Concrete: For Civil and Architecture students. Content does not belong to me

1. CONCRETE

2. CONCRETE INGREDIENTS:
Concrete is made up of three basic components: water, aggregate (rock, sand, or gravel) and
Portland cement. Cement, usually in powder form, acts as a binding agent when mixed
with water and aggregates.
Why Concrete?
• Ingredients of concrete are easily available in most of the places.
• Unlike natural stones, Concrete is free from defects and flaws.
• Concrete can be manufactured to desired strength with an economy.
• The durability of concrete is very high.
• It can be cast to any desired shape.
• The casting of concrete can be done in the working site which makes it economical.
• Maintenance cost of concrete is almost negligible.
• The deterioration of concrete is not appreciable with age.
• Concrete makes a building fire-safe due to its noncombustible nature.
• Concrete can withstand high temperatures.
• Concrete is resistant to wind and water. Therefore, it is a very useful in storm shelters.
• As a sound proofing material cinder concrete could be used.

3. GRADES OF CONCRETE
Sr. No. GRADE PROPORTION SIZE OF AGGREGATES USE
1 M5 1:5:10 40MM AND DOWNSIZE For lean concrete
bases and ordinary
masonry wall
foundation.
2 M7.5 1:4:8 40MM AND DOWNSIZE
3 M10 1:3:6 20MM AND DOWNSIZE
4 M15 1:2:4 20MM AND DOWNSIZE For structural
purposes with
reinforcement in
slabs, beams and
columns.
5 M20 1:5.5 20MM AND DOWNSIZE
6 M25 1:1:2 20MM AND DOWNSIZE

4. PROPERTIES OF CONCRETE
Following are the properties of fresh concrete:
1. Setting: The transition process of changing of concrete from plastic state to hardened state. Setting of
concrete is based or related to the setting of cement paste. Thus cement properties greatly affect the
setting time.
2. Workability: Workability is often referred to as the ease with which a concrete can be transported, placed
and consolidated without excessive bleeding or segregation.
3. Bleeding: Bleeding in concrete is sometimes referred as water gain. It is a particular form of segregation, in
which some of the water from the concrete comes out to the surface of the concrete, being of the lowest
specific gravity among all the ingredients of concrete.
4. Segregation: There are considerable differences in the sizes and specific gravities of the constituent
ingredients of concrete. Therefore, the materials show a tendency to fall apart.

5. PROPERTIES OF CONCRETE
5. Hydration: Concrete derives its strength by the hydration of cement particles. Of course, the rate of
hydration is fast to start with, but continues over a very long time at a decreasing rate
6. Air Entrainment: Air entrainment reduces the density of concrete and consequently reduces the strength.
Many times it is intentionally done. A concrete maker does so by introducing air bubbles by adding to the mix
an air entraining agent.
7. Fluidity or consistency: It is the capability of being handled and of flowing into formwork and around any
reinforcement, with assistance of compacting equipment
8. Compaction: Air entrapped during mixing and handling should be easily removed by compaction
equipment, such as poker vibrators
9. Stability or cohesiveness: fresh concrete should remain homogenous and uniform. No segregation of
cement paste from aggregates (especially coarse ones.

6. Following are the properties of set concrete:
1. Strength of concrete: The strength of concrete is basically referred to compressive strength of the concrete.
2. Concrete Creep: Deformation of structure under sustained load. Basically, long term pressure or stress on
concrete can make it change shape. This deformation usually occurs in the direction the force is being applied.
Like a concrete column getting more compressed, or a beam bending.
3. Shrinkage: Concrete is subjected to change in its volume due to the moisture content being evaporated as it
gets set. Volume change is one of the most detrimental properties of concrete, which affects the long-term
strength and durability.
4. Modulus Of Elasticity: Young's modulus ( E ) describes tensile elasticity, or the tendency of an object to
deform along an axis when opposing forces are applied along that axis; it is defined as the ratio of tensile
stress to tensile strain. It is often referred to simply as the elastic modulus.
5. Water tightness (impermeability): Water tightness is the ability of concrete to keep water out or
in. Watertight is a versatile range of specialized ready mix concretes designed to protect a structure from
water ingress or to retain water within a structure.
PROPERTIES OF CONCRETE

