Presentation on RM Concrete

7/27/2019 Presentation on RM Concrete

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READY MIX CONCRETE:

AN OVERVIEW

BY

BHUPENDRA SINGH RAGHAVA

M TECH - CONSTRUCTION MANAGEMENT

SEM- I


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READY MIX CONCRETE RMC is a specialized material in which the cement

aggregates and other ingredients are weigh-batched at aplant in a central mixer or truck mixer, before delivery to

the construction site in a condition ready for placing bythe builder.

Thus, `fresh' concrete is manufactured in a plant awayfrom the construction site and transported within the

requisite journey time. The RMC supplier provides two services, firstly one of

processing the materials for making fresh concrete andsecondly, of transporting a product within a short time.


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HISTORY OF RMC First introduce by Architect Jurgen Heinrich Magens, he

get his patented of RMC in Germany in 1903.

The first concrete mixed off site and delivered to aconstruction site was effectively done in Baltimore,

United States in 1913 just before the First World War.

The first concept of transit mixer was also born in 1926 in

the United States. In 1939, the first RMC plant was installed in United

Kingdom and in 1933 first specifications on RMC was

published in United Kingdom.


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Figure: Transit mixer in late 1940s and Concrete pump in late 1940s

(Ambuja Cement Literature Vol. 90)


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In India RMC was first initially was used in 1950 duringthe construction sites of Dams like like Bhakra Nangal,Koyna.

RMC was first fully established in Pune in the year 1991by private companies which was close later.

RMC was successfully established sometime after 1994 inIndia.

As per the available record upto 2003, there are around 76RMC plant in 17 cities with a total capacity of around3875 CuM/hr, producing 3.8 million CuM of concrete peryear.


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ADVANTAGES OF RMC SUPERIOR QUALITY

REDUCED THE WASTAGES OF MATERIAL

ELIMINATE THE PROBLEM OF STORAGE OF

MATERIAL REDUCE SUPERVISION & LABOUR COST

SAFE & HYGENIC CONDITION

FLUCTUATION OF RAW MATERIAL COST & NON-AVABILITY OF MATERIAL ELIMINATE

REDUCES THE PROBLEM OF INSPECTION, CHECKING& TESTING

ROADS & FOOTHPATH ARE NOT BLOCKED

IMPROVE THE ENVIRONMENT


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SCOPE OF RMC IN INDIA The World Bank's India Cement industry Restructuring Project"

under which a technical study report on the development of market

for bulk cement in India was made in 1996, proved to be positive

development towards modernization of cement distribution system inIndia, including setting up Ready mix concrete Plants.

The objective of this technical study was to formulate an action plan

for the development of market for bulk cement in large cement

centres in India and for gradual shift. from the traditional mode of

transportation in bags to bulk transportation through setting up ofready mixed concrete plants in different parts of the country. The

recommendation of the action plan provided a useful guidance

towards expanding bulk cement market thus paving a way for

installation or ready mixed concrete plants in India


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According to Cement Manufacturers Association, RMC is being

increasingly recommended for all major public construction work

such as highways, flyovers.

In India it can grow to consume 40-45 percent of cement by 2015

through setting up of RMC plants in various consumption centers.

According to European Ready Mixed Concrete Organization

(ERMCO) .The marketing of RMC should no more be in terms of

strength grades only, but a combination of strength durability

classification as per the Concrete Codes which improves thesellability of RMC in terms of the requirements of the projects.

Appropriate environmental, safety and health regulations for the

working force need to be kept in mind in the management and

operation of RMC.


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Figure : RMC Market Potential (CE&CR, June 2001, pg.no.30)


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TYPES OF BATCHING

PLANTS1) Centrally Mixed Concrete or Wet batch mixer

In Centrally mixed concrete, the mixing is done at a central plant& the mixed concrete is then transported usually in the truckagitator truck which revolves slowly so as to prevent segregationand undue stiffening of the mix.

2) Truck mixed concerte or Dry batch concrete plant

In the truck mixed concrete, the materials is batched at a centralplant but are mixed in a mixer truck either in transit to the site or

immediately prior to the concrete is being discharged. Transit-mixing permits a longer haul and is less vulnerable in case ofdelay, but the capacity of a truck used as a mixer is only 63 percent, or even less, of the drum while for central-mixed concrete is80 percent.


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BATCHING AND MIXING

PLANTSa) Storage of Materials

i) Cement

Cement is generally stored in silos. The loading of cement is done with the help of pneumatic

blower systems

Figure: Pneumatic blower system on a

cement bulker unloading cement

into silos.(Ambuja Cement Literature Vol. 12)


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ii) Water

Water is generally stored in tanks located close to the plant. Itis accurately measured by a water gauge and microprocessorcontrolled system.

