rmc report

7/27/2019 Rmc Report

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QUALITY CONTROL IN READY MIX CONCRETE

A PROJECT REPORT

Submitted by

Harsh Patel

Bharat Purohit

Dinesh Chaudhri

Jigar Shah

In fulfillment for the award of the degree

Of

BACHELOR OF ENGINEERING

in

CIVIL

GOVERNMENT ENGINEERING COLLEGE, PALANPUR

Gujarat Technological University, Ahmedabad

December, 2011


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GOVERNMENT ENGINEERING COLLEGE, PALANPUR

Civil Engineering Department

2012

CERTIFICATE

Date:

This is to certify that the dissertation entitled QUALITY

CONTROL IN READY MIX CONCRETE has been carried out by

HARSH PATEL, BHARAT PUROHIT, DINESH CHAUDHRI, JIGAR

SHAH under my guidance in fulfillment of the degree of Bachelor of

Engineering in Civil (7th Semester) of Gujarat Technological University,

Ahmedabad during the academic year 2011-12.

INTRNAL GUIDE:

Prof. Vijay R Sharma

Prof. Upendra R Singh

External guide:

Bharat P Patel

Head of the Department

Prof. S A Trivedi


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ACKNOWLEDGEMENTS

Knowledge in itself is a continuous process. I would have never succeeded in

completing my task without the cooperation, encouragement and help provided to me by

various personalities with deep sense of gratitude.

I express my sincere thanks to my esteemed and worthy supervisor, Prof.Vijay R

Sharma, Department of Applied Mechanics, for his invaluable guidance, wild discussions,

sincere encouragement and constructive criticism during the conceptualization, of this study.

The prolonged interactions with him even at odd hours of the day have really inculcated inme the spirit of an independent practicing engineer.

I wish to express my sincere thanks to Prof. Upendra R Singh. Appreciation is also

extended to, Prof. S A Trivedi, Head of Department, Government Engineering College

Palanpur for his immense guidance, gratuitous and mind provoking ideas.The technical guidance and constant encouragement made it possible to tie over the

numerous problems, which so ever came up during the study. My greatest thanks are to all

who wished me success. Above all I render my gratitude to the Almighty who bestowed self-confidence, ability and strength in me to complete this work.

Finally, yet importantly, I would like to express my heartfelt thanks to my beloved

parents for their blessing, my friends for their wishes for the successful completion of this

training.


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ABSTRACT

Ready Mixed Concrete is a specialized material in which the cement

aggregates and other ingredients are weigh-batched at a plant in a centralmixer or truck mixer, before delivery to the construction site in a condition

ready for placing by the builder

In order to ensure that concrete produced is of desired quality, it is

Necessary that quality control is exercised at all the stages right from Receipt

of raw material to delivery of concrete at site. Thus, while planning to use

Ready Mixed Concrete, it should be ensured that producer of Ready Mixed

Concrete has adopted quality assurance programme. Quality control system

should be prevalent at Ready Mixed Concrete plant. Quality Assurance

Programme for Ready Mixed Concrete can be broadly divided into three

components i.e. Forward control, Immediate control and retrospective control.

RMC manufacturer should have laboratory facilities to carry out necessary

tests to ensure quality control at all stages during production of concrete.

In the present work a series tests were carried out to make comparative

studies of various properties of Ready mix concrete and Experimental

investigation has been carried out to study the working of Ready Mix Concrete

plant . Tests have been performed for Quality control of materials used at plant,

Compressive Strength indicated that compressive strength is as per the

requirement or not.


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List of Figure

Figure No Figure Description Page No

Figure3.5 Silos 10

Figure 3.6 Admixture container 10

Figure 3.7 Mixing machine 11

Figure 3.8 Truck Mixer 12

Figure 3.9 Truck Mixer 13

Figure 3.10 Placing of RMC 15


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LIST OF TABLES

Table No Table Description Page No

Table 4.1.1(a) Sieve analysis for Fine

Aggregate

19

Table 4.1.1(b) Properties of Fine Aggregate 20

Table 4.1.2(a) Sieve Analysis for Coarse

Aggregate

21

Table 4.1.2(b) Properties of coarse

aggregate

21

Table 4.2 Moisture Content 22

Table 4.3 Compressive Strength of

cement

23

Table 4.6 Compression test on the

concrete cube

30


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TABLE OF CONTENTS

Pages

Acknowledgement i

Abstract ii

List of Figures iii

List of Tables iv

Table of Contents v

Chapter : 1 Introduction(page 1 starts)

1.1 General 1

1.2 Quality control 2

1.3 Forward control 2

1.4 Control of quality of raw material 2

1.5 Immediate control 2

1.6 Retrospective control 3

Chapter : 2 Literature Review(page 4 starts)

Chapter : 3 RMC Plant(page 7 starts)

3.1 Advantages 7

3.2 Disadvantages 7

3.3 Materials 8

3.3.1 Aggregates 8

3.3.2 Cementations Materials 8

3.3.3 Water 8

3.3.4 Admixtures 9

3.4 Types of RMC 9


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3.5 Silos 10

3.6 Admixture Container 10

3.7 Stationary or central mixers 11

3.8 Truck Mixer 12

3.9 Transport of Concrete 13

3.9.1 General 14

3.9.2 Time in Transport 14

3.10 Placing of RMC 14

3.11 Consolidation 15

3.11.1 Hand Compaction 16

3.11.2 Compaction by Vibration 16

3.11.3 Compaction By Pressure and Jolting 17

3.11.4 Compaction by Spinning 17

3.12 Curing 17

3.13 Finishing 18

Chapter : 4 Quality Assurance(page 19 starts)

