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STUDY OF MATERIAL TESTING AND MIX DESIGN PROCEDURE OF READY MIX CONCRETE PROJECT REPORT
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ABSTRACT:
Ready-mix concrete (RMC) is a ready-to-use material, with predetermined mixture of Cement,
sand, aggregates and water. RMC is a type of concrete manufactured in a factory According
as per specifications of the customer, at a centrally located batching Plant. It is then send or
Delivered to a worksite, often in truck mixers capable of mixing the ingredients of the concrete
Concrete en route or just before delivery of the batch. This results in a precise mixture, allowing
Specialty concrete mixtures to be developed and implemented on construction sites. The second
Option available is to mix the concrete at the batching plant and deliver the mixed concrete
to the Site in an agitator tuck, which keeps the mixed concrete in correct form.
This project deals with the advantages, disadvantages and the quality control in the preparation
of the concrete, mix design of M20 and the preparation procedure followed at the ready mix plant.
INTRODUCTION:
Ready Mix Concrete (RMC) is a specialized material in which the cement
aggregates and other ingredients are weigh-batched at a plant in a central mixer or truck
mixer, before delivery to the construction site in a condition ready for placing by the
builder. Thus, `fresh' concrete is manufactured in a plant away from the construction site
and transported within the requisite journey time. The RMC supplier provides two
services, firstly one of processing the materials for making fresh concrete and secondly, of
transporting a product within a short time.
It is delivered to the worksite, often in transit mixers capable of mixing the
ingredients of the concrete just before the delivery of batch. This results in a precise
mixture, allowing specialty concrete mixtures to be developed and implemented on
construction sites. The second option available is to mix the concrete at the batching plant
and deliver the mixed concrete to the site in an agitator truck, which keeps the mixed
concrete in correct form.In the case of the centrally mixed type, the drum carrying the concrete
revolves slowly so as to prevent the mixed concrete from "segregation" and prevent its
stiffening due to initial set. However, in the case of the truck-mixed concrete, the batched
materials (sand, gravel and cement) are carried and water is added just at the time of
mixing. In this case the cement remains in contact with the wet or moist material and
this phase cannot exceed the permissible period, which is normally 90 minutes.
The use of the RMC is facilitated through a truck-mounted 'boom placer' that can
pump the product for ready use at multi-storied construction sites. A boom placer can pump
the concrete up 80 meters.
HISTORY:
The Idea of Ready Mix Concrete (RMC) was first introduced by Architect Jurgen
Heinrich Magens, he got his patent of RMC in Germany in 1903. In 1907, he discovered
that the available time for transportation could be prolonged not only by cooling fresh
concrete but also by vibrating it during transportation. So this gave rise to a concrete which
is made in the off site.
The first concrete mixed off site and delivered to a construction site was effectively
done in Baltimore, United States in 1913, just before the First World War. The increasing
availability of special transport vehicles, supplied by the new and fast growing automobile
industry, played a positive role in the development of RMC industry.
The first concept of transit mixer was also born in 1926 in the United States. In
1939, the first RMC plant was installed in United Kingdom and in 1933, first specifications
on RMC was published in United Kingdom.
Between the years 1950 and 1980 considerable growth of RMC took place in the
United States with the maximum supply of 31 million cubic meters in the year 1974.
However, on an average RMC supplies were 25 million cubic meters per year between
1974 to 1980.
RMC IN INDIA:
In India RMC was first initially was used in 1950 during the construction sites of
Dams like Bhakra Nangal, Koyna. At the construction the transportation of concrete is
done by either manually or mechanically using ropeways & buckets or conveyor systems.
RMC at Pune in the year 1991. However, due to various pit falls and problems this
plant did not survive for long and was closed. Within a couple of months in the year 1993,
two RMC plant were set up in Mumbai to commercially sell RMC to the projects where
they were installed. Unitech Construction set up one plant at Hiranandani Complex and
Associated Cement Companies set up another plant at Bharat Diamond Bourse
Commercial Complex. These plants were later allowed to sell RMC to other projects also.
Thus RMC was successfully established sometime after 1994 in India.
RMC producers from outside India soon became interested in the Indian market
and therefore two very well known producers set their foot on the Indian soil i.e. Fletcher
Challenge Ltd. From New Zealand and RMC Ready Mix of UK.
