dos &don'ts in concrete works

8/3/2019 Dos &Don'Ts in Concrete Works

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DOS AND DON¶TSDOS AND DON¶TS

IN SITE ACTIVITIESIN SITE ACTIVITIESOF CONCRETEOF CONCRETE

WORKSWORKS



Workability of Concrete Workability of Concrete

IS:456IS:456--20002000Concrete mix proportions chosen shouldConcrete mix proportions chosen shouldbe such that the concrete is of adequatebe such that the concrete is of adequateworkability for the placing conditions of workability for the placing conditions of concrete and for proper compaction withconcrete and for proper compaction withthe means availablethe means available

Note : For most placing conditions, internalNote : For most placing conditions, internal

vibrators are suitable. The diameter of thevibrators are suitable. The diameter of theneedle based on the density & spacing of needle based on the density & spacing of reinforcement and member thickness. Forreinforcement and member thickness. Fortremie concrete vibrators are not used.tremie concrete vibrators are not used.



Compaction of ConcreteCompaction of Concrete

How to Vibrate ?How to Vibrate ?Spread the concrete uniformly in layersSpread the concrete uniformly in layersnot more than 300 to 500 mm depthnot more than 300 to 500 mm depth

Do not move the concrete sideways usingDo not move the concrete sideways usingpokerpoker

Vibrate systematically, inserting theVibrate systematically, inserting thevibrator vertically at intervals equal to 8 tovibrator vertically at intervals equal to 8 to10 times the diameter of the tube10 times the diameter of the tube

Push the poker about 150 mm into thePush the poker about 150 mm into theprevious layer to obtain maximumprevious layer to obtain maximum

adhesionadhesion



Compaction of ConcreteCompaction of Concrete

How to Vibrate ?How to Vibrate ?I n forms with sloping floors, first fill withI n forms with sloping floors, first fill withconcrete to make a level surface and thenconcrete to make a level surface and thenstart vibrating at the deepest partstart vibrating at the deepest partPush the poker straight down. WhenPush the poker straight down. When

vibrating concrete floor slabs, insert at anvibrating concrete floor slabs, insert at anangle to improve contact betweenangle to improve contact betweenconcrete and tube.concrete and tube.Concrete is thoroughly vibrated when theConcrete is thoroughly vibrated when the

surface round the poker goes glossy andsurface round the poker goes glossy andno more large bubbles appear (normally itno more large bubbles appear (normally it

takes 10takes 10- -20 seconds)20 seconds)



Improper

HandlingTechnique

s of Internal

Vibrators



Improper Handling Techniques of Internal Vibrators



Improper

HandlingTechniques of

Internal Vibrators



C ompaction of C oncreteMethod of Poker Insertion



C ompaction of C oncreteMethod of C ompaction



Concrete must be placed.Concrete must be placed.Where bars are lappedWhere bars are lapped

check their thickness and spacingcheck their thickness and spacing

Lapped bars can create problems



eave room for vibration !

µ*!?!----- after all I¶ve said !¶



Ties and bracings for Ties and bracings for

Lateral S tabilityLateral S tabilityVertical loads transmitted to base by tubes. TiesVertical loads transmitted to base by tubes. Tiesshould be of push/pull typeshould be of push/pull typeTies,Ties, bracingsbracings shouldshould bebe inin positionposition asas specifiedspecified. .

ContinuousContinuous diagonaldiagonal bracingbracing tubestubes shouldshould bebeconnectedconnected to to everyevery nodenode pointpoint..ForFor nominalnominal loads,loads, provideprovide oneone diagonaldiagonal bracingbracingforfor sixsix rectangularrectangular formsforms byby thethe verticalvertical tubestubes. .ForFor heavyheavy loadsloads andand windwind force,force, thethe numbernumber of of bracingsbracings shouldshould bebe calculatedcalculated andand providedprovided forfor..



B race B race couplerscouplers

Diagonal Diagonal bracing layoutbracing layout



F oundation for scaffoldsF oundation for scaffolds

Scaffolds require foundation to support withoutScaffolds require foundation to support withoutundesirable deformation. Load in tube isundesirable deformation. Load in tube istransmitted through a plain or adjustable base totransmitted through a plain or adjustable base to

foundation or spreader of timber, conc or steel.foundation or spreader of timber, conc or steel.Design of foundation supports for scaffold pipesDesign of foundation supports for scaffold pipesresting on river bed and in water requires specialresting on river bed and in water requires specialattention. Traditionally timber ballies (150attention. Traditionally timber ballies (150- -

200mm dia.) are driven to refusal and brazed at200mm dia.) are driven to refusal and brazed attop, above water level to receive the scaffoldingtop, above water level to receive the scaffoldingsystem.system.