4.1 Test of Sieve Analysis 19

4.1.1 Test for Fine Aggregate 19

4.1.2 Test for coarse Aggregate 20

4.2 Moisture Content 22

4.3 Compressive Strength of Cement 22

4.4 Admixtures 23

4.4.1 Plasticizers 24

4.4.2 Super plasticizers 24

4.4.3 Retarders 24

4.4.4 Retarding Plasticizers 25


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4.4.5 Accelerators 25

4.4.6 Accelerating Plasticizers 25

4.4.7 Air-entraining Admixtures 26

4.4.8 Mineral Admixtures 26

4.5 Tests on Concrete Cubes 27

4.5.1 Testing of Fresh Concrete 27

4.5.2 Testing of Hardened Concrete 28

4.6 Compressive strength 29

Chapter : 5 Conclusion(page 31 starts)

Chapter : 6 References(page 33 starts)


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Chapter : 1 INTRODUCTION

1.1 General:

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. Ready mixed concrete is suitable for

small and medium projects where cost of development of adequate infrastructure for

producing quality concrete will be disproportionate. Ready Mixed Concrete is also

convenient for congested site where adequate space is not available for storage of raw

materials and other concrete manufacturing operations. For large construction project like

important bridges etc. where adequate space is available, site mixed concrete appears to be

more suitable, provided adequate quality control is exercised at all the stages similar to the

control being exercised by the Ready Mixed Concrete plants.

As PER Indian Standard code of practice (IS 4926) Ready Mixed Concrete (RMC) is defined

as The concrete delivered in plastic condition and requiring no further treatment before

being placed in position in which it is to set and harden. Instead of being batched and mixed

on site, concrete is delivered for placing from central batching plant. 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. Sometimes Materials such

as water and some varieties of admixtures can be transit-mixed (also known as Transit

Mixture), that is they can be added to the concrete at the jobsite after it has been batched to

ensure that the specified properties are attained before placement. Here materials are batched

at a central plant and are completely mixed in the Batching Plant or partially mixed in transit.

Transit-mixing keeps the water separate from the cement and aggregates and allows the

concrete to be mixed immediately before placement at the construction site (Dry Concrete).

This method avoids the problems of premature hardening and slump loss that result from


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potential delays in transportation or placement of central-mixed concrete. Additionally,

transit-mixing allows concrete to be hauled to construction sites further away from the plant.

There are several types of RMC plants varying in type of mixing and capacity of concrete

production. These plants are generally available in capacities varying from 15 cum/hour to

200 cum/hour. 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. Metropolitan cities are hard-pressed for storage space. Therefore, RMC greatly relieves

the space problem.

1.2 Quality control:

In order to ensure that concrete produced is of desired quality, it is Necessary that quality

control is exercised at all the stages right from receipt of raw material to delivery of concrete

at site. Thus, while planning to use Ready Mixed Concrete, it should be ensured that

producer of Ready Mixed Concrete has adopted quality assurance programme. Quality

control system should be prevalent at Ready Mixed Concrete plant.

1.3 Forward control:

Forward control covers all the aspects which are to be taken care prior to production of

concrete i.e. control of material quality and storage, mix design and modifications, plant

maintenance etc.

1.4 Control of quality of raw material:

A control system should be operated to provide assurance that all materials purchased and

used in the production of concrete conform to standards specified. It may include visual

checks, sampling and testing and certification/ information from suppliers of materials.

1.5 Immediate control:

Immediate control is concerned with instant action to control the quality of concrete being

produced. Broadly it includes following:


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Adjustment for surface moisture content of fine and coarse aggregates:

For producing the desired mix concrete the amount of water to be added depends upon the

surface moisture content of aggregates. There should be standard arrangement for testing

surface moisture content of coarse and fine aggregates. This test should be conducted daily.

1.6 Retrospective control:

Retrospective control is concerned with those factors that influence the control of concrete

quality which can not be assessed at the time of production. Strength of concrete and

permeability are such factors which can not be assessed at the time of production. Broadly

mix performance is the main factor that has to be taken care by the producer. The producer

should introduce suitable control procedure to monitor the performance of design mix.

Quality control system should be operated to check the strength of design mix from random

sampling of actual quality of concrete produced at the plant. Cube test results should be

compared with targeted strength of the concrete. In case, substantial difference is observed in

the two values, proper analysis should be made for the factors which would have resulted in

deviation from the targeted strength of design mix. Subsequently, corrective action should be

taken.


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Chapter : 2 LITERATURE REVIEW

As early as 1909, concrete was prepared by a horse-drawn mixer that used paddles turned by

the carts wheels to mix concrete en route to the jobsite. In 1916, Stephen Stepanian of

Columbus, Ohio, developed a self-discharging motorized transit mixer that was the

predecessor of the modern readymixed concrete truck.

Theoretical models of industry dynamics was explored by Jovanovic (1982) and

Hopenhayn (1992). They were study the effect of firms learned about theirproductivities on

the entry and exit process and an industrys steady-state.but they have received limited

empirical scrutiny.

Syverson (2004) documents productivity dispersion in the ready-mix concrete industry using

data from the U.S. Census Bureau. Productivity is defined as the residual of the regression of

log output on log salaries and log assets. Syverson conjectured that competition plays a key

role in eliminating unproductive plants, which limits the dispersion of productivity.

Moreover, there was a smaller share of low productivity plants in large markets than small

ones. Goal was to explore the mechanism for plant selection in more detail, instead of

focusing on the cross-sectional implications of plant selection considered by Syverson

(2004).

