Concrete Construction: Batching of mixes; casting process, compaction and curing; requirement of mix design and casting of test cubes – removing cubes from moulds and curing for strength tests; bar-bending equipments and preparation of reinforcement for R C C works

1. Concrete

2. Introduction
• The most widely used construction material.
• Second only to water as the most consumed
substance on earth.
Q? Why concrete is most popular construction material
among common people?

3. Fine Aggregates:
25 - 30%
Coarse Aggregates:
30 to 50%
Matrix (paste):
• Water: 15 – 20%
• Cementitious materials
(cement, pozzolans & slag):
7 – 15%
• Air: 1 – 8%
• Chemical Admixtures: < 2%
Constituents of Concrete

4. Production of Concrete:
 Material
 selection and
 Proportions
 Process
 Mixing
 Transportation
 Placement
 Compaction
 Curing

5. MATERIAL

6. Cement
 Cement is the mixture of calcareous, siliceous,
argillaceous and other substances. Cement is
used as a binding material in mortar, concrete,
etc.
 Cement is a fine powder which sets after a few
hours when mixed with water, and then hardens
in a few days into a solid, strong material.
Cement is mainly used to bind fine sand and
coarse aggregates together in
concrete. Cement is a hydraulic binder, i.e. it
hardens when water is added.

7. Chemical Composition of
cement
Lime 63%
Silica 22%
Alumina 06%
Iron oxide 03%
Gypsum 02 to 05%

8. Function of composition of
cement
(i) Lime(CaO):
Lime forms nearly two-third (2/3) of the cement.
Therefore sufficient quantity of the lime must be
in the raw materials for the manufacturing of
cement. Its proportion has an important effect on
the cement. Sufficient quantity of lime forms di-
calcium silicate and tri-calcium silicate in the
manufacturing of cement.
Lime in excess, causes the cement to expand
and disintegrate.

9. (ii) Silica (SiO2):
The quantity of silica should be enough to form di-
calcium silicate and tri-calcium silicate in the
manufacturing of cement. Silica gives strength to the
cement. Silica in excess causes the cement to set
slowly.
(iii) Alumina (Al2O3):
Alumina supports to set quickly to the cement. It also
lowers the clinkering temperature. Alumina in excess,
reduces the strength of the cement.
(iv) Iron Oxide (Fe2O3):
Iron oxide gives colour to the cement.
(v) Calcium Sulphate (or) Gypsum (Ca SO4) :
At the final stage of manufacturing, gypsum is added to
increase the setting of cement.

11. MANUFACTURING OF CEMENT
(1) Mixing and crushing of raw
materials
a.Dry process
b.Wet process
(2) Burning
(3) Grinding

12. (a) Dry process:
In this process, the raw materials are
changed to powdered form in the absence
of water.
 In this process calcareous material such
as lime stone (calcium carbonate) and
argillaceous material such as clay are
ground separately to fine powder in the
absence of water and then are mixed
together in the desired proportions.
 Water is then added to it for getting thick
paste and then its cakes are formed,
dried and burnt in kilns.
 This process is usually used when raw
materials are very strong and hard.

13. (b) Wet process:
In this process, the raw materials are changed
to powdered form in the presence of water.
 In this process, raw materials are pulverized
by using a Ball mill, which is a rotary steel
cylinder with hardened steel balls. When the
mill rotates, steel balls pulverize the raw
materials which form slurry (liquid mixture).
 The slurry is then passed into storage tanks,
where correct proportioning is done. Proper
composition of raw materials can be
ensured by using wet process than dry
process. Corrected slurry is then fed into
rotary kiln for burning.
 This process is generally used when raw materials are
soft because complete mixing is not possible unless
water is added.

14. Among wet process and dry
process, which is economical?

15. (2) Burning:
 The raw slurry (wet Process) or raw meal (dry process),
obtained by one of wet or dry process is called charge.
 Charge is introduced into a rotary Kiln. The rotary kiln
consists of a steel cylinder about 150meters long and
4meter diameter and rotates 30 to 60 turns per hour.
 At one end of the cylinder a screw conveyer is arranged
which slowly allows the charge into the cylinder.
 In the other end of the cylinder, a burner is arranged.
Coal or burning oil is burnt at this end.
 The charge entering the cylinder slowly moves towards
the hot end. At the burning end of the kiln, the
temperature is around 1600 to 1900 degrees centigrade.
 At this end some chemical reactions takes place
between oxides of calcium , aluminium and silica.
 Mixture of calcium silicates and calcium aluminates is
formed.
 The resultant product consists of grey hard balls called
clinker cement.

