Ready Mixed Concrete Final

8/7/2019 Ready Mixed Concrete Final

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Ready mixed concrete

Dept. of Civil Engg.. G.E.C Hassan 1

1. INTRODUCTION

Concrete is one of the major components of a structure, particularly a multistoriedstructure, where in it accounts for 30% - 50% of the total cost. The quality of concrete

has also a very direct bearing a on the strength & durability of the structure as a whole. Itis in this context that RMC assumes relevance.

Few things are more aggravating to produce on a worksite than concrete. Bags of cement, sand, aggregate (gravel) & possibly other additives must be delivered to the

construction area. A supply of clean water is also necessary, along with a rented concretemixing hopper. Even after all the dusty & heavy ingredients have been loaded into the

Hooper, one small error in the wet/dry ratio can render an entire batch of concreteunusable. One common solution to this messy & time consuming problem is ³READY

MIX CONCRETE´

RMC is a specialized material in which the cement aggregates and other ingredientsare weigh-batched at a plant in a central mixer or truck mixer, before delivery to the

construction site in a condition ready for placing by the builder. Thus, `fresh' concrete ismanufactured in a plant away from the construction site and transported within the

requisite journey time. The RMC supplier provides two services, firstly one of processingthe materials for making fresh concrete and secondly, of transporting a product within a

short time.

This enables the places of manufacture and use of concrete being separated andlinked by suitable transport operation. This technique is useful in congested sites or at

diverse work places and saves the consumer from the botheration of procurement, storageand handling of concrete materials. Ready mix concrete is produced under factory

conditions and permits a close control of all operations of manufacture and transportationof fresh concrete. Due to its durability, low cost and its ability to be customized for

different applications, ready mix concrete is one of the most versatile and popular building materials.

RMC is usually ordered in units of cubic yards or meters. The use of the RMC isfacilitated through a truck ±mounted µboom placer¶ that can pump the product for ready

use at multi-storied construction sites. A boom placer can pump the concrete up to 80meters. It must remain in motion until it is ready to be poured, or the cement may begin

to solidify. The RMC concrete is generally released from the hopper in a relatively steadystream through a tough system. Workers use shovels and hoes to push the concrete into

place.





2. HISTORY: Ready mix concrete was first patented in Germany in 1903; its commercial delivery was

not possible due to lack of transportation needs. The first commercial delivery was made

in Baltimore, USA in 1913. The first Revolving Drum Type Transit Mixer was developedin 1926.

In 1931, an RMC plant was set up for the construction of Heathrow airport, London.In the mid 90¶s there were about 1100 RMC plants in UK consuming about 45% of

cement produced in that country. By 1997, in Europe there were 5850 companies producing a total of 305 million cusecs of RMC.

In USA by 1990, around 72% (more than 2/3rd

) of cement produced was being used by various RMC plants. In Japan the first RMC plant was set up in 1949. By 1992, Japan

was the then largest producer of RMC, producing about 18,196 million tons of concrete.In many other countries of the world including some of the developing countries like

Taiwan, Malaysia etc, RMC industry is well developed.The leading RMC supplier worldwide is the Mexican Concrete & cement company

CEMEX, & their main competitor is France-based Lafarge.

In INDIA, RMC plant arrived in 1950¶s and the use of RMC was restricted to onlymajor construction projects such as, Bhakra Dam. Later on RMC was used for other large projects such as construction of long span bridges, industrial complexes etc. The RMC

plant was set up in Pune in 1993.The concept of RMC is still catching up in the country, cement majors are keenly

focusing on entering the new area in a big way. Cement majors, including AssociatedCement Companies, Grasim, L&T, India cements, Priyadarshini cements, Chettinad

cement & Madras cements, are foraying into the RMC business & the share of RMC isexpected to go up from present levels of around5% of the total cement production to the

global average of 70%. The teething troubles has been overcome by the RMC Industry &at present there are over 37 RMC plants delivering over 1 lakh cubic meters of mixed

concrete every month. RMC plants are working in Delhi area also.