7. 6. Expansion:
Concrete may expand on hardening due to the following two reasons:
Thermal Expansion: In massive concrete works, when the upper layers are laid before the lower layers
have completely set, there can arise a phenomenon of thermal expansion in the lower layers. This is
because the heat of hydration gets accumulated in those layers and may attain magnitudes beyond
acceptable limits.
Chemical Reactions: Alkali-aggregate reactions are known to cause definite expansion in the concrete. The
reaction between amorphous silica of aggregates and oxides of potassium and sodium – from the cement
used in aggregate yield crystalline structures of bigger volumes. This change becomes harmful because
these gel-structures are not as stable and strong as those formed by reaction between calcium oxide and
silica. They become the cause of cracking and quicker deterioration of hardened concrete.
PROPERTIES OF CONCRETE

8. PRODUCTION OF CONCRETE Various stages of production of concrete are as follows:
1. Batching
2. Mixing
3. Transporting
4. Placing
5. Compacting
6. Curing
7. Finishing

9. BATCHING:
Batching is the process of measuring concrete mix ingredients by either
mass or volume and introducing them into the mixer . To produce
concrete of uniform quality, the ingredients must be measured accurately
for each batch.
It can be done in two ways:
• VOLUME BATCHING: This method is generally adopted for small jobs .
Gauge boxes are used for measuring the fine and coarse aggregate. The
volume of gauge box is equal to the volume of one bag of cement. Gauge
bow are also called as farmas. They can be made of timbers or steel. They
are made generally deep and narrow. Bottomless gauge boxes are generally
avoided. While filling the gauge boxes the material should be filled loosely,
no compaction is allowed.

10. WEIGHT BATCHING : Batching by weight is more preferable to volume batching ,as it is more accurate
and leads to more uniform proportioning. It does not have uncertainties associated with bulking. It’s
equipment falls into 3 general categories :
Semi automatic Fully automatic

11. MIXING
The mixing should ensure that the
mass becomes homogeneous,
uniform in colour and consistency.
Methods of Mixing :
1. Hand- mixing: Mixing ingredients
of concrete by hands using ordinary
tools like, hand shovels etc. This
type of mixing is done for Less
output of concrete.
Pictures
showing
Hand- mixing
of concrete

12. 2. Stationary Mixers:
Concrete is sometime mixed at jobsite in a stationary mixer having a size of 9 cubic meter.
Tilting typeNon-Tilting type

13. 3. Ready mix concrete: Ready mixed concrete is proportioned and mixed off at
the project site and is delivered to the construction area in a freshly mixed and
unhardened state. It can be manufactured by any of the following methods:
Central-mixed concrete: Mixed completely in a stationary mixer and delivered
in agiating and no agiating trucks
Agiating truck Agiating truck Non-Agiating truck
Central-mixed concrete

14. TRANSPORTING AND PLACING OF CONCRETE
• Mixing, transporting, and handling of concrete should be carefully coordinated with
placing and finishing operations.
• Concrete should not be deposited more rapidly than it can be spread, struck off,
consolidated, and bull floated and deposited continuously as near as possible to its
final position.
• In slab construction, placing should be started along the perimeter at one end of the
work with each batch placed against previously dispatched concrete.
• Do not dump the concrete in separate piles and then level and work them together.
• It should not be deposited in large piles and moved horizontally into final position.

15. Bucket & Ropeway Truck mixer
Mortar PanWheel barrow
MEANS OF TRANSPORTING CONCRETE

16. CRANE &
BUCKETBELT CONVEYOR
SKIP AND
HOIST:

17. COMPACTION
• Compaction of concrete is process adopted for
expelling the entrapped air from the concrete
• In the process of mixing , transporting and placing of
concrete, air is likely to get entrapped in the
concrete.
• It has been found from the experimental studies that
1% air in the concrete approximately reduces the
strength by 6%.
• If we don’t expel this air, it will result into
honeycombing and reduced strength.
Different methods of compaction are:
1. Hand Compaction
1. Rodding
2. Ramming
3. Tamping
2. Compaction by Vibration
1. Internal vibrator
2. Formwork Vibrator
3. Table Vibrator
4. Platform vibrator
5. Surface vibrator
Hand compaction is used for
ordinary and unimportant
structures. Workability should
be decided in such a way that
the chances of honeycombing
should be minimum. The
various methods of hand
compaction are as given
below:
a. Using a rod
b. Tamping
c. RammingUsing a rod
TampingRamming

18. COMPACTION BY VIBRATION
Vibration is imparted to the
concrete by mechanical means. It
causes temporary liquefaction so
that air bubbles come on to the
top and expelled ultimately.
Mechanical vibration is done
using vibrators of multiple types .
For Example: Internal vibrators,
External vibrators, Table or
platform Vibrators, Surface
vibrators etc. Internal vibrator
External vibrator
Platform vibrator Table vibratorSurface/Screed Board vibrator

