5.4 R.C.C. WORK

5.4.1 Introduction: Concrete is a product obtained artificially by hardening the mixture of cement,

sand, coarse aggregate and water in predetermined proportion. Concrete is very good in compression and weak in tension. Thus, combination of steel and concrete provides ideal as these two materials

are used to take up stresses and are suitable for such combination which is called Reinforced Cement Concrete.

So, R.C.C. contains of two parts 1) Reinforcement

2) Concreting 5.4.2 Procedure

a) Reinforcement: At site, TMT bars (Fe415) are used as reinforcement.

In TMT bars carbon levels are restricted much lower than the specification, which result in excellent ductility, high bend ability and superior weld ability.

After doing P.C.C than centre line for column is marked on P.C.C with the help of centre line drawing and it is marked with mortar

Than footing reinforcement (Jali) is laid on P.C.C as per Bar Bending Schedule

Than column reinforcement is laid on marked point on P.C.C and it’s checkedvertically through plumb

Basic Construction Technique

Centre line for column should also coincinde with centre line of footing And it is checked by measuring diagonal distance from column in all four side’s

Than support for column is placed with the help of Bars

Cover of 50 mm is being provided. b) Concreting

All plain concrete shall be preferably mixed in a drum type power driven

machine mixer with required mix of M 25. The mixing of each batch in the concrete mixer shall continue for not less than

two minutes after the materials and water are in the mixer.

Than concreting is done with the help of chute. Here concreting is done

through chute to avoid seggregation Concreting for R.C.C is done upto the required depth as per the design.

Basic Construction Technique

5.4.3 Checking/ Verification for R.C.C Work:

Particulars A) Pre-Construction: 1) Size of footing as per drawing 2) Check the dimension and diagonals of formwork box of footing 3) Level marking up to which concreting is to be done 4) Check supports of formwork 5) Check reinforcement and minimum cover. 6) Footing should be cleaned thoroughly and cement slurry is poured before concreting

B) During Construction: 1) Check the quantity of material 2) Check the proportion and mixing of material 3) To check that concreting is done through chute so that there is no segregation 4) Check for the required concrete level marking 5) Mixing method 6) Check that compaction is done at regular interval with the help of needle vibrator C) Post Construction: 1) De-shuttering of footing after 24 hours 2) Curing to be done with sprinkling

Tools Equipments1) Theodolite 1) Batch Mixer2) Line string 2) Needle Vibrator3) Plumb bob 3) Excavator4) Hammer 4) Tractor5) Measuring tape 30 m

6) Buckets 7) Spade

8) Pickaxe 9) Trowel 10) Chalk 11) Punja

12) Thapi (Wooden float) 13) Rammer

Basic Construction Technique

5.5 CONCRETING

This is the most important activity as far as frame construction is concerned because cement which is the vital material is widely used in this & thus it should be carried out carefully. On our site it was done by pipeline in slab and beam and manually for column and footing. Concreting involves following stages.

Batching & Mixing Transporting•It can be either volumetric or weigh batching •Carrying concrete from the place of mixingbut at site mostly weigh batching is carried to the place of delivery is known as theout. transporting of concrete.

•Weigh batcher was used at our site. The •From the RMC plant concrete is transportedprocess is described in earlier chapter. through miller with the help of hydraulic

•Similarly mixing is done in pan mixer at pump.RMC plant & in tilting mixer for concrete •In case of concrete mixer it is transportedmixer. manually through buckets.

Compacting Placing•Various types of mechanical vibrators based •Concrete is placed only after the surface ison site conditions & amount of concreting thoroughly cleaned and oiled.are used. •The source of concrete is placed at sufficient

•At our site needle vibrator is used with height to avoid segregation and40mm diameter of needle. simultaneously rough levelling is also carried

•Compaction is carried out simultaneously out.along with placing by dipping the needle in •Sometimes chutes are also used for placing.the paste for short time period at a point.

Finishing Curing•With respect to some fixed reference point •Various types of curing methods such aswhich can be either adjacent surface or some pounding, sprinkling, wetting, steam curingrods with markings placed there, etc are adopted.Approximate levelling is done. •At our site pounding, sprinkling and wetting

•Floating or towelling is adopted for are used as they are simple & easy.finishing until the surface seems to be fairly smooth & levelled.

Basic Construction Technique

Concreting for Column

• First marking f or starter of thecolumn.

• Then formwork is provided andthen checks its verticality usingplumb bob, dori and tape.

• Then Reinforcement and coversare provided and start concretingwork.

• First concreting is done for 100mm sothat the cement slurry doesn'tcomes out form bottom.

• Remaining height of concreting isdone after 1hr.

• Concrete is compacted by usingneedle vibrator.

• The formwork can be removedafter 24 hours.

• Curing should be done up to 14days after concreting.

Concreting for Slab and Beam

• First shuttering level is checked .• Then the dowel is coming out of

the column are checked for the laplength.

• Covers for beam sides and slabare checked.

• Then concreting is done for beamand s lab.

• Concreting start s from one cornerand carried out towards the othercorner continuously.

• Iron rods are used to check depthof slab.

• Finishing is done with help ofwooden muster.

• Curing should be done up to 21days after concreting.

Basic Construction Technique

The following points should be kept in mind while working & supervision.