Figure: Transit mixer in late 1940¶s and Concrete pump in late 1940¶s (Ambuja CementLiterature Vol. 90)





3. METHODS OF PRODUCTION: There are 2 general methods of producing RMC: Transit or Truck mixing

Central Mixing Shrink Mixing

3.1 Transit Mixing: In Transit Mixing, the dry materials are proportioned at the RMC plant, the water

being added & the mixing done en route to the job in a truck mixer, which essentiallyconsists of a mixer drum mounted on a conventional chassis. Power for rotating the drum

is obtained either from the truck engine or from an independent petrol engine. The truck mixer is provided with a water supply tank with equipment for measuring the quality of

water entering the drum, & a revolution counter indicating the extent of mixing.As soon as the mixer drum is charged with its complete batch of materials from the

batching plant, the truck proceeds to the concrete pouring point, the mixing operationtaking place en route, the water level and the mixing controls being operated by the

driver; where the length of the haul is long, delivery of freshly mixed concrete is assured by starting the mixing operation towards the end of the haul. On arrival at the worksite,

the concrete is discharged over detachable chutes into receptacles or directly on to theforms.

3.2 Central Mixing: In central mixing, both the operations of proportioning & mixing are carried out at a

batching plant & deliver the mixed concrete to the site in an agitator truck, which keepsthe mix concrete in correct form.

In case of centrally mixed type, the drum carrying the concrete revolves slowly soas to prevent the mixed concrete from ³segregation´ & prevent its stiffening due to initial

set.





Central mixing is resorted to when there is likely to be a considerable period lag between the time of mixing and the time of placing. With agitation a maximum of one

and half hours between mixing & placing can be allowed.Another important consideration in favour of central mixing method is the fact that

more concrete can be transported in a single trip when the truck-mixer is used as an

agitator. The effect of this is to reduce the transportation charges, all other factors beingequal.

3.3 Shrink Mix:

Concrete that is partially mixed in a plant mixer and then discharged into the drumof the truck mixer for completion of the mixing is called shrink mixed concrete. Central

mixing plants that include a stationary, plant-mounted mixer are often actually used toshrink mix, or partially mix the concrete. The amount of mixing that is needed in the

truck mixer varies in these applications and should be determined via mixer uniformitytests. Generally, about thirty turns in the truck drum, or about two minutes at mixing

speed, is sufficient to completely mix shrink-mixed concrete.





PLACING OF CONCRETE:





4. MATERIALS REQUIRED FOR RMC:

Admixtures: A substance added to the basic concrete to alter one or more properties of

the concrete, i.e. fibrous materials for reinforcing, water repellent treatment and colouring

compounds.

Air-entrainment admixtures (mainly used in concrete exposed to freezing andthawing cycles)

Water reducing admixtures ,plasticisers ( reduce the dosage of water whilemaintaining the workability)

Retarding the admixtures(mainly used in hot weather to retard the reaction of hydration)

Super plasticiser or high range water reducer(significantly reduce the dosageof water while maintaining the workability)

Miscellaneous admixtures such as corrosion inhabiting, shrinkage reducing,

coloring.pumping etc.

Aggregate: Inert particles (i.e. gravel, sand, and stone) added to cement and water to

form concrete.

Cement: Dry powder that reacts chemically with water to bind the particles of

aggregate, forming concrete. Portland cement is typically used in concrete production.

Fly Ash: Fly ash is a by product of coal fired electricity generating power plants. Mainly

composed of combustible elements such as carbon, hydrogen and oxygen (nitrogen and

sulfur being minor elements), and non-combustible impurities (10 to 40%) usually

present in the form of clay, shale, quartz, feldspar and limestone. As the coal travels

through the high-temperature zone in the furnace, the combustible elements of the coal

are burnt off, whereas the mineral impurities of the coal fuse and chemically recombine

to produce various crystalline phases of the molten ash. The molten ash is entrained in the

flue gas and cools rapidly, when leaving the combustion zone (e.g. from 1500°C to

200°C in few seconds), into spherical, glassy particles. Most of these particles fly out

with the flue gas stream and are therefore called fly ash.

