quite descriptive content on concrete

1. SUBMITTED BY:-

2. OVERVIEW

3. WHAT IS CONCRETE?
• Concrete is one of the most commonly used
building materials.
• a composite material made from several readily
available constituents (aggregates, sand, cement,
water).
• is a versatile material that can easily be mixed to
meet a variety of special needs and formed to
virtually any shape.
• has many applications and is used to make
pavements, pipe, structures, foundations, roads,
bridges/overpasses, walls and footings for gates.

4. ADVANTAGES…
• Ability to be cast
• Economical
• Durable
• Fire resistant
• Energy efficient
• On-site fabrication

5. COMPONENTS OF CONCRETE..
concrete
1. cement
2.aggregates
natural
Crushed
rocks
Igneous rocks
Sedimentary
rocks
Metamorphic
rocks
Gravel
sand
artificial
3. steel
4.water

6. Concrete is basically a mixture of two components: Paste & Aggregates
The paste, usually comprised of Portland cement and water, binds the aggregates
(sand and gravel or crushed stone) into a rock-like mass as the Paste hardens
because of the chemical reaction of the cement and water.
Therefore, total 4 components are required, namely:
1. Cement 2. Aggregates 3. Steel (for reinforcement - RCC) 4. Water

7. 1. CEMENT
• Before the introduction of ordinary Portland Cement,
lime was used as a cementing material.
• Most of the cement concrete work is done with
Portland cement only.
• Used because its ‘rapid hardening cement’ &
‘high alumina cement’ ---- special varieties.
• Portland cements are hydraulic cements,
i.e., they set & harden by reacting with water
to form a paste. The paste ordinarily constitutes
about 25% to 40% of the total volume of concrete.
• is the most energetically expensive.
(fuel consumption per ton of clinker produced is high & so have emissions)
Portland
cement
Oxides of
calcium
Oxides of
aluminium
Oxides of
silicon
Portland cement
Heating limestone
with clay
Grinding clinker
with a source of
sulphate(gypsum)
clinker

8. 2. AGGREGATES (60-80%)
• Inert or chemically inactive materials.
• Bound together by means of cement.
• classified into 2-----Fine and coarse aggregates, makes up the bulk of a concrete
mixture.
Fine Aggregates Coarse Aggregates
Natural river sand is used as
fine aggregate but where
natural sand is not available
economically, the finely
crushed stone may be used.
Broken stone is generally
used.

9. •The nature of work decides the maximum size of the coarse aggregate. For thin slabs
& walls, the max. size of coarse aggregate should be limited to 1/3 the thickness of the
concrete section.
•Aggregates used should be hard durable & clean, should be completely free from
lumps of clay, organic & vegetable matter, fine, dust, etc. The presence of all such
debris prevents adhesion of aggregates & hence reduces the strength of concrete.

10. •May also be classified in the following 2 categories, namely: Natural & Artificial
Aggregates
•Natural Aggregates: the term natural suggests that it is used loosely to assign
aggregates which need only be removed from their natural deposits as unconsolidated
sediments. Thus the aggregates obtained from such deposits are called gravel & sand.
•Those produced from boulders stone are known as crushed stones
•Thus it can be divided into 3, namely : Crushed rock aggregate, Gravel & Sand
a) Crushed rock: obtained by crushing rock pieces into suitable sizes. Therefore, it is
evident that the quality of it will be controlled by nature & type of rock from
which it is crushed.
• 3 major divisions of rocks------igneous, sedimentary, metamorphic
SandGravelCrushed rocks
Natural
Aggregates

11. Igneous rocks Sedimentary rocks Metamorphic rocks
•originally formed by cooling
from a molten rock material
known as magma
•formed by the deposition
of products of weathering
on the pre-existing rocks.
•have either igneous or
sedimentary origins but as a
result of intense heat or
pressure or both, they have
been altered or changed into
rocks possessing different
properties

12. Igneous rocks Sedimentary rocks Metamorphic rocks
• Plutonic(granite &
diorite) are brittle due to
the presence of large
crystals.
• Hypabyssal are medium
grained & best road stones
due to the inter grown
texture they possess.
• Calcareous---- calcium
carbonate predominates
& lime stones.
• Dolomites &
chalk(unsuitable for
construction
purposes) are main
varieties.
• Limestones & dolomites
have excellent adhesion
to cement & bituminous
binders.
•the hornfels, formed due to
the thermal metamorphism
are considered best for road
constructions.
•The gneiss & granulites have
the same quality of road
making as granites of coarse
variety.