Lucia, Haltiwanger, and Krizan (1998) investigate the micro-foundations of aggregate

productivity growth. They decompose changes in aggregate productivity into three effects:

productivity changes within the plant, entry of more efficient producers and exit of

unproductive ones and reallocation of output from inefficient plants to efficient ones.He wasillustrated that the effect of policies such as entry subsidies and demand fluctuations on the

evolution of aggregate productivity, a task which was beyond the reach of Lucia,Haltiwanger, and Krizan (1998).

Foster, Haltiwanger, and Syverson (2005) investigate the role of a plants profitability and

productivity in the exit decision. Dunne, Klimek, and Roberts (2006) were also look atentry and exit decisions of several geographically differentiated producers (including ready-


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mix concrete). Plants that were built by firms with previous industry experience have lower

exit rates than those of newer entrants. But It was difficult to gage if these other

characteristics of firms can explain the dispersion of productivity present in the data.

Most interesting was the large effect of being a high productivity plant, with a coefficient

was variance units in the Hotz and Miller (1993) estimated small profits and in the

Aguirregabiria and Mira (2006) estimated more ten earlier. This effect is far more than the

effect of the first competitor on profits. Inpreliminary work used the proxy variabletechniques of Olley and Pakes (1996)andAckerberg, Frazer, and Caves (2006) decreases

the magnitude of productivity dispersion by 50%, separting true productivity dispersion

which firms react to by investing more or purchasing more materials and dispersion due to

measurement error.

In the ready-mix concrete industry, plants using the same bundle of inputs produce

substantially different amount of concrete. The average plant in the 75th percentile of

productivity produces four times the output of a plant in the 25th percentile. But, the exit rate

of a plant below the median level of productivity is 3% versus an exit rate of 6% for a plant

above the median. Why do these enormous differences in productivity translate into small

differences in exit rates? First, in this industry, productivity has little persistence. Thus

current productivity does not provide much information on the net present value of

productivity over the plants expected lifetime. Second, sunk costs slow the exit of

unproductive producers, since it is costly to enter the industry. Using entry and exit

information, they were fond a 20% difference in output between plants in the 25th and 75th

percentile which use the same inputs. Thus, even a conservative measure of productivity

dispersion finds substantial differences in productivity. An unanswered question is whether

31 the magnitude of this dispersion can be reduced through the subsidy.

Ready Mix Concrete industry in India is continuously growing. This industry is exposed torisks from internal as well as external sources. It is important to address these risks, so that

industry shall gain credibility and confidence of the customers, and shall have expected profit

margins.Proposed paper presents a risk quantification approach for risks in RMC plants inIndia, using Expected Monetary Value (EMV) analysis. It is developed using guidelines

available in literature in the area of risk management.


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In the context of India, the trend of using ready mix concrete is growing steadily. Demand of

RMC is increasing in housing as well as in infrastructural projects. Like other industries,RMC industry is exposed to various risks. In European countries, there is an awareness and

understanding about importance of risks and its management. Operation managers on RMC

Plants in the European countries are expected to work on risk management at production

plant and delivery sites.

Unless the risks are addressed properly, the RMC industry in India shall not gain credibility,

confidence of customers and will also cause reduction in profit margins.The risk causes canbe categorized into internal risk causes and external risks causes. In the literature, the wordRisk has been used in many different meanings with many different words such as hazard

or uncertainty. They gives different laws for solution by EMV of risk management.

The general consensus in this literature, available in the field of risk management,

incorporates four steps in the process of risk management. These are Risk identification, Risk

Analysis, Risk Response planning and Risk Monitoring and control (Thevendran and

Mawdesley 2004).Failure to perform effective risk management can cause projects to exceed

budget, fall behind schedule, miss critical performance targets, or exhibit any combination of

these troubles (Carbone and Tippett, 2004).

They made major report and published in discussion between the experts and engineers and

architects to risk management in mega cities of INDIA for risk management of RMC plant or

industries. And they give conclusion by method of EMV that it is may be vary in cost of

RMC plant in the limit. This approach can be made suitable for incorporating andimplementing with a computer aided decision support system, provided precise data is made

available.


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Chapter : 3 RMC PLANT

3.1 ADVANTAGES:

Ready Mixed Concrete offers following benefits over the site mixed concrete.

i) Quality assured concrete:- Concrete is produced under controlled conditions using

consistent quality of raw material.

ii) High speed of construction- Speed of construction can be very fast in case RMC is used.

It has come to notice that RMC was used in MSRDC flyovers in Mumbai wherein 25 piles

(200 m3) were cast in one day. Similarly, deck slabs of 370m3 were cast in one day and the

projects are being completed 3-5 months ahead of schedule.

iii) Versatility in uses and methods of placing: The mix design of the concrete can be tailor

made to suit the placing methods of the contractor.

iv) Timely deliveries in large as well as small pours.

v) No need for space for storing the materials like coarse and fine aggregate, cement, water

and admixtures.

vi) No delay due to site based batching plant erection/ dismantling; no equipment to hire; no

depreciation of costs.

vii) Reduced noise and air pollution; less consumption of petrol and diesel and less time loss

to business.

Viii) A centralized concrete batching plant can serve a wide area.

ix) Labors associated with production of concrete is eliminated.