The fly ash is then collected in electrostatic precipitators or bag houses and the

fineness of the fly ash can be controlled by how and where the particles are collected.





5. READY MIX CONCRETE PLANT:

A ready mix concrete plant is a permanent installation with mechanical handling for

the storage, proportioning & mixing of materials. The location, size of the plant & layout

are governed by a number of considerations, depending upon local conditions which

require careful study before the design and construction of the plant are undertaken.

5.1 LOCATION:

In the operation of a RMC concern, the transportation of the concrete to the site of the

job is generally one of the most expensive items & the RMC plant should, as far as

possible, be situated in the centre of the market. This may be difficult proposition in a

very large cities where works requiring. RMC may be situated beyond the economical

radius for operations. In such cases; it may prove more economical to operate two or more small plants, spread out to reduce the length of the haul, than to concentrate

production in a single large plant.

Another important consideration in the selection of a site is the facility of deliveryof materials to the plant. Location near the rail-head, from which a siding can be

constructed to the plant, would be more advantages in unloading the materials direct fromthe wagons to their respective stockpiles.

5.2 SIZE OF PLANT:

The size of plant will depend chiefly on the potential demand for which the plant

has to cater. This in turn is dependent upon the quality of concrete construction carriedout in a town or city.

Towns & cities undergoing a critical housing storage or those which are in the

process of industrial expansion would naturally provide a fruitful field for RMCoperation.

However, with increasing confidence amongst architects, engineers, contractors &the public in a product of guaranteed quality & offered at rates which are competitive

enough to induce the adoption of RMC in preference to site-mixed concrete, the demandwill soar. The size should, therefore, be selected taking into account potential future

increase in production.





5.3 LAYOUT:

The plant layout should be so arranged that it satisfies that it satisfies the following

considerations: firstly, it ensures the maximum efficiency in operation; secondly, it provides adequate space for the storage of materials & thirdly, it does not hamper future

expansion.

For faster operation & in order to reduce the traffic hazard within the plant, a one

way traffic should be adopted with vehicles entering & leaving from separate gateways &the equipment being so arranged that the truck-mixers collect first the dry materials from

the weigh-batchers, then the water, and make a direct exit into the street. In order tofurther reduce the amount of driving all the weighing equipment should preferably be

located near the front of the site or to close to the street exit, leaving the rear for thereceipt and the storage of materials.

The unloading & stockpiling of aggregates should be as close as possible to the

overhead compartment bins so that a minimum length of conveyer belts is required.Besides reducing the initial investment it will afford faster operation & a reduction in

production cost.

Adequate space for the stockpiling of materials is very necessary to meet with the

irregular supply of cement & aggregates. This calls for the provision of sufficient spaceto accommodate the storage of materials to provide for a reserve stock of cement &

aggregates equivalent to 7-10 days normal consumption.





6. STATIC EQUIPMENT:

The static equipment required for RMC plant can be divided into the followingcategories:

Equipment for unloading aggregates & cement, stockpiling them in their respective storage areas & elevating them into the overhead compartment bins.

Overhead compartment bins for storing cement & various sizes of sand, Coarse

aggregates with weigh-batchers for accurate proportioning & discharge chutes. Water storage tank.

Stationary mixers for central mixing plants. Office building & testing laboratory.

6.1 UNLOADING, STOCK PILING AND ELEVATING MATERIALS:

Aggregates may be delivered to the plant in railway wagons, Lorries or in

barges if the plant is sited near a water-front. Arrangements for unloading the materialsmay be either mechanical or manual, but mechanical handling is invariably adopted for

elevating into the storage bins.

In case of a fully mechanized system, a crawler crane, derrick or belt conveyorsare used for various operations. A crawler crane or derrick with a clamshell bucket will

unload the aggregates, stockpile them on the ground and place the aggregates into theoverhead compartment bins. In order to perform these operations efficiently the crane or

derrick should have a boom length which can conveniently reach above the tops of

overhead storage bins and the entire layout should be so arranged that only the minimumchange in the boom angle is necessary for any of the operations.