Deshuttering of formworkDeshuttering of formwork

Vertical forms Vertical forms Vertical formwork to be in position until concreteVertical formwork to be in position until concretestiffens sufficiently to sustain itself i.e. finalstiffens sufficiently to sustain itself i.e. finalsetting time of concrete (4setting time of concrete (4- -6 hrs)6 hrs)

I ncreased time before deshuttering results inI ncreased time before deshuttering results inreduced number of rereduced number of re- -uses without any technicaluses without any technicalbenefit; also hinders commencement of curing.benefit; also hinders commencement of curing.Steel formwork absorbs solar heat, leading toSteel formwork absorbs solar heat, leading to

fast evaporation of water from concrete, leavingfast evaporation of water from concrete, leavinginsufficient water for hydration.insufficient water for hydration.



DeshutteringDeshuttering

Construction jointsConstruction jointsFormwork of vertical construction joints shouldFormwork of vertical construction joints shouldbe removed within 2be removed within 2- -3 hrs of concreting to3 hrs of concreting toensure removal of cement mortar laitance andensure removal of cement mortar laitance and

expose aggregates before final setting of expose aggregates before final setting of concrete. I t should never be left for more than 12concrete. I t should never be left for more than 12hrshrsI f the formwork is to be left for longer period, theI f the formwork is to be left for longer period, the

face of formwork in contact with concrete shouldface of formwork in contact with concrete shouldbe coated with a surface retarder to facilitatebe coated with a surface retarder to facilitatetreatment of concrete surfacetreatment of concrete surface



WorkmanshipWorkmanship

ConcretingConcretingConcreting by experienced gangs. 2 level control.Concreting by experienced gangs. 2 level control.

Method of control by pour card recommended.Method of control by pour card recommended.

Placing and compacting under supervision.Placing and compacting under supervision.Regular control by qualified staff, surveillance byRegular control by qualified staff, surveillance by

QA team.QA team.

Proper curing checked by independentProper curing checked by independentsupervisors and documentedsupervisors and documented



S potting the pumpS potting the pump

Position pump so that pipelines are short andPosition pump so that pipelines are short andstraight and do not need repositioning often.straight and do not need repositioning often.Keep room for 2 concrete trucks at pump hopperKeep room for 2 concrete trucks at pump hopper

When there is no room for 2 trucks, alternateWhen there is no room for 2 trucks, alternatearrangement should be made like fixing a chutearrangement should be made like fixing a chuteor using one frontor using one front- -discharge and other reardischarge and other rear- -discharge concrete trucks.discharge concrete trucks.

Set truck mounted placing booms on level groundSet truck mounted placing booms on level ground



Concrete P lacement by P umpsConcrete P lacement by P umps

Locating The P umpLocating The P umpPosition the pump close to the concretingPosition the pump close to the concretinglocation. For safe operation, the truck pumplocation. For safe operation, the truck pumpshould not be too close to a open excavationshould not be too close to a open excavation

Provide locked storage area for standby equip,Provide locked storage area for standby equip,replacement parts, extra hose and line sectionsreplacement parts, extra hose and line sectionsPrepare a scale drawing of the job site, pumpsPrepare a scale drawing of the job site, pumpsand TM¶s to plan best arrangementand TM¶s to plan best arrangementI f not possible to provide access to both sides of I f not possible to provide access to both sides of

pump hopper due to congested location, a chutepump hopper due to congested location, a chutecan be provided for unloading the second truckcan be provided for unloading the second truck



P ipelineP ipelineAll pipelines should be laid either vertically orAll pipelines should be laid either vertically orhorizontally but never inclined.horizontally but never inclined.Pipe diameter varies from 100 to 200mm.Pipe diameter varies from 100 to 200mm.Resistance due to velocity of flow is more than volumeResistance due to velocity of flow is more than volumeof concrete being moved; for horizontal surfaces higherof concrete being moved; for horizontal surfaces higherdia pipes can be used, for high rise pumping smallerdia pipes can be used, for high rise pumping smallerdia pipes are recommended.dia pipes are recommended.During concreting, pipes should never be added, butDuring concreting, pipes should never be added, but

broken back towards the pump, starting at the farthestbroken back towards the pump, starting at the farthestpoint first and finishing close to pump.point first and finishing close to pump.