3.2 DISADVANTAGES:

i) As the Ready Mixed Concrete is not available for placement immediately after preparation

of concrete mix, loss of workability occurs. In addition, there are chances of setting of

concrete if transit time involved is more. Therefore, generally admixture like plasticizers/

super plasticizers and retarders are used. Addition of retarders may delay the setting time

substantially which may cause placement problems. In addition, it may also affect the


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strength of concrete. Therefore, it is necessary that the admixtures i.e. plasticizers and super

plasticizers/ retarders used in Ready Mixed Concrete are properly tested for their suitability

with the concrete. In case loss of strength is observed, the characteristic strength may have to

be enhanced so that after loss of strength, required characteristic strength is available.

ii) Because of large quantity of concrete available in short span, special placing and form

work arrangement are required to be made.

iii) Concretes limited time span between mixing and going-off means that ready mix should

be placed within 2hours of batching at the plant.

3.3 Materials:

3.3.1 Aggregates:

The first consideration in proportioning a concrete mix is the aggregates since they will make

up the largest portion of most concrete mixes - about 65% to 80% by volume. Consideration

should be given to all properties of both the coarse and fine aggregates including: hardness,

absorption, specific gravity, alkali reactivity and gradation. The coarse (also referred to as

stone) aggregate and fine (also referred to as sand) aggregate are graded materials - that is

they are a compilation of multiple sized particles as opposed to only one or two particle sizes.

This graded characteristic results in a denser product than the same volume of like-sized

particles due to fewer voids between the particles.

3.3.2 Cementations Materials:

Since the cementitious material and water form the paste or "glue" that binds the aggregates

together, maximizing its quality is prudent. The paste serves to fill the voids between the

coarse and fine aggregate particles as well as to bind these particles into a solid mass.

Cementitious material is sometimes referred to in units of sacks.

3.3.3 Water:

Water combines with the cementitious material during a reaction referred to as hydration to

create hardened concrete. The weight of the water in the mix (added water plus free moisture


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on the aggregates) divided by the weight of cementitious material forms what is referred to as

the water-cementitious material ratio (w/c). This characteristic of the concrete mix

determines, to a great extent, the overall quality of the concrete relative to its engineering

properties such as density, strength, abrasion resistance, and shrinkage to name a few. Two

portions of water exist in a concrete mix. The first portion is that water necessary to hydrate

the cementitious materials. The second is that portion necessary to make the concrete

workable enough to be molded into the shape of its intended purpose.

3.3.4 Admixtures:

A wide range of chemicals have been developed to enhance the performance of concrete

and/or its engineering properties. These products are usually liquids or powders which areadded to the concrete during the batching process. Some of their effects to the concrete

include:

i) Reducing the amount of water of convenience needed to place the concrete, thereby,

reducing the overall water cementitious material ratio while maintaining acceptable

workability.

ii) Retarding the "set" or hardening rate of the concrete.

iii) Accelerating the "set" or hardening rate of the concrete.

iv) Reducing adherence of concrete to forms during manufacturing of pre-cast concrete

products.

3.4 Types of RMC:

RMC can be classified according to ingredients mixed in concrete. These may be on the basis

of Cementitous Material i.e. Fly ash is a part of Cement or not and Admixture is used or not.

Otherwise, there are two principal categories of ready mixed concrete.

i) Dry Concrete: All the ingredients are mixed in dry form without mixing water in it. All

these materials are sent in rotating drum and measured water quantity is sent in separate

Water container. The water is mixed at site when it reaches there.


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ii) Green Concrete: All the ingredients are mixed together including the measured water

quantity at Concrete Batching Plant itself. They are sent in rotating drum or in transit mixture

to the site of concreting.

3.5 Silos:

Fig.3.5 SILOS

Cement Storage Silo is basically used for storing loose cement and some times used for

storing Fly ash. At Venus industries we provide solution for the same. We had Cement silos

for various capacity like 35, 50, 75, 100 & 150 MT storage capacity. Cement silo comes with

following accessories (Optional)

i) Maximum minimum level indicatorii) High pressure safety valveiii) Cement silo fluidizing systemiv) Screw conveyorv) Cement silo filter system

3.6Admixture Container:


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Admixture container contains the admixture in a liquid form. Generally admixture like water

reducing agents/retarders are used in Ready Mixed Concrete for retention of workability and

to avoid setting of concrete. IS: 9103 Specification for admixtures for Concrete may be

referred to judge the suitability of admixtures.

Fig3.6 ADMIXTURE CONTAINER

3.7 Stationary or central mixers:

Stationary mixers shall not be loaded in excess of the manufacturers rated capacity. The

mixing time shall be measured from the time all the materials required for the batch,

including water, are in the drum of the mixer. The mixing time shall not be less than that

recommended by the manufacturer. Where a continuous mixing plant is used the complete

mixing time shall be sufficient to ensure that the concrete is of the required uniformity.


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Fig3.7 Mixing machine

3.8 Truck Mixer:

Fig3.8 Truck Mixer


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Truck mixers or agitators shall not be loaded in excess of the manufacturers rated capacity.

In order to system produce a satisfactory mix, and where there is no data available to

establish different period and speed revolutions, mixing shall continue for not less than 60

revolutions of the truck mixer drum at a rate of not less than 7 revolutions/min. All

completely truck mixed concrete shall be visually inspected for uniformity prior to leaving

the plant. When a truck mixer or agitator is used for transporting concrete which has been

mixed before leaving the plant, the concrete shall be agitated during transit and re-mixed at

the site for at least 2 min so that the concrete is of the required uniformity. Where water is

added to the concrete in the truck mixer through the truck mixer water meter and when such

water is being accounted for in the total water within the mix, it shall be ensured that the

truck mixer water meter is in operational condition and properly calibrated. Where a water

meter is not available, water must be measured in a suitable container before being added to

the truck mixer.