Another arrangement is to install a belt conveyer in a tunnel beneath the

aggregate stockpile with shaker in the roof of the tunnel to control the discharge of various aggregates on to the conveyer. The conveyer in turn feeds an elevator, which

empties the aggregates at the top of the bin into the appropriate compartment.

The initial investment required for small-sized plant can be effectively cut down by using a portable belt-conveyer for unloading the aggregates from the wagons and the

stockpiling them on the ground. Transportation of the materials to the bottom of the

storage bins is then done by means of Dobin- type dumpers fitted with pneumatic tyresand having a capacity of about 1.5cu.yd, from which the materials are tipped into a pit atthe foot of the bin and conveyed up into the compartment by means of an elevator.

When the aggregates are delivered to the plant in Lorries, they are easily unloaded

directly to the stockpile and any of the methods described above can be used for conveying and elevating into the storage bins.





Cement will generally be delivered to the plant either in bulk or in bags and itsstorage under moisture-proof conditions is very essential. Cement can be unloaded from

wagons either by hand-operated scoops or power shovels onto a hopper adjacent to

wagon door, which feeds by means of a screw conveyer a closed-typed bucket elevator the silo or storage bin in which the cement is kept. Cement can also be unloaded andstored by a portable pump which forces the cement into the storage bin through a pipe-

line.

6.2 INLINE BINS:

Inert raw materials like fine & coarse aggregates are stored in bins called as

³Inline Bins´ where the trucks carrying fine & coarse aggregate can dump the materialseasily. The aggregates required are fed by the means of aggregate belt conveyer. On the

aggregate belt conveyer the aggregate are weighed automatically by means of computer

from computer room present on the plant.

INLINE BINS

6.3 SILOS:

Cement & Fly ash are stored in an airtight container called as ³Silos´; the requiredquantity of cement & Fly ash is extracted by the silos. There are two Cement silos & one

silo of Fly ash. The capacity of cement silo is 2 x 130 tons = 260 tons.

Cement & Fly ash are to feed holding hopper with the help of a screw conveyer. Aheavy duty cement screw conveyer is fixed in inclined position to convey the cement





from Manual Feeding Hopper to Cement Hopper. A suitable drive unit is also provided todrive the screw.

The screw conveyer body and the screw are manufactured from heavy duty µC¶

class pipe and the flutes are fabricated from 5mm plate. Running clearances provided

between body and flutes for smooth running. The screw is supported on both ends by bearing and at center by hanger bearing having renewable hard bush. These bearing can be adjusted with setting nuts so as to have proper alignment.

The screw conveyer is provided with suitable vertical supports. One inlet

connection is provided at the bottom end where manual-feeding hopper is connected &one discharge connection at the top from where the cement is discharged to cement

weighing hopper. Flexible joint is provided between discharge connection & cementweighing hopper. Two cleaning pockets, one in the middle and another at the bottom side

are also provided for emergency removal of cement from conveyer.

Weigh-batchers are of many different types. They may be manually or automaticallyoperated and fitted either with bean scales and tell-tale dial or a spring less full readingdial.

.

SILOS

6.4 WATER STORAGE:

A RMC plant generally makes provision for adequate storage of water to meet its

requirements for 2 to 3 days. Control over quantity of mixing water is an essentialrequirement in concrete making for it bears a direct relation to the strength and quality of

the finished product. Equipment for the accurate measurement of water is, therefore, anecessary item in any ready mix concrete plant.





The device adopted for the measurement of water will depend upon the method of mixing and type of mixers. In a central mixing plant, this is introduced into the mixer

slightly ahead of the materials and the apparatus is of necessarily installed near the mixer and at the plant site. Measurement of correct quantity of water at the plant site can be

transit mixing also when correct amount of water required for a batch of concrete

introduced into a compartment of mixer, and fed into the drum by truck driver duringtransit.However, modern truck mixers are equipped with calibrated water gauges and

controls for the introduction of water into drum and responsibility of ensuring the correctmeasurement of water then devolves on driver.

6.5 STATIONARY MIXER:

The stationary mixer used in central mixing plant is of two types: Rotary mixer

Tilting mixer

In Rotary Mixer, the drum is cylindrical and revolves about ahorizontal axis. The drum has an opening at each end for charging anddischarging.