The modern plants have new electronic MFM 85 moisturerecorders .

Figure:

Electromechanical weighing system used

on modern batching plant for cement and aggregates (Amubuja

Cement Literature Vol.no.12)


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iii) Aggregates

Vertical Production Plant

In this the aggregates are stored above the batching and

mixing elements, in one or more silos.These plants are not suitable for relocation at short

intervals of time.

As the aggregates are stored in silos it is relatively easy to

protect the aggregates from very low temperature inwinter period.


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Figure: Schematic view of the Vertical Batching Mixing

Plant with vertical aggregate and cement storage silos.

( Ambuja Cement Literature Vol.12)


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Horizontal Production Plant

They can be again broadly classified into four types

i) Star pattern aggregate storage

ii) Storage in tall silo

iii) Storage in pocket silo

iv) Inline aggregate storage silos

The star bin storage of aggregates is most popular in India

mainly because of climate conditions.

A storage capacity of upto 1500 CuM is possible


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Figure: Horizontal Batching Mixing Plant

with vertical aggregates & cement silos

(Amubuja Cement Literature Vol.no.12)


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Figure: Rear view of the batching mixing plant with star pattern having four

aggregate storage bins



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b) MIXING ARRANGEMENTS

There are various types of concrete mixers used on the

concrete production plant. The two basic types are free fall

mixers and power mixers

Free fall mixer consists of a rotating drum with bladefixed on the drum's interior. As the drum rotates, the

material inside is lifted and dropped.

Most of the imported plants have power mixer. The power

mixer sets in motion the materials positively. Thematerials get thoroughly mixed by rotating arms.


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Figure: Cross sectional view of the single shaft

compulsory power mixer.


Figure: Twin shaft compulsory power mixer



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c) CONTROL SYSTEMS

Figure: a) Fully automatic control panel of a modern

mixing plant.

b) Microprocess Control System on the modern

mixing plant.



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d) TRANSPORTATION EQUIPMENT: - TRANSIT MIXER

Normal capacity 4 to 12 CuM

Hydrulic Drive of Mixer Separate engine or driven by truck engine

Water tank capacity 192 to 2000 litres

Mixer trucks Twin axles for 4 CuM capacity

Three axles for 6 to 7 CuM capacity, three/four

axles for 8 to 10 CuM capacity, Semi trailer

truck for 10 to 12 CuM.


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SAMPLING OF CONCRETE As per IS 4926-2003 After the truck-mixer has re-mixed

its delivery on site allow at least the first one-third of a m3

of concrete to be discharged prior to taking any samples.

Take at least 4 incremental samples from the remainder of

the load avoiding sampling the last cubic metre of

concrete.

As per BS 1881: Part 101 & Part 102, describe the

recommended sampling methods for ready mixed concrete

in British code. Using a standard scoop, this can collect

about 5kg of normal weight concrete.


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SAMPLING OF CONCRETE BS1881: Part 102(The Alternative Method) An initial discharge of at least 0.3 m3 is made before

a sample of six scoopfuls is collected from the moving

stream; The sample is then re-mixed on a non-absorbent

surface and split into two equal parts. Each part is then

tested or slump, with the average of the two tests recorded

as the test result.The Alternative method of collecting

sample

(CE&CR, June 2001, pg. no. 35)


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TESTING OF CONCRETE COMPRESSIVE TEST

As per IS 456 -2000, a result is the average of the

compressive test specimens made for the same sample of

concrete. Individual variation should not be more than 15

Percent of the average.

SLUMP TEST

According to ASTM C94-94, the time during which thecement and moist aggregate are allowed to remain in

contact is limited to 90 minutes; BS 5328: part 3: 1990

allows 2 hours.


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The 90 minutes limit can be relaxed by the purchaser.With the use of retarding admixtures, the time limit can be

extended to 3 or even 4 hours.

The United States Bureau of Reclamation provides for an

extension of 3 to 6 hours in the time of contact between

cement and wet aggregate in transport prior to mixing.

In IS 4926-2003, The general requirement is that concrete

shall be discharged from the truck-mixer within 2 h of thetime 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.


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NEED TO BE SPECIFIED FOR

RMC Characteristic strength or grade (N/mm2) Target workability or slump in mm required at site

Maximum water to cement ratio

Minimum cement content

Maximum aggregate size

Type of cement

Mineral admixture and its proportion (Kg/m3) Maximum aggregate size

Rate of gain of strength (for formwork removal or prestressing etc.)