13. Igneous rocks Sedimentary rocks Metamorphic rocks
• Volcanic are fine-grained
& excellent for building
constructions.
Basalt & andesite are the main
varieties
• Siliceous-----silicon
predominates;
• Sandstones(frequently
used in construction
work & as road stones
where they are available)
• quartzite(quite hard;
good in adhesion to
cement but poor in
bitumen) are the main
varieties.
Schist, slate and phyllite are
highly foliated; on crushing,
they break down into platy
fragments which, in mass
aggregate, produce large voids
Slate
schist

14. b) Gravel: the term is used to mean the coarse material resulting from the
disintegration of natural rock due to weathering & carried away by water & then
deposited on the river banks.
•Therefore, largely it possess
properties of basic rock
constituents, & usually the hard
varieties are found dumped along
river banks or along strata which had been under water.
•Variety like boulders, do not require any special tests when used as soiling or base
course.
c) Sand: final residue of the mineral grains resulting from the weathering action
upon the rocks are sand, & has reached after many cycles of deposition &
weathering. Most imp mineral is quartz & is hardly affected by the ordinary
weathering agents.
• for use in concrete, tested for shape and surface smoothness. If the particles have
angular shapes, the sand has a high void content and a high water demand. It
takes more fluid (cement paste) to surround an angular. If the fluid present is
insufficient to coat the surface area, the concrete mixture is harsh and difficult to
place and finish.

15. • Artificial aggregates: Foamed blast furnace slag(obtained as a by-product in
the manufacture of steel) is the only artificially prepared aggregate needed in the
construction.
• If slag is manufactured under controlled conditions,
it can certainly prove to be an excellent aggregate of uniform
quality.
Iron slag
(produced
with
controlled
amt of water)
Applied to the
molten slag to
trap the
steam
Gives a
porous
products
Crushed to
sizes suitable
as an
aggregate

16. 3. STEEL
• Concrete is strong in compression, as the aggregate efficiently carries the compression
load. However, it is weak in tension as the cement holding the aggregate in place can
crack, allowing the structure to fail. Reinforced concrete adds either steel reinforcing
bars to carry
tensile loads.
• The bars diameter vary from 5mm – 40mm.
• Sometimes the square bars or twisted bars
or ribbed-tor steel are also used.
• For road slabs, the reinforcement may also
consist of sheets of rolled steel of suitable thickness.
• The hyrib, a steel lath can also be used.
For a strong, ductile and durable construction
the reinforcement needs to have the following properties
at least:
•High relative strength
•High toleration of tensile strain
•Good bond to the concrete
•Thermal compatibility, not causing unacceptable stresses
in response to changing temp.
•Durability

17. 4. WATER: least expensive but most imp ingredient.
• Combining water with cement forms a cement paste by the process of hydration.
The cement paste glues the aggregate together, fills voids within it, and makes it
flow more freely.
•Impure water used to make concrete can
cause problems when setting or in causing
premature failure of the structure.
•Therefore, only fresh drinking water(free from alkali, acid, oil,
etc.) is preferable.
Low water-
cement ratio High water-
cement ratio
Low polarity=strong &
durable concrete
High polarity=weak
concrete

18. Why Use Admixtures?
•added to improve qualities or for
changing different physical properties in
its fresh & hardened stages, known as
admixture.
•Some admixtures are: alum, aluminium
sulphate, barium oxide, bitumen,
calcium chloride, coal ash, common salt,
iron oxide, lime, mineral oils, organic
oils, potassium chloride, silicate of soda,
tar products, volcanic ashes, zinc
chromate, etc.
advantages of admixtures:
i. Adjusting the final setting times of concrete
ii. Higher early& ultimate strength
iii. Higher slump & self-levelling concrete
iv. Increasing durability of concrete
v. Lesser water-cement ratios
vi. Reducing quantity of cement
vii. Reduction in the permeability of concrete
viii. Time saving in terms of repair &
maintenance.
•decrease water
content
•increase workability
•retard or accelerate
setting time
•reduce segregation
•reduce the rate of
slump loss
•modify the rate and/or
capacity for bleeding