Precautions

Mixing  time  in  no  case  should  be  less  than  2 min.Discharge  height  for  concrete  mixer  shouldn’t be  more  than  70  cms.

Joints  in  pipeline  should  be  checked.

Pipeline  should  be  thoroughly  cleaned  with water  &  then  with  cement  slurry.

Concrete  should  be  placed  as  nearly  as possible.Time  between  mixing  &  placing  shouldn’t exceed  30min.

Concrete  shouldn’t  be  heaped  at  one  place.

Vibrators  should  be  continuously  operated while  they  are  being  withdrawn.

Vibrators  should  be  inserted  vertically.

Old  work  should  be  flushed  with  cement slurry  prior  to  concreting.Curing  must  be  constantly  done  for  at  least  7 days.

Purpose

To  achieve  homogenous  &  consistent  mix.

To  avoid  segregation.

To  avoid  leakage  of  concrete.

To   impart   lubrication   to   the  upcoming concrete.

To  save  manpower  &  time.

To  avoid  setting  of  concrete.

To   avoid   displacement   of   formwork.  

To  formation  of  holes  inside  concrete.

To  avoid  flow  of  concrete  into  mould.

To  have  proper  bond  between  old  &  new work.To  avoid  shrinkage  cracks  &  loss  of  moisture. 

5.6 REINFORCING

This is also one of the important activities as steel, which contributes significantly to the economy of the project is most widely used. Also it imparts tensile strength to the structure in which concrete is lacking. Thus it also important from safety point of view. The procedure adopted for reinforcement in beam, column, slab and other structures is almost same. For the construction of any floor first of all the columns are cast and thereafter beam and slabs are cast. The procedure is as under.

The reinforcement for shear walls is provided in same manner as that for column.

The reinforcement for staircase is similar to that of slab.

Basic Construction Technique

ColumnReinforcement

•Cutting & bending ofrebar is carried outaccording to structuraldrawing.

•For providing longitudinalreinforcement, rebar’s aretied to dowels by bindingwires providing sufficientlap length. These arecontinued to the nextfloor with dowels ifrequired.

•Similarly the transversereinforcement is providedby using lateral ties.

BeamReinforcement

•According to structuralDrawing cutting &Bending is carried out.

•Then bottom bars are laidFirst according to design.These bars rest on covers& stirrups provided forshear reinforcement.

•Then top bars areprovided which are tied tothe stirrups.

• The whole skeleton isSupported by chairs &Other support s and isPlaced to its location onlyAfter completion.

SlabReinforcement

•According to structuralDrawing cutting &bending is carried out.

•Main reinforcement isconstructed first and thendistribution steel is laidwhich will be runningperpendicular to for mer.

•Rebar’s are provided withalternate bent up sand thiswill be provided coverthrough speciallydesigned steel chairs

The following points should be kept in mind while working & supervision.

Precautions Purpose

Proper  cover  should  be  provided. To protect  steel from  getting corroded.

Sufficient  lap  length should  be  provided.

Bars  should  be  properly  tie d  with  bindingwires.Sufficient  development  should  be  provided.

D dowels  should be  properly left  out.

Stirrup  joints must  be  provided  in  alternatedirections.

Two  bars  can  ac t  as  continuo us  &  resistshearing.To avoid  displacement  of  rebar’s.

To anchorage  beam  &  column  junction.

To provide  enough  lap  length

To perform  well during  shearing  action. 

Basic Construction Technique

5.7 SHUTTERING

This activity forms the skeletal framework for any structure. This skeleton will help tosupport the concrete when it is in plastic state. Thus it will help to hold the structure till itgains its strength and also works as a mould to define its shape. This will also finalize thealignment as well as level hence it requires special consideration. The procedure is asunder.

Column & Shear   wall Beam  & SlabStaircase

•First of all starter isProvided by marking itsCentre & its edges. T henconcreting is done. StarterMay or may not beProvided but it is preferableSo that formwork getsStability.

•Then formwork is erectedover it. For columns 'C'Shaped formwork isPrepared first, erected &Then closed in case ofplywood or conventionalSteel forms. Otherwise i t isErected as straight forwardedas in case of wall.

•Ties are then provided toKeep distance amongsheets.

•Now the alignment ischecked with plumb b oband the props used tosupport the formwork areadjusted.

•Finally on getting desiredplumb, props are fixedrigidly.

•On the casted column beambottom is marked & thevalve plates supported bythe props are laidhorizontally between twocolumns. The level is thenchecked with level pipe.

•T hen the side forms areerected according to thedimensions and on thatslab forms are laid in withcontinuity. Simultaneouslypr ops along with wedges &ledgers are provided.

•T he ledgers a re spaced atregular intervals of 3", 6",9" depending ondimensions. They aregenerally laid orthogonal tothe main reinforcement.

•Sometimes 'Camber' is alsoprovided de pending ondimensions to avoiddeflection whileconcreting.

•Here also the bottom formsare laid first with propssupporting it.

•Then the side forms areerected according to thealignment of stair.

•Now the markings aremade on side forms forplacing the riserplanks. This can be donewith the help of spirit levelor level pipe.

•Then after the risers arefixed but only after rebar’sare laid.

•The treads are left open forconcreting and finishingbut they are casted bymatching the top & bottomof the successive risers.