19. Use of Internal vibrator Use of External vibrator
Use of External vibratorUse of Surface vibrator

20. CURING OF CONCRETE
Curing of concrete is defined as the process of maintaining the
moisture and temperature conditions of concrete for hydration
reaction to normally so that concrete develops hardened
properties over time. The main components which needs to be
taken care are moisture, heat and time during curing process.
Methods of Curing
a. Water curing: This is done by covering the concrete with
gunny bags and sprinkling water over them
b. Steam curing: This is done by artificial heat while the concrete
is maintained in moist condition.
c. Curing by Infra-red radiations: It is suitable for hollow
concrete products where the heater could be placed in the
voids.
d. Electrical curing: This is done by passing alternating current of
low voltage through electrodes in the form plates covering the
entire area of two opposite faces of concrete
e. Chemical curing: Done by spreading chemical membrane on
to the concrete. Liquid membrane forming curing compounds
such as sodium silicate (water glass) to prevent or retard
evaporation of moisture of concrete.

21. DURATION FOR CURING
• No. of days for curing is relative to the strength the concrete gains on time.
• Approximately 14 litres of water is required to hydrate each bag of cement .
• Soon after the concrete is placed .The increase in strength is very rapid (upto 3 to 7 days) and
continues but slowly thereafter for an indefinite period.
• Accordingly the gain is:
1. 40% strength in 3 days
2. 65% strength in 7 days
3. 90% strength in 14 days
4. 99% strength in 28 days.

22. CONCRETING UNDERWATER:
Concrete could be placed underwater by means of:
1. Bottom duck buckets which are water tight buckets being
carried through water and made to open upon reacing the
place of deposition.
2. By filling cement bags with dry or semi-dry mix of cement
and aggregate sand lowering them to the place of deposition
3. By using tremie pipe. The concrete is poured through funnel
into the pipe whose bottom end is closed using the polythene
membrane. Once the concrete is completely filling the pipe is
being removed.
Using Tremie pipe

23. FINISHING:
The finish of the ultimate product is not that pleasant in concrete. In past couple of decades efforts
have been made to develop surface finishes to give better appearances to concrete structures and
are as follows:
a. Formwork finishes: by careful preparation of formwork, proper mix design and good
workmanship smooth finishes can be achieved .prefabricated units can be produced to a fine
finish
b. Surface treatments: These treatments depends upon the purpose the surfaces is to be used. For
example: a pavement surface should be plane but with sufficient roughness to exhibit skid
resistance. Hence the concrete after levelling is rocked , broomed or scratched to make the
surface rough.
c. Applied Finishes: The exterior surfaces of concrete surfaces could be modified to give a pleasant
look. The concrete surface is roughened cleaned and wetted. Over this a cement mortar ratio of
1:3 is applied. This mortar rendering can be given a number of surface finishes such as sand
facing, rough cast finish, pebble dash etc.

24. Rough Cast Concrete Pebble Dash Concrete
Stamped
concrete

25. CONCRETE SAMPLING
• For sampling two types of specimens either cubes of 15cm
X 15cm X 15cm or 10cm X 10cm x 10cm depending upon
the size of aggregate are used.
• The concrete mix is from the same batch which is being
used for casting the slab , beam , column etc.
• The concrete is poured in the mould and tempered
properly so as not to have any voids.
• After 24 hours these moulds are removed and test
specimens are put in water for curing. The top surface of
these specimen should be made even and smooth. This is
done by putting cement paste and spreading smoothly on
whole area of specimen.
• These specimens are tested for their compressive strength
and hardness after 7 days curing or 28 days curing.
MOULD
CONCRETE
IN MOULD

26. CUBE TEST:
• Around 6 cube specimens of 15cm x 15cm x 15cm size
Mix. M15 or above are prepared.
• The proportion and material for making these test
specimens are from the same concrete used in the field.
• These specimens are tested by compression testing
machine after 7 days curing or 28 days curing.
• Load should be applied gradually at the rate of 140
kg/cm2 per minute till the Specimens fails. Load at the
failure divided by area of specimen gives the
compressive strength of concrete.
• Minimum three specimens should be tested at each
selected age.
• If strength of any specimen varies by more than 15 per
cent of average strength, results of such specimen should
be rejected. Average of three specimens gives the
crushing strength of concrete. The strength requirements
of concrete.

