READY MIX CONCRETE

SYNOPSIS

Ready-mix concrete is a type of concrete that is manufactured in a factory or batching

plant, according to a set recipe, and then delivered to a worksite, by truck mounted transit

mixers . This results in a precise mixture, allowing specialty concrete mixtures to be

developed and implemented on construction sites. The first ready-mix factory was built

in the 1930s, but the industry did not begin to expand significantly until the 1960s, and it

has continued to grow since then.

Ready-mix concrete is sometimes preferred over on-site concrete mixing because of the

precision of the mixture and reduced worksite confusion. However, using a pre-

determined concrete mixture reduces flexibility, both in the supply chain and in the actual

components of the concrete.

Some leading ready-mix concrete suppliers worldwide are the Mexican concrete

companies PCM and Cemex; their main competitor is France-based Lafarge

Ready Mixed Concrete, or RMC as it is popularly called, refers to concrete that is

specifically manufactured for delivery to the customer's construction site in a freshly

mixed and plastic or unhardened state. Concrete itself is a mixture of Portland cement,

water and aggregates comprising sand and gravel or crushed stone. In traditional work

sites, each of these materials is procured separately and mixed in specified proportions at

site to make concrete. Ready Mixed Concrete is bought and sold by volume - usually

expressed in cubic meters. RMC can be custom-made to suit different applications.

Ready Mixed Concrete is manufactured under computer-controlled operations and

transported and placed at site using sophisticated equipment and methods. RMC assures

its customers numerous benefits

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CONTENTS

Certificate

Acknowledgement

Synopsis

Page number Introduction 1

Definition of Ready Mix Concrete 2

Selection of materials 3-5

Mixing of concrete 6-8

Transportation of RMC 9-12

Properties 13-14

Advantages&Disadvantages 15-17

ACC Concrete 18-19

Goals 20

Important technical terms 21-22

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Ready mix concrete

Introduction:

z Concrete is a mixture of portland cement, water, aggregates, and in some

cases, admixtures.

z The cement and water form a paste that hardens and bonds the aggregates

together.

z Concrete is often looked upon as “man made rock”.

z Concrete is a versatile construction material, adaptable to a wide variety of

agricultural and residential uses

z Concrete has strength, durability, versatility, and economy.

z It can be placed or molded into virtually any shape and reproduce any

surface texture

z Concrete is the most widely used construction material in the world.

z In the United States almost twice as much concrete is used as all other

construction materials combined.

z Demand for concrete with higher strength and better quality, coupled with

larger and faster mixer trucks, led to the emergence of the ready-mix

concrete industry in the post-World War II period.

z The ready-mix concrete producer has made concrete an appropriate

construction material for many agricultural applications.

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DEFINITION

What is Ready Mixed Concrete

Ready Mixed Concrete, or RMX as it is popularly called, refers to concrete that is

specifically manufactured for delivery to the customer's construction site in a freshly

mixed and plastic or unhardened state. Concrete itself is a mixture of Portland Cement,

water and aggregates comprising sand and gravel or crushed stone. In traditional work

sites, each of these materials is procured separately and mixed in specified proportions at

site to make concrete. Ready Mixed Concrete is bought and sold by volume - usually

expressed in cubic meters. RMX can be custom-made to suit different applications.

RMC Process

Ready-mix concrete (RMC) is a ready-to-use material, with predetermined mixture of

cement, sand, aggregates and water. RMC is a type of concrete manufactured in a factory

according to a set recipe or as per specifications of the customer, at a centrally located

batching plant.

It is delivered to a worksite, often in truck mixers capable of mixing the ingredients of the

concrete en route or just before delivery of the batch. This results in a precise mixture,

allowing specialty concrete mixtures to be developed and implemented on construction

sites. The second option available is to mix the concrete at the batching plant and deliver

the mixed concrete to the site inan agi tator truck, which keeps the mixed concrete in

correct form.

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Materials used for the manufacture of RMC

z Portland Cement

z Aggregate - sand, gravel, crushed rock

z Water

z Admixtures - when necessary

Portland Cement

z Portland cement was named for the Isle of Portland, a peninsula in the English

Channel where it was first produced in the 1800's.

z Since that time, a number of developments and improvements have been made in

the production process and cement properties.

z The production process for portland cement first involves grinding limestone or

chalk and alumina and silica from shale or clay.

z The raw materials are proportioned, mixed, and then burned in large rotary kilns

at approximately 2500°F until partially fused into marble-sized masses known as

clinker.

z After the clinker cools, gypsum is added, and both materials are ground into a fine

powder which is portland cement.

Three types of portland cement are used for agricultural applications:

Type I

Type I cement is the general purpose and most common type. Unless an alternative is

specified, Type I is usually used.

