meters.Two variants of transit mixer are available in the industry:Mixed concrete is transported and is kept agitated all along at a speed of 3-6 rpm.Concrete is batched at batching plant and mixing is done in the truck, either during transit or immediately prior to discharge at site.71Tuesday, July 28, 2015Prof. V.M.Agrawal72Transporting of concretePumps and pipelinesUsed for inner inaccessible areas of structure or buildingRequires sophisticated and heavy duty pumps and pipe line system.Used in high rise buildings for slab casting.Blockage is the common problem in pipe line concreting. Through cleaning of pipe line is mandatory after every use.72Tuesday, July 28, 2015Prof. V.M.Agrawal73Direct discharge, Manual transport in containers and short chutes.Free fall of concrete over a height of 2m is to be avoided.short chutes with proper lower end treatment are simple to use.Metallic, half round in section, stiffened at places may last to handle about 1500m3 of concrete.Long chutes are less desirable.73Tuesday, July 28, 2015Prof. V.M.Agrawal74Burrows and dumper trucksManual wheel burrow capacity up to 80 kg of concrete.Power Burrows up to 800 kg and 300m haul and can haul to a 20 % gradient.Dumpers and Trucks (Horizontal transport) are used for long hauls. Because of the jolting on the ground, ordinary trucks and dumpers tend to cause segregation of concrete during transit.74Tuesday, July 28, 2015Prof. V.M.Agrawal75Dumper trucks

75Tuesday, July 28, 2015Prof. V.M.Agrawal76Mono rail systemMonorail system needs a track and consists of a power wagon mounted on the single rail track, which can move at a speed of 80-90 m/min.Segregation of concrete may take place due to jolting of concrete in the wagon over each rail joints, hence wet mix are generally unsuitable for monorail transport.when the rail track runs over the slab form, the wagon can directly discharge on the form.76Tuesday, July 28, 2015Prof. V.M.Agrawal77Elevating tower and hoist (vertical transport)Elevating towers are used for lifting concrete buckets, which can be distributed using a chute or by other means such as barrows, etc.Hoists operate on a similar principle.A cantilever platform hoist operates along a steel lattice mast.Concrete skip can be used directly, that can tilt and discharge the concrete on some distribution system.77Tuesday, July 28, 2015Prof. V.M.Agrawal78Cranes and cable ways (2D & 3D)Cranes or cableways may be used for three dimensional transport of concrete.

Cable way is useful in river valley projects.

Cranes of various types are also useful in high rise building construction in congested sites.

Depending upon the site, cranes may be any one of the following types such as tower crane, crawler mounted, or wheel mounted, or a hydraulic crane.

The main consideration in selecting the crane is height and radius of operation 78Tuesday, July 28, 2015Prof. V.M.Agrawal79Cableways

79Tuesday, July 28, 2015Prof. V.M.Agrawal80Belt conveyorDischarge can be as high as 115 cubic m/hour on a narrow strip of belt The main consideration in selecting the crane is height and radius of operation.Conveying concrete through a limited elevation of 30 degree is possible.For wet mixes the capacity of the belt is reduced as the inclination through which concrete can be lifted is also lowered.80Tuesday, July 28, 2015Prof. V.M.Agrawal81Belt conveyorConcrete tends to segregate in steep inclines as the belt passes over the rollers, this problem is less acute in drier mixes.Segregation at the discharge point may be avoided using proper hopper and the chute arrangement.In case of a breakdown of machines, large amount of concrete in the belt needs removal by other means and the belt is to be cleaned and washed.Their initial cost of setting up is also high.81Tuesday, July 28, 2015Prof. V.M.Agrawal82Under water concretingUnder water placing of concrete poses a number of problems, as concrete cannot be compacted and concrete may get mixed with water.Whenever, possible under water connecting, is to be avoided.To overcome the problems mentioned above, concrete must be self compacting and wet enough to flow under its own weight, and must be placed with least disturbances.82Tuesday, July 28, 2015Prof. V.M.Agrawal83Under water concreting

83Tuesday, July 28, 2015Prof. V.M.Agrawal84Transporting of concrete










93Tuesday, July 28, 2015Prof. V.M.Agrawal94Workability of concreteIt is the amount of useful internal work necessary to produce full compaction. Internal work includes:Overcome internal friction between individual particleSurface friction between formwork and concreteSome amount of Wasted energy94Tuesday, July 28, 2015Prof. V.M.Agrawal95Workability of concreteTests for workabilitySlump cone testVeBe testCompaction factor test

95Tuesday, July 28, 2015Prof. V.M.Agrawal96Slump cone test and compaction factor test

96Tuesday, July 28, 2015Prof. V.M.Agrawal97Vebe test

Measured in seconds (time)97Tuesday, July 28, 2015Prof. V.M.Agrawal98Comparison And Interpretation Of Results From Workability Tests.

