CONCRETE TECHNOLOGY

The main difference between load bearing structure and framed structure
is their members who are responsible for bearing and transferring the load
to the subsoil
Load bearing structure
• the oldest and commonest type of structure, and the structure
in which the loads of the roofs as well as lateral loads such
as earthquake, wind etc. are borne by walls. It is also known as
wall bearing structure.
•load-bearing members are beams and columns.
•vertical load transfer path is from slab/floor to walls and walls
to load bearing footing i.e. soil.
•Limited storey buildings can only be constructed. So far
buildings up to 6 storeys have gone up. In many countries, even
14 storeys have been built only with masonry.
•poor resistant to earth quake, as they are constructed with
masonry units like stone, brick bonded together.
Framed structure
• structure having the combination
of structural components i.e. beam, column and slab
connected to resist the gravity and different
lateral loads. It is also known as beam column
structure.
• load-bearing members are beams and column.
• vertical load transfer path is from slab/floor
to beams, beams to columns and columns
to load bearing footings and then to soil.
• Multi storey buildings of any heights can
be constructed. Buildings are usually designed for
office, hotel, residential apartment and contain the
means of vertical circulation in the form of stairs and
lifts occupying up to 20% of the floor area.
• more rigid and more resistant to Earthquake as
entire frame made of column, beam and slabs act as
one unit.

• walls are thicker.
• beams and columns are not there. Hence walls
must be built first.
• less carpet area is available, as walls are thicker
and hence carpet area efficiency of planning is less.
• Rarely used form of construction at present.
• Excavation for this type of construction is more.
• more labor intensive.
• Speed of construction is less.
• more material intensive. Hence dead load is
also more. It consumes less cement and steel.
• Cost of repair of load bearing structure is less.
• Skilled as well as non-skilled worker can construct.
• Thickness of wall increases with increase in
height. Hence plan dimension changes on all floor.
• Room dimensions cannot be changed as walls have
to be above walls only.
• large span areas are not possible. Limitation of
span i.e. room sizes.
• Load bearing walls can be from Brick, Stone,
concrete block, etc.
Framed structure
• walls are thinner.
• walls are constructed after the frame is ready.
• more carpet area is available, as walls are thinner.
• Most used form of construction.
• Excavation for this type of construction is less for
a similar building.
• less labor intensive, but it needs different skills.
• Speed of construction is more.
• less material intensive. It
consumes more cement and steel.
• Cost of repair of framed structure is more.
• Only skilled workers are needed for its
construction.
• Thickness of wall remains same with increase
in height. Hence plan dimension does not change
on different floor.
• Room dimension can be altered.
• large span areas are possible. No Limitation of
span i.e. room sizes.
• Frame can be of RCC frame, Steel, Wooden, etc.

Framed structure
• Large openings in walls are possible.
• Design is not simple you need design skills and
software tools.
• used for High rise buildings and for Low rise buildings
where good soil for resting load bearing foundation is
not available, say up to 1.5 to 2.00 mt and
simultaneously cost of bricks is also more.
• Generally, RCC framed structure is constructed first
and the external as well as partition walls are
constructed later, hence speed is more.
• Minimum acceptable compressive strength of
bricks can be used for infill walls as its importance
structurally is not critical.
• The frame is an active structural element and all
components are important hence if any change in the
structural element is done it may endanger the safety
of the entire building. However, walls can be altered.
• Limitations for providing openings in walls, which
will affect the light and ventilation in room.
• Design is simple.
• used in low rise buildings where good soil for
foundation is available at 1.2 to 1.5 mt, such
construction is often limited to relatively low
structures, because load-bearing walls become
massive in tall structures.
• Walls have to be built first as they support the slab
/ roof and hence all walls have to be built
simultaneously which is time consuming.
• Bricks having good compressive strength, as
defined by local codes, mostly 75 kg per cm2 are
needed as these are the elements which ultimately
take the load.
• Walls are the active structural elements and thus
no change in it can be done at any time. Walls
cannot be altered.

EXAMPLES
•Load bearing structure
IIM Ahmedabad

• Framed structure
Burj Al Arab

RCC AND PCC
RCC
It refers to reinforcement cement concrete.
composite material made from concrete
and steel reinforcement.
we knew that concrete is weak in
tension and strong in compression, hence
Steel reinforcement is added to
improve tensile resistance.
PCC
It refers to plain cement concrete.
mixture of cement, fine aggregate(sand), and
coarse aggregate without reinforcement
spread on the soil surface before concreting
main structure to avoid direct contact of
reinforcement of concrete with soil and water.
Before starting any RCC masonry work directly on the excavated soil, the PCC concrete is
made to form a flat surface and it is avoided to keep the concrete perpendicular to the soil
so that the mixture is mixed with the soil and the water removed by the PCC It can also be
weakened to prevent soil.

