Civil Miniproject AbhilashReddy

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STUDY OF MATERIAL TESTING AND MIX DESIGN PROCEDURE OF READY MIX CONCRETE

By

B.B. ABHILASH REDDY

08241A0101

DEPARTMENT OF CIVIL ENGINEERING

GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING AND TECHNOLOGY

BACHUPALLY, KUKATPALLY, HYDERABAD, ANDHRA PRADESH, INDIA.

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ACKNOWLEDGEMENTS

I take this opportunity to express my deep and sincere gratitude to Mr.

.SATHEESH KUMAR , Head of south division ,LAFARGE India PVT Ltd. for his great

encouragement and esteemed guidance during the course of this work .

I am thankful to Mr. N.BALASUBRAMANYAM ,head of plant, LAFARGE India

PVT Ltd for his guidance during my work. I am thankful to him for his greatest technical

and moral support during the dissertation of work.

I would like to express my sincere thanks to my uncle Ms. P. SOWMYA .Who

helped me in finding this opportunity in the organization as internship programme .

B.ABHILASH REDDY

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STUDY ON READY MIX CONCRETE

ABSTRACT:

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

as per specifications of the customer, at a centrally located batching Plant. It is then send or

Delivered to a worksite, often in truck mixers capable of mixing the ingredients of the concrete

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 in an agitator tuck, which keeps the mixed concrete in correct form.

This project deals with the advantages, disadvantages and the quality control in the preparation

of the concrete, mix design of M20 and the preparation procedure followed at the ready mix plant.

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STUDY AREA

My study area comes under southern zone of India, Andhra Pradesh, Hyderabad. In

Hyderabad, I have done my project in LAFARGE India pvt .Ltd .The average atmospheric

temperature is 30°c. The location is far away from city. It is located in bachupally , in order

to prevent pollution of the city.

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Contents:

1.Introduction 1

1.1General. 1

1.2Objective 2

1.3Necessity 3

1.4History 5

1.5Scope 7

2.Materials for RMC 8

2 .1Aggregate 8

2.2 Cement 9

2.3Admixture 10

2.4 Fly ash 11

2.5Water 12

3.Equipments required 14

3.1 Batching plant 14

3.1.1 Storage of materials 14

3.1.2. Mixing arrangements 16

3.1.3. Control systems 17

3.2Transportation equipment 17

4. Mixing process 19

4.1Transit mixed concrete 19

4.2 .Shrink mixed concrete 21

4.3 Central mixed concrete 21

5.0 Tests on materials 24

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5.1 Tests on fine aggregates 24

5.2 Tests on coarse aggregates 31

5.3 Tests on fresh concrete 45

5.4 Tests on water 47

5.5 Tests on hardened concrete 47

6.0 Mix design 48

7.0 Merits and Demerits 53

7.1 merits of RMC 53

7.2demerits of RMC 53

8. Operational Aspect 54

8.1 Consumer Aspects 54

8.2 Producer information 55

8.3 Consumer checks 56

8.4 Checks at site 56

8.5 checks at site during concrete 57

8.6 Unnecessary restrictions 57

8.7 constraints faced by RMC 59

9.0 conclusion 61

10.0 bibliography 62

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List of Tables

1.4.1 Number of RMC plants 7

3.1.2.1 Most common designs 16

3.2.1 Capacities of transit mixers 18

5.1.1 Fine aggregate test results 27

5.2.1 Coarse aggregate test results 34

5.2.2 Flakiness index 43

5.2.3 Elongation index test result 44

6.1 Sieve analysis test results 49

6.2 Fine aggregate test results 49

6.3 samples 52

6.4 material contents in M20 52

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List of figures

1. Truck mixed concrete 20

2. Central mixed concrete 20

3. Slump cone apparatus 45

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1.INTRODUCTION: 1.1General introduction:

Ready Mix Concrete (RMC) is a specialized material in which the cement

aggregates and other ingredients are 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 is manufactured in a plant away from 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 and secondly, of

transporting a product within a short time.

It is delivered to the worksite, often in transit mixers capable of mixing the

ingredients of the concrete just before the delivery of 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 in an agitator truck, which keeps the mixed

concrete in correct form.

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 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-storied construction sites. A boom placer can pump

the concrete up 80 meters.

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 mechanized 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 computerized control

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of aggregates and water as per mix designs. It minimizes cement wastage due to bulk

handling and there is no dust problem and therefore, pollution-free.

Ready mix concrete is usually ordered in units of cubic yards or meters. It must

remain in motion until it is ready to be poured, or the cement may begin to solidify. The

ready mix concrete is generally released from the hopper in a relatively steady stream

through a trough system. Workers use shovels and hoes to push the concrete into place.

Some projects may require more than one production run of ready mix concrete, so more

trucks may arrive as needed or additional batches may be produced offsite and delivered.

However there are some disadvantages of RMC to, like double handling, which

results in additional cost and losses in weight, requirement of go downs 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 unorganized preparation at site are 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.

1.2 OBJECTIVE:

The main objective to choose this topic is that an engineer should have the

knowledge of advantages of RMC and disadvantages of Site mixed concrete. As RMC is

being widely used in bigger and medium size of projects today, Engineer should be aware

of the technicality of the RMC and the operational work, to ensure the quality of work and

the Site Engineer should know what are the steps to be taken to check the concrete in

RMC, what is required to be specified for RMC, what is the information required to be

supplied by the RMC supplier, what checks are necessary by the consumer before ordering

RMC, what are the checks needed at site prior and after to receipt of RMC.

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1.3 NECESSITY:

Normally the concrete operation carried out in India , is of site mixed, which is

having some disadvantages which are shown below:

Quality Assurance not guaranteed.

Constant control on aggregates for size, shape & grading not exercised on site.

Arbitrary batching and mixing by volume. Strict water-cement ratio not exercised.

Wastage of materials.

Retarded speed.

Concreting operations prolonged beyond day light without proper lighting.

Manual operation.

Speed restricted depending on mixers.

Restricted spaces.

Storages of aggregates and cement.

Blocking of roads / approaches

Dust pollution

RMC is the perfect solution for the above disadvantages and offers the following

advantages by its usage, which makes it necessary as a part of the construction:

Generally speaking, the quality of concrete will be superior than site mixed

concrete. However, it will greatly depend on the controls and checks exercised at

site and at RMC producer's plant.

There is a considerable wastage of materials on site due to poor storage conditions

and repeated shifting of the mixer location. This is prevented if RMC is used.

In most cities, the plot area is barely sufficient to store reinforcement steel,

formwork, concrete and other construction materials. Using RMC can cause less

congestion and better housekeeping on the site resulting in efficient working

environment.

Obtaining RMC at site can reduce supervision and labour costs which would

otherwise be required for batching and mixing of concrete at site.

Many sites in cities, house their work force on the site itself to reduce the time and

cost of daily travel. This creates unsafe and unhygienic conditions on the site as

well as for the surrounding areas. This will reduce to a certain extent if RMC is

utilized.

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Fluctuation of raw material prices and their availability has always caused delays

and problems of inventory and storage for site producers of concrete. This is totally

avoided when RMC is used.

Availability of labour gangs intermittently has always posed problems to concrete

producers on site. This can now be avoided. Besides these labour gangs are difficult

to supervise and control as they are only interested in completing the concreting

operations as fast as possible. This results in addition of excess water and

inadequacies in batching/mixing.

A problem of inspection, checking and testing of all concrete materials on site is

avoided. However, to a certain extent these checks and tests may be required to be

done at RMC producers' plant.

Concrete mix design and its control due to variations of material properties is

avoided as RMC producers are responsible for the same and supply concrete as

specified by the purchaser as per the requirements of the construction site.

In public places it creates fewer nuisances. Congested roads and footpaths are often

blocked by carelessly stored concrete materials. RMC allows a much better flow of

road traffic as well as pedestrian movement.

It .improves the environment and around the site. Nuisance due to stone dust and

cement particles is reduced considerably. To a certain extent even noise pollution is

reduced.

The modern RMC plants have an automatic arrangement to measure surface

moisture on aggregates this greatly helps in controlling the water to cement ratio

(w/c) which results in correct strength and durability.

RMC plants have proper facilities to store and accurately batch concrete admixtures

(chemical and mineral). To improve properties of concrete both in plastic and in

hardened stage this accuracy is useful.

In general, RMC plants have superior and accurate batching arrangements than the

weigh batchers used on site.

RMC plants have superior mixers than the rotating drum mixers generally used for

mixing concrete materials at site.

RMC plants have efficient batching and mixing, facilities which improve both

quality and speed of concrete production.

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Temperature control of concrete in extreme weather conditions can be exercised in

a much better manner than done at site.

RMC helps encourage" mechanization and new technologies like pumped concrete

bulk transportation of cement production of self-compacting concrete and high

strength high performance concrete.

New materials like micro silica and fibers can be safely used in RMC which in

conventional concrete may pose problems.

Introduction of RMC improves the rate of supply of concrete in the formwork and

thereby automatically improves quality of formwork, layout of reinforcement steel

and its detailing and safety / strength of scaffolding and staging.

1.4 HISTORY:

The Idea of Ready Mix Concrete (RMC) was first introduced by Architect Jurgen

Heinrich Magens, he got his patent of RMC in Germany in 1903. In 1907, he discovered

that the available time for transportation could be prolonged not only by cooling fresh

concrete but also by vibrating it during transportation. So this gave rise to a concrete which

is made in the off site.