Tuesday, July 28, 2015Prof. V.M.Agrawal99Pumping of concretePumping is used for both transporting and placing of concrete.Combines both vertical and horizontal transport in one.It can place concrete in congested sites with little access otherwiseSmall or large quantities of concrete can be placed in the form, continuously at a very fast rate.

Tuesday, July 28, 2015Prof. V.M.Agrawal100Pumping of concretePumping of concrete requires use of mix having special properties suited to pumping itself.Pumping rates ranges from 10 to 75 cubic meter/hour.Concrete can be pumped to a distance of 90-300 m horizontally.Concrete can be pumped from 30 to 90 m vertically. Tuesday, July 28, 2015Prof. V.M.Agrawal101Types of pump

Tuesday, July 28, 2015Prof. V.M.Agrawal102Types of pump

Tuesday, July 28, 2015Prof. V.M.Agrawal103Pumping pressure requirement

Tuesday, July 28, 2015Prof. V.M.Agrawal104Concrete flowFlows in form of plug separated from pipe wall by a layer of lubricating later.No relative velocity between aggregate particle for a straight pipe of constant cross section.Lubricating layer near pipe boundary is essential for pumpability.Compacting effect of pressure consolidates and forces grout out.Trowelling effect due to frictional drag at boundary pulls grout out.

Tuesday, July 28, 2015Prof. V.M.Agrawal105Concrete flow

Tuesday, July 28, 2015Prof. V.M.Agrawal106Concrete flowWhen mortar which has enough water and is sufficient to fill in all the voids in aggregate and is more to create lubricating layer it is said to be SATURATED.In Saturated concrete radial and axial pressures are same and fine content is important. Too much cohesiveness due to excess cement and fines may prevent formation of lubricating layer.

Tuesday, July 28, 2015Prof. V.M.Agrawal107Pumpability

Tuesday, July 28, 2015Prof. V.M.Agrawal108Pumpability

Fines must be sufficient to resist passage of water i.e., blocked filter effect.Tuesday, July 28, 2015Prof. V.M.Agrawal109Pumpability

Tuesday, July 28, 2015Prof. V.M.Agrawal110Effect of pumping on concreteDrier consistencyIncrease In TemperatureSlight increase in air contentNo change in strength or shrinkageAlthough aluminum pipes may cause loss of strength as it reacts with C3A and C2A.

Tuesday, July 28, 2015Prof. V.M.Agrawal111Dos and donts in transportation



Tuesday, July 28, 2015Prof. V.M.Agrawal114Placing of concretePlacing concrete within earth mould in single layer.All the loose earth must be removedAny root, shrubs, or vegetation must be clearedIf earth is dry, sprinkling of water must be done, so that surface does not absorb moisture from concrete.If earth is wet, water and slush must be cleaned properly before placing of concrete.If any seepage is observed it should be effectively diverted or stopped before placing of concrete.Use of polyethylene sheet or film should be used in between concrete and ground to prevent moisture exchange and to stop vegetation growth inside concrete mass.114Tuesday, July 28, 2015Prof. V.M.Agrawal115Placing of concretePlacing concrete in layers within earthfor general works concrete should be placed in layers of 15- 30 cm. In mass concrete the layer can be of 25-45 cm.The thickness of layer is determined by method of compaction, size and mode of vibration.All the layers must be placed quickly enough to avoid joints.All the layers must be cleaned by water jets and scrubbing of surface must be performed before laying the successive layer.Rich cement slurry must be applied in the previous layer to assure proper bonding.