3.9 Transport of Concrete:

Fig3.9 Truck Mixer


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3.9.1 General:

Ready-mixed concrete shall be transported from the mixer to the point of placing as rapidly

as practicable by methods that will maintain the required workability and will prevent

segregation, loss of any constituents or ingress of foreign matter or water. The concrete shall

be placed as soon as possible after delivery, as close as is practicable to its final position to

avoid re-handling or moving the concrete horizontally by vibration. If required by the

purchaser the producer can utilize admixtures to slow down the rate of workability, however

this does not remove the need for the purchaser to place the concrete as rapidly as possible.

The purchaser should plan his arrangements so as to enable a full load of concrete to be

discharged within 30 min of arrival on site. Concrete shall be transported in a truck-mixer

unless the purchaser agrees to the use of non-agitating vehicles. When non-agitating vehiclesare used, the mixed concrete shall be protected from gain or loss of water.

3.9.2 Time in Transport:

The general requirement is that concrete shall be discharged from the truck-mixer within 2

hours of the time of loading. However, a longer period may be permitted if retarding

admixtures are used or in cool humid weather or when chilled concrete is produced.

The time of loading shall start from adding the mixing water to the dry mix of cement and

aggregate or of adding the cement to the wet aggregate whichever is applicable.

3.10Placing of RMC:When a concrete mix has been properly designed, batched, mixed and transported, it is

relevant that this concrete is also placed in the member in a correct manner. Different

situations require different care and therefore suitable method of placing concrete is adopted.


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Fig3.10 Placing of RMC

3.11Consolidation:

After placement, the concrete needs to be worked to eliminate voids and entrapped air and to

consolidate the concrete into the corners of the formwork and around the reinforcing steel.

Consolidation or Compaction of concrete is the process adopted for expelling the entrapped

air from concrete. If this entrapped air is not removed fully, the concrete loses strength

considerably. It is seen that 5 percent voids reduce the strength of concrete by about 30

percent and 10 percent voids reduce the strength of concrete by about 50 percent. Thecompaction of concrete is one of the major activities in the manufacturing of quality

concrete. The methods adopted for compacting the concrete are:

i) Hand Compaction


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ii) Compaction by Vibration

iii) Compaction by Pressure and Jolting

iv) Compaction by Spinning

3.11.1 Hand Compaction:Hand compaction consists of rodding, ramming or tamping. It is adopted only in case of

unimportant concrete work of very small magnitude. When hand compaction is adopted, the

consistency of concrete is maintained at a higher level. The thickness of the layer of concrete

is limited to 15 to 20 cm. In rodding, the concrete is poked by a rod to pack the concrete

between the reinforcement and sharp corners and edges. It is done continuously over the

complete area so as to expel the entrapped air. Ramming should not be permitted in case of

reinforced concrete or upper floors as it can disturb the reinforcement or formwork. Light

ramming can be permitted only in un reinforced foundation concrete or in ground floor

construction. Tamping is one of the usual methods for compacting the= roof or floor slab or

road pavements where the thickness of concrete is relatively less and the surface is to be

finished smooth and level.

3.11.2 Compaction by Vibration:Most of the concrete now placed in building construction is compacted by vibration.

Compaction of concrete by vibration has completely revolutionalised the concrete

technology. It is now possible to use low slump stiff mixes for production of high quality

concrete with desired strength and impermeability. A concrete with about 4 cm slump can be

placed and compacted fully in a heavily reinforced concrete work which is not at all=

possible with hand compaction where a slump of about 12 cm may be required. Actually, the

action of vibration is to set the particles of fresh concrete in motion, reducing the friction

between them and effecting a temporary liquifaction of concrete which enables easy

settlement. The concrete flows or liquifies under the shear forces accompanying the vibration

and the concrete is compacted away from the vibrator. Vibration by itself does not affect the

strength of concrete which is controlled by water/cement ratio. But by permitting use of less

water, i.e. stiff mix, concrete of higher strength and better quality can be made for a given


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cement factor. All the potential advantages of vibration can be fully harnessed if proper

control is exercised in the design and manufacture of concrete and the type of vibrator

required and its correct use is made. The different kinds of= vibrator available and which are

in use are as follows :

i) Internal Vibrator

ii) External Vibrator

iii) Screed Board Vibrator

iv) Table and Platform Vibrator

3.11.3 Compaction By Pressure and JoltingThis method is considered very effective for very dry concrete as is used in casting of hollow

blocks, cavity blocks and solid concrete blocks. The stiff concrete is vibrated, pressed and

jolted. This compacts the concrete into dense form which possesses good strength and

volume stability. By employing great pressure, a concrete of very low water cement ratio can

be compacted to yield very high strength. This method is mostly employed in the laboratory.

3.11.4 Compaction by SpinningSpinning is one of the recent methods of concrete compaction. The plastic concrete when

spun at very high speed gets compacted by centrifugal force. It is used for compaction &

fabrication of concrete spun pipes.

3.12 Curing

We have seen in Unit 2, on cement and lime, that concrete derives its strength by the

hydration of cement particles. This hydration is fast to start with but continuous for a long

time at a decreasing rate. Cement requires a water/cement ratio of 0.23 for hydration and 0.15

for filling the voids in gel pores. Therefore, theoretically a water/cement ratio of 0.38 would

satisfy the requirement of water for hydration with no capillaries. Practically a water/cement


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ratio of 0.5 will be required for complete hydration in a sealed container. However, in

practice, water is lost from the paste by evaporation or by absorption of water by aggregates,

formwork, or subgrade. If this moisture loss brings the internal relative humidity below about

80%, hydration will stop and strength development drops. Therefore, to ensure continued

hydration the loss of moisture would require replenishment or by some means to prevent the

loss itself. The desirable conditions are a suitable temperature and ample moisture. Curing is

the process by which a favourable environment is created to ensure uninterrupted hydration.