The first concrete mixed off site and delivered to a construction site was effectively

done in Baltimore, United States in 1913, just before the First World War. The increasing

availability of special transport vehicles, supplied by the new and fast growing automobile

industry, played a positive role in the development of RMC industry.

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.

Between the years 1950 and 1980 considerable growth of RMC took place in the

United States with the maximum supply of 31 million cubic meters in the year 1974.

However, on an average RMC supplies were 25 million cubic meters per year between

1974 to 1980.

By 1990, in the United Sates there were 3700 RMC producers existing and 75% of

cement consumed by the construction industry was being utilized by RMC producers. In

1990 RMC plant in Japan were consuming nearly 70% of the total cement produced. In

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Malaysia, RMC plants utilized nearly 16% of the total cement consumed in the year 1990.

In UK, 43% of the total cement consumed is being used by RMC plants.

RMC IN INDIA:

In India RMC was first initially was used in 1950 during the construction sites of

Dams like Bhakra Nangal, Koyna. At the construction the transportation of concrete is

done by either manually or mechanically using ropeways & buckets or conveyor systems.

RMC at Pune in the year 1991. However, due to various pit falls and problems this

plant did not survive for long and was closed. Within a couple of months in the year 1993,

two RMC plant were set up in Mumbai to commercially sell RMC to the projects where

they were installed. Unitech Construction set up one plant at Hiranandani Complex and

Associated Cement Companies set up another plant at Bharat Diamond Bourse

Commercial Complex. These plants were later allowed to sell RMC to other projects also.

Thus RMC was successfully established sometime after 1994 in India.

RMC producers from outside India soon became interested in the Indian market

and therefore two very well known producers set their foot on the Indian soil i.e. Fletcher

Challenge Ltd. From New Zealand and RMC Ready Mix of UK.

As per the available record up to 2003, there are around 76 RMC plant in 17 cities

with a total capacity of around 3875 CuM/hr, producing 3.8 million CuM of concrete per

year.

Table1.4.1:Number of RMC plants and their capacities in leading metropolitan cities

of India.

Metro No. of Plants Capacity

(M3/hr)

Mumbai and

Navi Mumbai

15 835

Bangalore 13 550

Delhi 11 660

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Chennai 11 480

Hyderabad 7 350

1.5. SCOPE OF RMC IN INDIA:

Though delayed, but not very much, there a ready mixed concrete industry is

developing and expanding at a fast pace in the country on a large scale. Over the period,

due impetus to this development has been provided by various front-line construction and

cement companies as well as technological bodies. 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 in India, 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 of ready 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.

According to Cement Manufacturers Association, RMC is being increasingly

recommended for all major public construction work such as highways, flyovers. In cities

like Bangalore and Chennai, even small house builders have started displaying a marked

preference for RMC instead of cement. According to the experts, there is lot of scope for

the development and growth of RMC in India. It can grow to consume 40-45 percent of

cement by 2015 through setting up of RMC plants in various consumption centres. For the

healthy growth of industry, RMC industry in India has to fine-tune its own practices to

following practices elsewhere in the advanced countries where RMC industry has been

operating successfully. European Ready Mixed Concrete Organization (ERMCO) has

defined the broad objectives to be achieved in design, management and operation of RMC

which remain same as that of designing, and execution of concrete construction projects.

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

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the sell ability 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.

2. MATERIALS REQUIRED FOR RMC:

2.1 AGGREGATE:

Aggregates are the important constituents in concrete. They give body to the

concrete, reduce shrinkage and effect economy. Earlier, aggregates were considered as

chemically inert materials but now it has been recognised that some of the aggregates are

chemically active and also that certain aggregates exhibit chemical bond at the interface of

aggregate and paste. The mere fact that the aggregates occupy 70-80 per cent of the

volume of concrete, their impact on various characteristics and properties of concrete is

undoubtedly considerable. To know more about the aggregates which constitute major

volume in concrete.

Aggregates are divided into two categories from the consideration of size

Coarse aggregate

Fine aggregate

The size of the aggregate bigger than 4.75 mm is considered as coarse aggregate and

aggregate whose size is 4.75 mm and less is considered as fine aggregate.

SAMPLING PROCEDURE FOR AGGREGATES USED IN CONCRETE:

All aggregates are to be sampled properly before taking them for testing. The

purpose of sampling is to get representative material for testing the wrong sampling

of aggregate may lead to any of the following:

Consuming of bad quality of aggregates in concrete by accepting the

bad quality of materials at site

Disputing with the suppliers.

There is a definite procedure for sampling of aggregates. The procedure is explained

below:

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Collect the aggregate sample from different locations at different depths from

the site immediately after unloading the aggregates from the trucks. Collect

the samples at least from 10 to 15 locations.

Thoroughly remix the sample collected from various places & depths of the

trucks or from the stocks.

Make a cone from the sample.

Flatten the cone sample to form a circle of uniform thickness.

Divide the cone in to four equal quarters.

Discard any two diagonally opposite segment of quartered sample.

Collect the remaining sample & remix.

Take this remixed aggregate for testing.

The material so sampled only should be taken for testing. The Indian standards

recommend to sample the aggregates as above. However it recommends collecting samples

from different sub lots which are not practical as it takes long time to build up the lots at

site. Hence the method suggested above may be conveniently adopted at site.

2.2 CEMENT:

Cement is a binder material which sets and hardens independently, and can bind

other materials together. Cement is made up of four main compounds tricalcium silicate

(3CaO SiO2), dicalcium Silicate (2CaO SiO2), tricalcium acuminate (3CaO Al2O3), and

tetra-calcium aluminoferrite (4caco Al2O3 Fe2O3).tetra-calcium aluminoferrite (4CaO

Al2O3 Fe2O3). In an abbreviated notation differing from the normal atomic symbols,

these compounds are designated as C3S, C2S, C3A, and C4AF, where C stands for

calcium oxide (lime), S for silica and A for alumina, and F for iron oxide. Small amounts

of uncombined lime and magnesia also are present, along with alkalis and minor amounts

of other elements.

2.3 ADMIXTURE:

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

concrete; i.e. fibrous materials for reinforcing, water repellent treatments, and colouring

compounds.

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Air-entraining admixtures (mainly used in concrete exposed to freezing and

thawing cycles)

Water-reducing admixtures, plasticizers (reduce the dosage of water while

maintaining the workability)

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

hydration)

Accelerating admixtures (mainly used in cold weather to accelerate the reaction of

hydration)

Super plasticizer or high range water-reducer (significantly reduce the dosage of

water while maintaining the workability)

Miscellaneous admixtures such as corrosion inhibiting, shrinkage reducing,

colouring, pumping etc.

Role of Admixture in Ready Mix Concrete:

The role of admixture is ready mixed of concrete is same as that in normal

concrete. However, admixture used in RMC is modified to meet the requirement of

pumpable concrete and other properties of concrete. The types of admixture used in RMC

are generally termed as Super plasticizers.

The history of admixture is as old as history of concrete. There are several types of

admixture available in market. But few admixtures namely Plasticizers and Super

plasticizers are of recent interest. These of admixture were initially developed in Japan and

German around 1970. IN India use of admixture was recognized after 1985.In 1990

admixture started to gain Importance after introducing Ready Mixed Concrete. The

importance of admixture was further recognized after revision on of IS: 456 - 1978. The

earlier versions of IS 456 have permitted to use w/c ratio as high as 0.65 in RCC works.

The Revised IS 456-2000 has Restricted the w/c ratio to 0.55 for mild exposure and

0.50 for moderate exposure ,0.45 for severe and very severe exposure and 0.40 for

extreme weathering conditions. The restriction on w/c ratio has made the use of

admixture all the more compulsory ingredient of concrete.

Admixture is used in RMC are of following types:

Chemical admixture

Mineral admixture

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Chemical and mineral admixture

In RMC admixture mainly perform the following functions:

Increasing workability

Accelerate or retard the setting time of concrete.

Reduce segregation and bleeding in concrete.

Improve pump ability.

2.4 FLY ASH:

Fly ash is a by-product from coal-fired electricity generating power plants. The coal

used in these power plants is mainly composed of combustible elements such as carbon,

hydrogen and oxygen (nitrogen and sulphur 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. Fly ash use improves

concrete performance, making it stronger, more durable, and more resistant to chemical

attack. Fly ash use also creates significant benefits for our environment.

The size of fly ash ranges from 1.0 to 100 micron & the average size is around 20

microns. It is found that particle size below 10 microns contributes towards early

Development of strength (7& 28 days). The particle size of fly ash between l0 & 40

microns Contributes towards the development of strength between 28 days & 1 year. The

particle size above 45 microns does not contribute towards development of strength even

after 1 year and for all practical purpose they should be considered only as sand.

The fly ash is generally used in the concrete in the following ways.

As partial replace for cement.

As partial replacement for sand.

As simultaneous replacement for both cement and sand.

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It is found that fly ash replacement from l0 to 30% increases the development of

Strength up to 3 month or even more depending on the fineness of fly ash & its reaction

with Calcium hydroxide released during primary hydration of cement.

Addition of fly ash as per replacement of cement improves the workability of

concrete for the same water content. This means that the water content can be reduced for fly

ash based concrete. This reduced water cement ratio to some extent can offset for initial

gain of Strength can range from 10 to 25 % of the difference in strength between the strength

of Normal concrete & fly ash concrete.