Type II

Type II cement releases less heat during hardening. It is more suitable for projects

involving large masses of concrete--heavy retaining walls, or deadmen for suspension

bridges.

Type III

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z Type III cement produces concrete that gains strength very rapidly.

z It is very finely ground and sets rapidly, making it useful for cold weather jobs

Water

z Good water is essential for quality concrete.

z It should be good enough to drink--free of trash, organic matter and excessive

chemicals and/or minerals.

z The strength and other properties of concrete are highly dependent on the amount

of water and the water-cement ratio.

Aggregates

z Aggregates occupy 60 to 80 percent of the volume of concrete.

z Sand, gravel and crushed stone are the primary aggregates used.

z All aggregates must be essentially free of silt and/or organic matter.

Admixtures

z Admixtures are ingredients other than portland cement, water, and aggregates.

z Admixtures are added to the concrete mixture immediately before or during

mixing

Air Entraining agents:

z are the most commonly used admixtures for agricultural concrete.

z produce microscopic air bubbles throughout the concrete.

z Entrained air bubbles:

y improve the durability of concrete exposed to moisture and freeze/thaw

action.

y Improve resistance to scaling from deicers and corrosive agents such as

manure or silage.

Retarding admixtures:

z are used to slow the rate of concrete hardening.

z They are useful for concrete that is placed during hot weather.

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Accelerating admixtures

such as calcium chloride, are used to increase the rate of hardening--usually during cold

weather

For ready mix concrete supply the purchaser should specify the

Following

a) Designated max. size of coarse aggregate

b) Desired / max. slump at the point of

delivery

c) Air content (for air entrained concrete)

d) Mix design requirement – such as cement content, max. water content &

admixtures

or minimum compressive strength at 28 days

e) Unit weight required (for structural lightweight concrete)

Mixing of concrete

In the case of the centrally mixed type, the drum carrying the concrete revolves slowly so

as to prevent the mixed concrete from "segregation" and prevent its stiffening due to

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initial set.

However, in the case of the truck-mixed concrete, the batched materials (sand, gravel and

cement) are carried and water is added just at the time of mixing. In this case the cement

remains in contact with the wet or moist material and this phase cannot exceed the

permissible period, which is normally 90 minutes.

The use of the RMC is facilitated through a truck-mounted 'boom placer' that can pump

the product for ready use at multi-storeyed construction sites. A boom placer can pump

the concrete up 80 metres.

RMC is preferred to on-site concrete mixing because of the precision of the mixture and

reduced worksite confusion. It facilitates speedy construction through programmed

delivery at site and mechanised operation with consequent      economy.     It also

decreases labour, site supervising cost and project time, resulting in savings. Proper

control and economy in use of raw material results in saving of natural resources. It

assures consistent quality through accurate computerised control of aggregates and water

as per mix designs. It minimises cement wastage due to bulk handling and there is no

dust problem and therefore, pollution-free.

• Done in order to ensure each particle of aggregate in fresh concrete will be coated

with the cement paste

• Also to give a homogenous even coloured product.

• First stage of mixing is called “BATCHING”.

• Batching is process where it involves weighing out or measuring out all of the

ingredients for a batch of concrete

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1.6 cuM. transit mixer

small batching plant for local small deliveries

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7 cuM. transit mix

Transportation 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 a pair of blades or fins

that wrap 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 and

causes 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 the concrete

is loaded and mixed, it is normally hauled to the job site with the drum turning at a speed

of less than 2 rpm.

The driver of the front discharge truck can drive directly onto the site and can

mechanically control the positioning of the discharge chute without the help of contractor

personnel.

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RMC delivery trucks

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Concept of Readymix Concrete

Concept of Readymix Concrete

Ready-mix concrete has cement, aggregates,water   and   other   ingredients,   which   are weighbatched   at a   centrally located   plant.This is   then  delivered   to the   construction site in transit mixers and can be used straightaway without any further treatment.

RMX - Adding value to concrete

Ready Mixed Concrete is manufactured under computer-controlled operations and

transported and placed at site using sophisticated equipment and methods. RMX assures

its customers numerous benefits:

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Uniform, consistent and assured quality of concrete

Flexibility in concrete design mixes

Easier addition of admixtures

Faster and speedier construction

Reduced inventories, material handling and storage of raw materials at sites

Savings in labour requirements, labour costs and supervision of labour

Reduced wastage of materials

The use of RMX is an environmental friendly practice that ensures a cleaner work place

and causes minimal disturbance to its surroundings. This makes its utility more

significant in crowded cities and sensitive localities

In contrast to this, conventional methods of making, transporting and placing concrete at

most construction sites are somewhat labour-intensive and suffer from practices which

may be erratic and not very systematic.