Tilting mixer type is equipped with a conical or bowl shaped drum

which revolves on an inclined axis, the concrete being discharged by tilting of drum.

6.6 OFFICE BUILDING & TESTING LABORATORY:

The provision of an office building to house the staff required for the receipt of

orders and the day to day administration of plant requires no elaborate set up and is madeto suit the requirements of a plant. A small testing laboratory, equipped with apparatus

for the scientific design of concrete mixers testing of samples to check that specifiedstrength and quality are being achieved is, however, a necessary adjust to a Ready-Mixed

concrete plant.





7. TYPES OF PRODUCTION PLANTS

Vertical Production Plant Horizontal Production Plant

7.1 Vertical Production Plant: In this the aggregates are stored above the batching and mixing elements, in one or

more silos. These plants ar e not suita ble for relocation at short intervals of time. As the

aggregates ar e stor ed in silos it is r elatively easy to protect the aggregates from very lowtem peratur e in winter period.

Figure: Schematic view of the Vertical Batching Mixing Plant with vertical aggregateand cement Storage silos. (Ambuja Cement Literature Vol.12)





7.2 Horizontal Production Plant:

They can be again broadly classif ied into four types i) Star pattern aggregate storage

ii) Storage in tall silo

iii) Storage in pocket siloiv) Inline aggregate storage silos

The star bin storage of aggregates is most popular in India mainly because of climateConditions. The aggregates can be stored exposed to ambient temperature in dif f erent

compartments f orming a star type patter n. A storage capacity of up to 1500 CuM is possible in this type. The star pattern aggregates are stored in four to six compartments.

They are bulked at a 45 degree flow angle against the batching plant 's bulkhead and partition wall of the compartments using a boom type dragline loader. The drag-line

operations are either fully manual, semi automatic or f ully automatic. Fully automaticdrag-line loader system o perator.

The star bin type plant requires more space and as the aggregates are stored in openthey heat up at high ambient temperatures and freeze at ver y low temperatures. These

types of plants are not suitable in extreme weather conditions.In silo type storage additional investment for loading equipment such as hopper ,

bucket elevator or conveyor belt plus rotary distribution are required. They have largeactive storage (upto 500 CuM) in a small areas. Loading is fully automatic, aggregates

are well protected in extreme climatic conditions and storage is very clean.

Figure: Schematic view of the Horizontal Batching mixing plant with the star pattern

aggregate storage bins at the rear & vertical storage silos. (Amubuja Cement LiteratureVol.no.12)





8. DELIVERY OF RMC

While ready mixed concrete can be delivered to the point of placement in a variety of

ways, the overwhelming majority of it is brought to the construction site in truck-mounted, rotating drum mixers. Truck mixers have a revolving drum with the axis

inclined to the horizontal. Inside the shell of the mixer drum are pair of blades or fins thatwrap in a helical (spiral) configuration from the head to the opening of the drum. This

configuration enables the concrete to mix when the drum spins in one direction andcauses it to discharge when the direction is reversed.

To load, or charge, raw materials from a transit mix plant or centrally mixed concrete

into the truck, the drum must be turned very fast in the charging direction. After theconcrete is loaded and mixed, it is normally hauled to the job site with the drum turning

at a speed of less than 2 rpm.

Since its inception in the mid-1920, the traditional truck-mixer has discharged

concrete at the rear of the truck. Front discharge units, however, are rapidly becomingmore popular with contractors. The driver of the front discharge truck can drive directly

onto the site and can mechanically control the positioning of the discharge chute withoutthe help of contractor personnel. Currently, because of weight laws, the typical truck

mixer is a 9 to 11 yd3 unit. The drums are designed with a rated maximum capacity of 63% of the gross drum volume as a mixer and 80% of the drum volume as an agitator.

Generally, ready mixed concrete producers, load their trucks with a quantity at or near therated mixer capacity. Fresh concrete is a perishable product that may undergo slump loss

depending on temperature, time to the delivery point on the job site, and other factors.