19. •Knowing the complete details of any admixture before its recommendation together
with the following factors, is very necessary :
i. Grading curves of aggregates & their respective properties
ii. Method of construction
iii. Quantity of cement per metre cube of concrete
iv. Requirement of slump & retention
v. temp. variations
vi. Type & make of cement
vii. Water-cement ratio
• Admixtures are classified into 5 types based on their respective activities in the
concrete mix, namely:
i. Accelerators
ii. Air entraining admixtures
iii. High range of water reducers or super plasticisers
iv. Normal range of water reducers or plasticisers
v. Retarders

20. Water Reducers Accelerators Retarders Shrinkage
Reducing
Admixtures
Corrosion
Inhibitors
are used for the
purpose of
reducing the
quantity of
mixing water
required to
produce a
concrete of given
consistency.
are added to
concrete for the
purpose of
shortening set
time and
accelerating early
strength
development.
are used to offset
acceleration and
unwanted effects
of high
temperature and
keep concrete
workable during
placement and
consolidation.
are used to
minimize drying
shrinkage
cracking in
concrete .
are used to
mitigate
corrosion of
reinforcing steel
in concrete.

21. SEA WATER FOR MIXING CONCRETE
• It is advisable as stated above, to use clean water fit for
drinking purpose for making cement concrete.
• at places where sea water is available in abundance and
potable water is costly, the sea water can be used for making
cement concrete.
• The problem using sea water for making cement concrete has
to be studied from the following two aspects :
1. Strength : below table shows the analysis of average sea
water.
• consist about 3.50% of dissolved salt .
• The approximate percentage of various salts are 78% of
sodium chloride , 15 %magnesium chloride and magnesium
sulphate and the rest 7 % of calcium sulphate, potassium
sulphate, etc.

22. Composition of average sea water
No. Constituent Contents in gm per
liter
1 Calcium (Ca) 0.43
2 chloride (Cl2) 19.80
3 Magnesium (Mg) 1.33
4 Potassium (K) 0.44
5 Sodium (Na) 11.00
6 Sulphate (so4) 2.76
Total: 35.72

23. 2. Corrosion of reinforcement: sea water does not lead to the
corrosion, provide the concrete is dense and there is enough
cover to the reinforcement.
• The maximum cement content for concreter permanently
under sea water should be 3 Kn per m3 & the minimum cover
the reinforcement should be 75mm
• however it is not advisable to take the risk of corrosion of
reinforcement for prestressed concrete and hence the sea
water should not be used for making prestressed concrete.

25. •From the above discussion we came to know that water hardens & set the concrete,
also it fills the voids of cement ,i.e., makes the concrete workable.
•So it is found that water required is about 0.50-0.60 times the weight of cement. This
ratio of the amt of water to the amt of cement is termed as water-cement ratio.
Imp pts to remember :
the strength of concrete is inversely proportional to the water-cement ratio.
ratio for structures which are exposed to weather should be very carefully
decided…like…structures which are regularly wetting & drying, which are continuously
under water.
2 thumb rules which decides the quantity of water in concrete…..
Weight of cement + Weight of total aggregate
28% 4%
30% 5%
Weight of
water =

26. Compressive Strength of various Water-Cement Ratio

27. PROPERTIES OF CONCRETE
• has relatively high compressive strength
• lower tensile strength
• The elasticity of concrete is relatively constant at low
stress levels but starts decreasing at higher stress
levels as matrix cracking develops.
• has a very low coefficient of thermal expansion, and
as it matures concrete shrinks.
• All concrete structures will crack to some extent, due
to shrinkage and tension.
• can be damaged by fire, aggregate expansion, sea
water effects, bacterial corrosion, leaching, physical
damage and chemical damage (from carbonation,
chlorides, sulfates and distillate water).