What is the role of REINFORCEMENT in
RCC?
Reinforced concrete is designed for 3 types for stresses: tensile, compressive, and shear &
torsion.
Since steel has high compressive strength hence compressive forces occurring within a structure
is shared by concrete and steel reinforcements.
When it comes to shear and torsional forces, transverse reinforcements (e.g. stirrups, ties,
spirals) are provided and supplement the shear and torsional capacity of a structure.
To summarize, reinforcements in RCC compliments the tensile/flexural capacity and
supplements the compressive, shear and torsional capacity of a structure.

Concrete mix
It's important to use the correct concrete mixing ratios to produce a strong, durable concrete
mix.
Some basic mixing ratios for concrete are 1:2:3, 1:3:3, 1:2:4. These mixing ratios are based on
the proportions of cement : sand : stone in that order. The ratio to be used will depend on what
psi strength we need.
To make concrete there are four basic materials you need:
Portland cement - We can buy this in a 50kg bag
Sand - Coarse or Fine will work (coarse sand will give stronger mix)
Aggregate (stone) - We can use 25mm,19mm,32mm stone for aggregate
Water - Clean cool water is best.

Ingredients in concrete mixture
•Cement
Cement makes up the smallest percentage of the mixture but it’s an essential ingredient in concrete. Cement
serves as the glue that keeps everything else together. It allows the ready mix to harden once it’s placed. There
are five different types of cement depending on what kind of concrete you’re looking to make:
Type I is used for most residential work
Type II is used in moderate sulfate conditions
Type III is used in climates where freezing is a risk
Type IV is used for special orders like industrial placements
Type V is used in extreme sulfate conditions
Types I and II are the most widely used residentially in the United States due to the relatively moderate climates
we experience here.

•Gravel and Sand
Gravel and sand aggregates make up about 70% of the mixture. This high percentage makes the
mixture more economical–as gravel and sand are both stronger and more cost-effective than the
cement. A good ready mix will include proportionate amounts of both large (gravel) and small
(sand).
The reason for this is that the gravel makes up the majority of the ready-mix and the smaller
sand particles do a good job of filling in any extra spots that could otherwise be filled by
unwanted air pockets.
Well, the ingredients that combine to create the most widely used building material in the
world–concrete. Each ingredient and its ratio impacts the final ready mix’s quality and type. It’s
important to get the best ready mix for our specific job.

•Air and Water
For a mixture to be effective, some amount of air entrainment (tiny air bubbles) is needed in the
concrete. Air-entrained cement ensures that excess water has a chance to expand when it
moves through the freeze-thaw cycle. These air bubbles, however, must be microscopically small
or else the ‘entrained’ air will turn into ‘entrapped’ air which leads to shrinkage and cracking.
Amongst all the other essential ingredients involved in creating a mixture, water tends to have
the largest impact. As a rule of thumb, the more water that you put into the mixture, the less
strength the hardened mixture will have. Shrinkage and cracking are also probable when too
much water is involved. Excess water will eventually evaporate out of the hardened concrete,
causing the concrete to shrink and eventually crack.
An ideal amount of water can be measured by water to cement ratio, which should vary
between 0.5 and 0.84. The higher the ratio, the weaker the concrete.

•Admixtures
One of the most important ingredients in high performance, long-lasting, durable and beautiful
concrete produced today are concrete admixtures. These are natural or manufactured chemicals
or additives added during concrete mixing to enhance specific properties of the fresh or
hardened concrete, such as workability, durability, or early and final strength.
To improve the properties of the concrete required. It can be divided in 2 groups that is:
Chemical
Mineral

Properties of ingredients
Ingredient Percentage in cement
Lime 60-65
Silica 17-25
Alumina 3-8
Magnesia 1-3
Iron oxide 0.5-6
Calcium Sulfate 0.1-0.5
Sulfur Trioxide 1-3
Alkaline 0-1
Cement is the binding material used in
construction works. Cement is the composition
of
• Cement

the best cement must be used for construction. Therefore, the properties of a cement must be investigated.
Although desirable cement properties may vary depending on the type of construction, generally a good cement
possesses following properties (which depend upon its composition, thoroughness of burning and fineness of
grinding).
Provides strength to masonry.
Stiffens or hardens early.
Possesses good plasticity.
An excellent building material.
Easily workable.
Good moisture-resistant.
Proper field tests and laboratory tests should be done to ensure the qualities of the cement.