27. CONCRETE SLUMP TEST:
• This test is performed to check the consistency of freshly made concrete. The slump test is done to make sure a concrete mix is
workable. The measured slump must be within a set range, or tolerance, from the target slump.
• Workability of concrete is mainly affected by consistency i.e. wetter mixes will be more workable than drier mixes, but concrete of
the same consistency may vary in workability. It can also be defined as the relative plasticity of freshly mixed concrete as indicative
of its workability.
Tools and apparatus used for slump test (equipment):
1.Standard slump cone (100 mm top diameter x 200 mm bottom diameter x 300 mm high)
2.Small scoop
3.Bullet-nosed rod (600 mm long x 16 mm diameter)
4.Rule
5.Slump plate (500 mm x 500 mm)

28. ADMIXTURES:
A. Chemical admixtures
I. Accelerators: An admixture which, when added to concrete, mortar, or grout, increases the rate of hydration of hydraulic cement,
shortens the time of set in concrete, or increases the rate of hardening or strength development.
II. Super Plasticizers: These are more recent and more effective type of water reducing admixtures also known as high range water reducer.
The main benefits of super plasticizers would be increased fluidity, Reduced W/C ratio, Very high early strength, Very high later age
strengths, Reduced shrinkage, especially if combined with reduced cement content. Improved durability by removing water to reduce
permeability and diffusion
III. Retarders: The function of retarder is to delay or extend the setting time of cement paste in concrete. These are helpful for concrete that
has to be transported to long distance, and helpful in placing the concrete at high temperatures. By their application a thin layer is formed
over the cement particles protecting them from hydration and increasing the setting time. Most normal retarders give some retardation,
30–90 minutes
IV. Water-reducing agents/ Plasticizers: Used
I. To increase the workability so as to ease placing in accessible locations.
II. Water reduction more than 5% but less than 12%.
III. The commonly used admixtures are Ligno-sulphonates and hydrocarbolic acid salts, Air entraining agents etc.
V. Air Entrained Admixtures: An addition for hydraulic cement or an admixture for concrete or mortar which causes air, usually in small
quantity, to be incorporated in the form of minute bubbles in the concrete or mortar during mixing, usually to increase its workability and
frost resistance.

29. B. Mineral admixtures
I. Cement based admixtures : These have cementing properties themselves.
For example: Ground granulated blast furnace slag (GGBFS)
II. Pozzolanic : A pozzolana is a material which, when combined with calcium
hydroxide (lime), exhibits cementing properties. Pozzolans are commonly
used as an addition (the technical term is "cement extender") to Portland
cement concrete mixtures to increase the long-term strength and other
material properties of Portland cement concrete and in some cases reduce
the material cost of concrete. Examples are: Fly ash, Silica Fume, Rice Husk
Ash
ADMIXTURES:

30. HEAVYWEIGHT CONCRETE
The main application for heavyweight concrete is for radiation shielding (medical or nuclear),
for offshore, heavyweight concrete is also used for ballasting of pipelines.
Heavyweight concrete uses heavy natural aggregates such as barytes or magnetite or
manufactured aggregates such as iron ore and/ or lead shot. The density depends on the
type of aggregate used and can achieve between 3'000 kg/m3 and close to 6'000 kg/m3.
As previously noted heavyweight concrete is mainly used for radiation protection. The critical properties of a
heavyweight concrete are:
• Homogeneous density and spatial closeness of the concrete
• Free from cracks and honeycombing
• Compressive strength is often only a secondary criterion due to the large size of the structure
• As free from air voids as possible
• Observe heat of hydration
• Keep shrinkage low

31. LIGHTWEIGHT CONCRETE
Lightweight means concrete and mortar with a low density. Concrete incorporating either aggregates
with a lower density or artificial voids are created to reduce the weight. The method used depends
mainly on the lightweight materials available, the application and the desired concrete properties.
LIGHTWEIGHT CONCRETE IS USED FOR:
• Lightweight construction (ceilings, walls, bridge decks, slabs)
• Levelling concrete
• Infill concretes
• Thermal insulation
CHARACTERISTICS OF LIGHTWEIGHT CONCRETES:
• Reduction in fresh concrete density and in hardened concrete density
• If lightweight concrete is used as an infill concrete with low load bearing requirements i.e. for
dimensional stability, highly porous concretes and mortars are generally produced (aerated
lightweight concrete)
• Lightweight concrete with good mechanical properties (i.e. compressive strength) is required,
special aggregates are used (naturally very porous but also dimensionally stable)