28. Desired Properties of Fresh Concrete
CONSISTENCY WORKABILTY SEGREGATION
•It is desirable that freshly
mixed concrete be relatively
easy to transport, place,
compact and finish without
harmful segregation.
• A concrete mix
satisfying these conditions is
said to be workable.
•Segregation refers to a
separation of the components
of fresh concrete, resulting in
a non-uniform mix
•The primary cause for this is
differences in size of
constituents of concrete.
Moreover, improper mixing,
placing and consolidation also
lead to segregation.
• Consistency is the fluidity
or degree of wetness of
concrete.
• it is a major factor
indicating
the workability of freshly
mixed concrete.
•Test methods for
measuring consistency is
SLUMP TEST
(most widely used test)
- Given in the Next slide

29. Slump Test
• The goal of the test is to measure the consistency of
concrete through out the mix.
• "Slump" is simply a term coined to describe how
consistent a concrete sample is.
• The test also further determines the workability of
concrete, how easy is it to handle, compact, and cure
concrete.
• By adjusting the cement-water ratio or adding
plasticizers to increase the slump of the concrete will
give a desired mix.

30. 10 cm
20 cm
30 cm
The slump cone is filled in 3 layers. Every layer
is evenly rodded 25 times.
Measure the slump by determining the vertical difference between
the top of the mold and the displaced original center of the top
surface of the specimen.

31. UNIFORMILTY DURABILITY
•Concrete uniformity is checked by
conducting tests on fresh and hardened
concretes.
oSlump, unit weight, air content
tests
oStrength tests
Due to heteregeneous nature of concrete,
there will always be some variations---
inadequate mixing leads to non-homogeneous
nature.
Shrinkage:
 decrease in volume of concrete
due to loss of water from structure is the
major cause of cracking in concrete, high
water content increases shrinkage, high
aggregate content decreases shrinkage,
moist curing decreases shrinkage.

33. • The aim of mixing is to blend all of the
ingredients of the concrete to form a uniform
mass and to coat the surface of aggregates with
cement paste.
• The process of rolling, folding and spreading of
particles is known as the mixing of concrete. The
thorough mixing also ensures that cement water
paste completely covers the surfaces of aggregates.
• The materials of mixing of concrete can be done
either with hand or with the help of a machine.
Mixing time should be sufficient to produce a uniform
concrete. The time of mixing depends on the type
of mixer and also to some properties of fresh
concrete.
 Undermixing → non-homogeneity
 Overmixing → danger of water loss, breakage
of aggregate particles

34.  Undermixing → non-homogeneity
 Overmixing → danger of water loss, breakage of aggregate particles
 Ready-Mix concrete: In this type ingredients are introduced into a mixer
truck and mixed during transportation to the site.
• Wet – Water added before transportation
• Dry – Water added at site
 Mixing at the site
• Hand mixed
• Mixer mixed

35. 1. HAND MIXING
• The mixing by hand is allowed in case of small
works or unimportant works where small quantity
of concrete is required.
• For important works, if hand mixing is so to be
adopted, it is advisable to use 10 per cent more
cement than specified.
Materials
(wood brick or
steel) stacked
on a water
tight platforms
thoroughly
mixed, at least
3 times, before
water is added
This mix should
be consumed
in minutes
after adding
water.

36. MACHINE MIXING
all the materials
including water,
are collected in a
revolving drum.
the drum is
rotated for a
certain period.
The resulting mix
is then taken out

37. The features of machine mixing are:
• is more efficient and it produces concrete of better quality in a short time.
• The mixers of various types and capacities are available in the market.
They may either be of tilting type or non-tilting type.
• For small works, a mixer capable of producing concrete of one bag of
cement, is used. For works such as roads , aerodromes, drams, etc., special
types of mixers are used.
•should be thoroughly washed and cleaned after use. If this precaution is
not taken, the cakes hardening concrete will be formed & are difficult to
remove at a later stage, also affects the efficiency of the mixer.
•inside portion of the mixer should be inspected carefully at regular
intervals. The damaged or broken blades should be replaced.
•The time of mixing the materials and the speed of the mixer are very
important factors, decides the strength of concrete formed. The mixing
time should be at least one minute and preferably two minutes. The mixer
should be rotated at a speed as recommended by the manufactures of the
mixer.
• the concrete discharged by the mixer should be consumed within 30
minutes.