Fly ash as a partial replacement for sand is uneconomical and sometimes it is

inevitable in pumping concrete especially when coarser types of fine aggregates are used in

concrete. It is also found that partial replacement of fly ash marginally increases the

strength Concrete due to filler effect in the initial stages and due to pozzolanic action in

28days.Simultaneous use of fly ash as a partial replacement of cement and sand is good

Proposal to increase strength, workability & pump ability of concrete.

2.5 WATER

The pH value of water should be in between 6.0 and 8.0 according to IS 456-2000.

Effect of Mixing Sea Water in Concrete:

The sea Water generally contains salinity of about 3.5% in which about 80% is

sodium chloride. Many researchers have been conducted to study the corrosion problem of

steel Embedded in concrete where sea water is used as mixing water in concrete

nevertheless the Indian standard is adamant & do not permit using sea water for mixing or

curing in reinforced Concrete constructions, but allows for using of sea water only for PCC

work that too under unavoidable circumstances.

Quality of Water for Curing Concrete Members:

Generally the water that is fit for mixing of water in concrete is also fit for curing.

However where appearance is important, water containing impurities which cause stains

should not to be used. The most important elements that cause stains in the concrete are

iron, and organic matters. It is also found that even sea water also causes stains in concrete.

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Hence water containing iron, organic matters and also sea water should not be used for

curing of concrete when appearance is also set as criteria for the acceptance of concrete.

Quality of Water for Curing Concrete Cubes:

The water that is fit for mixing and curing of water for concrete is also fit for

curing of cubes which are cured under water. However the curing water should not to be

allowed to remain in stagnant condition in water tanks for long time. As a guideline the

water tanks shall be cleaned twice a week or when ph value of water reaches a value more

than 9. The cleaned Water tanks shall be refilled with fresh water every time.

The cleaning of water is necessary to remove algae and fungus materials developed

inside the water tanks which otherwise alters the setting and strength gaining properties of

Concrete. The low results of such cubes may call for in situ tests resulting in consequential

Delay of the project.

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3. EQUIPMENTS REQUIRED:

3.1 BATCHING PLANT:

The principal functional elements of every stationary concrete production Plant

comprises of the following:

Storage of materials - Silos, containers and bins

Batching arrangement

Measuring and recording equipment

Mixing equipment

Control systems

Electrical, hydraulic and pneumatic drives

Conveying systems (belt / screw conveyors)

3.1.1 Storage of Materials

i) Cement

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

pneumatic blower systems either installed on bulk carriers or a separate system available at

the plant. If baggage cement is used then the cement is loaded using a compressed air

loader and a splitter unit.

Cement is weighed separately, and is transported from the silo into a mechanical or

electro mechanical weigher by means of a screw conveyor.

ii) Water

Water is generally stored in tanks located close to the plant. It is accurately

measured by a water gauge and microprocessor controlled system. The modern plants have

new litronic MFM 85 moisture recorders. These recorders actually measure the moisture

present in sand while the entire batch flows past. A recording unit calculates the average

moisture value of the sand and passes on the information to the batching control unit to

allow corrective action to be taken. The system operates to an accuracy of as low as 0.2%

relative moisture.

Consistency of the mix is generally checked by visual observation later confirming

it with a workability test like the slump test. However, in modern plants consistency of the

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concrete mix is checked by a remote recording system which is automatic, easy and more

accurate.

If concrete is very dry (stiff) the electrical resistance of the batch is measured and if

the concrete is wet the motor output is measured.

Accurate maintenance of the workability (consistency) of one cubic meter batch of

concrete may depend on as little as one litre or less of water. It is scarcely conceivable that

such a production process could be controlled without actually measuring the workability

and later correcting the consistency.

iii) Aggregates

The storage of aggregates is done in various way depending on the type of plant.

There are basically three types of plants generally in use.

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 in winter period.

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. The aggregates can be stored exposed to ambient temperature in different

compartments forming a star type pattern. 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 fully automatic. Fully automatic

dragline loader system operator.

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The star bin type plant requires more space and as the aggregates are stored in open

they heat up at high ambient temperatures and freeze at very 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 large

active storage (up to 500 CuM) in a small areas. Loading is fully automatic, aggregates are

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

3.1.2 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. Most of our indigenously manufactured

plants have free fall mixer. Free fall mixer consists of a rotating drum with blade fixed on

the drum's interior. As the drum rotates, the material inside is lifted and dropped. The drum

is loaded and emptied by changing the direction of rotation, dropping a flap or tipping it.

Most of the imported plants have power mixer. The power mixer sets in motion the

materials positively. The materials get thoroughly mixed by rotating arms. These mixers

have shorter mixing time; give better homogeneity, consistency and strength to the

concrete. Besides, they have better facility for inspection. The following are the most

common designs.

Table 3.1.2.1: most common designs

Power Mixer Capacity CuM

(Compacted

concrete)

Output CuM/hr

(Compacted

concrete)

Max. Aggregate size

(mm)

Mixing Time (Sec)

30 15

Single Shaft 3 120 --- 150

Twin Shaft 3.5 120-150 --- 190

Pan Type 3 120 --- 64

Pan type with

additional agitator

3 --- 140 64

If mixing is to be done on difficult concrete mixes, additional agitator is provided.

The pan type mixer with additional agitator or two agitators is claimed to be far in advance

of any if other mixer. Using additional agitators almost halves the mixing time. The

additional agitator is driven by a separate hydraulic system and can be set to any speed

between 0 to 200 revolutions per minute.

25

3.1.3 CONTROL SYSTEMS

Almost all imported production plants offer automatic systems for control

functions. These are required for better quality control, higher economy and superior

working conditions. Fully automatic plant control systems with multiple inputs for up to

120 mixes or template control system are usually housed in a container or control room of

the plant. Micro processor controlled production plants represent the state of the art in the

developed countries.

These controls are operated from main desk. It also has material availability

monitor and printer plus an additional batching monitor. The entire plant can be operated

by just one person. Microprocessor control besides having fully automatic running facility

offers number of additional features like statistical data recording and processing, a printer

unit, moisture adjustment arrangement, customer address, memory etc.

All you need to do is push the required mix template into the slot and press the

"start" button and the control system does the rest. Aggregate and cement weighment,

moisture correction, overrun correction and additive weighment are done accurately to give

the concrete mix of desired strength and workability.

The built in trouble shooting programs are most valuable and have a high reliability

factor. Even upto 1500 mixes of different types can be stored along with names and

addresses of the consumer and other data which is required to be stored in the computer for

operation of the plant. The mix data with quantity can be if required printed by the printer

which is very useful for invoicing the consumer for the concrete supplied to them.

3.2 TRANSPORTATION EQUIPMENT: TRANSIT MIXER

There are developments taking place all over the world for different types of

concrete equipments. However, the transit mixer is one of the most .popular equipments

out of several modes available. In India too, a number of transit mixers are in use all over

the country which are mainly mounted on Indian truck chassis. The mixer drum is either

manufactured in India or is improved. However, in general, the hydraulic system is

improved.

There are several types and capacities of transit mixers available as given below:

26

Table 3.2.1: capacities of transit mixers

Normal Capacity 4 to 12 CuM

Hydraulic 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 for 10 to 12 CuM.

In India 4 Cum. Truck mixers are popular while the 6 and 7 Cum. Truck mixers

mounted on a 3 axle chassis enjoy a leading position on all world markets as it has a

favorable cost- performance ratio, large selection of chassis, good maneuverability and is

more suited to general batch size requirements.

27

4. MIXING PROCESS:

Thorough mixing of the materials is essential for the production of uniform

concrete. The mixing should ensure that the mass becomes homogeneous, uniform in

colour and consistency. There are three methods adopted for mixing Ready Mix Concrete.

Following are the three types of mixing process of RMC

1. Transit Mixed (or "truck-mixed") Concrete

2. Shrink Mixed Concrete

3. Central Mixed Concrete

4.1 TRANSIT MIXED (OR "TRUCK-MIXED") CONCRETE

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.

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 becoming

more 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 without

the help of contractor personnel.

Currently, because of weight laws, the typical truck mixer is a 7 to 8.5 m3. 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 the rated 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.

28

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

concrete shall 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, when

conditions 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

compensate for loss of air, high temperatures or long delivery times. The ready mixed

concrete producer will assist the purchaser in such circumstances.

Fig1: truck mixed transit

28 fig f

Fig2: central mixed concrete

29

4.2SHRINK MIXED CONCRETE

Concrete that is partially mixed in a plant mixer and then discharged into the drum

of 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 to

shrink 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 uniformity tests.

Generally, about thirty turns in the truck drum, or about two minutes at mixing speed, is

sufficient to completely mix shrink-mixed concrete.

4.3 CENTRAL MIXED CONCRETE

Central-mixing concrete batch plants include a stationary, plant-mounted mixer that

mixes the concrete before it is discharged into a truck mixer. Central-mix plants are

sometimes referred to as wet batch or pre-mix plants. The truck mixer is used primarily as

an agitating haul unit at a central mix operation. Dump trucks or other non-agitating units

are sometimes be used for low slump and mass concrete pours supplied by central mix

plants. About 20% of the concrete plants in the US use a central mixer. Principal

advantages include:

Faster production capability than a transit-mix plant

Improved concrete quality control and consistency and

Reduced wear on the truck mixer drums.