As per the available record up to 2003, there are around 76 RMC plant in 17 cities
with a total capacity of around 3875 CuM/hr, producing 3.8 million CuM of concrete per
year.
SCOPE OF RMC IN INDIA:
Though delayed, but not very much, there a ready mixed concrete industry is
developing and expanding at a fast pace in the country on a large scale. Over the period,
due impetus to this development has been provided by various front-line construction and
cement companies as well as technological bodies. The World Bank's “ India Cement
industry Restructuring Project" under which a technical study report on the development of
market for bulk cement in India was made in 1996, proved to be positive development
towards modernization of cement distribution system in India, including setting up Ready
mix concrete Plants.
The objective of this technical study was to formulate an action plan for the
development of market for bulk cement in large cement centres in India and for gradual
shift. From the traditional mode of transportation in bags to bulk transportation through
setting up of ready mixed concrete plants in different parts of the country. The
recommendation of the action plan provided a useful guidance towards expanding bulk
cement market thus paving a way for installation or ready mixed concrete plants in India.
According to Cement Manufacturers Association, RMC is being increasingly
recommended for all major public construction work such as highways, flyovers. In cities
like Bangalore and Chennai, even small house builders have started displaying a marked
preference for RMC instead of cement
MATERIALS REQUIRED FOR RMC
Aggregates are the important constituents in concrete. They give body to the
concrete, reduce shrinkage and effect economy. Earlier, aggregates were considered as
chemically inert materials but now it has been recognised that some of the aggregates are
chemically active and also that certain aggregates exhibit chemical bond at the interface of
aggregate and paste. The mere fact that the aggregates occupy 70-80 per cent of the
volume of concrete, their impact on various characteristics and properties of concrete is
undoubtedly considerable. To know more about the aggregates which constitute major
volume in concrete.
Aggregates are divided into two categories from the consideration of size
Coarse aggregate
Fine aggregate
The size of the aggregate bigger than 4.75 mm is considered as coarse aggregate and
aggregate whose size is 4.75 mm and less is considered as fine aggregate
CEMENT:
Cement is a binder material which sets and hardens independently, and can bind
other materials together. Cement is made up of four main compounds tricalcium silicate
(3CaO SiO2), dicalcium Silicate (2CaO SiO2), tricalcium acuminate (3CaO Al2O3), and
tetra-calcium aluminoferrite (4caco Al2O3 Fe2O3).tetra-calcium aluminoferrite (4CaO
Al2O3 Fe2O3). In an abbreviated notation differing from the normal atomic symbols,
these compounds are designated as C3S, C2S, C3A, and C4AF, where C stands for
calcium oxide (lime), S for silica and A for alumina, and F for iron oxide. Small amounts
of uncombined lime and magnesia also are present, along with alkalis and minor amounts
of other elements.
ADMIXTURE:
A substance added to the basic concrete mixture to alter one or more properties of the
concrete; i.e. fibrous materials for reinforcing, water repellent treatments, and colouring
compounds.Air-entraining admixtures (mainly used in concrete exposed to freezing and
thawing cycles)
Water-reducing admixtures, plasticizers (reduce the dosage of water while
maintaining the workability)
Retarding admixtures (mainly used in hot weather to retard the reaction of
hydration)
Accelerating admixtures (mainly used in cold weather to accelerate the reaction of
hydration)
Super plasticizer or high range water-reducer (significantly reduce the dosage of
water while maintaining the workability)
Miscellaneous admixtures such as corrosion inhibiting, shrinkage reducing,
colouring, pumping etc
Role of Admixture in Ready Mix Concrete:
The role of admixture is ready mixed of concrete is same as that in normal
concrete. However, admixture used in RMC is modified to meet the requirement of
pumpable concrete and other properties of concrete. The types of admixture used in RMC
are generally termed as Super plasticizers.
The history of admixture is as old as history of concrete. There are several types of
admixture available in market. But few admixtures namely Plasticizers and Super
plasticizers are of recent interest. These of admixture were initially developed in Japan and
German around 1970. IN India use of admixture was recognized after 1985.In 1990
admixture started to gain Importance after introducing Ready Mixed Concrete. The
importance of admixture was further recognized after revision on of IS: 456 - 1978. The
earlier versions of IS 456 have permitted to use w/c ratio as high as 0.65 in RCC works.