115Tuesday, July 28, 2015Prof. V.M.Agrawal116Placing of concretePlacing concrete within timber or steel formworkEnsure that reinforcement is correctly placed and is having appropriate cover.The joints between planks of shutters must be properly and effectively plugged so that slurry does not escapes when vibrated.All the support to the formwork should be checked to ensure that it can sustain the load of fresh concrete, vibration effect and working load.All the surfaces should be applied with mould releasing agents or shuttering oil for easy stripping.Ensure that reinforcement is free from oil. Also in congested reinforcement (beam column joint) ensure proper compaction. 116Tuesday, July 28, 2015Prof. V.M.Agrawal117Compaction Of ConcreteCompaction of concreteNeed VibratorsFresh concrete mechanism under vibrationExecutionSpecial vibration

117Tuesday, July 28, 2015Prof. V.M.Agrawal118Compaction by VibrationPlaced concrete contains air voids (30%).Compaction confirms ultimately to the shape of the form.Compaction is required to drive entrapped air out to densify concrete.Increase homogeneity and uniformity are the other benefits.This compaction is achieved through vibration.Self compacting concrete does not need vibration.118Tuesday, July 28, 2015Prof. V.M.Agrawal119Concrete VibrationEnergy for compaction is supplied through oscillatory motion of vibration (nearly SHM).Vibration is usually generated by means of rotating eccentric machine part having a frequency and amplitude of vibration.Although the frequency can be easily measured in air, it is difficult to measure within concrete although that is more relevant.119Tuesday, July 28, 2015Prof. V.M.Agrawal120Types of vibratorsInternal vibratorFlexible shaft type (Most common)Form vibratorVibrating tableSurface vibrator120Tuesday, July 28, 2015Prof. V.M.Agrawal121Types of vibratorsInternal vibratorImmersionSubmersibleflexible shaft type

121Tuesday, July 28, 2015Prof. V.M.Agrawal122Types of vibratorsFlexible shaft type is most common, it ranges from a diameter of 20 to 180 mm.Vibration is usually generated by means of rotating eccentric mechanical part having a frequency and amplitude of vibration.Although the frequency can be easily measured in air, it is difficult to measure within concrete although that is more relevant.122Tuesday, July 28, 2015Prof. V.M.Agrawal123Immersion vibrators

a2 is the amplitude of vibration at a distance R2From center line of vibrator. is coef. Of dampinga1 is the amplitude of vibration at the surface of the vibrator having a radius equal to R1

123Tuesday, July 28, 2015Prof. V.M.Agrawal124Immersion vibratorsP is plastic concrete, M is Mass concrete, T is thin member, C stands for congested, S stands for slump, St stands for structure & O stands for open forms

124Tuesday, July 28, 2015Prof. V.M.Agrawal125Form vibratorsForm vibrator are external vibrators, transmits impulses both in plane and perpendicular to the form.Form is vibrated and the vibration is transmitted from the form to concrete.Acceleration is 1g-3g for adequate amplitude.Both rotary and reciprocating types are used and can either be electrically (3000-6000rpm) pneumatically (6000-2000 cycle/min) driven.125Tuesday, July 28, 2015Prof. V.M.Agrawal126Form vibratorsReciprocating type accelerates in a given direction and imparts impact causing vibration.Reciprocating vibrators are usually pneumatically driven.Frequencies are in the range of 1000-5000 cycles/minute.The impulses are mostly perpendicular to the form126Tuesday, July 28, 2015Prof. V.M.Agrawal127VibratorsVibrating table are usually used for pre-cast elements, frequency < 6000 vibrations/min and amplitude > 0.12mm.Surface vibrators exerts their effects at top surface and include:Vibrating screed,pan type vibrator,Vibrating roller screed,vibrating plate and vibratory roller for pavement concrete.127Tuesday, July 28, 2015Prof. V.M.Agrawal128VibratorsForm vibrators are used where it is impractical to use internal vibrators.Vibrating screed are used in thin slabs.High frequency and low amplitude vibrations generally results in more efficient compaction.128Tuesday, July 28, 2015Prof. V.M.Agrawal129Fresh concrete under vibrationPrior to compaction concrete is a mass of separate particles coated with mortar held in a pile by arching action of coarser particle.The arching is result of friction between aggregate particles, surface tension & cohesive forces of the cement paste.The voids caused by arching are filled with air up to about 30%.129Tuesday, July 28, 2015Prof. V.M.Agrawal130Fresh concrete under vibrationVibratory impulse liquefy the mortar portion of concrete and thus reduce the internal friction resulting in consolidation by force of gravity.In vibrated concrete friction is re-established, cohesion is restored and strength increases.The velocity of compression waves generated is 45m/sec in the beginning of vibration and increases to 240 m/sec at the end.With the increase in velocity of compression waves, the compaction also increases. 130Tuesday, July 28, 2015Prof. V.M.Agrawal131Fresh concrete under vibrationThe waves moves water more than the solids and generates hydraulic pressure within interstitial water filled space.The pressure is maximum in most constricted space and causes reduced internal friction giving the paste temporary fluidity.131Tuesday, July 28, 2015Prof. V.M.Agrawal132Fresh concrete under vibrationConsolidation of concrete takes place in two stages.In the first stage vertical settlement of coarse aggregate takes place in a manner similar to packing of granular material and shape of the aggregate plays a major role, air voids up to 5% remains after this stage.In the second stage concrete behaves like liquid and air voids are removed from the surface forcing mortar to appear at the surface .132Tuesday, July 28, 2015Prof. V.M.Agrawal133Measurement of compaction Unit weight can be a measure of compactionVarious density gauges can be used