It has been recognized that the quality of concrete shows all round improvement with

efficient uninterrupted curing. There are several methods by which concrete can be cured.

Curing methods are generally categorized as below :

i) Water Curing

ii) Membrane Curing

iii) Curing at Elevated Temperatures

iv) Miscellaneous Methods of Curing

3.13 Finishing:

Finishing is the last operation in manufacture of concrete. It is very important in case of

concrete road pavement, airfield pavement and flooring. Surface finishes may be grouped in

following categories :

i) Formwork Finishes

ii) Surface Treatment

iii) Applied Finishes


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Chapter : 4 QUALITY ASSURANCE

4.1 Test of Sieve Analysis:

Aggregate gradation (sieve analysis) is the distribution of particle sizes expressed as a

percent of the total dry weight. Gradation is determined by passing the material through a

series of sieves stacked with progressively smaller openings from top to bottom and

weighing the material retained

on each sieve. Sieve sizes to be checked for compliance for the various mixtures aredesignated in the specifications. Gradations are expressed on the basis of the total percent

passing, which indicates the total percent of aggregate by weight that will pass a given size

sieve.

Some of the descriptive terms used in referring to aggregate gradation are:

i) Coarse aggregate all of the material retained on the No. 10 sieve (2.00mm).

ii) Fine aggregate or soil mortar all of the material passing the No. 10 (2.00mm) sieve.

4.1.1 Sieve analysis for Fine Aggregate:

Table 4.1.1(a) Total weight of sample is 1000 gm

Sieve Size Mass retained Percentage

Retained

Cumulative

Percentage

Retained

Percent

Passing

4.75mm 5.0 0.5 0.5 99.5

2.36 mm 78.0 7.80 8.30 91.7


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1.18 mm 185.0 18.5 26.80 73.2

600m 227.0 22.7 49.50 50.5

300m 281.0 28.1 77.6 22.4

150m 223.8 22.38 99.98 0.20

2.50 0.20 0.20 =262.6

4.1.1(b) Properties of Fine Aggregate:

Table 4.1.1(b) Properties of fine aggregate

S. No Properties of the aggregate Test results of

fine aggregate

Indian Standard

1 Specific gravity 2.5 IS: 2386 1963

(Part-3)2 Flakiness index - IS: 2386 1963

(Part-3)

3 Elongation index - IS: 2386 1963

(Part-2)

4 Fineness modulus 2.79 IS: 2386 1963

(Part-2)

5 Bulk density 1.3 IS: 2386 1963

(Part-2)

6 Water absorption 0.89 IS: 2386 1963

(Part-2)


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4.1.2 Sieve Analysis for Coarse Aggregate:

Total weight of sample is 1000 gm

Table 4.1.2(a) Sieve Analysis of Course Aggregates (10mm)

Sieve Size Mass Retained

(gm)

Percentage

Retained

Cumulative

Percentage

Retained

Percent

Passing

20 mm 0 0 0 100

10 mm 2516 83.89 83.87 16.13

4.75 mm 474 15.8 99.67 0.33

PAN 10 0.33 = 183.54

Properties of coarse aggregate:

Table 4.1.2(b) Properties of fine aggregate and coarse aggregate

S. No Properties of the aggregate Test results of

coarse

aggregate

1 Maximum size 20mm

2 Specific gravity (10 mm) 2.04

3 Specific gravity (20 mm) 2.825

4 Total water absorption (10 mm) 1.6432%

5 Total water absorption (20 mm) 3.645%

6 Moisture content (10 mm) 0.806%

7 Moisture content (20 mm) 0.705%


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8 Fineness modulus (10 mm) 6.46

9 Fineness modulus (20 mm) 7.68

4.2Moisture Content:i) Clean the container, dry it and weigh it with the lid (Weight W1).

ii) Take the required quantity of the wet soil specimen in the container and weigh it with the

lid (Weight W2).

iii) Place the container, with its lid removed, in the oven till its weight becomes constant

(Normally for 24hrs.).

iv) When the soil has dried, remove the container from the oven, using tongs.

v) Find the weight W3 of the container with the lid and the dry soil sample.

Table 4.2

Nominal maximum size of aggregate (mm) Water content per m3 of concrete (Kg)

For Grades up to M 35

10 208

20 186

40 165

For Grades above M 35

10 200

20 180


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4.3 Compressive Strength of Cement:

A compression test is a method for determining the behavior of materials under a

compressive load. Compression tests are conducted by loading the test specimen between

two plates and then applying a force to the specimen by moving the crossheads together. The

compression test is used to determine elastic limit, proportionality limit, yield point, yield

strength and compressive strength.

Compressive Strength:- It is the maximum compressive stress that a material is capable of

withstanding without fracture. Brittle materials fracture during testing and have a definite

compressive strength values. The compressive strength of ductile materials is determined by

their degree of distortion during testing.