Therefore the use of Ready Mixed Concrete can prove to more cost effective in the

longer term while ensuring that structures are built faster and using concrete that comes

with higher levels of quality assurance

Hurdles to set up new Plant:

Plant to be located in an area where Concrete Consumptions are there, as the

concrete has to be transported. Good water source at the plant site. In case

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of Non-availability of potable water in and around the location of plant, water

has to be transported from distant location.

. properties

Desired properties of hardened ready-mixed concrete include durability, strength, water

tightness, and resistance to abrasion. All of these characteristics are influenced by the

quality of the component materials and their proportions. Sometimes, expert assistance

is required and our Technical Services Center works with customers and specifiers to

optimize the mix designs.

Workability

z Workability is the property that determines the ease with which freshly mixed

concrete can be placed and finished without segregation.

z Workability is difficult to measure but redi-mix companies usually have

experience in determining the proper mix.

z Therefore, it is important to accurately describe what the concrete is to be used

for, and how it will be placed.

Durability

z If acceptable materials are used, the properties of concrete, such as durability,

freeze/thaw resistance, wear resistance, and strength depend on the cement

mixture.

z A mixture with a sufficiently low ratio of water to cement plus entrained air, if

specified, is the most desirable

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These properties--and thus the desired concrete quality--can only be fully achieved

through proper placement and finishing, followed by prompt and effective curing.

For thousands of years man has been mixing aggregates, cement and water together to

build structures. Many ancient structures such as the Great Pyramids and the Coliseum

were bonded together with cement mortars. Today, ready-mixed concrete is frequently

used to construct highways, bridges, dams, buildings, airports, sewer systems, tunnels,

home foundations, driveways, and sidewalks.

Applications

The growth of RMC is predominantly driven by demand from the metro cities. In cities

like Mumbai, the     mandatory     use     of     RMC      is in construction of flyovers

provided the requisite impetus to growth, according to an ICRA analysis. RMC is

particularly useful when the building activity is located in congested sites where little

space is available for siting the mixer and for stock piling of aggregates. The use of RMC

is also advantageous when only small quantities of concrete are required or when

concrete is to be placed only at intervals.

Even as the concept of ready-mix concrete (RMC) is still catching up in the country,

cement majors are keenly focussing on entering the new area in a big way. Anticipating

huge potential for the product, cement majors, including Associated Cement Companies,

Grasim, L&T, India Cements, Priyadarshini Cements, Chettinad Cement and Madras

Cements, are foraying into the RMC business

Advantages of Ready mix Concrete over Site mix Concrete

A centralised concrete batching plant can serve a wide area.

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The plants are located in areas zoned for industrial use, and yet the delivery trucks

can service residential 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

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. Some

sites are just too far away, though this is usually a commercial rather than

technical issue.

Generation of additional road traffic; furthermore, access roads, and site access

have to be able to carry the weight of the truck and load. Concrete is approx.

2.5tonne per m². This problem can be overcome by utilising so-called 'minimix'

companies, using smaller 4m³ capacity mixers able to access more restricted sites.

Concrete's limited timespan between mixing and going-off means that readymix

should be placed within 2 hours of batching at the plant. Concrete is still usable

after this point but may not conform to relevant specifications

However there are some disadvantages of RMC to, like double handling, which 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. Aggregates get mixed and impurities creep

in because of wind, weather and mishandling at site. Improper mixing at site, as there is

ineffective control and intangible cost associated with unorganised preparation at site are

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other drawbacks of RMC. There are always possibilities of manipulation; manual error

and mischief as concreting are done at the mercy of gangs, who manipulate the concrete

mixes and water cement ratio.

Utilization of Fly ashThough the scope for utilization of fly ash in Readymix concrete

is very high, the concept of fly ash as an additive to concrete

is still at very initial stage and it is not popular among majority

of actual users of concrete

Advantage of Readymix Concrete over Sitemix Concrete:

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.

Labour associated with production of concrete is eliminated.

Time required is greatly reduced.

Noise and dust pollution at site is reduced.

Organisation at site is more streamlined.

Redefining the pace and quality of construction

ACC set up India's first commercial Ready Mix Concrete (RMX) plant in Mumbai in

1994. Today this business has been reorganized as a separate company called ACC

Concrete Limited which is one of the largest manufacturers of RMX in India with over

30 modern plants in major cities such as Mumbai, Bangalore, Kolkata, Chennai, Delhi.