133Tuesday, July 28, 2015Prof. V.M.Agrawal134Measurement of compaction

134Tuesday, July 28, 2015Prof. V.M.Agrawal135Execution of compaction

Vibration shall be completed when is in dormant period 135Tuesday, July 28, 2015Prof. V.M.Agrawal136Execution of compaction Penetrate vertically to sufficiently embed in concrete, held stationary and removed slowly (7.5 cm/sec).At regular spacing to ensure compaction of all portions if required with adequate overlap.A minimum of 10 sec is necessary for complete compaction .Vibration time needed is given by:136Tuesday, July 28, 2015Prof. V.M.Agrawal137Execution of compaction

For V < 25 liters

For V > 25 liters

t = total needed vibration time (s) for V liters concrete= diameter of the needle vibrator in mm.S= Slump of the concrete in cmA = Coefficient representing shape of aggregate. For rounded aggregate A=1 for crushed aggregate A=5F=Coefficient representing denseness of steel; F=1.5 for very dense and F= 1 for no reinforcement137Tuesday, July 28, 2015Prof. V.M.Agrawal138Execution of compaction D is spacingR radius of action

138Tuesday, July 28, 2015Prof. V.M.Agrawal139Execution of compaction q = volume of compacted concrete cu.m/hru= utilization factor.R= radius of actions= thickness of the layer in mt= time of vibration in one placet1= time of moving the vibrator from one place to another

139Tuesday, July 28, 2015Prof. V.M.Agrawal140Imperfections in compaction

140Tuesday, July 28, 2015Prof. V.M.Agrawal141Curing of concreteHydration Reaction of cement with water takes time.Hydration takes place at 100% Relative Humidity.Loss of water by evaporation shall be prevented and replenished.Self-desiccation cause internal water loss and needs replenishing.Maintain conducive temperature.Needed for capillary segmentation.141Tuesday, July 28, 2015Prof. V.M.Agrawal142Results of poor CuringPoor strength development.Drying shrinkage and resultant cracks, may be aggravated by high ambient temperature and low Relative Humidity.Poorly segmented capillaries resulting in lower durability of concrete.142Tuesday, July 28, 2015Prof. V.M.Agrawal143Effect of moist curing on strength

w/c = 0.5143Tuesday, July 28, 2015Prof. V.M.Agrawal144Methods of curingMoist (water) Curing.Ponding.Spraying.Covering with wet sand,wetted Hessian or absorbent covering. Form retention and covering concrete prior to setting.Membrane curing (spray/ hand applied resins and waxes).Water proof plastic sheeting.Steam curing144Tuesday, July 28, 2015Prof. V.M.Agrawal145Comparison of ponding and hessian

145Tuesday, July 28, 2015Prof. V.M.Agrawal146Effect of temperature at casting and curing

146Tuesday, July 28, 2015Prof. V.M.Agrawal147Curing time Curing by form work, covering, membrane stops evaporation losses but do not replenish the moisture loss due to self desiccation.Pozzolana blended cement or concretes with pozzolana requires more number of curing days for strength development.IS 456 recommendations: at least, 7 days for OPC and 10 days for Blended cement/ concrete with mineral admixtureFor dry and hot condition these periods are 10 &14

147Tuesday, July 28, 2015Prof. V.M.Agrawal148Steam curing

Steam cured concrete w/c=0.5, curing applied immediately after casting148Tuesday, July 28, 2015Prof. V.M.Agrawal149Steam curing

Steam curing cycle149Tuesday, July 28, 2015Prof. V.M.Agrawal150

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