MCM 511 - Concreting Equipment

7/27/2019 MCM 511 - Concreting Equipment

1/32

MCM 511

CONSTRUCTION EQUIPMENT

MANAGEMENT

Concreting Equipments

Prof. Debopam Roy


2/32

Concreting Methods & Equipments

Batching & Mixing

Transportation

Placing

Compaction

Finishing &Curing

Weigh Batcher

Mixer

Batching Plant

Builders Hoist

Bogey/Barrow

Transit Mixer

Chute

Crane Bucket

Pump

Boom Placer

Slip Form

Needle Vibrator

Form Vibrator

Surface Vibrator

Aggregate

Cement

Water

Batching

Mixing

Handling and

transporting

Placing

Finishing

Curing

Compaction


3/32

Batching & Mixing

Batching is weighing or volumetricallymeasuring and introducing into themixer the ingredients for a batch ofconcrete

Manual / Volumetric Batching Cement added by bags,

Aggregate & Water added

volumetrically using forma. Nominal mix design used.

For small jobs

Semi Automatic / Weigh Batching Cement added by bags.

Aggregate added by weight.

Water added volumetrically.

Mix Design can be used. For medium jobs

Automatic Batching Cement added in bulk from silo by

weight

Aggregate & Water added by weight

Automatic plant operating as per mix

design For large jobs

The concrete should be mixedthoroughly until it is uniform inappearance, with all ingredientsevenly distributed.

Portable Stationary Mixer Low capacity mixers

Mixing executed near the placement

location, and concrete transported byhead-load/ bogey/ hoist

For small jobs

Ready Mix Plant Large capacity

Automatic Batching

Transportation by transit mixers

For large jobs May cater to multiple projects


4/32


5/32

Batching & Mixing

Weigh Batcher weighs different

aggregates one at a timeand loaded on top of thosepreviously weighed

May have one or morebuckets for unloading ofdifferent aggregates

Weigh beam Scales or dialtype scales may be used

Weighed materialtransferred to mixerhopper

Local Brands are mostcommon


6/32

Batching & Mixing

Portable Stationary mixers Small machines for mixing concrete near the structure

Components added manually

After mixing concrete is transported by manual/semi-mechanicalmeans

Sequence: Add 10% water, Add cement; Add aggregate along with 80%water; Add balance 10% water

Specifications usually require minimum of one minute mixing forstationary mixers of upto 1 yd3 with an increase of 15 seconds for eachadditional 1 yd3 capacity

The mixer drum speed is usually 18 to 20 r.p.m

Some times the total volume of the unmixed ingredients is given as aprefix. Thus, a total 10/7 mixer takes 10 cu.ft. of unmixed material andgives 7 cu.ft. of mixed concrete per batch

Mixers are specified by the volume of mixed concrete discharged aftermixing of each batch, expressed in m3 or ft3


7/32

Batching & Mixing

10/7 ConcreteMixer

Non Tilting

Concrete Mixer

Pan Mixer

Hand Feed

Concrete Mixer


8/32

Batching & Mixing

Ready Mix (RMC) Plant /Batching Plant Centrally located

Automatic/Semi Automaticplant

Produce concrete as per setrecipe

High capacity of production;better level of quality control

Preferred over on-site concretemixing because of the precisionof the mixture and reduced

work site confusion Plant capacity defined by

production in cum/hr. Rangesfrom CP 30 to CP 120

Leading Manufacturer:SCHWING STETTER


9/32

Batching & Mixing

Parts of RMC plant :

Aggregate Feeding System Radial Boom scraper

Ramp Cold Bins Conveyor

Radial Conveyor Cold Bins Conveyor

Cement Feeding System Bag Splitting Cement Feed hopper & Screw Conveyor

Cement Silo & Screw Conveyor

Water & Admixture Tank

Pan Mixer

Discharge Unit

Control Cabin


10/32


11/32

Batching & Mixing


12/32

Batching & Mixing

Advantages of Ready Mix Concrete A centralised concrete batching plant can serve a wide area.

The plants are located in areas zoned for industrial use, and yet the delivery trucks can serviceresidential districts or inner cities.

Better quality concrete is produced.

Elimination of storage space for basic materials at site.