The Revised IS 456-2000 has Restricted the w/c ratio to 0.55 for mild exposure and
0.50 for moderate exposure ,0.45 for severe and very severe exposure and 0.40 for
extreme weathering conditions. The restriction on w/c ratio has made the use of
admixture all the more compulsory ingredient of concrete.
FLY ASH:
Fly ash is a by-product from coal-fired electricity generating power plants. The coal
used in these power plants is mainly composed of combustible elements such as carbon,
hydrogen and oxygen (nitrogen and sulphur being minor elements), and non combustible
impurities (10 to 40%) usually present in the form of clay, shale, quartz, feldspar and
limestone. As the coal travels through the high-temperature zone in the furnace, the
combustible elements of the coal are burnt off, whereas the mineral impurities of the coal
fuse and chemically recombine to produce various crystalline phases of the molten ash.
The molten ash is entrained in the flue gas and cools rapidly, when leaving the combustion
zone (e.g. from 1500°C to 200°C in few seconds), into spherical, glassy particles. Most of
these particles fly out with the flue gas stream and are therefore called fly ash. The fly ash
is then collected in electrostatic precipitators or bag houses and the fineness of the fly ash
can be controlled by how and where the particles are collected. Fly ash use improves
concrete performance, making it stronger, more durable, and more resistant to chemical
attack. Fly ash use also creates significant benefits for our environment
Effect of Mixing Sea Water in Concrete:
The sea Water generally contains salinity of about 3.5% in which about 80% is
sodium chloride. Many researchers have been conducted to study the corrosion problem of
steel Embedded in concrete where sea water is used as mixing water in concrete
nevertheless the Indian standard is adamant & do not permit using sea water for mixing or
curing in reinforced Concrete constructions, but allows for using of sea water only for PCC
work that too under unavoidable circumstances.
Quality of Water for Curing Concrete Members:
Generally the water that is fit for mixing of water in concrete is also fit for curing.
However where appearance is important, water containing impurities which cause stains
should not to be used. The most important elements that cause stains in the concrete are
iron, and organic matters. It is also found that even sea water also causes stains in concrete. Hence water containing iron, organic matters and also sea water should not be used for
curing of concrete when appearance is also set as criteria for the acceptance of concrete.
MIXING ARRANGEMENTS
There are various types of concrete mixers used on the concrete production plant. The two
basic types are free fall mixers and power mixers. Most of our indigenously manufactured
plants have free fall mixer. Free fall mixer consists of a rotating drum with blade fixed on
the drum's interior. As the drum rotates, the material inside is lifted and dropped. The drum
is loaded and emptied by changing the direction of rotation, dropping a flap or tipping it.
Most of the imported plants have power mixer. The power mixer sets in motion the
materials positively. The materials get thoroughly mixed by rotating arms. These mixers
have shorter mixing time; give better homogeneity, consistency and strength to the
concrete. Besides, they have better facility for inspection. The following are the most
common designs.
CONTROL SYSTEMS
Almost all imported production plants offer automatic systems for control
functions. These are required for better quality control, higher economy and superior
working conditions. Fully automatic plant control systems with multiple inputs for up to
120 mixes or template control system are usually housed in a container or control room of
the plant. Micro processor controlled production plants represent the state of the art in the
developed countries.
These controls are operated from main desk. It also has material availability
monitor and printer plus an additional batching monitor. The entire plant can be operated
by just one person. Microprocessor control besides having fully automatic running facility
offers number of additional features like statistical data recording and processing, a printer
unit, moisture adjustment arrangement, customer address, memory etc.
All you need to do is push the required mix template into the slot and press the
"start" button and the control system does the rest. Aggregate and cement weighment,
moisture correction, overrun correction and additive weighment are done accurately to give
the concrete mix of desired strength and workability
4.2SHRINK MIXED CONCRETE
Concrete that is partially mixed in a plant mixer and then discharged into the drum
of the truck mixer for completion of the mixing is called shrink mixed concrete. Central
mixing plants that include a stationary, plant-mounted mixer are often actually used to
shrink mix, or partially mix the concrete. The amount of mixing that is needed in the truck
mixer varies in these applications and should be determined via mixer uniformity tests.
Generally, about thirty turns in the truck drum, or about two minutes at mixing speed, is
sufficient to completely mix shrink-mixed concrete.