Water should not to be added to the mix unless the slump is less than that which is

specified. If water is added, it should be added all at once and the drum of the truck mixer should be turned minimum of 30 revolutions, or about two minutes, at mixing speed.





The ASTM C 94, Specification for Ready Mixed Concrete, indicates that the concreteshall be discharged on the job site within 90 minutes and before 300 revolutions after

water was added to the cement. The purchaser may waive this requirement, whenconditions permit.

In certain situations, air-entraining, water reducing, set-retarding or high-range water reducing admixtures may need to be added to concrete prior to discharge to compensatefor loss of air, high temperatures or long delivery times. The ready mixed concrete

producer will assist the purchaser in such circumstances.





AN OVERVIEW OF RMC PLANT





9. READY MIX CONCRETE COMPARED TO SITE MIX CONCRETE

PARTICULARS SITE-MIXEDCONCRETE READYMIXEDCONCRETE

PRODUCTION

Raw Material Near Mixer at site At Batching plant

Weighing Manual Computerised

Moisture Control Approximate Lab Control

W/C ratio Manual(approx.) Computerised

Dosing of admixture Manual(approx.) Computerised

Mixing Tilting mixer Non tilting single shaft mixer

Discharge Platform Transit mixer/pump

Rate 3 Cu.m/hr 30 Cu.m/hr

QUALITY

Degree of Control fair excellent

Yield variable consistent

Testing of fresh concrete once in 25 batches every batch

RAW MATERIALS

Selection/Sourcing Client/consultant skilled RMC personnel

Testing Client/consultant skilled RMC personnel

storage multi locational single point

storage space large limited and compact

requirement

DELIVERY Manual Transit Mixer

PLACING

Mode Manual/Hoist/Crane Concrete pump

Rate 1.5 Cu.m./hr 30 Cu.m./hr.





10. ADVANTAGES & DISADVANTAGESOF USING READY

MIX CONCRETE:

ADVANTAGES :

RMC is more advantageous to the consumer from both the technical and economical

aspects of concrete-making.

Assures consistent quality through accurate computerized control of aggregates and water

as per mix designs. It facilitates speedy construction through programmed delivery at site and mechanized

operation with consequent economy. Elimination of material storage on congested building site-no need to allocate place at

site for storage of cement, aggregate, sand.

It minimizes cement wastage due to bulk handling and there is no dust problem andtherefore pollution-free.

Save contractor¶s time, usage of Labor¶s energy to mix concrete and also saves project

time. Multi transportation of raw materials.

Creates a clean pollution free (noiseless and dust less) environment.

DISADVANTAGES :

Double handling results in additional cost and losses in weight.

Requirement of godowns for storage of cement and large area at site for storage of raw

materials. Aggregate get mixed and impurities creep in because of wind, weather and mishandling

at site.

There are always the possibilities of manipulation, manual error and mischief asconcreting are done at the mercy of gangs, who manipulate the concrete mixes and water cement ratio.





11. Industry Standards f or Truck Mixers:

Each batch of concrete must be mixed not less than 70and not more than 100 revolutionsof the drum.

Agitating speed is usually about 2 to 6 rpm.

Mixing speed is generally about 8 to 12 rpm. Concrete is to be delivered and unloaded within 1 to 2 hours or before the drum revolved

300 times after the introduction of water to the cement and aggregate.

Ordering of RMC:

Amount or structural dimensions.

Cement content (bags per cubic yard). Water-cement ratio.

Strength of concrete needed. Type of aggregate

Size of aggregate. Slump

Admixtures (type and amount) Time of delivery.

Clean-up Equipment:

Clean all the tools that comes in contact with concrete. Wash any mud or dirt from the frame of the mixers.

Rinse out the interior of the drum thoroughly. Clean any hardened concrete from tools or equipment by scraping and wire brushing to

remove. Hammering on a mixer to loosen concrete is not advisable because this will damage the

drum or the mixer. Always clean the mixer as soon as possible after use. A weak vinegar solution (10% acetic acid) is sometimes used to clean the cement film off

the exterior of mixers. Areas cleaned in this manner should be relaxed to protect themixers.