Elimination of procurement / hiring of plant and machinery

Wastage of basic materials is avoided.

Labor associated with production of concrete is eliminated.

Time required is greatly reduced.

Noise and dust pollution at site is reduced.

Reduce cost.

Disadvantages of Ready-Mix Concrete The materials are batched at a central plant, and the mixing begins at that plant, so the

traveling time from the plant to the site is critical over longer distances

Generation of additional road traffic; furthermore, access roads, and site access have to beable to carry the weight of the truck and load. Concrete is approx

Concrete's limited timespan between mixing and going-off means that readymix should beplaced within 120 minutes of batching at the plant.


13/32

Handling & Transportation

Methods used to handle and place concrete should be based onseveral objectives, including

Economy

The prevention of segregation

Final placing before concrete attains initial set

Proper handling and transporting of concrete is as important tothe end result as are the other factors of water - cement ratio,mix design, correct batching and thorough mixing

The mode of transportation depends on the distance betweenthe mixing & placing

Part of mixing can be done during transportation Method of transportation can be manual / semi manual /

mechanical


14/32


Manual

For small jobs concrete

may be transported by

human chain through

head-load


15/32


Builders Hoist Can be used for vertical lifts

Popular in building projects

Concrete Unloaded on a Bucketwhich is lifted along a tower bywinch-pulley arrangement

Buggies & Barrows For horizontal transportation/along

ramp, for maximum distance of70m

Equipped with pneumatic tyres toprevent segregation and easiermovement

Hand buggies superior to wheelbarrows because the two wheelsprovide a better balance for theload

Power driven buggies of 0.5 cumcapacity & 25kmph speed are alsoavailable


16/32


Transit Mixers RMC is mixed partially in the plant,

and completed in the truck mixer.Water is added partially in theplant, and balance added from thetank of the TM

Maintains the concrete in workablestate through agitation, or turningof the drum, until delivery

The interior of the drum on aconcrete mixing truck is fitted witha spiral rotating blade whichagitates the mix

On reaching site, the concrete is

unloaded from the rear Capacity : 6 cum. May need

periodic maintenance to retaincapacity

Leading Manufacturer: SCHWINGSTETTER


17/32


Operation of Transit Mixer The inside of a transit mixer uses a

simple Archimedes' screw to mix and tolift the concrete to the delivery chute

In one rotational direction, the concreteis pushed deeper into the drum(Charging). When the drum rotates inthe other direction, the Archimedes'screw-type arrangement "discharges",or forces the concrete out of the drum

70 to 100 revolutions of the drum or blades atthe rate of rotation specified by themanufacturer, required to produce the specifieduniformity of concrete.

Not more than 100 revolutions at mixing speed

are allowed. After 100 should be done at a ratedesigned for agitation

Agitating speed is usually 2 to 6 rpm, whilemixing speed is generally about 6 to 18 rpm

Concrete should be delivered with in one andhalf hour or before the drum has revolved 300times.


18/32

Placing

Chutes & Drop pipes Can be used for placing concrete to lower

elevation

Chutes should have a round bottom &slope should be steep enough forconcrete to flow continuously withoutsegregation

Drop pipes should have a diameter of atleast 8 times the maximum aggregatesize at top, and 6 times at bottom

Crane Bucket Bottom dump cylindrical buckets with

central discharge gates can be used

Using a crane to lift the bucket to desiredheight, this method can be used to placeconcrete at a higher elevation

Gates on the smaller buckets areoperated manually, while the gates onthe larger buckets are operated bycompressed air or other mechanicalmethods


19/32

Placing

Pump / Boom Placer Pressure applied to a continuous column of

fresh concrete in a pipe - Rigid or flexible

Mix should be properly proportioned

Outer layer should provide lubrication

Pump must be fed concrete of uniform

workability and consistency Concrete should be supplied steadily

Effective pumping ranges vary from 80 to300 m horizontally and 20 to 100 m vertically

Capacities varies from 10 m3/hr to 150 m3 /hr pipe diameters from 4 to 6 inch

Maximum size of the aggregate is usually 20to 25 mm

Pumps may be mounted on trucks, trailers orskids. Truck mounted pump and boomcombination (Boom Placer) particularlyefficient and cost effective in saving laborand eliminating need for pipelines to carryconcrete