Defective support Defective support of concrete of concrete

pipelinepipeline

Correct supportCorrect support



P umping of ConcreteP umping of Concrete

Lubricating Mix Lubricating Mix For lubricating a pipeline, lubricating mixFor lubricating a pipeline, lubricating mixpumped immediately before the first regularpumped immediately before the first regularconcrete mixconcrete mix

I t consists of two parts of cement one part of I t consists of two parts of cement one part of sand and water. ( used for > 100 m pipeline)sand and water. ( used for > 100 m pipeline)The consistency of the mix should be softThe consistency of the mix should be softFor short pipelinesFor short pipelines ± ± lorry mounted concretelorry mounted concrete

pumps with placing booms cement & water usedpumps with placing booms cement & water usedQuantity of lubricating mix depends on lengthQuantity of lubricating mix depends on length

and diameter of the pipelineand diameter of the pipeline



S ite Management for P umpingS ite Management for P umping

Small pours should be discouraged.Small pours should be discouraged.Large volumes should be pumped continuously.Large volumes should be pumped continuously.Keep many locations ready for concrete at aKeep many locations ready for concrete at a

time.time.Pumping only in daylight barring exceptions.Pumping only in daylight barring exceptions.Pours to start early. Smaller pours may bePours to start early. Smaller pours may bestarted later but should be completed beforestarted later but should be completed beforesunset.sunset.Arrange for checking of concrete slump regularly.Arrange for checking of concrete slump regularly.Concrete delivered to pump must be of consistentConcrete delivered to pump must be of consistentquality throughout period of pumping.quality throughout period of pumping.



P umped ConcreteP umped Concrete -- B lockagesB lockagesU nsuitable concreteU nsuitable concrete

mixmix Slump below 50 mmSlump below 50 mm Slump above 150 mmSlump above 150 mm

I nadequate finesI nadequate fines Cement other than OPCCement other than OPC

Change in c/s of Change in c/s of pipelinepipeline

Over size aggOver size aggparticlesparticles

Sharp Bends inSharp Bends in

pipelinepipeline

Sudden starts, stopsSudden starts, stopsToo long a lineToo long a line

Getting air into theGetting air into thesystemsystem

No mix in the hopperNo mix in the hopperI nadequate concI nadequate conc

pressurepressure

Grout leaking jointsGrout leaking jointsAbsence of initialAbsence of initial

lubricating mortarlubricating mortar



P umping of Concrete P umping of Concrete Maintaining the P ump & P ipelineMaintaining the P ump & P ipeline

The concrete pipeline should be visuallyThe concrete pipeline should be visuallyinspected for damage each dayinspected for damage each day

Pipeline wall thickness shall be tested usingPipeline wall thickness shall be tested usingultrasonic thickness gaugeultrasonic thickness gauge

Pipeline that has become worn must be replacedPipeline that has become worn must be replaced

when its safe working pressure falls below thewhen its safe working pressure falls below thepressure capacity of the concrete pumppressure capacity of the concrete pump



Large volume pumpingLarge volume pumping Aspects to be checked Aspects to be checked

Sequence and speed of placing concreteSequence and speed of placing concretePump locations and movementsPump locations and movementsAdequate provision of pipes and fittingsAdequate provision of pipes and fittings

Access to pumps for two or more trucksAccess to pumps for two or more trucksWater, compressed air and groutWater, compressed air and groutControl of concrete productionControl of concrete productionA controller to regulate truck movement byA controller to regulate truck movement by

proper communication with pump and truckproper communication with pump and truckdriversdriversFloodlighting for night work.Floodlighting for night work.



Training of pump operatorsTraining of pump operators

Basics of concrete, requirements for pumpabilityBasics of concrete, requirements for pumpabilityOperating and maintaining pumps and vehiclesOperating and maintaining pumps and vehicles

Boom operationBoom operation

Rigging pipelinesRigging pipelinesConcrete placingConcrete placing

Rectifying concrete blockagesRectifying concrete blockages

Cleaning and inspecting equipmentCleaning and inspecting equipmentSafetySafety



Contract P lanningContract P lanning

Check contract docs, drawings, quantities, siteCheck contract docs, drawings, quantities, siteaccess, services, working space, material source,access, services, working space, material source,

Technical information : concrete, grade, cement,Technical information : concrete, grade, cement,aggregate, admixtures, w/c, workability, testing,aggregate, admixtures, w/c, workability, testing,reinforcement, formwork, temp/ancillary worksreinforcement, formwork, temp/ancillary works

Planning : Management plan, site layout,Planning : Management plan, site layout,temporary/supporting works, test schedule,temporary/supporting works, test schedule,labour requirements, daily concrete demandlabour requirements, daily concrete demand

dos &don'ts in concrete works

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