38. Grade Mixes of Concrete…
General expression
cement : sand : aggregate = 1 : n : 2n
As per IS:456-2000,
concrete is
designated in 7
grades---- M10,
M15, M20, M25,
M30, M35 & M40
(M = mix
number = specified
compressive strength of
that mix at 28 days)
•M5 & M7.5…simple
foundations for
masonry walls
< M15 ….not to be
used in RCC work
M5 –
1: 5: 10
M7.5-
1: 4: 8
M10-
1: 3: 6
M15-
1: 2: 4
M20-
1: 1.5: 3
M25-
1: 1: 2

39. CONSOLIDATION OF CONCRETE
• The main consideration of consolidation of concrete
is to eliminate air bubbles and thus to give maximum
density to the concrete
• The importance of consolidation of concrete can be
seen from the fact that a presence of 5% of voids
reduces 30% strength of concrete
• The difference between voids and pores is
o voids are the gaps between two individual
particles.
o pores represent the openings within the
individual particles

40. THE PROCESS OF CONSOLIDATION IS DIVED IN TO TWO PARTS
HAND CONSOLIDATION VIBRATORS
CONSOLIDATION

41. HAND CONSOLIDATION
• The consolidation of concrete is carried out by
hand methods which includes ramming , tamping
, spading and slicing with suitable tools and its
require use fairly wet concrete .
• It should however be remembered that
wherever feasible , the hand compaction should
be preferred because the use of vibrator may
lead to segregation of the aggregates .
• The concrete mixes which can be hand
compacted should not be compacted by the use
of vibrators

42. VIBRATORS
• THESE ARE THE MECHANICAL DEVICES USED TO COMPACT
CONCRETE IN THE FORMWORK.
• Vibrators to make harsh and stiff concrete mix,
with a slump of about 40 mm or less is workable
• The quality of concrete can be improved
by use of vibrators as less water will be required or in
other way, economy can be achieved by adopting a leaner
mix when vibrators are used.
• The use of vibrators result in the reduction of consolidation
time they are used where the rapid progress of work is
great importance.

43. TYPES OF VIBRATORS
INTERNAL
VIBRATORS
SURFACE
VIBRATORS
FORM
VIBRATORS
VIBRATING
TABLE

44. INTERNAL VIBRATORS
• These vibrators consist of steel tube which
inserted in fresh concrete .
INTERNAL VIBRATORS SURFACE VIBRATORS
These vibrators consist of steel tube which
called the POKER its inserted in fresh concrete .
Its connect with electric motor.
These vibrators are mounted on platforms or
screeds. They are used to fine concrete surface
on bridge floors, roads slabs, station platforms.
They are available in 40 mm to 100 mm dia. The
size is depend on us the spacing between
reinforcing bars in concrete . The frequency is
about 3000 to 6000 r.p.m
These vibrators are found to be more effective
for compacting very dry concrete because
vibrators acting same direction of gravity to the
concrete
When poker inserted then the internal vibrators
should be inserted and withdrawn and its
working continues when its withdrawn .
The vibrators used to the movement of fine
material to the top and its finishing operations
We can used vibrators vertically or slight
inclination The vibrators are efficient then other
types and its commonly used .

45. FORM OR SHUTTER VIBRATORS VIBRATING TABLE
These vibrators are attached to the formwork
and external centering of wall, columns
These are in the form of rigidly built steel
platforms mounted on flexible springs and
they are operated by electromagnetic.
These vibrators require more power because
of loss of some in vibrating the rigid shutters.
They are found to be very effective in
compacting stiff and harsh concrete mixes and
they are invariably used in the preparation of
pre-cast structural products in factories and
test specimens in laboratories.
They are also have and they cannot be
clamped at as many points as possible for
uniform compaction of concrete.
The table are vibrated either mechanically or
by placing the springs under the supports of
tables. Its 3000 to 7200 vibrations per minute.
It means the consolidation of concrete will be
achieved in less time and vice versa.