Table 4.3 Compressive Strength

4.4 ADMIXTURES:

Admixtures are commonly classified by their function in concrete but often they exhibit

some additional action. The classification is as follows:

i) Plasticizers

ii) Super plasticizers

iii) Retarders and retarding plasticizers

iv) Accelerators and Accelerating Plasticizers

v) Air-entraining Admixtures

33 GRADE 43 GRADE 53 GRADE

3 days (N/mm2) 16.7 24.2 29.01

7 days (N/mm2) 23 33.9 40.2

28 days (N/mm2) 35.04 44.07 56.09


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vi) Mineral Admixtures

4.4.1 Plasticizers:

The action of plasticizers is mainly to fluidify the mix and improve the workability of

concrete, mortar or grout. The mechanisms that are involved could be explained in the

following way:

Retarding Effect: The plasticizer will get adsorbed on the surface of cement particles and

form a thin sheath. This thin sheath inhibits the surface hydration reaction between water and

cement as long as sufficient plasticizer molecules are available at the particle/solution

interface. The quantity of available plasticizers will progressively decrease as the polymers

become entrapped in hydration products.

4.4.2 Super plasticizers:

They are chemically different from normal plasticizers. Use of super plasticizer permits the

reduction of water to the extent up to 30 percent without reducing workability in contrast to

the possible reduction up to 15 per cent in case of plasticizers. The use of super plasticizer is

practiced for production of flowing, self leveling, and self compacting and for the production

of high strength and high performance concrete.

Super plasticizers can produce:

i) At the same w/c ratio much more workable concrete than the plain ones,ii) For the same workability, it permits the use of lower w/c ratio,iii)As a consequence of increased strength with lower w/c ratio, it also permits a

reduction of cement content.

4.4.3. Retarders


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A retarder is an admixture that slows down the chemical process of hydration so that

concrete remains plastic and workable for a longer time than concrete without the retarder.

Retarders are used to overcome the accelerating effect of high temperature on setting

properties of concrete on hot weather concreting. The retarders are used in casting and

consolidating large number of pours without the formation of cold joints. They are also used

in grouting oil wells. Retarding admixtures are sometimes used to obtain exposed aggregate

look in concrete. Perhaps the most common known retarder is calcium sulphate. It is inter

ground to retard the setting of cement. Perhaps the most common known retarder is calcium

sulphate. It is inter ground to retard the setting of cement.

4.4.4 Retarding Plasticizers:

It is mentioned earlier that all the plasticizers and super plasticizers by themselves show

certain extent of retardation. Many a time this extent of retardation of setting time offered by

admixtures will not be sufficient. Instead of adding retarders separately, retarders are mixed

with plasticizers or super plasticizers at the time of commercial production. Such commercial

brand is known as retarding plasticizers or retarding super plasticizers.

4.4.5 Accelerators:

Accelerating admixtures are added to concrete to increase the rate of early strength

development in concrete to

i) permit earlier removal of formworkii) reduce the required period of curingiii)advance the time that a structure can be placed in serviceiv)partially compensate for the retarding effect of low temperature during cold weatherv) concreting in the emergency repair work.

4.4.6 Accelerating Plasticizers:


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Certain ingredients are added to accelerate the strength development of concrete to

plasticizers or super plasticizers. Such accelerating super plasticizers, when added to concrete

result in faster development of strength. The accelerating materials added to plasticizers or

super plasticizers are triethenolamine chlorides, calcium nitrite, nitrates and fluosilicates etc.

The accelerating plasticizers or accelerating super plasticizers manufactured by well known

companies are chloride free.

4.4.6 Air-entraining Admixtures:

Perhaps one of the important advancements made in concrete technology was the discovery

of air entrained concrete. Air entrained concrete is made by mixing a small quantity of air

entraining agent or by using air entraining cement. These air entraining agents incorporate

millions of no-coalescing air bubbles, which will act as flexible ball bearings and will modify

the properties of plastic concrete regarding workability, segregation, bleeding and finishing

quality of concrete. It also modifies the properties of hardened concrete regarding its

resistance to frost action and permeability.

Air entrainment will affect directly the following three properties of concrete

i) Increased resistance to freezing and thawing.

ii) Improvement in workability.

iii) I Reduction in strength.

4.4.7 Mineral Admixtures:

The use of pozzolanic materials is as old as that of the art of concrete construction. It has

been amply demonstrated that the best pozzolans in optimum proportions mixed with

Portland cement improves many qualities of concrete, such as:

i) Lower the heat of hydration and thermal shrinkage.

ii) Increase the water tightness.

iii) Reduce the alkali-aggregate reaction.

iv) Improve resistance to attack by sulphonate soils and sea water.

v) Improve extensibility.

vi) Lower susceptibility to dissolution and leaching.


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vii) Improve workability.

viii) Lower costs.

In addition to these advantages, contrary to the general opinion, good pozzolans will not

unduly increase water requirement or drying shrinkage.

4.5Tests on Concrete Cubes:Testing of concrete is very essential to ensure that the desired properties of the concrete is

achieved after the concrete hardened. If we would not control at early stage, i.e. at the time of

fresh concrete, it will not be possible to achieve the same. Testing of fresh concrete as well as

hardened concrete is carried out to ensure proper quality control.

4.5.1 Testing of Fresh Concrete:

The concrete in fresh state is tested for workability. Workability Unfortunately, no test can

measure directly workability. However, workability itself could not be precisely defined as

has been mentioned in earlier sections. Numerous attempts have so far been made to quantify

this very important and vital property of fresh concrete. But none of these methods are

satisfactory for precisely measuring this property although some of them may provide useful

information within a range of variation in workability.

Following three methods incorporated in IS 1199 1959 are found to be useful to measure

workability of concrete at frequent intervals during progress of work in the field.

i) Core test

ii) Compacting factor test.

iii) Vee-Bee consistometer test.