Leading Manufacturer: SCHWING STETTER


20/32

Compaction

Purpose of Compaction is toremove entrapped air

Normally mechanical vibratorsare inserted into the concrete forcompaction

In case of heavily reinforcedsection, form-vibrators may beused, and in thin slabs, surfacevibrators may be used

All types of compactors aremostly available locally

Needle Vibrator Internal vibrators have a vibrating

casing or head which is immersedinto the concrete and vibrates at ahigh frequency against theconcrete

Powered by electric motors orcompressed air or gasoline


21/32

Compaction

Needle Vibrator Whenever possible, the vibrator should be

lowered vertically into the concrete atregular interval and allowed to descend bygravity

In thin slabs vibrator should be inserted at

an angle, so that the head is fullyimmersed.

Adequacy of internal vibrator is judged byexperience and by changes in the surfaceappearance of each layer. Usually takes 5to 15 sec.

Changes to watch are embedment of largeaggregates, the leveling of surface, theappearance of thin film of glistering pasteand cessation of large bubbles ofentrapped air escaping at the surface

The length of time that a vibrator can beleft in the concrete will depend on theslump of concrete, the power of thevibrator, and the nature of the section

being vibrated


22/32

Compaction

Form Vibrators Attached to the outside of the form or

mould

They vibrate the form which in turnvibrates the concrete

Generally used in large pre-cast

concrete plant Also useful for consolidating concrete

in members that are very thin orcongested with reinforcement, Tosupplement the internal vibration, Forstiff mixes where internal vibratorscannot be used

Should be equipped with controls sothat frequency and amplitude can becontrolled according to size of elementand consistency of the cement.

Increasing the frequency anddecreasing the amplitude as vibratingprogresses will improve consolidation


23/32

Compaction

Surface Vibrators Exert their effect at the top

surface of the concrete andconsolidate the concrete from thetop down

Used mainly in the slabconstruction

Operate in the range of 3,000 to6,000 vibrations per minute

Vibratory screeds give positivecontrol of the strike off operationand save a great deal of labour

However, it should not be used onconcrete with slumps in excess of75 mm. Surface vibration of suchconcrete will result in an excessaccumulation of moisture and finematerial on the surface and thusreduce wear resistance


24/32

Slipform

Slip forming, continuous poured, continuouslyformed, or slipform construction is aconstruction method in which concrete ispoured into a continuously moving form

Used for tall structures (chimneys, towers), aswell as horizontal structures (PQC, Kerb,Gutter)

Slipforming enables continuous, non-interrupted, cast-in-place "flawless" (i.e. no

joints) concrete structures which have superiorperformance characteristics to piecewiseconstruction using discrete form elements

Concrete needs to be workable enough to be

placed into the form and packed, yet quick-setting enough to emerge from the form withstrength

The slip forming technique was in use by theearly 20th century for building silos, but wasintroduced to buildings & industrial structuresin the late 1960s

Leading brands: Slipform Intl (Vertical), PowerCurber/Arrow (Horizontal), Wirtgen (Paving)


25/32

Slipform

Vertical Slip Form The concrete form may be surrounded by a platform

on which workers stand, placing steel reinforcing rodsinto the concrete and ensuring a smooth pour.

Together, the concrete form and working platform areraised by means of hydraulic jacks.

Generally, the slipform rises at a rate which permits

the concrete to harden by the time it emerges fromthe bottom of the form

Horizontal Slip Form For kerbs, gutters, concrete is laid down, vibrated,

worked, and settled in place while the form itselfslowly moves ahead.

For concrete pavements, a slipform paver with largescreed is used, and the concrete is laid continuously

The slip form machine (Power Curber / Kerb Castingmachine) consist of a bucket, a conveyor, and a mouldfabricated as per desired section , mounted on acrawler track / wheel axles

After the concrete sets, expansion joints are cut intothe kerb/drain power saws

In addition to curb and gutter work, the machine pourshighway safety barrier, bridge parapet, sidewalk, golf

cart paths, agricultural foundations, irrigation ditchesand stadium risers


26/32

Slipform

Slipform Paving The paver usually performs screeding, consolidation

and initial finishing.