47.  Concrete surfaces are kept
wet for a certain period after
placing of concrete so as to
promote the hardening of
cement.
 Consists of a control of temp.
& of the moisture movement
from & into the concrete.
Such
processes
are
termed as
CURING

48. Following are the purposes of curing:
1. protects concrete surface from sun and wind
2. the presence of water is essential to cause the chemical action which
accompanies the setting of concrete .
3. Strength of concrete gradually increases with age, if curing is efficient.
4. By proper curing, durability is increased & shrinkage is reduced.
5. Resistance of concrete to abrasion is increased.
Effects of improper curing:
• Compressive strength is reduced
• Cracks will be formed due to shrinkage
• Durability decreases
• Frost & weathering resistances are decreased
• Rate of carbonation increases
• Surfaces are coated with sand & dust which leads to reduction of abrasion
resistance

49. Above mentioned disadvantages are more prominent for those structures
which are either directly exposed or those which have large surfaces compared
to depth such as roads, canals, bridges, etc, to avoid the cracks (necessary to
protect even before setting).
Factors affecting evaporating of water from concrete:
a) Air temp.
b) Fresh concrete temp.
c) Humidity
d) Wind velocity
• The evaporation of water in the first few hours can leave very low amt of
water in the concrete for hydration, leads to several cracks (average loss of
water varies from 2.5-10N/m2 per hour).
• Major loss occurs in the top 50mm layer & over a period of 3 hours, the
loss could be about 5% of the total volume of that layer.

50. Curing
Tips
Period
of
curing

51. Curing Methods –
Factors to be considered while selecting any mode of curing :
a. temp. should be kept min. for dissipation of heat & hydration
b. Prevention of water evaporation
Therefore, the methods should be employed in proper way & proper
supervision.
Specialized curing techniques are :
1) Ponding with water
2) Covering concrete with wet jute bags
3) Covering concrete with wet sand, saw dust, etc.
4) Covering concrete with water-proof paper & polyethylene sheets
5) Sprinkling or spraying with water
6) Applying curing compounds

52. •Methods 1 to 5 are
conventional ones & all suffer
from the common defect of
late beginning by which time
some harm has been affected
to the concrete.
•Ponding is the best
method….consists of little
earthen dams which are built
over the entire surface to be
cured.
•The squares thus formed are
then flooded with water to a
depth of about 50mm or so.
•Effective for horizontal
surfaces & not vertical.
•The method of covering
concrete surfaces with wet
jute bags, wet sand, saw dust,
polyethylene, etc. is difficult
in maintaining, especially at
places having winds blowing
at high speeds.

53. •The last method of applying the
curing compounds is a simple one
& can be brought about by spraying
while the concrete is wet.
•The application is carried out by
tree sprayers which are use for
spraying insecticides.
•Nozzle should be regularly cleaned
by water or white cement, should
be held at a distance of 0.7m-1m
from the surface & should be
confirmed that full area is covered .
•Pressure should be maintained in
the pump to effect fine spray.
Spraying of water is the most
common method but is not properly
employed because there should be
continuous supply of water to the
surface.

54. TYPES OF CEMENT CONCRETE
 Water proofing cement concrete
 Coloured concrete
 Light weight concrete
 No fines concrete
 Pre cast concrete
 Ready mix concrete
 Transit mix concrete

55. WATER PROOFING CEMENT CONCRETE
Info… How to obtain dense concrete…
It is used for certain types of works like
water storage tanks, reservoirs,basement
walls,roofs,swimming pools, sewage
units,etc. So, the concrete should be dense
and free from cracks.
•Using high class Portland cement of
guaranteed quality.
•Taking extreme care to adopt correct
grading and proportioning of the sand,
aggregate and cement.
•Using clean and non-porous aggregates.
•Mixing thoroughly to the right consistency
using the right amount of water.
•Placing, tamping and curing carefully.
•Making use of suitable water-proofing
compound.

56. COLOURED CONCRETE
Making… Use…
•By addition of suitable
colouring pigments to the
extent of about 8 to 10% of
the weight of cement.
•By using coloured cement for
the preparation of cement
concrete.
•By selecting agregates
possessing the required
colours.
•Manufacture of items for
public welfare
•Ornamental finishes in
buildings
•Preparing park lanes
•Separating lines of traffic of
road surfaces
•Underground pedestrian
crossings, etc

57. LIGHT-WEIGHT CONCRETE
Info… Advantages…
The bulk density of ordinary concrete is
about 23 kN/m^3. The concrete having
bulk density between 5 to 18 kN/m^3 is
known as the light-weight concrete .
•The local industrial waste, if found
suitable for light-weight concrete, can
be economically utilized.
•The reduction in weight of concrete
helps easy removal, transport and
erection of pre-cast products.
•The use of light-weight concrete results
in the reduction of cost to the extent of
about30 to 40% or so.
•The light-weight concrete has
comparatively less tendency to spall.
Hence, its fire resistance is greater as
compared to the ordinary concrete.
•The light-weight concrete has generally
a lower thermal expansion than
ordinary concrete.