• chemically inert. It should not react with the cement or admixture and form an undesirable
compound.
• free from organic or vegetable matter. The organic matter may decompose later and leave the
voids in concrete thus reducing the strength of the concrete.
• free from salt. The salts produce patches on the concrete surface and adversely affects the
durability of the concrete.
• contain sharp, angular and coarse grains. Round and smooth particles result in lesser strength
as they don’t interlock among selves.
• well graded. Well-graded sand fills more voids as compared to the poorly-graded or uniform
sand.
• hard. The sand particles should not crush under the load.
• Sand

Physical
It plays a very important role. Now the different
physical properties of aggregates include:
Shape and surface texture.
Size.
Gradation / Size distribution.
Fineness modulus.
Bulk density.
Density and specific gravity.
Water absorption and moisture content.
Chemical
There are three important chemical properties of
aggregates:
Soundness.
Permeability and porosity.
Alkali-aggregate reaction.
• Aggregate

• Water
•Water for construction is same as drinking water. It should be free from such impurities as:
 suspended solids
 organic matter
 dissolved salts
• which may adversely affect the properties of the concrete, especially the setting,
hardening, strength, durability, pit value, etc.
•It should be clean and not contain sugar, molasses or Gur or their derivatives, or sewage, oils, organic
substances.
• The water shall be tested in an approved Laboratory for its use in preparing concrete / mortar.

Concrete grades
Grade of concrete is defined as the
minimum strength the concrete must
possess after 28 days of construction
with proper quality control. Grade of
concrete is denoted by prefixing M to
the desired strength in MPa.
Concrete Grade Mix Ratio
Compressive Strength
MPa (N/mm2
) psi
Normal Grade of Concrete
M5 1 : 5 : 10 5 MPa 725 psi
M7.5 1 : 4 : 8 7.5 MPa 1087 psi
M10 1 : 3 : 6 10 MPa 1450 psi
M15 1 : 2 : 4 15 MPa 2175 psi
M20 1 : 1.5 : 3 20 MPa 2900 psi
Standard Grade of Concrete
M25 1 : 1 : 2 25 MPa 3625 psi
M30 Design Mix 30 MPa 4350 psi
High Strength Concrete Grades

Role of water as mixing agent
It's purpose as mixing agent is broken down into two main things:
Bonding: water as an ingredient in the concrete that mixes with cement to form paste is called a
binder. It establishes/increases the bond between the cement, the aggregate and the admixture. It is
also responsible for the process of hydration that leads to the hardening of concrete to form different
structures.
Workability: this is the ease of ferrying and mixing concrete. It can also be regarded as the fluidity of
the concrete. Thanks to Water, concrete can be easily mixed to form the desired mixture. The role of
water is to reduce external friction between the concrete and whichever equipment being used to
mix it. It will also reduce internal friction between the aggregate and the cement. It is because of the
workability facilitated by water that concrete can be moulded into different shapes before it can
harden.
It is virtually and practically impossible to implement any type of construction without water in the
concrete mix. It is also important to note that excessive water in concrete might lead to better
workability but it will in the long run compromise the strength of the concrete.

Concrete test for workability
Workability of concrete is defined as the ease and homogeneity with which a freshly mixed concrete
or mortar can be mixed, placed, compacted and finished. Strictly, it is the amount of useful internal
work necessary to produce 100% compaction. To assure that we perform:
SLUMP TEST
It is the most common method for measuring the workability of freshly mixed concrete.
This test in normally measured by filling an ABRAMS CONE with a sample from fresh batch of
concrete.
A cone is placed with the wide side down on level (non-absorptive level)
Then filled in 3 layers of equal volume with each layer being tamped with a steel rod to consolidate
the layer.
Then cone is lifted off after 2 min, the enclosed material slumps a certain amount owing to gravity.
This Photo by Unknown author is licensed under CC BY.

Container Top diameter (mm) Bottom diameter (mm) Height (mm)
Upper hopper 254 127 279
Lower hopper 229 127 229
Cylinder 152 152 305
Distance between bottom of upper hopper and top of lower hopper = 203 mm
Distance between bottom of lower hopper and top of cylinder = 203 mm

Concrete test for strength
Compressive strength of concrete depends on many factors such as water-cement ratio, cement
strength, quality of concrete material, quality control during the production of concrete, etc. To
assure its strength we perform:
CUBE TEST
Cubical molds of size 15cm x 15cm x 15cm are commonly used. Concrete is poured in the 10
molds and appropriately tempered so as not to have any voids.
These specimens are tested by compression testing machine after-
Time period No. of molds tested
Day 1 1st 2 cubes
Day 3 Next 2 cubes
Day 7 Next 2 cubes
Day 14 Next 2 cubes
Day 28 Next 2 cubes
Load should be applied gradually at the rate of 140 kg/cm2 per minute till the Specimens fails.

