2. • Cement concrete is a mixture of cement, sand, crushed rock and
water which when placed in the skeleton of forms and allowed
to cure, becomes hard such as stone.
• Concrete has attained the status of a major building materials
in all branches of modern construction.
Concrete
3.
4. • When first mixed the water and cement constitute a paste
which surrounds all the individual pieces of aggregate to make
a plastic mixture.
• A chemical reaction called hydration takes place between the
water and cement, and concrete normally changes from a
plastic to a solid state in about 2 hours.
• Concrete continues to gain strength as it cures.
5. • It has a high compressive strength and its strength depends on the
proportion in which cement, sand, stones and water are mixed.
• It is free from corrosion and there is no appreciable effect of
atmospheric agents on it.
• It hardened with a age and the process of hardening continuous for a
long time after the concrete has attained sufficient strength.
• As it is weak in tension, steel reinforcement is placed in it to take up
the tensile stresses. This is termed as “Reinforced cement concrete”.
• It has a tendency to be porous. This is due to the presence of voids
which are formed during and after its placing.
• It forms a hard surface, capable of resisting abrasion.
Properties of Concrete
10. • The cement concrete in which no reinforcement is provided is
called as plain cement concrete. It has the following
properties.
It has high compressive strength
It is free from corrosion
It has a tendency to shrink
Plain Cement Concrete
11.
12. • The plain cement concrete in which reinforcement is embedded
for taking tensile and compressive stresses is known as
reinforced cement concrete.
• The reinforced cement concrete is used in the form of steel
bars, wire mesh, etc.
Reinforced Cement Concrete
13.
14. • Prestressed concrete is a form of concrete used in construction which is "pre-
stressed" by being placed under tension or compression prior to supporting any
loads beyond its own dead weight.
• This compression is produced by the tensioning of high-strength "tendons"
located within or adjacent to the concrete volume, and is done to improve the
performance of the concrete in service.
• Tendons may consist of single wires, multi-wire strands or threaded bars, and
are most commonly made from high-tensile steels, carbon fiber or aramid fiber.
• The essence of prestressed concrete is that once the initial compression has
been applied, the resulting material has the characteristics of high-strength
concrete when subject to any subsequent compression forces, and of ductile
high-strength steel when subject to tension forces.
Pre stressed Cement Concrete
15.
16.
17. • PSC is commonly used in the construction of bridges, large column free slabs
and roofs. PSC sleepers and electric piles are commonly used.
18. • One of the disadvantage on normal
concrete is the high self weight which
has a density of 2200 to 2600 kg/m3.
• This heavy self weight causes heavy load.
• In order to make an economical
concrete, attempts were made in the
past to reduce the self weight of
concrete.
• As a result the light weight concrete
was developed whose density various
from 300 to 1850 kg/m3.
Light Weight Cement Concrete
19. • By using porous lightweight aggregate of low apparent specific gravity, i.e.
lower than 2.6. This type of concrete is known as lightweight aggregate
concrete.
• By introducing large voids within the concrete or mortar mass; these
voids should be clearly distinguished from the extremely fine voids
produced by air entrainment. This types of concrete is variously knows as
aerated, cellular, foamed or gas concrete.
• By omitting the fine aggregate from the mix so that a large number of
interstitial voids is present; normal weight coarse aggregate is generally
used. This concrete as no-fines concrete.
Classification of Lightweight Concrete
20. • By replacing the usual mineral aggregate by cellular porous or light weight
aggregate, light weight concrete can be produced.
• Pumice – is used for reinforced concrete roof slab, mainly for industrial
roofs in Germany.
• Foamed Slag – was the first LWA suitable for reinforced concrete that was
produced in large quantity in the UK.
• Expanded Clays and Shales – capable of achieving sufficiently high
strength for prestressed concrete.
• Sintered Pulverised – fuel ash aggregate – is being used in the UK for a
variety of structural purposes and is being marketed under the trade
name Lytag
lightweight aggregate concrete
21. • By introducing gas or air bubbles in mortar, aerated concrete can be
produced.
• This concrete is a mixture of water, cement and finely crushed sand with air
or gas introducing agents.
• There are several ways in which aerated can be manufactured. One
important way is by the formation of gas or air bubbles using finely
powered metal ( Usually aluminium power ).
• Chemical reaction takes place in the concrete and finely large quality of
hydrogen gas is liberated which gives the cellular structure.
Aerated Concrete
22.
23. • By omitting sand fraction from the aggregate, no-fine concrete can be
produced.
• This concrete is made up of only single-sized aggregate of size passing of
20 mm and retained on 10 mm course aggregate, cement and water.
• The single sized aggregate makes a good no-fine concrete, which in
addition gives large voids and hence is light in weight.
No-fines concrete
24.
25. • Fiber-reinforced concrete (FRC) is concrete containing fibrous material
which increases its structural integrity.
• It contains short discrete fibers that are uniformly distributed and
randomly oriented.
• Fibers include steel fibers, glass fibers, synthetic fibers and natural fibers
each of which lend varying properties to the concrete.
• In addition, the character of fiber-reinforced concrete changes with
varying concretes, fiber materials, geometries, distribution, orientation,
and densities.
• Fibre reinforced concrete is having better tensile strength, ductility and
resistance to cracking.
Fibre Reinforced Cement Concrete
26.
27. • The following are some of the important tests conducted on concrete:
1. Slump test.
2. Compaction factor test.
3. Crushing strength test.
Tests on Concrete
29. • This test is conducted to determine the workability of concrete. It needs a
slump cone for test.
• Slump cone is a vessel in the shape of a frustum of a cone with diameter at
bottom 200 mm and 50 mm at top and 300 mm high.
• This cone is kept over a impervious platform and is filled with concrete in
four layers.
• Each layer is tamped with a 16 mm pointed rod for 25 times.
• After filling completely the cone is gently pulled up.
• The decrease in the height of the concrete is called slump.
• Higher the slump, more workable is the concrete.
31. • This is another test to identify the workability of concrete.
• This test is conducted in the laboratory.
• The test equipment consists of two hoppers and a cylinder fixed to a stand, the
dimensions and the distances between the three vessels being standardized.
• Vessel A and B are having hinged bottoms whereas cylinder C is having fixed bottom.
• Top vessel A is filled with the concrete to be tested.
• As soon as it is filled, the hinged door is opened.
• Concrete is collected in vessel B.
• Then the hinged door of B is opened to collect concrete in cylinder C.
• The concrete in cylinder C is weighted. Let it be W1.
• Now cylinder is again filled with the sample of concrete in 50 mm layers, which is
compacted by ramming and vibrating.
• Then the weight of compacted concrete is determined. Let this weight be W2.
• The ratio W1/W2 is termed as compaction factor.