30

There are several types of plant mixers, including:

Twin shaft mixer

Tilt drum mixer

Horizontal shaft paddle mixer

Pan mixer

Slurry mixer

Twin shaft mixer:

Twin-shaft mixers are ideal for the ready-mix and precast concrete industries

where large volumes of high quality concrete are demanded. The powerful twin-shaft

mixer, with counter rotating shafts, delivers fast mixing action and rapid discharge and

handles mix designs with coarse aggregates up to 6 inches in diameter. Generally most the

RMC plants in India uses Twin-shaft mixer.

The tilting drum mixer:

Tilting drum mixer is the most common American central mixing unit. Many

central-mix drums can accommodate up to 12 yd3 and can mix in excess of 200 yd3 per

hour. They are fast and efficient, but can be maintenance-intensive since they include

several moving parts that are subjected to a heavy load.

Horizontal shaft mixers:

Horizontal shaft mixers have a stationary shell and rotating central shaft with

blades or paddles. They have either one or two mixing shafts that impart significantly

higher horsepower in mixing than the typical drum mixer. The intensity of the mixing

action is somewhat greater than that of the tilt drum mixer. This high energy is reported to

produce higher strength concrete via to thoroughly blending the ingredients and more

uniformly coating the aggregate particles with cement paste. Because of the horsepower

required to mix and the short mixing cycle required to complete mixing, many of these

mixers are 4 or 5 yd3 units and two batches may be needed to load a standard truck or

agitator.

31

Pan mixers:

Pan mixers are generally lower capacity mixers at about 4 to 5 yd3 and are used at

precast concrete plants.

Slurry Mixing

The slurry mixer is a relative newcomer to concrete mixing technology. It can be

added onto a dry-batch plant and works by mixing cement and water that is then loaded as

slurry into a truck mixer along with the aggregates. It is reported to benefit from high

energy mixing. Another advantage is that the slurry mixer reduces the amount of cement

dust that escapes into the air.

32

5. TESTS ON MATERIALS:

All the ingredients used for preparation of the concrete, are thoroughly tested for

their quality and physical properties in a well equipped laboratory attached to the plant for

conformity to relevant Indian Standard Codes. The moisture probe determines the water

content in the sand and aggregates. This accordingly helps in fixing the proportion of water

to be added for the preparation of the mix. The sand being used is passed through the

mechanized sieving system, before feeding for mixing.

Trial mixes are carried out and tested to ensure that each and every batch of

concrete coming out of the plant meets the parameters of client’s requirements. The sand

being used is passed through the mechanized sieving system, before feeding for mixing.

5.1TESTS ON FINE AGGREGATE:

SEIVE ANALYSIS:

A gradation test is performed on a sample of aggregate in a laboratory. A typical

sieve analysis involves a nested column of sieves with wire mesh cloth (screen).

A representative weighed sample is poured into the top sieve which has the largest

screen openings. Each lower sieve in the column has smaller openings than the one

above. At the base is a round pan, called the receiver.

The column is typically placed in a mechanical shaker. The shaker shakes the

column, usually for some fixed amount of time. After the shaking is complete the

material on each sieve is weighed. The weight of the sample of each sieve is then

divided by the total weight to give a percentage retained on each sieve.

The size of the average particles on each sieve then being analysis to get the

cutpoint or specific size range captured on screen.

The results of this test are used to describe the properties of the aggregate and to

see if it is appropriate for various civil engineering purposes such as selecting the

appropriate aggregate for concrete mixes and asphalt mixes as well as sizing of

water production well screens.

The results of this test are provided in graphical form to identify the type of

gradation of the aggregate.

33

A suitable sieve size for the aggregate should be selected and placed in order of decreasing

size, from top to bottom, in a mechanical sieve shaker. A pan should be placed underneath

the nest of sieves to collect the aggregate that passes through the smallest. The entire nest

is then agitated, and the material whose diameter is smaller than the mesh opening pass

through the sieves. After the aggregate reaches the pan, the amount of material retained in

each sieve is then weighed

Preparation

In order to perform the test, a sample of the aggregate must be obtained from the source.

To prepare the sample, the aggregate should be mixed thoroughly and be reduced to a

suitable size for testing. The total weight of the sample is also required

Reporting of results:

The results are presented in a graph of percent passing versus the sieve size. On the graph

the sieve size scale is logarithmic. To find the percent of aggregate passing through each

sieve, first find the percent retained in each sieve. To do so, the following equation is used,

%Retained = ×100%

Where WSieve is the weight of aggregate in the sieve and WTotal is the total weight of the

aggregate. The next step is to find the cumulative percent of aggregate retained in each

sieve. To do so, add up the total amount of aggregate that is retained in each sieve and the

amount in the previous sieves. The cumulative percent passing of the aggregate is found by

subtracting the percent retained from 100%.

%Cumulative Passing = 100% - %Cumulative Retained.

The values are then plotted on a graph with cumulative percent passing on the y axis and

logarithmic sieve size on the x axis.

METHODS

There are different methods for carrying out sieve analysis, depending on the

material to be measured.

34

Throw-action sieving

Here a throwing motion acts on the sample. The vertical throwing motion is

overlaid with a slight circular motion which results in distribution of the sample amount

over the whole sieving surface. The particles are accelerated in the vertical direction (are

thrown upwards). In the air they carry out free rotations and interact with the openings in

the mesh of the sieve when they fall back. If the particles are smaller than the openings,

they pass through the sieve. If they are larger, they are thrown upwards again. The rotating

motion while suspended increases the probability that the particles present a different

orientation to the mesh when they fall back again, and thus might eventually pass through

the mesh.

Modern sieve shakers work with an electro-magnetic drive which moves a spring-

mass system and transfers the resulting oscillation to the sieve stack. Amplitude and

sieving time are set digitally and are continuously observed by an integrated control-unit.

Therefore sieving results are reproducible and precise (an important precondition for a

significant analysis). Adjustment of parameters like amplitude and sieving time serves to

optimize the sieving for different types of material. This method is the most common in the

laboratory sector.

Horizontal sieving

In a horizontal sieve shaker the sieve stack moves in horizontal circles in a plane.

Horizontal sieve shakers are preferably used for needle-shaped, flat, long or fibrous

samples, as their horizontal orientation means that only a few disoriented particles enter the

mesh and the sieve is not blocked so quickly. The large sieving area enables the sieving of

large amounts of sample, for example as encountered in the particle-size analysis of

construction materials and aggregates.

Tapping sieving

A horizontal circular motion overlies a vertical motion which is created by a

tapping impulse. These motional processes are characteristic of hand sieving and

produce a higher degree of sieving for denser particles (e.g. abrasives) than throw-

action sieve shakers.

35

EXPERIMENT RESULTS:

For Fine aggregate

Table 5.1.1 fine aggregate test results

Sieve size Retained

(grams)

% Retained Cumulative

(%)

% finer

4.75 17.5 1.75 1.75 98.25

2.36 mm 59 5.9 7.65 92.35

1.18 mm 283 28.3 35.95 64.05

600 µ 198 19.8 55.75 44.25

300 µ 194 19.4 75.15 24.85

150 µ 111.5 11.1 86.25 13.75

Pan 137.5 13.8 100 0

Result: From Table 4 of IS 383 the sample is from grading zone II

SPECIFIC GRAVITY:

In Concrete technology, Specific gravity of aggregates is made use of in design

calculations of concrete mixes. With the specific gravity of each constituent known, its

weight can be converted into solid volume and hence a theoretical yield of concrete per

unit volume can be calculated.

Preparation of Test Sample

Fine Aggregate

a. Obtain a test sample of approximately 1100 grams from the material to be tested by one

of the following methods:

(1) Use of a sample splitter

(2) Method of quartering after being thoroughly mixed and in a damp condition

(3) By taking small scoops of material from various places over the field sample,

after it has been dampened and thoroughly mixed. In order to avoid segregation, the

material must be damp enough to stand in a vertical face when cut with a trowel.

This method of sample reduction is applicable to sands only.

36

b. If the material has been continuously wet before being received on the job, it may be

assumed to be saturated. Otherwise, the sample must be saturated by immersing it in water

for period of not less than 15 hours.

c. After soaking, pour off the free water, spread the wet sample on a flat, nonabsorbent

surface, and allow it to come to a surface-dry condition by natural evaporation of free

moisture. Circulation of air by means of a fan may also be used to attain the surface-dry

condition. The sample should be stirred frequently to secure uniform drying.

Test Procedure

Weigh the saturated-surface-dry sample to the nearest 0.5-gram. For ease in

calculations, the fine aggregate sample may be brought to exactly 1000 grams

weight, and the coarse aggregate sample may be brought to exactly 2000 grams

weight.

Place the sample in the appropriate pycnometer containing approximately two

inches of water.

Nearly fill the pycnometer jar with water at the same temperature plus or minus 3°F

(1.7°C) as used in the calibration.

Screw the cap down into the proper position by lining up the mark on the

pycnometer top and the jar.

Entirely fill the pycnometer by adding additional water through the hole in the

pycnometer top.

Hold one finger over the hole in the top and gently roll and shake the pycnometer to

remove any trapped air in the sample.

When further rolling and shaking brings no more air bubbles to the top, fill, dry and

weigh as in step C3.

BULK DENSITY TEST:

Objective:

Calculating the bulk density of fine aggregate samples.