12. INFORMATION TO BE SUPPLIED BY THE PRODUCER

Name or number of the ready-mixed concrete depot.

Serial number of the ticket.

Date.

Truck number.

Name of the Purchaser.

Name and location of site.

Grade or mix description of the concrete.

Specified target workability.

Minimum cement content (if specified).

Type of cement and grade (if specified).

Maximum free water-cement ratio (if specified).

Nominal maximum size of aggregate.

Generic type or name of any chemical and

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13. STRUCTURES BUILT IN RMC

Structures Built With RMC in India:

55nos. of flyovers in Mumbai.

Mumbai-Pune expressway (95kms) 9nos. of mini flyovers in Chennai.

Super structures on station building of metro railway project at Chennai. M45 grade RMC using 30% OPC for worli out fall project in Mumbai.

Tidal Park at Chennai. Many residential flats-houses in Chennai, Bangalore and Mumbai etc.

Structures built with RMC in the World:

Petronas Towers of Kuala Lumpur.

World Trade Centre, New York, USA. Golden Gate Bridge, San Francisco.

Changai International Airport, Singapore. Sydney Opera House, Australia.

Euro Tunnel (UK/France)

PETRONAS TOWERS OPERA HOUSE





TALOJA FLYOVER







15. GENERAL PRECAUTIONS:

AT THE TIME OF CASTING:

Check and ensure that the concrete cover blocks are intact and not disturbed during

concreting operations.

Closely supervise the proper batching of ingredients, water content, mixing and testing of fresh concrete in case of concrete made at site. However, for RMC this aspect is taken

care of as the degree of quality control is very high. Beams should be cast first in layers and properly compacted with vibrators.

One carpenter & helper should be present below slab shuttering to ensure that props arenot disturbed and shuttering remains intact in position during & after concreting.

One bar bender should be present to ensure that no displacement of steel reinforcementtakes place.

Do not allow very smooth finish to concrete slab. Do not allow spunk ling of dry cement

for finishing, avoiding micro shrinkage cracks. Ensure that top reinforcement bars (for negative movement) are not disturbed during

concreting by placing the chairs firmly and properly.

Avoid formation of cold joints in the slabs. For concreting during summer season, cover freshly casted slab with moist gunny bags

after 4-5 hours of casting. In case of rain, high winds and hot temperature cover the slab with tarpaulin to protect it

from getting damaged. Do not allow drastic drying of green concrete to avoid plastic shrinkage cracks.

Closely supervise the compaction and finishing process of concrete.

AFTER CONCRETING OF SLAB:

Deshuttering of vertical sides of beams, columns only after 24 hours.

Cursing of slab for 14 to 20 days depending upon the type of structure. Deshuttering of slab after 7, 10 or 15 days depending upon span of slab and type of

cement used. Deshuttering of beams after 14 or 21 days depending upon span.

Checking all spots of honeycombing and finishing which rich cement sand mortar.

BEFORE CASTING OF SLAB:

Check concealed electric conduit work, junctions and all electrical points, MS boxes as per electrical layout plan.

Check the reinforcement and obtain approval from RCC consultant.

Check the standby arrangement for water in case of electricity failure Decide the position of concrete joints in case of a big slab after consulting the RCC

consultant. Ensure removal of wooden pieces, paper, etc. from slab/beam before casting





Ensure that shuttering and scaffolding is firm and proper Ensure all joints in formwork are properly sealed to avoid slurry leakage. Instead of using

mud, jute, paper, etc. it is desirable to use putty of used grease and cement (50:50). Iteffectively seals joints and remains intact during vibration of concreting. Strip of

aluminum foil to cover gap can also used.

Make arrangement of wooden planks and steel chairs and place them on slab for labor movement. Do not allow labour to directly walk on reinforcement.

Check if vibrator is in working condition and adequate labour is available.

Sprinkle little water over shuttering just before placing the concrete. Ensure sufficient light arrangements in case of late evening concreting and provide safety

measures.

Ensure that concrete cover blocks of proper size are provided at site as per requirements of BIS

standards.





Ready Mix Concrete Truck
















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Ready Mixed Concrete Final