Hyderabad, Goa, Pune and Ahmedabad

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ACC's pioneering efforts in introducing RMX coupled with the promotion of bulk

cement handling facilities have been responsible for redefining the pace and quality of

construction activity in metropolitan cities and in mega infrastructure projects

Numerous landmark structures in India's metro cities have been built using ACC

Concrete - mega housing projects, townships, commercial complexes, factories, bridges,

flyovers, roads and railways. Prestige projects such as the Mumbai-Pune Expressway, the

Indore-Dewas bypass, Kolkata and Delhi Metro Rail projects. Most of the new bridge

and fly-overs in Mumbai used ACC Concrete and could perhaps not have been completed

on schedule without it.

Small building projects and individual home builders seeking high levels of quality

assurance can also now usher in the same sophistication and value addition into their

construction as some of India's mega projects using ACC RMX- at virtually no extra cost.

ACC Concrete - State-of-the-art

ACC Concrete is manufactured at modern fully computerized plants which have state-of-

the-art machinery and equipment by machinery suppliers of global repute - fully

automated Batching Plants, well-equipped laboratories for testing raw materials and fresh

concrete, Transit mixers, Mobile and stationary pumps capable of discharging concrete at

high elevations and over long distances.

A large fleet of the latest models of Transit Mixers and Concrete Pumps to suit different

terrains and work sites ensures that our customers get timely and uninterrupted supply of

premium quality concrete as per their requirement as well as its efficient and timely

placement at the work site.

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Quality - the 'Q' factor in ACC Concrete

ACC Concrete is supplied in a variety of grades and compositions to meet specific

demands of customized applications - from simple requirements for small homes to High

Performance Concrete to meet the complex needs of mega projects.

Each of our plants has a fully equipped laboratory with the latest in testing machines to

carry out routine and detailed tests of raw materials as well as fresh finished concrete.

These in-plant laboratories are backed by the facilities of ACC's reputed Research centre

at Thane which serves as a focal research and testing laboratory centre for cement and

concrete.

ACC Concrete customers can avail of a range of options in our testing and quality control

services - from simple tests and analyses of raw materials and concrete to non-destructive

testing of hardened concrete.

ACC Concrete - a wide range

High Strength Concrete

High Performance Concrete

Self-leveling Concrete

Self-compacting Concrete

Coloured Concrete

Concrete made with binary and ternary blends of cements

Early strength Concrete

Fibre reinforced Concrete

Reason for backlog

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The Ready mix concrete business in India is in its infancy. For example, 70% of cement

produced in a developed country like Japan is used by Ready Mix concrete business

there. Here in India, Ready Mix concrete business uses around 2% of total cement

production.

In early 70s both pricing and distribution of cement was controlled due to shortage of

supply, Readymix concrete technology could not be implemented as investors felt that

Ready mix concrete plant will starve due to non-availability of cement. The levy of

additionl Taxes & Duties on RMC, entry tax, excise duty also contributed to the slow

development of the concept.

Government bodies, private builders, architects/engineers, contractors, and

individuals are to be made fully aware about the advantages of using

ready mix concrete.

Government bodies / consultants to include ready mix concrete as mandatory in

their specification for execution.

Government helps necessary for the growth of Industry :

.

Government specifications for CPWD and PWD jobs should include Readymix

concrete as an mandatory item.

Tax breaks are required for the growth of RMC

Developers / Contractors to be discouraged from piling up materials like metal,

sand etc. on roads/foot paths.

Goals:

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z To determine the most economical and practical combination of readily available

materials.

z To produce a concrete that will meet requirements under specific conditions of

use.

z The majority of concrete used for agricultural applications is supplied by ready-

mix producers.

z With an understanding of these goals, the customer can communicate better with

the ready-mix supplier, and obtain concrete that is suited to the project at hand.

A properly proportioned concrete mix will provide:

Workability of freshly mixed concrete.

z Workability is the property that determines the ease with which freshly mixed

concrete can be placed and finished without segregation.

z Workability is difficult to measure but redi-mix companies usually have

experience in determining the proper mix.

z Therefore, it is important to accurately describe what the concrete is to be used

for, and how it will be placed.

Durability, strength, and uniform appearance of hardened concrete.

z If acceptable materials are used, the properties of concrete, such as durability,

freeze/thaw resistance, wear resistance, and strength depend on the cement

mixture.

z A mixture with a sufficiently low ratio of water to cement plus entrained air, if

specified, is the most desirable.

These properties--and thus the desired concrete quality--can only be fully achieved

through proper placement and finishing, followed by prompt and effective curing

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Economy

z Proportioning should minimize the amount of cement required without

sacrificing quality.

z Quality depends on the amount of cement and the water-cement ratio.

z Hold the water content to a minimum to reduce the cement requirement.

CONCLUSIONS

Better quality concrete is produced.

Time required is greatly reduced.

Noise and dust pollution at site is reduced.

Flexibility in design .

Adding admixtures is easy.

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