Bulk Density:

When dealing with aggregates it is important to know the voids that presents

between the aggregate particles, so that we decide whether to fill them with finer aggregate

37

or with cement paste. We all know that the Density we often deal with equals the mass

divided by the volume, when using this law to measure the density of aggregates the

volume we use is the volume of aggregate + the volume of the voids, and in this case we

get a new quantity called the Bulk Density. Bulk Density = Mass of the aggregate \

Volume of aggregate particles with voids between them. This bulk density is used to

convert quantities by mass to quantities by volume. Bulk density depends on several

factors: Size distribution of aggregates, Shape of particles and degree of compaction. There

are two methods this quantity is measured by

Loose method.

Compaction method.

Apparatus and Materials:

1. Container.

2. Glass Plate.

3. Fine and Coarse aggregate sample.

4. Water

5- Weighting Machine.

Procedure:

It is the same procedures for fine and coarse aggregate samples.

1. Weighing the empty container with the glass plate.

2. Fill the container with coarse aggregate to over flowing and then using the plate to level

the surface, and the weight of the container and the plate and the coarse sample is found.

(W1)

3. Empty the container from the coarse aggregate and refill it with the fine aggregate to

over flowing and then level the surface using the plate, and the weight of the container and

the plate and the fine sample is found. (W2)

4. Empty the container again and this time we fill it with water till the rim of it and place

the plate on it, no water bubbles should present on the surface, and we weight the container

and the plate and the water. (W3)

EXPERIMENT RESULTS:

Dry Loose Bulk Density of fine aggregate:

Weight of container = 2.540 Kg

Weight of total Sample in container = 4.580 Kg

38

Container Volume = 3 lit

Dry loose bulk density =

= 1526 gm / lit

Dry Compacted Bulk Density of fine aggregate:





= 1686 gm / lit

AFTER ABSORPTION TEST:

This test helps to determine the water absorption of coarse aggregates as per IS:

2386 (Part III) – 1963. For this test a sample not less than 2000g should be used.

The apparatus used for this test are:

Wire basket, perforated, electroplated or plastic coated with wire hangers for

suspending it from the balance

Water-tight container for suspending the basket

Dry soft absorbent cloth – 75cm x 45cm (2 nos.)

Shallow tray of minimum 650 sq.cm area

Air-tight container of a capacity similar to the basket and Oven.

Procedure to determine water absorption of Aggregates.

i) The sample should be thoroughly washed to remove finer particles and dust, drained and

then placed in the wire basket and immersed in distilled water at a temperature between 22

and 32oC.

39

ii) After immersion, the entrapped air should be removed by lifting the basket and allowing

it to drop 25 times in 25 seconds. The basket and sample should remain immersed for a

period of 24 + ½ hrs afterwards.

iii) The basket and aggregates should then be removed from the water, allowed to drain for

a few minutes, after which the aggregates should be gently emptied from the basket on to

one of the dry clothes and gently surface-dried with the cloth,transferring it to a second dry

cloth when the first would remove no further moisture.The aggregates should be spread on

the second cloth and exposed to the atmosphere away from direct sunlight till it appears to

be completely surface-dry.The aggregates should be weighed (Weight ‘A’).

iv) The aggregates should then be placed in an oven at a temperature of 100 to 110oC for

24hrs. It should then be removed from the oven, cooled and weighed (Weight ‘B’).

Formula used is Water absorption = [(A - B)/B] x 100%.

Two such tests should be done and the individual and mean results should be reported.

EXPERIMENT RESULT:

Weight of Saturated Surface Dry (SSD) sample (A) =725.00 gm.

Weight of Oven dry Sample (B) =705.00 gm.

Weight Absorption = X 100

= X 100

= 2.83 %

5.2 TESTS ON COARSE AGGREGATES:

SEIVE ANALYSIS:

A gradation test is performed on a sample of aggregate in a laboratory. A typical

sieve analysis involves a nested column of sieves with wire mesh cloth (screen).

A representative weighed sample is poured into the top sieve which has the largest

screen openings. Each lower sieve in the column has smaller openings than the one

above. At the base is a round pan, called the receiver.

40

The column is typically placed in a mechanical shaker. The shaker shakes the

column, usually for some fixed amount of time. After the shaking is complete the

material on each sieve is weighed. The weight of the sample of each sieve is then

divided by the total weight to give a percentage retained on each sieve.

The size of the average particles on each sieve then being analysis to get the

cutpoint or specific size range captured on screen.

The results of this test are used to describe the properties of the aggregate and to

see if it is appropriate for various civil engineering purposes such as selecting the

appropriate aggregate for concrete mixes and asphalt mixes as well as sizing of

water production well screens.

The results of this test are provided in graphical form to identify the type of

gradation of the aggregate.

A suitable sieve size for the aggregate should be selected and placed in order of decreasing

size, from top to bottom, in a mechanical sieve shaker. A pan should be placed underneath

the nest of sieves to collect the aggregate that passes through the smallest. The entire nest

is then agitated, and the material whose diameter is smaller than the mesh opening pass

through the sieves. After the aggregate reaches the pan, the amount of material retained in

each sieve is then weighed

Preparation

In order to perform the test, a sample of the aggregate must be obtained from the source.

To prepare the sample, the aggregate should be mixed thoroughly and be reduced to a

suitable size for testing. The total weight of the sample is also required

Reporting of results:

The results are presented in a graph of percent passing versus the sieve size. On the graph

the sieve size scale is logarithmic. To find the percent of aggregate passing through each

sieve, first find the percent retained in each sieve. To do so, the following equation is used,

%Retained = ×100%

41

Where WSieve is the weight of aggregate in the sieve and WTotal is the total weight of the

aggregate. The next step is to find the cumulative percent of aggregate retained in each

sieve. To do so, add up the total amount of aggregate that is retained in each sieve and the

amount in the previous sieves. The cumulative percent passing of the aggregate is found by

subtracting the percent retained from 100%.

%Cumulative Passing = 100% - %Cumulative Retained.

The values are then plotted on a graph with cumulative percent passing on the y axis and

logarithmic sieve size on the x axis.

METHODS

There are different methods for carrying out sieve analysis, depending on the

material to be measured.

Throw-action sieving

Here a throwing motion acts on the sample. The vertical throwing motion is

overlaid with a slight circular motion which results in distribution of the sample amount

over the whole sieving surface. The particles are accelerated in the vertical direction (are

thrown upwards). In the air they carry out free rotations and interact with the openings in

the mesh of the sieve when they fall back. If the particles are smaller than the openings,

they pass through the sieve. If they are larger, they are thrown upwards again. The rotating

motion while suspended increases the probability that the particles present a different

orientation to the mesh when they fall back again, and thus might eventually pass through

the mesh.

Modern sieve shakers work with an electro-magnetic drive which moves a spring-

mass system and transfers the resulting oscillation to the sieve stack. Amplitude and

sieving time are set digitally and are continuously observed by an integrated control-unit.

Therefore sieving results are reproducible and precise (an important precondition for a

significant analysis). Adjustment of parameters like amplitude and sieving time serves to

optimize the sieving for different types of material. This method is the most common in the

laboratory sector.

42

Horizontal sieving

In a horizontal sieve shaker the sieve stack moves in horizontal circles in a plane.

Horizontal sieve shakers are preferably used for needle-shaped, flat, long or fibrous

samples, as their horizontal orientation means that only a few disoriented particles enter the

mesh and the sieve is not blocked so quickly. The large sieving area enables the sieving of

large amounts of sample, for example as encountered in the particle-size analysis of

construction materials and aggregates.

Tapping sieving

A horizontal circular motion overlies a vertical motion which is created by a

tapping impulse. These motional processes are characteristic of hand sieving and

produce a higher degree of sieving for denser particles (e.g. abrasives) than throw-

action sieve shakers.

EXPERIMENT RESULTS:

For Coarse aggregate

Table 5.2.1 coarse aggregate test results

Sieve size Retained

(grams)


(%)

% finer

25 mm 0 0 0 0

20 mm 569 11.38 11.38 88.62

12.5 mm 3661 73.22 84.6 15.4

10 mm 619 12.38 96.98 3.02

4.75 130 2.6 99.58 0.42

Pan 21 0.42 100 0

RESULT: From Table 2, of IS 383 the sample is the single sized nominal aggregate

43

SPECIFIC GRAVITY TEST:

In Concrete technology, Specific gravity of aggregates is made use of in design

calculations of concrete mixes. With the specific gravity of each constituent known, its

weight can be converted into solid volume and hence a theoretical yield of concrete per

unit volume can be calculated.

Preparation of Test Sample

Coarse Aggregate

a. Sieve the test sample over the No. 4 (4.75 mm) sieve. The sample should be of sufficient

size to produce approximately 2100 grams of material retained on the No. 4 sieve. Discard

the material that passes this sieve.

b. Immerse the sample (plus No. 4 sieve size) in water for a period of not less than 15

hours.

c. After soaking, pour off the free water and allow the sample to come to a saturated

surface dry condition by spreading the sample on a flat, non-absorbent surface. The forced

circulation of air by means of a fan, if available, may hasten this process. The sample

should be stirred frequently to secure uniform drying. The predominance of free moisture

may be removed initially by rolling the sample back and forth in a clean, dry, absorbent

cloth.

d. The sample may be considered to be saturated-surface-dry when the particles look

comparatively dull as the free moisture is removed from their surfaces. For highly

absorptive aggregates, the saturated-surface-dry condition is reached when there is an

absence of free moisture.