A typical track-mounted, self-propelled paveroperates at speeds between 1 and 2.5 m/minute

Some pavers are equipped to place reinforcing steel(if needed), dowel bars and tie rods as well

First, an auger spreads the concrete in front of thestrike off plate. Second, the strike off plate (screed)removes excess portions of the auger-placedconcrete and brings the slab near its final elevation.Third, the concrete is consolidated by a group ofvibrators. Fourth, a tamper pushes large aggregateparticles below the slab surface. Finally, the profilepans level off the slab at the right elevation andprovide initial finishing

Transverse joints across the paving lanes are saw-cutinto the pavement

Longitudinal center joints are commonly formed byuse of a continuous polyethylene strip the paverdisperses as it moves along


27/32

Problem

To execute a 500 cum pour, using a 90 cum/hr

boom placer, at a distance of 50kms (at

medium traffic) from the central batching

plant CP -110, assuming 80% productivity ofplant & boom placer, what is the optimum no.

of 6cum transit mixers to be deployed? How

much time will it take to finish the concretingusing 10 TMs?


28/32

Dos & Donts - Batching

DOSUse consistent quality of rawmaterialsUse central batching plants &design mix for important jobsCalibrate weigh batcherregularly.In volume batching havedifferent sized farmas readilyavailableDesign size of batch so that1bag cement is required.Prevent dusting of cementusing canvas tremies for fall.Make allowance for bulking ofsand &moisture absorption ofcoarse aggregate.

DONTSDump head loads ontoweighing pans.Dump different raw materialssimultaneously.Gauge cement by volumebatching.Make farmas larger than 50L.Compact aggregates intofarmas.Allow intermingling ofbatches, loss of materialsduring transfer


29/32

Dos & Donts - Mixing

DOSFeed ingredients simultaneouslywith same period of flow. Aportion of water should precede&follow the introduction of otheringredients.Butter the drum before use&remove hardened concrete fromdrum &blade.Use skip hopper for charging&chute for discharging.Add final part of water to transitmixer just prior to delivery&rotate at a slower speed whenused as agitator.Test slump at regular intervals&use a slump slightly greaterthan that required for placing.

DONTSAllow loss of material duringcharging/mixing/discharging.Allow incomplete/over mixing.Allow considerable variations inproperties of the mix in different

portions of a batch.Load mixers in excess of 10%more than rated capacity.Allow accumulation of hugeamount concrete at site due tounscheduled movement of transitmixers.

Use transit mixers for concretewith low slump/large aggregates.


30/32

Dos & Donts - Transportation

DOSUse agitator trucks ifbatching-mixing plant isdistant from site/RMC isused.

Provide properwalkways&staging, largebuckets if concretetransported manually.Provide sloped covered

chute, downpipes, etc tounload concrete fromhoist/conveyer ontoplatform.

DONTSAllow delay intransportation/split inbatch.Use manual means for

vertical transportation.For pump concrete use ano of bends &interruptions, small/Alpipes, stiff mix.

Allowsegregation/bleedingduring discharge due tolack of end-control


31/32

DOSUse light hoppers, roundedchutes, vertical falls (


32/32

Dos & Donts - Compaction

DOSUse the largest possible diameter ofpoker that the formwork&reinforcement layout can permit.Insert the poker quickly and allow itto penetrate by its own weight to thebottom of the layer as fast aspossible, Extend poker about 100mmto the previous layer.Slowly withdraw poker after airbubbles stop emerging and pitchbecomes constant..Poker insertion must be staggered&made at regular intervals.Use external vibrators if poker cannotprovide sufficient compaction.Mount the form vibrator on a steel

plate attached to a ]/I beam whichrun along formwork touching formfasteners. Use a suitable spacing sothat intensity of vibration is uniform.

DONTSTouch formwork/reinforcement withpoker.Use poker to make concrete flowthrough long distance.Insert poker at the tip of the heap.Use sharp bends in flexible drive.Proceed in downward direction.Use form vibrators on top of verticalformwork.

MCM 511 - Concreting Equipment

Documents

Transcript of MCM 511 - Concreting Equipment