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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.