Test Procedure

Weigh the saturated-surface-dry sample to the nearest 0.5-gram. For ease in

calculations, the fine aggregate sample may be brought to exactly 1000 grams

weight, and the coarse aggregate sample may be brought to exactly 2000 grams

weight.

Place the sample in the appropriate pycnometer containing approximately two

inches of water.

44

Nearly fill the pycnometer jar with water at the same temperature plus or minus 3°F

(1.7°C) as used in the calibration.

Screw the cap down into the proper position by lining up the mark on the

pycnometer top and the jar.

Entirely fill the pycnometer by adding additional water through the hole in the

pycnometer top.

Hold one finger over the hole in the top and gently roll and shake the pycnometer to

remove any trapped air in the sample.

When further rolling and shaking brings no more air bubbles to the top, fill, dry and weigh.

EXPERIMENT RESULT:

Saturated surface dry (SSD) sample weight (A) = 500.00 gm.

Pycnometer + water + SSD sample (B) =1847.00 gm.

Pycnometer + water (C) =1539.00 gm.

Oven dry Sample (D) =498.00 gm.

Specific gravity =

=

= 2.5937 gm/c

45

AGGREGATE IMPACT VALUE TEST:

This test is done to determine the aggregate impact value of coarse aggregates as

per IS: 2386 (Part IV) – 1963. The apparatus used for determining aggregate impact value

of coarse aggregates is Impact testing machine conforming to IS: 2386 (Part IV)- 1963,IS

Sieves of sizes – 12.5mm, 10mm and 2.36mm, A cylindrical metal measure of 75mm dia.

and 50mm depth, A tamping rod of 10mm circular cross section and 230mm length,

rounded at one end and Oven.

Preparation of Sample:

i) The test sample should conform to the following grading:

Passing through 12.5mm IS Sieve – 100%

Retention on 10mm IS Sieve – 100%

ii) The sample should be oven-dried for 4hrs. at a temperature of 100 to 110oC and cooled.

iii) The measure should be about one-third full with the prepared aggregates and tamped

with 25 strokes of the tamping rod.

A further similar quantity of aggregates should be added and a further tamping of

25 strokes given. The measure should finally be filled to overflow, tamped 25 times and

the surplus aggregates struck off, using a tamping rod as a straight edge. The net weight of

the aggregates in the measure should be determined to the nearest gram (Weight ‘A’).

Procedure to determine Aggregate Impact Value:

i) The cup of the impact testing machine should be fixed firmly in position on the base of

the machine and the whole of the test sample placed in it and compacted by 25 strokes of

the tamping rod.

ii) The hammer should be raised to 380mm above the upper surface of the aggregates in

the cup and allowed to fall freely onto the aggregates. The test sample should be subjected

to a total of 15 such blows, each being delivered at an interval of not less than one second.

Reporting of Results:

i) The sample should be removed and sieved through a 2.36mm IS Sieve. The fraction

passing through should be weighed (Weight ‘B’). The fraction retained on the sieve should

also be weighed (Weight ‘C’) and if the total weight (B+C) is less than the initial weight

(A) by more than one gram, the result should be discarded and a fresh test done.

46

ii) The ratio of the weight of the fines formed to the total sample weight should be

expressed as a percentage.

Aggregate impact value = (B/A) x 100%

iii) Two such tests should be carried out and the mean of the results should be reported.

EXPERIMENT RESULT:

Total Weight of Sample passing on 12.5 mm sieve & retained on 10 mm sieve(A) =325gm.

Weight of the sample retained on 2.36 sieve (B) = 77 gm.

Impact value = X 100

= X 100

= 23.69%

BULK DENSITY TEST:

Objective:

Calculating the bulk density of fine aggregate samples.

Bulk Density:

When dealing with aggregates it is important to know the voids that presents

between the aggregate particles, so that we decide whether to fill them with finer aggregate

or with cement paste. We all know that the Density we often deal with equals the mass

divided by the volume, when using this law to measure the density of aggregates the

volume we use is the volume of aggregate + the volume of the voids, and in this case we

get a new quantity called the Bulk Density. Bulk Density = Mass of the aggregate \

Volume of aggregate particles with voids between them. This bulk density is used to

convert quantities by mass to quantities by volume. Bulk density depends on several

factors: Size distribution of aggregates, Shape of particles and degree of compaction. There

are two methods this quantity is measured by

Loose method.

Compaction method.

47

Apparatus and Materials:

1. Container.

2. Glass Plate.

3. Fine and Coarse aggregate sample.

4. Water

5. Weighting Machine.

Procedure:

It is the same procedures for fine and coarse aggregate samples.

1. Weighing the empty container with the glass plate.

2. Fill the container with coarse aggregate to over flowing and then using the plate to level

the surface, and the weight of the container and the plate and the coarse sample is found.

(W1)

3. Empty the container from the coarse aggregate and refill it with the fine aggregate to

over flowing and then level the surface using the plate, and the weight of the container and

the plate and the fine sample is found. (W2)

4. Empty the container again and this time we fill it with water till the rim of it and place

the plate on it, no water bubbles should present on the surface, and we weight the container

and the plate and the water. (W3)

EXPERIMENT RESULT:

DRY LOOSE BULK DENSITY TEST:

Coarse aggregate – 20mm





= 1366.67 gm / lit

48






= 1248 gm / lit

DRY COMPACTED BULK DENSITY TEST:






= 1484 gm / lit






= 1402 gm / lit

49

WATER ABSORPTION TEST:

This test helps to determine the water absorption of coarse aggregates as per IS: 2386

(Part III) – 1963. For this test a sample not less than 2000g should be used. The apparatus

used for this test are:

Wire basket, perforated, electroplated or plastic coated with wire hangers for

suspending it from the balance

Water-tight container for suspending the basket

Dry soft absorbent cloth – 75cm x 45cm (2 nos.)

Shallow tray of minimum 650 sq.cm area

Air-tight container of a capacity similar to the basket and Oven.

Procedure to determine water absorption of Aggregates.

i) The sample should be thoroughly washed to remove finer particles and dust, drained and

then placed in the wire basket and immersed in distilled water at a temperature between 22

and 32oC.

ii) After immersion, the entrapped air should be removed by lifting the basket and allowing

it to drop 25 times in 25 seconds. The basket and sample should remain immersed for a

period of 24 + ½ hrs afterwards.

iii) The basket and aggregates should then be removed from the water, allowed to drain for

a few minutes, after which the aggregates should be gently emptied from the basket on to

one of the dry clothes and gently surface-dried with the cloth,transferring it to a second dry

cloth when the first would remove no further moisture.The aggregates should be spread on

the second cloth and exposed to the atmosphere away from direct sunlight till it appears to

be completely surface-dry.The aggregates should be weighed (Weight ‘A’).

iv) The aggregates should then be placed in an oven at a temperature of 100 to 110oC for

24hrs. It should then be removed from the oven, cooled and weighed (Weight ‘B’).

Formula used is Water absorption = [(A - B)/B] x 100%.

Two such tests should be done and the individual and mean results should be reported.

50

EXPERIMENT RESULT:

Coarse aggregate – 20mm:

Weight of Saturated Surface Dry (SSD) sample (A) =705.00 gm.

Weight of Oven dry Sample (B) =703.00 gm.


= X 100

= 0.28 %

Coarse aggregate – 12mm:

Weight of Saturated Surface Dry (SSD) sample (A) = 653.50 gm.

Weight of Oven dry Sample (B) = 650.00 gm.


= X 100

= 0.54 %

51

FLAKINESS INDEX TEST:

Flakiness Index is the percentage by weight of particles in it, whose least dimension

(thickness) is less than three-fifths of its mean dimension. The test is not applicable to

particles smaller than 6.3 mm in size.

Procedure for using Gauge for Flakiness Index

A balance of suitable capacity, gauge for Flakiness Index and a set of Sieves of

relevant sizes as per the specified Standard will be required.

Sample size will be such that at least 200 pieces of any fraction to be tested will

become available. The aggregates will be dried to a constant weight in an oven at a

temperature of 110º ± 5ºC and weighed to the nearest 0.1g. The aggregates will then be

sieved through the set of prescribed sieves.

Each fraction is then gauged for thickness through the slots of the gauge. All the

pieces passing through the gauge are collected and weighed to an accuracy of 0.1 percent

of the weight of the sample.

The Flakiness Index is the total weight of the material passing various gauges and

sieves expressed as a percentage of the total weight of the sample gauged.

EXPERIMENT RESULT:

Table 5.2.2 flakiness index

Passing through

IS Sieve

Retained on

IS Sieve Weight Of The

Sample

Retained

Weight Of The

Sample Passed

Total Weight

Of The Sample

40 25 0 0 0

25 20 1947 361 2308

20 16 1278 246 1524

16 12.5 501 276 777

12.5 10 281 75 356

10 6.3 104 41 145

∑=999 ∑=5110

Flakiness index = X 100

= X 100

52

=19.54 %

ELONGATION INDEX TEST:

The elongation index on an aggregate is the percentage by weight of

particles whose greatest dimension (length) is greater than 1.8 times their mean dimension.

The elongation index is not applicable to sizes smaller than 6.3 mm.

