Introduction to Concrete Technology

1. CONCRETE TECHNOLOGY
GENERAL

2. MANUFACTURE OF PORTLAND
CEMENT
RAW MATERIALS FOR CEMENT
Calcareous Materials
e.g: Lime stone
Chalk
Marl
Argillaceous materials
e.g: Clay
Shale

3. • There are three process:
Wet process
Dry process
Semi dry process

6. Calcareous material such as lime stone brought
from the quarries is first crushed to small
fragments, and stored in silos.
Argillaceous material such as clay is thoroughly
mixed with water in a container known as wash
mill. This washed clay is stored in storage basins.
 Crushed limestone from silos and wet clay from
storage basins are allowed to fall in a channel in
correct proportions.

7. • This channel leads the materials to wet grinding
mills, where they are brought into intimate
contact to form what is known as slurry.
• The slurry is a liquid of creamy consistency with
water about 35 to 50 percent. Grinding is carried
out either in ball mill or tube mill or both.
The slurry is led to correcting basin it is constantly
stirred. At this stage the chemical composition is
adjusted as necessary.

8. The corrected slurry is stored in storage tanks and
kept in a homogeneous condition by the
agitation(disturbance) of slurry.
The corrected slurry is fed in a rotary kiln from
upper end. The rotary kiln is an important
component of cement factory.
• It is thick steel cylinder of diameter anything
from 3meters to 8 metres, lined with refractory
materials.

9. • The length of the rotary kiln may vary anything
from 30 meters to 200 meters.
• It is so arranged than the kiln rotates once in
every minute about its longitudinal axis.
• The corrected slurry is injected at the upper end
of rotary kiln.
• Hot gases or flames are forced through the lower
end of kiln.

11. • Portion of the kiln near its upper end is known as
dry zone and in this zone water of slurry is
evaporated.
• As the slurry gradually descends, there is rise in
temperature and in next section of kiln, carbon
dioxide from the slurry is evaporated.
• Small lumps, known as nodules, are formed at
this stage.

12. • These nodules then gradually roll down passing
through zones of rising temperature and
ultimately reach to the burning zone, where
temperature is about 1500˚C to 1700˚C.
• In burning zone, calcined product is formed and
nodules are converted into small hard balls which
are known as clinkers.
• The size of clinkers varies from 3 mm to 20mm.

13. • The clinkers drops into a rotary cooler where it is
cooled under controlled conditions.
• The clinkers weighs about 1100 to 1300 gms per
litre. The litre
Clinkers as obtained from the rotary kiln are
finely ground in ball mills and tube mills.
During grinding, a small quantity about 2 to 3 %,
of gypsum is added to prevent flash setting of
cement.

14. • The finely ground cement is stored in silos. it is
then weighed and packed in bags by automatic
machines.
• Each bag of cement contains 50 kg or about
0.035m3 of cement. These bags are carefully
stored in dry place.

16. DRY PROCESS

18. Advantages of dry process:
• It increases the productivity of labour.
• The fuel consumption is less. For the production
of one ton of cement, the dry process required
100 kg of coal while the wet process requires
350kg of coal.
• The capital expenditure is less.

19. SEMI DRY PROCESS
• In the semi dry process raw materials are
crushed and fed to a grinding mill to convert it
into fine powder.
• The dry powder called raw mix is pumped in a
blending silo where the correct proportions are
adjusted and intimately mixed by compressed air.
• This blended meal is now sieved and fed into a
rotating dish called granulator and about 10-14%
water is added at the same time.

20. • In this way the meal is converted into hard pallets
of about 15mm diameter.
• The pallets are baked by means of hot gases
available from the kiln.
• These baked pallets are fed into the kiln.
• The subsequent operations are same as wet
process.

21. COMPOSITION OF CONCRETE
• Concrete is composed of,
• Concrete = cement + sand + aggregates +
water + admixtures + air

23. CEMENT
• The mixture of cement and water is called Paste.
• The function of the paste is to bind sand
aggregate particles by the chemical process of
hydration.
• It also fills the void between sand and aggregates
particles.
• The strength of concrete depends upon the
properties of cement, sand and aggregates.

24. AGGREGATES
• The aggregates occupy about 75% of the volume
of concrete and hence their influence on various
properties of concrete is considerable.
• Properties of aggregates greatly affect the
properties of concrete such as workability,
strength, durability and economy.

26. • Aggregates are generally cheaper than cement
and impart greater volume stability and durability
to concrete.
• The aggregates is used primarily for the purpose
of providing bulk to the concrete.
• The most important function of the fine
aggregate is to assist in producing workability and
uniformity in mixture.

27. • The fine aggregate also assists the cement paste
to hold the coarse aggregate particles in
suspension.

28. WATER
• It has been estimated that for C2s and C3S
compounds, on an average 23% of water by
weight of cement is required for chemical
reaction.
• This 23% of water chemically combines with
cement and, therefore, it is called bound water.
• A certain quantity of water is imbibed within gel
pores. This water is known as gel water.

29. • If the quantity of water is inadequate to fill up the
gel pores, the formation of gel itself will stop and
if formation of gel stops there is no question of
gel pores being present.
• Gel water of about 15% by weight of cement is
required.
• Therefore a total 23+15 =38% of water by weight
of cement is required for complete hydration.

30. • If less than 38% of water is used than complete
hydration is not possible as the volume available
is insufficient to accommodate all the products of
hydration.
• Hence the strength of concrete will be reduced.
• If more than 38% of water is used, then the excess
water will cause undesirable capillary cavities and
concrete becomes porous.

31. ADMIXTURES
• Admixtures is defined as a material other than
the basic ingredients of concrete cement,
aggregates and water added to the concrete mix
immediately before or during mixing to modify
some properties of concrete in the fresh or
hardened state.
• They should not adversely affect any property of
concrete.

32. • The use of admixtures like accelerators, retarders, air
entraining agents, pozzolanic materials, water
proofing admixtures is being practiced by Indian
construction industry since long back.
• The properties commonly modified using admixtures
are setting time, workability, air entrainment,
dispersion etc.
• The admixture is generally added in a relatively small
quantity ranging from 0.005 to 2% by weight of cement.
• Overuse of admixtures have detrimental effects on the
properties of concrete.

33. AIR
• The air voids in the mass of concrete can be
classified in two groups.
• Entrapped air
• Entrained air
• Air voids present in the mass of concrete makes
the concrete porous and reduce its density.
• The compressive strength of concrete reduces
and permeability of concrete increases. Durability
of concrete also decreases.

34. • Entrapped Air
• The entrapped air is the
voids present in the
concrete due to
insufficient compaction.
• The size of voids may
range from 10 to 1000
microns or more.
• The voids are not
uniformly distributed
throughout the
concrete mass.
• Entrained Air
• The entrained air is the
intentionally
incorporated minute
spherical bubbles.
• The size of air bubbles
may range from 5 to 80
microns.
• The air bubbles are
uniformly distributes
throughout the mass of
concrete.

35. STRENGTH MECHANISM
• When water is added to cement, ingredients of
cement react chemically with water and form
various complicated chemical compounds. The
chemical reaction that take place between
cement and water is referred as hydration of
cement.