58. NO-FINES CONCRETE
Info… Advantage… Limitations…
The no-fines concrete
consists of cement, coarse
aggregate and water.
•As compared to the
conventional concrete, the
drying shrinkage of no-fines
concrete is relatively low.
•As there is absence of
capillary passages, there is no
transmission of water by
capillary action.
•It is a type of light-weight
concrete and hence it grants
the advantages associated
with the light-weight
concrete construction.
•It possesses better insulating
characteristics than
conventional concrete
because of the presence of
large voids.
•As no-fines concrete has
little or no cohesion in the
fresh state, it requires long
time for the removal of
forms.
•It is highly permeable as
compared to the
conventional concrete and
hence, the rendering of walls
becomes essential.
•The compressive, bond and
flexural strengths of no-fines
concrete are considerably
lower than those of
conventional concrete.

59. Info… Advantage… Limitations…
•The unit weight of no-fines
concrete is about two-thirds
of the unit weight of
conventional concrete.
Hence, the pressure on
formwork is greatly
reduced.
•As no-fines concrete does
not segregate, it can be
dropped from a
considerable height and
placed in very high lifts.

60. PRE-CAST CONCRETE
Info… Advantage… Limitations…
The main difference between
pre-cast concrete and cast-in-
situ concrete is that the
former is a factory made
product while the latter is
prepared at site of work.
•Very rapid speed of erection
•Good quality control
•Entire building can be
precast-walls , floors ,beams
,etc.
•Rapid construction on site
•High quality because of the
controlled conditions in the
factory
•Prestressing is easily done
which can reduce the size
and number of the structural
members.
•Very heavy members
•Connections may be difficult
•Somewhat limited building
design flexibility
•Need for repetition of forms
will affect building design.
•Joints between panels are
often expensive and
complicated.
•Skilled workmanship is
required in the application of
the panel on site.
•Cranes are required to lift
panels.

61. The procedure for preparing pre-cast products is as
follows…..
•The moulds, which may be of timber, steel or sand, are
prepared to the shape of the product.
•The reinforcement, if any, is put up in the moulds.
•The concrete is mixed in the desired proportion and placed in
the mould.
•The finishing of the product is then carried out. The ordinary
products such as fence-posts, sleepers, etc. are left as they
are, while products such as spun pipes are finished during the
process of manufacture.
•The products are then sufficiently cured in specially
constructed tanks.
•The products are then dispatched for use at site of work.

62. READY MIX CONCRETE
Info… Advantages of ready-mix
concrete over site-mix
concrete…
Disadvantages of ready-mix
concrete over site-mix
concrete…
Ready mix concrete is a type
of concrete that is
manufactured in a factory or
batching plant, according to a
set recipe, and then
delivered to a worksite, by
truck mounted transit mixers.
•A centralized concrete
batching plant can serve a
wide area.
•Better quality concrete is
produced.
•Storage space for basic
materials at site is not
required.
•It eliminates
procurement/hiring of plant
and machinery.
•Wastage of basic materials is
avoided.
•It saves labour associated
with production of concrete.
•It reduces time required to
prepare concrete.
•It also reduces noise and
dust pollution at site.
•The materials are batched at
a central plant, and the
mixing begins at that plant,
so the travelling time from
the plant to the site is critical
over longer distances.
•Some sites are just too far
away, though this is usually a
commercial rather than
technical issue.
•Access roads and site access
have to be able to carry the
weight of the truck and load.
•Ready mix concrete is to be
placed within a limited time
span after batching at the
plan.

63. TRANSIT-MIX CONCRETE
The concrete that is mixed, either wet
or dry, en route to a job site is called TRANSIT-
MIX CONCRETE.