The test is conducted by using metal length guage of the description. A sufficient

quantity of aggregate is taken to provide a minimum number of 200 pieces of any fraction

to be tested. Each fraction shall be guaged individually of length ion the metal gauge. The

total amount retained by the gauge length shall be weighed to an accuracy of at least 0.1

per cent of weight of the test sample taken. The elongation index is the total weight of the

material retained on the various length gauges expressed as a percentage of the total weight

of the sample gauged. The presence of elongated particles in excess of 10 – 15 per cent is

generally considered undesirable, but no recognized limits are laid down.

Indian standard explain only the method of calculating both flakiness index and elongation

index. But the specification does not specify the limits. British standards BS 882 of 1992

limits the flakiness index of the coarse aggregate to 50 for natural gravel and to 40 for

crushed coarse aggregate. However, for wearing surfaces a lower value of flakiness index

are required.

EXPERIMENT RESULT:

Table 5.2.3 elongation index test result

Passing through

IS Sieve

Retained on

IS Sieve Weight Of The

Sample

Retained

Weight Of The

Sample Passed

Total Weight

Of The Sample

40 25 0 0 0

25 20 38 2270 2308

20 16 81 1443 1524

16 12.5 129 648 777

12.5 10 64 292 356

10 6.3 45 100 145

∑= 357 ∑=5110

Elongation index = X 100

= X 100

53

= 6.96%

5.3 TESTS ON FRESH CONCRETE:

SLUMP TEST:

After the fresh concrete is prepared Slump test is done. Slump test is the most

commonly used method of measuring workability of concrete which can be employed

either in laboratory or at site of work. It is not a suitable method for very wet or very dry

concrete .It does not measure all factors contributing to workability, nor is it always

representative of the placability of the concrete.

Fig3: Slump cone apparatus

The apparatus for conducting the slump test essentially consists of a metallic mould in the

form of a frustum of a cone having the internal dimensions as under:

54

Bottom diameter: 20 cm

Top diameter: 10 cm

Height: 30 cm

The mould is then filled in four layers, each approximately l/4 of the height of the

mould. Each layer is tamped 25 times by the tamping rod taking care to distribute the

strokes evenly over the cross section.

After the top layer has been rodded, the concrete is struck off Level with a trowel and

tamping rod. The mould is removed from the concrete immediately by raising it slowly and

carefully in a vertical direction.

This allows the concrete to subside. This subsidence is referred as SLUMP of concrete.

The difference in level between the height of the mould and that of the highest point of the

subsided concrete is measured. This difference in height in mm is taken as Slump of

Concrete.

If the concrete slumps evenly it is called true slump. If one half of the cone slides

down, it is called Shear slump. In case of a shear slump, the slump value is

measured as the difference in height between the height of the mould and the

average value of the subsidence. Shear slump also indicates that the concrete is

non-cohesive and shows the characteristic of segregation.

55

5.4 TESTS ON WATER:

pH Value

Chloride

Sulphite

Nitrite

5.5 TESTS ON HARDENED CONCRETE:

Compressive Strength

Flexure Strength

56

6. MIX DESIGN

The procedure for designing concrete mix as per new code is highlighted using an M20

concrete.

Design stipulations for proportioning

a. Grade designation: M20

b. Type of cement: OPC 43 grade, IS 8112

c. Max. Nominal size of aggregate. : 20 mm

d. Minimum cement content: 300 kg/m3

e. Maximum water cement ratio: 0.55

f. Exposure condition: Mild

g. Degree of supervision: Good

h. Type of aggregate: Crushed angular aggregate

i. Maximum cement content: 450 kg/m3

j. Chemical admixture: Not used

Test data for materials

Cement used: OPC 43 grade

Specific gravity of cement : 3.15

Specific gravity of

a. Coarse aggregate: 2.59

b. Fine aggregate: 2.59

Water absorption

a. Coarse aggregate: 0.28 %

b. Fine aggregate: 0.59 %

Free (surface) moisture

a. Coarse aggregate: Nil

b. Fine aggregate: 2.0 %

57

Sieve analysis

a. Coarse aggregate : Conforming to Table 2 of IS 383

Table 6.1: sieve analysis results

Sieve size Retained

(grams)


(%)

% finer

25 mm 0 0 0 0

20 mm 569 11.38 11.38 88.62

12.5 mm 3661 73.22 84.6 15.4

10 mm 619 12.38 96.98 3.02

4.75 130 2.6 99.58 0.42

Pan 21 0.42 100 0

b. Fine aggregate : Conforming to Zone II of IS 383

Table 6.2 fine aggragate results

Sieve size Retained

(grams)


(%)

% finer

4.75 17.5 1.75 1.75 98.25

2.36 mm 59 5.9 7.65 92.35

1.18 mm 283 28.3 35.95 64.05

600 µ 198 19.8 55.75 44.25

300 µ 194 19.4 75.15 24.85

150 µ 111.5 11.1 86.25 13.75

Pan 137.5 13.8 100 0

Target strength for mix proportioning

f’ck= f’ck +ks

From Table 1 of IS 10262:2009 standard deviation, s = 4.6 N/mm2

Therefore target strength = 20+1.65 x4.6 = 27.60 N/mm2

58

Selection of w/ c ratio

From Table 5 of IS 456:2000, maximum water cement ratio = 0.55 (Mild exposure)

Based on experience adopt water cement ratio as 0.50. 0.5 < 0.55, hence ok

Selection of water content

From Table 2, maximum water content = 186 litres (for 25 mm – 50 mm slump range and

for 20 mm aggregates)

Estimated water content for 75 mm slump = 186 + 3/100 x 186 = 191.6 litres

Calculation of cement content

Water cement ratio = 0.50

Cement content = 191.6/0.5 =383 kg/m3 >320 kg/m3(given)

From Table 5 of IS 456, minimum cement content for mild exposure condition = 300

kg/m3, Hence OK

Proportion of volume of coarse aggregate and fine aggregate

content

From Table 3, volume of coarse aggregate corresponding to 20 mm size aggregate and fine

aggregate (Zone II) for water-cement ratio of 0.50 =0.60

DETERMINATION OF COARSE AND FINE AGGREGATE CONTENT:

V= [W + + . ] x

V= [W + + . ] x

59

V = absolute volume of fresh concrete

Sc =specific gravity of cement.

W= mass of water (kg )per m3 of concrete

C= mass of cement (kg) per cu.m. of concrete.

p = ratio of fine aggregate to total aggregate by absolute volume.

fa,Ca= total masses of fine and coarse aggregates by absolute volume.

Sfa, Sca= specific gravities of fine and coarse aggregates (saturated surface dry condition)

For the Specified Max. Size of aggregate of 20 mm, the amount of entrapped air in

the wet concrete is 2%

Amount of Fine aggregate, Fa required

1 m3 = [191.6 + + . ] x

Fa = 544.01 Kg/m3

Amount of Coarse aggregate, Ca required

1 m3 = [191.6 + + . ] x

Ca = 1183.02 Kg/m3

The Mix Proportion then becomes

Water = 191.61 kg/m3

Cement = 383 Kg/m3

Fine Aggregate = 544 Kg/m3

Coarse Aggregate = 1183 Kg/m3

Aggregates are assumed to be in Saturated-Surface-Dry (SSD). Otherwise corrections are

to be applied while calculating the water content. Necessary corrections are also required

to be made in mass of aggregates.

60

Volume of Each cube = 0.15 x 0.15 x 0.15 m3

= 3.375 x 10-3

m3

For Preparing 8 Cubes the required amount of concrete = 3.375 x 10-3

x 8

= 0.027 m3

The amount of materials required for 8 cubes

Cement =10.341 kg

Fine aggregate = 14.688 kg

Coarse Aggregate:

20 mm = 19.17 Kg

12 mm = 12.771 Kg

Water = 5.18 Kg

Compressive Strength using Accelerated Curing Tank Test

Grade of Concrete M20

Table 6.3 samples

Sample Weight (Kg) Strength (N/mm2) Average Strength

(N/mm2)

Sample-1 8.520 19.9

19.99 Sample-2 8.460 20.08

The actual strength = [8.09 + (1.64 * Average strength)]

= 40.8736 N/mm

Mix proportions for making 1 of concrete:

Table 6.4 material contents in M 20:

Water

Cement

Fine Aggregate

Coarse Aggregate

191.61 kg/m3

383 Kg/m3

544 Kg/m3

1183 Kg/m3

61

7.MERITS AND DEMERITS:

7.1MERITS OF RMC:

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.

Organization at site is more streamlined.

Durable & Affordable

No storage space required either for raw materials or for the mix.

Lower labour and supervisory cost.

No wastage at site.

Environment friendly.

Availability of concrete of any grade.

7.2 DEMERITS OF RMC:

Need huge initial investment.

Not affordable for small projects (small quantity of concrete)

Needs effective transportation system from R.M.C to site.

Traffic jam or failure of vehicle creates problem if proper dose of retarder is not

given.

Labours should be ready on site to cast the concrete in position to vibrate it and compact it.

62

8. OPERATIONAL ASPECT

8.1 NEEDS TO BE SPECIFIED BY CONSUMER FOR RMC

The following needs to be specified very clearly:

Characteristic strength or grade (N/mm2)

Target workability or slump in mm required at site

Exposure conditions for durability requirements

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 case of 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)

Permissible wastage

Mode of measurement.

63

8.2 INFORMATION TO BE SUPPLIED BY THE PRODUCER

The RMC supplier must provide the following information to the consumer if and when

requested:

Nature and source of each constituent material including the name of the

manufacturer in case of branded products like cement, admixtures etc.

Proportion of quantity of each constituent per CuM of fresh concrete.