While slump cone test is responsive to medium range of workability, compacting factor test

is more accurate and can be performed for a wide range of workability, i.e. for concrete

mixes of high to very low workabilities. The Vee-Bee test is better suited for low and very

low workabilities. However, slump cone test being simple and easy to perform is most


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widely used. It is needless to say that workability being single most important property of

fresh concrete, it is to be measured at regular interval when concreting is in progress at site

and if any deviation found in workability immediately corrective measure is to be taken in

mix proportion, aggregate grading, water cement ratio, quantity of admixtures added in each

batch and any other parameter which affects workability.

4.5.2 Testing of Hardened Concrete:

Testing of hardened concrete forms the last stage of quality control. One of the purpose of

the testing hardened concrete is to conform that the concrete made at site has acquired the

desired strength. Two types of testing is done on hardened concrete :

i) Destructive testing of hardened concrete, and

ii) Non-destructive testing of hardened concrete.

i) Destructive Testing of Hardened Concrete:

For destructive testing, a specimen is separately made of concrete which is being used in

actual structure and cured for specified period. The specimen is then tested for destruction

thus giving intrinsic strength of concrete at the time of testing which has also been used inactual structure.

Destructive testing may lead to determination of following strengths of concrete.

ii) Non-Destructive Testing of Hardened Concrete:

If the specimen tested is not taken to destruction, the testing method adopted is called non-

destructive testing method. As the specimen is not taken to destruction, this method can be

adopted on actual structure and hence no specimen like cubes, cylinders, beams etc. are to be

cast separately. This method of testing allows repeated testing of the same specimen and thus

make possible a study of the variation in proportion with time which is essential requirement

of quality control.


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Non-destructive testing method adopted not only for quality control and ensuring compliance

with specification but also can be made for specific purposes like determination of strength

of concrete at transfer of pre-stress or at the time of striking formwork.

Many attempts have been made to evolve and devise non-destructive testing methods but

only few of them proved to be successful and adopted in practice.

The following tests are carried out for non-destructive testing of concrete.

i) Rebound Hammer test

ii) Ultrasonic Pulse Velocity method

iii) Resonant Frequency method

4.6 Compressive strength:

i) Direct tensile strength

ii) Tensile strength in flexure.

However, the most common of all these tests on hardened concrete is the compressive

strength test. This is because, firstly, compressive strength test is easiest to perform,

secondly, though not all but almost all desirable characteristics of concrete, if not

quantitatively, but at least qualitatively can be related to the compressive strength due to the

intrinsic importance of compressive strength of concrete in construction. It should be

remembered that no tests are end to themselves. In fact they themselves seldom leads to a

complete conclusion, hence to have these results of any practical value, they should be

interpreted with background of right experience.


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COMPRESSION TEST ON THE CONCRETE CUBE:

Table 4.6 Compressive strength of cube

GRADE OF CONCRETE STRENGTH OF CONCRETE

ON 7TH

DAY in %

STRENGTH OF CONCRETE

ON 28TH

DAY in %

M20 70.5 109.4

M20 74.1 110.7

M25 73.0 108.4

M30 72.9 104.9

M35 75.3 111.5


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Chapter : 5 CONCLUSION

In this present study with the stipulated time and laboratory set up an afford has been taken to

enlighten the use of Ready Mix Concrete like in construction work in accordance to their

proficiency.

Based on the findings of this study, the following conclusions are made:

i) This study has shown that Quality control tests and evaluations are required during the

manufacturing process to produce predictable high quality concrete.

ii) Quality of concrete, however, depends not only on the quality of the ingredients from

which it is made but also on many more parameters, like batching, mixing, transportation,

placement, consolidation, curing, finishing and water cement ratio.

iii) The compressive strength of concrete increases with decrease in water cement ratio.

iv) The concrete remains in wet form by continuously adding water to the ready mix, but the

strength decreases by adding more water.

v) Specific Quality control tests and evaluations are required during the manufacturing

process to produce predictable high quality concrete.

vi) Speed of construction can be very fast in case RMC is used.

vii) Loss of workability occurs in ready mix concrete preparation. Addition of retarders may

delay the setting time substantially which may cause placement problems. In addition, it mayalso affect the strength of concrete. Therefore, it is necessary that the admixtures i.e.

plasticizers and super plasticizers/ retarders used in Ready Mixed Concrete are properly

tested for their suitability with the concrete.


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viii) The result shows that the concrete prepared at RMC plant has as much strength as the

concrete prepared at the site.

ix) The quality of concrete prepared at the RMC plant is controlled and maintained properly

as same as the concrete prepared at the site.

x) The test result shows that the concrete prepared at the RMC plant will have same strength

after the transportation at the site.


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Chapter : 6 REFERANCES

(i) M.S. SHETTY, Concrete Technology Theory and Practice, S. Chand Publication.

(ii) J.D. Dewar and R. Anderson, Manual of Ready Mix Concrete, Blakie Academic

Professional, an imprint of Chapmen and Hell, UK.

(iii) Bhanja, S. and Sengupta, B., Investigation on the compressive strength of silica

fume concrete using statical methods, Cement and Concrete Research-32, 2002.

(iv) IS: 10262-1982, Recommended Guidelines for Concrete Mix Design. IS: 383-1970

(Second Revision), Specifications for Coarse and Fine Aggregates from Natural Resources

for Concrete.

(v) Manual of Ready Mix Concrete published by Ready Mix Concrete manufacturers

Association (RMCMA), Mumbai.

(vi) IS 4926 : 2003, Ready Mix Concrete, Code of practice

(vii) IS 2383 : 1963 (Part1 to Part 8), Methods of Test for Aggregates for Concrete

(viii) IS 383 : 1970 Specification for Coarse and Fine Aggregate from Natural Sources for

Concrete

(vii) SP 23 : 1982, Hand Book on Concrete Mixes.

rmc report

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