Maximum temperature of concrete at the time of placing (in extreme climatic conditions or in caseof massive concrete pours)

Type of surface finish desired.

Method of placing

Rate of supply desired to match the placing and compaction speed planned at site. Quantity of concrete required.

Lift and lead of concrete transportation and placement at site.

Frequency of concrete testing

Details of materials and their required tests.

Permeability tests required (if any)

Placing of concrete in formwork to be under scope of RMC supplier (if required)

Mode of measurement.


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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

Quantity of concrete in m.

Time of loading.

Signature of the plant operator.

A statement warning the purchaser of the precautions needed to be taken when working with cement

and wet concrete.mineral admixtures included.


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CHECKS BY CONSUMER

BEFORE ORDERING THE RMC Reliability of the plant and transit mixers

Calibrations of all measuring devices and their accuracy.

Mode of operation of plant should preferably be fully

automatic and not manual. Quality of materials proposed to be used.

Adequacy of quantity of materials proposed to be used.

Compliance of concrete specifications based on the mix

parameters specified. Adequacy of testing facilities

Time likely to be taken by transit mixers from plant to site andback.


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CHECKS NEEDED AT SITE

PRIOR TO RECEIPT OF RMC Reinforcement layout

Adequacy of formwork

Openings and chutes provided Adequacy of manpower and equipment

Proper approach for transit mixers

Proper platform to receive concrete.

If pumping is proposed, the location of the pumpshould be approachable from both sides


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CHECKS NEEDED AT SITE

DURING CONCRETING Proper co-ordination between the RMC supply and placing and

compacting gangs.

Proper signaling or communication at site is necessary.

Workability of concrete within accepted limits. Adequacy of cohesiveness of concrete for pumpability.

Water addition or chemical admixtures are not added duringtransportation .

Temperature of concrete at the time of receipt at site (ifspecified).

Continuous and steady supply at site and speedy unloading

Retempering should not be allowed.

UNNECESSARY RESTRICTIONS ON


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UNNECESSARY RESTRICTIONS ON

SUPPLIERS OF RMC BY

PURCHASER Insistence on use of cement and admixtures of specific brands

Inappropriately low water to cement ratio

Restriction on use of water reducing admixtures

Insisting on Indian Standard method of concrete mix design

Frequency of testing

Fixed slump insisted upon

Ambiguous specifications

Concrete Field strength should not be less than Target strength


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THE CONSTRAINTS FACED BY

RMC PRODUCERS AT PRESENT High Cost Delayed payments and long credit by consumers

RMC plants in cities are not permitted to be installed inresidential zones.

High cost of the plant and equipment results in high capital

costs. Bad quality of roads and traffic congestion and intermittent

signals often delay the deliveries in metros.

Availability of trained and skilled manpower for operations andmaintenance of plant and equipment.

Delays in placing, compacting and finishing at consumer's endcauses delays in unloading of transit mixer and stiffening of theconcrete mix.

Quality of formwork and its adequacy


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PROMOTING RMC IN INDIA Ban any storage of materials at any construction site.

No public space shall be occupied by building materials during

construction.

Government should come out and insist on RMC and quality.

Transit mixers movements should be allowed through out 24

hrs.

Government should given some taxes & import duties benefit.

The government and local bodies can encourages the use of

ready mixed concrete


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CONCLUSION DURABLE CONSIDERATION

OVERALL ECONOMY

REALISATION OF THE ADVANTAGES BY

ENGINEERS AND CONSTRUCTION INDUSTRY

WIDELY ADOPTED THROUGH OUT THE WORLD


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REFRENCES Kaushal Kishore (June 2001), RMC: Some Technical Aspects,

Civil Engineering & Construction Review.

Sanjay Bahadur(June 2001), RMC- A Non-Negotiable Approach toDurable Urban Infrastructure, Civil Engineering & Construction

Review. Kshemendra Nath (June 2001), RMC- The Need for Partnership,

Civil Engineering & Construction Review.

Danish Rashid (June 2001), RMC: The Indian Answer to WorldClass Construction, Civil Engineering & Construction Review.

IS 4926-2003, Standard on Ready mixed concreteCode ofPractice, BIS, New Delhi.

RMC on the move (Oct. 2003), Ambuja Technical Literature, Vol.No. 90

Mechanisations of concreting, Part I- Batching, Mixing &Transporting (Dec. 1996), Ambuja Technical Literature, Vol. No. 12


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THANK YOU


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Presentation on RM Concrete