Generic type of the active constituent of the chemical admixture and its solid

content.

Chloride content in all constituent materials.

Compatibility of cement and chemical/mineral admixtures.

Compatibility of admixtures with one another when more than two types of

admixtures are proposed.

Initial and final setting time of concrete when admixture is used.

Details of plant and machinery (capacity CuM/hr), storage (CuM) availability, type

of facilities to dose admixtures, type of moisture measurement arrangement, type of

mixer, rated capacity (CuM/min.) of the mixer.

Availability of number of transit mixers and their capacities.

Details of last calibrations done on various weighing /dosing equipments

Testing facilities available at RMC plant

Capacity and type of concrete pump and placing equipment available (if required).

64

8.3 CHECKS BY CONSUMER BEFORE ORDERING THE RMC

The following need to be looked into by the consumer:

Reliability of the plant and transit mixers for consistent and continuous concrete

supply as per requirement.

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 and back.

8.4 CHECKS NEEDED AT SITE PRIOR TO RECEIPT OF RMC

Reinforcement layout for proper concrete placement without segregation

Adequacy of formwork to take the hydrostatic pressure and adequacy of loading on

propping system to match the speed of placing.

Openings and chutes provided, at predetermined locations, between reinforcement

bars to lower the placing hose (if pumped concrete is planned) to avoid segregation

of concrete

Adequacy of manpower and equipment for placing, compacting, finishing and

curing of concrete.

Proper approach for transit mixers free from all encumbrances ego water logging,

material stacking etc.

Proper platform to receive concrete.

Proper precautions required to be taken to ensure that concrete from the transit

mixer is unloaded at the fastest possible speed does not take more than 30 minutes.

If pumping is proposed, the location of the pump should be approachable from both

sides.

65

8.5CHECKS 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.

Ensure that water addition or chemical admixtures are not added during

transportation by RMC unauthorized persons and without the knowledge of the site

in charge of the consumer.

Temperature of concrete at the time of receipt at site (if specified).

Continuous and steady supply at site and speedy unloading of the Monitor speed

and progress of placing to avoid formation of cold joints transit mixers.

Monitor proper placement without segregation.

Monitor placement of concrete at the closest possible point to its final location.

Arrange for curing as soon as finishing is completed. This is specially required in

case of slabs, pathways and roads in hot/warm weather.

Retempering should be prohibited as experiments shows the addition of water to

RMC truck at the construction site may result in substantial reduction in strength.

The reduction in strength was found to be proportional to the increase in slump.

Large increase in slump means higher reduction in strength. When the amount of

water added is not controlled, reduction of strength may be as high as 35%. In cases

where controlled amount of water is added to restore the slump within the

specification’s limits (100 ±25 mm), the reduction of strength may be below 10%.

8.6THE UNNECESSARY RESTRICTIONS ON SUPPLIERS OF RMC

BY PURCHASER

Insistence on use of cement and admixtures of specific brands: This selection

should be left to the RMC supplier as they have to decide this based on the

comparability study.

Inappropriately low water to cement ratio. This should be left to the RMC supplier

or alternatively high strength of concrete specified.

66

Restriction on use of water reducing admixtures. It is almost mandatory to use

water reducing and or slump retaining admixtures. Hence such restrictions can

cause quality problems.

Insisting on Indian Standard method of concrete mix design: It must be understood

that IS 10262 (1982) only gives guidelines on design of concrete mixes. It does not

cover high strength cements now available and does not cater to effects of

admixtures. It also does not recommend changes necessary for RMC and pumpable

concrete mixes. Concrete mixes designed by this method are generally found to be

non-cohesive and require higher cement contents (uneconomical). The option of

concrete mix design should be and must be left to the RMC supplier.

Frequency of testing: This is often changed by the consumer than that specified in

clause 6.3.2 of IS 4926 (2003). However, this needs to be mutually discussed and

finalised prior to placement of order.

Fixed slump insisted upon: Many a times fixed slump value is insisted upon by the

consumer. This is practically not possible. Variations are likely to occur and should

be within the limits say ± 25 mm as stated in clause 6.2.1 of IS 4926 (2003).

Ambiguous specifications: Many consumers give ambiguous specifications. Both

the specifier and the supplier need to resolve the ambiguity specially those dealing

with specifications like durability as per IS 456 (2000) without mentioning

exposure conditions or presence of chemicals in ground water and subsoil. Also

specifying target mean strength instead of characteristic strength required without

mentioning the accepted failure rate or standard deviation.

Concrete Field strength should not be less than Target strength: Such a

specification that the field strength should not be less than the target strength

should not be less than the target strength belies the understanding of the definition

of characteristics strength. If the requirement is for an M30 grade concrete, then the

field strength of concrete should not be less 30 N/mm2 within a confidence limit of

95%. If the specification insists on target strength to be achieved in the field as

well, then the concrete requested automatically becomes M39 or its equivalent.

This makes the concrete unnecessarily expensive.

67

8.7 THE CONSTRAINTS FACED BY RMC PRODUCERS AT

PRESENT

RMC cost is likely to be slightly higher than site produced concrete of the same

quality. This may be mainly due to sales taxes. However, to some extent if RMC

consumer has no objection to addition of flyash or ground granulated blast furnace

slag of required quality and consistency then perhaps the cost becomes more

competitive with site produced concrete. RMC plants having accurate computerised

batching and excellent mixing facilities can produce good quality RMC if they are

careful in selecting the mineral admixture.

Delayed payments and long credit period insisted upon by consumers affect their

cash flow.

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

results in their installation nearly 10-20 kms. away from their potential consumers

located in residential zones.

High cost of the plant and equipment results in high capital costs. However, many

multinationals have started producing plant and equipment in our country. Hence

costs have reduced. However, one has to be careful as quality of performance has

dropped in comparison with equipment directly imported from countries like

Germany.

Bad quality of roads and traffic congestion and intermittent signals often delay the

deliveries in metros.

Availability of trained and skilled manpower for operations and maintenance of

plant and equipment. As new plants come up, skilled workers keep changing jobs

for better prospects.

Price variations of all concrete ingredients specially cement.

Non availability of consistent and good quality aggregates, mineral admixtures etc.

Non-availability of bulk cement supply in most of the cities where RMC is

marketed.

Difficulty in immediate availability of spares or additional inventory carrying cost

required to be kept in case of essential spares.

Stipulations of pollution control board causing difficulty to obtain license for

running RMC plant. Such clearances are not required if similar plants are installed

on the construction site itself.

68

Workability retention in hot weather.

Site oriented problems at the consumer end such as the following:

Delays in placing, compacting and finishing at consumer's end causes delays in

unloading of transit mixer and stiffening of the concrete mix.

Quality of formwork and its adequacy to take proper vertical loads and hydrostatic

pressures, due to faster rate of supply and placing is often not taken care of at sites

receiving concrete.

Reinforcement layout and planning of placement, compaction and curing must be

properly organised at site to suit the speed of supply and placement of RMC.

In many countries, specialist agencies do pumping and placing of concrete. In our

country, the onus of pumping and placing is either placed on the RMC supplier or

on the construction site.

Concrete cube failures and their acceptance criteria due to site inadequacies or

sampling should not be attributed to RMC supplier.

Plastic shrinkage cracks due to inadequate curing at site often results in blaming the

RMC supplier.

69

9. CONCLUSION:

The concrete quality produced in RMC plant is highly consistent with low

deviation order. It provides a high degree of overall strength of hardened concrete and the

performance of the structure at a later date. RMC operations are highly mechanized and

fully controlled through electronic controls and hence reduce the probability of errors in

various operations. It is also environment friendly and brings down pollution due to dust at

construction can also be accelerate with the use of RMC. The use RMC in civil

construction is widely adopted throughout the world. The beginning made in India is in

tune with the developments outside and RMC uses provide numerous benefits to the

consumers.

Conventional approach to durable concrete structures, namely specifying maximum

water cement ratio, minimum cement content and cement type, is now always satisfactory,

especially under aggressive environmental condition. Site manufactured concrete cannot

assure the same quality of concrete and that from controlled ready mix batching plant

backed by advanced technology and project management. The advantages of RMC are

particularly evident in construction projects with aggressive exposure conditions.

Ready mix concrete has gained acceptance in Indian industry due to several

advantages including quality control and overall economy. RMC plants are proliferating,

especially in urban regions, not only because of the space restrictions around construction

site but also due to the realisation of the advantages by engineers and construction

industry.

70

10. BIBLIOGRAPHY:

Concrete Technology Theory and Practice, M.S SHETTY, S.Chand- New Delhi.

*“RMC in India” (June 2001), Civil Engineering & Construction Review

IS 4926-2003, Standard on Ready mixed concrete – Code of Practice, BIS, New

Delhi.

IS 383, Indian Standard specification for coarse and fine aggregates from natural

sources for concrete ( Second Revision )

IS 10262-2009, Indian Standard Concrete Mix Proportioning- guidelines (First

Revision)

IS 456-2000, Indian Standard Plain and Reinforced Concrete - Code of Practice

(Fourth Revision )

“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

WEBSITES:

http://www.jklakshmi.com/calculator.html

http://www.lntecc.com/concrete/lntreadymix.asp

http://www.rdcconcrete.com/

http://www.scribd.com/

http://www.wikipedia.org/

http://www.jklakshmi.com/calculator.html

http://www.rdcconcrete.com/

http://www.scribd.com/

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