CENTRAL MIXED CONCRETE
Central-mixing concrete batch plants include a stationary, plant-mounted mixer that
mixes the concrete before it is discharged into a truck mixer. Central-mix plants are
sometimes referred to as wet batch or pre-mix plants. The truck mixer is used primarily as
an agitating haul unit at a central mix operation. Dump trucks or other non-agitating units
are sometimes be used for low slump and mass concrete pours supplied by central mix
plants. About 20% of the concrete plants in the US use a central mixer. Principal
advantages include:
Faster production capability than a transit-mix plant
Improved concrete quality control and consistency and
Reduced wear on the truck mixer drums.
TESTS ON MATERIALS:
All the ingredients used for preparation of the concrete, are thoroughly tested for
their quality and physical properties in a well equipped laboratory attached to the plant for
conformity to relevant Indian Standard Codes. The moisture probe determines the water
content in the sand and aggregates. This accordingly helps in fixing the proportion of water
to be added for the preparation of the mix. The sand being used is passed through the
mechanized sieving system, before feeding for mixing.
Trial mixes are carried out and tested to ensure that each and every batch of
concrete coming out of the plant meets the parameters of client’s requirements. The sand
being used is passed through the mechanized sieving system, before feeding for mixing.
AGGREGATE IMPACT VALUE TEST:
This test is done to determine the aggregate impact value of coarse aggregates as
per IS: 2386 (Part IV) – 1963. The apparatus used for determining aggregate impact value
of coarse aggregates is Impact testing machine conforming to IS: 2386 (Part IV)- 1963,IS
Sieves of sizes – 12.5mm, 10mm and 2.36mm, A cylindrical metal measure of 75mm dia.
and 50mm depth, A tamping rod of 10mm circular cross section and 230mm length,
rounded at one end and Oven
WATER ABSORPTION TEST:
This test helps to determine the water absorption of coarse aggregates as per IS: 2386
(Part III) – 1963. For this test a sample not less than 2000g should be used. The apparatus
used for this test are:
Wire basket, perforated, electroplated or plastic coated with wire hangers for
suspending it from the balance
Water-tight container for suspending the basket
Dry soft absorbent cloth – 75cm x 45cm (2 nos.)
Shallow tray of minimum 650 sq.cm area
Air-tight container of a capacity similar to the basket and Oven.
ELONGATION INDEX TEST:
The elongation index on an aggregate is the percentage by weight of
particles whose greatest dimension (length) is greater than 1.8 times their mean dimension.
The elongation index is not applicable to sizes smaller than 6.3 mm.
The test is conducted by using metal length guage of the description. A sufficient
quantity of aggregate is taken to provide a minimum number of 200 pieces of any fraction
to be tested. Each fraction shall be guaged individually of length ion the metal gauge. The
total amount retained by the gauge length shall be weighed to an accuracy of at least 0.1
per cent of weight of the test sample taken. The elongation index is the total weight of the
material retained on the various length gauges expressed as a percentage of the total weight
of the sample gauged. The presence of elongated particles in excess of 10 – 15 per cent is
generally considered undesirable, but no recognized limits are laid down.
Indian standard explain only the method of calculating both flakiness index and elongation
index. But the specification does not specify the limits. British standards BS 882 of 1992
limits the flakiness index of the coarse aggregate to 50 for natural gravel and to 40 for
crushed coarse aggregate. However, for wearing surfaces a lower value of flakiness index
are required
CONCLUSION:
The concrete quality produced in RMC plant is highly consistent with low
deviation order. It provides a high degree of overall strength of hardened concrete and the
performance of the structure at a later date. RMC operations are highly mechanized and
fully controlled through electronic controls and hence reduce the probability of errors in
various operations. It is also environment friendly and brings down pollution due to dust at
construction can also be accelerate with the use of RMC. The use RMC in civil
construction is widely adopted throughout the world. The beginning made in India is in
tune with the developments outside and RMC uses provide numerous benefits to the
consumers.
Conventional approach to durable concrete structures, namely specifying maximum
water cement ratio, minimum cement content and cement type, is now always satisfactory,
especially under aggressive environmental condition. Site manufactured concrete cannot
assure the same quality of concrete and that from controlled ready mix batching plant
backed by advanced technology and project management. The advantages of RMC are
particularly evident in construction projects with aggressive exposure conditions.Ready mix concrete has gained acceptance in Indian industry due to several
advantages including quality control and overall economy. RMC plants are proliferating,
especially in urban regions, not only because of the space restrictions around construction
site but also due to the realisation of the advantages by engineers and construction
industry