Age Strength percent
1 day 16%
3 days 40%
7 days 65%
14 days 90%
28 days 99%
Grade of Concrete
Minimum
compressive
strength
N/mm2 at 7 days
Specified
characteristic
compressive
strength (N/mm2)
at 28 days
M15 10 15
M20 13.5 20
M25 17 25
M30 20 30
M35 23.5 35
M40 27 40
M45 30 45

Curing of concrete
Curing is the process in which the concrete kept moist to protect it from loss of moisture due to
atmospheric temperature and hydration reaction.
Or we can say that
Curing is the process of controlling the rate and extent of moisture loss from concrete during
cement hydration.
Purpose
The reaction between cement and water is called hydration. It is an exothermic reaction
(the reaction which releases heat).
After adding water to the concrete mix, hydration starts, which makes the concrete to dry
out quickly due to an exothermic reaction which releases heat. To complete the hydration
process, concrete is kept moist to attain the maximum strength of concrete as soon as possible.

Curing of concrete
Procedure
Draining water on the concrete surface cures the concrete. Water cooler than 50C is not suitable
for curing concrete. As the hydration reaction in concrete expels heat and keep concrete warm,
Using cold water less than 50C on concrete may lead to cracking and failing. Alternate drying and
wetting on the concrete surface causes volumetric changes in concrete and ultimately leads to
cracking.
Time period
The minimum period for curing concrete to attain maximum strength is 28 Days. The early
strength of concrete is most important, and it is responsible for the ultimate strength of
concrete.

Curing of concrete
From the graph, it is clear that concrete attained 50% of its
design strength when it cured for 3-7 Days. 75% of
Compressive strength achieved in 14 days. 90% of Concrete
design strength achieved in 28 days. So it is clear as time
increases on the concrete strength increased.
Adding admixtures, the time period of 28 days is reduced to 15 days.

Formwork
Formwork is the mold used during the building to give the desired structural form by
pressing concrete into the mold. Formwork is often used in various shapes and sizes depending
on our design materials in the form of PCC, RCC operates in Building, Road, Corridor Lining,
Hydroelectric power Dam, Agriculture Headwork, Sewage Pipeline, Works, etc.
Types of Formwork:
Timber Formwork
It should comply with the following
requirements:
• It ought to be well seasoned
• It ought to be light in weight
• Timber must be easy to work with nails
without splitting.
• It’s supposed to free from loose loops.
Engineered formwork
are built out of prefabricated structures of steel, aluminum,
timber, plywood and plastics. The two major advantages of
formwork systems compared to traditional formwork are-:
• speed of construction
• lower life cycle costs

Scaffolding
It is a temporary structure used to support a work crew and materials to aid in the
construction, maintenance and repair of buildings, bridges and all other man-made structures.
Scaffold must fulfil a diverse set of requirements:
- creation of safe and productive working areas
- providing access to working areas at higher levels
- carrying area and/or point loads

Concrete companies
• RDC Concrete (India) Pvt Ltd http://www.rdcconcrete.com/
• UltraTech RMC (Aditya Birla
Group) http://www.adityabirla.com/about/Ready-mix-concrete
• Concrete India http://www.ciconcreteindia.com/about-us.php
• ACC Limited http://www.acclimited.com/products/ready-mixed-concrete#
• Unicon ReadyMixhttp://uniconreadymix.com
• Prism RMC www.rmcindia.com
• Alcon Cement Company http://www.alcongoa.com/details.php?id=3
• Apollo Inffratech Private
Limited http://www.alcongoa.com/details.php?id=3
• Niraj Cement Structurals Ltd http://www.niraj.co.in/index.html
• India Cements Ltd http://www.indiacements.co.in/
• SKYWAY RMC PLANTS PVT. LTD. http://www.skywaygroup.co.in/
•Bharat Cement Products http://www.godrejconstruction.com
•Godrej & Boyce Mfg Co Ltd
•IJM Concrete Products Pvt Ltd http://www.ijmconcrete.com
•JK Lakshmi Cement Ltd http://www.jklakshmi.com/
•Nuvoco Vstas Corp. Ltdhttp://www.nuvoco.in/
•Madras Cements Ltd http://www.ramcocements.in
•RMC Readymix (India) (A Division of Prism
Cement Limited)http://www.rmcindia.com
•S V Concrete Products Pvt Ltd http://www.svconcrete.co.in
•Sarvani RMC Industry http://sarvaniconcrete.com/
•Trishul Concrete Products
Limited http://www.indiacements.co.in/ready-mix-concrete.html
•Vishwas Group Of Companieshttp://www.vishwasgroup.org/

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