16. The percentage of important compound formed in cement
is given below:
(bogue's compound of cement)

18. (3) Grinding:
• Clinker cement is cooled, ground to fine
powder and mixed with 2 to 5 percent of
gypsum (Calcium sulphate Ca SO4) .
(added for controlling the setting time of
cement)
• Finally, fine ground cement is stored in
storage tanks from where it is drawn for
packing.

19. Hydration of cement
 The chemical reactions that take place between
cement and water is referred as hydration of
cement.
 On account of hydration certain products are
formed. These products are important because
they have cementing or adhesive value.
 Out of all cement compounds (bogue's
compound of cement), the strength of cement is
contributed mainly by silicates.
 Silicates react with water and produce a gel
called Calcium Silicate Hydrate or ‘C-S-H’ gel.
 This gel is initially weak and porous, but with the
passage of time it becomes stronger and less
porous.

22. Q? Is it desirable to put in as much cement as
possible in a concrete mix provided cost is not a
constraint.
Q? What is the maximum cement content to be used
in concrete? [cl. 8.2.4.2, pg 19, IS456]

23.  In the order of reaction with water, C3A is the first to
react with it and imparts setting to the cement paste.
Hence C3A is responsible for setting.
 Strength contribution by C3A is negligible and therefore
can very well be neglected.
 Strength of cement is mainly contributed by silicates i.e.
C3S and C2S.
 In the category of silicates, C3S is quicker in reacting with
water as compared to C2S. Therefore the initial strength
up to 7 days is mainly given by C3S.
 After 7 days when most of C3S has already exhausted,
C2S also start reacting with water. The strength between
7 and 28 days is contributed mainly by C2S and a part is
contributed by C3S

24. Which cement to use?
The choice of the cement depends upon the
nature of work, local environment, method of
construction etc.
The different type of cement has been achieved by
different methods like :

25. Types of cement

26. (a) Ordinary Portland Cement (OPC):
It is the most commonly produced and used
cement. It is available in three different grades.
(b) Rapid Hardening cement (RHC):
It is also called ‘Early Strength Cement’ because
its 3 days strength is almost equal to 7 days strength of
OPC. One type of this cement is manufactured by
adding calcium chloride (CaCl2) to the O.P.C in small
proportions. Calcium chloride (CaCl2) should not be
more than 02%.
In RHC, strength development is very fast. This is
because of following reasons:
 Higher fineness of cement. The specific surface of this
cement is increased to 320 m2/kg as compared to
225 m2/kg for OPC.
 Higher quantity of C3S in cement as compared to
C2S. C3S is more reactive in comparison to C2S.

28. The sulphate present in the soil or surrounding environment
reacts with free Ca(OH)2 available in the concrete and CaSO4
is formed. There is no dearth of free Ca(OH)2 as it is available in
abundance in the set cement. The CaSO4 thus produced
reacts with hydrate of calcium aluminate and form an
expansive compound called calcium sulpho-aluminate which
causes expansion and cracks in the set cement. Sulphate
attack is further accelerated if it is accompanied by alternate
wetting and drying also, which normally takes place in marine
structures of the tidal zone.

30. (d) Sulphate Resistant Cement (SRC):
It is modified form of O.P.C and is specially
manufactured to resist the sulphates. In certain
regions/areas where water and soil may have
alkaline contents and O.P.C is liable to
disintegrate, because of un favorable chemical
reaction between cement and water, S.R.C is
used. This cement contains a low %age of C3A
not more than 05%.
The quantity of C3A can be controlled simply by
blending OPC with slag cement.
Limitation:
This cement requires longer period of curing (why?). It
develops strength slowly, but ultimately it is as strong
as O.P.C.

31. (e) Portland slag cement:
It is produced by blending OPC clinkers with slag in
suitable proportion (20-25%) and grinding together.
The slag can be separately added to OPC while making
concrete.
Limitation of slag cement:
It develops strength slowly, but ultimately it is as strong
as O.P.C.

32. (e) Portland Pozzolana cement:
It is produced by blending OPC clinkers with pozzolana
in suitable proportion (20-25%) and grinding together.
It develops strength slowly, but ultimately it is as strong
as O.P.C.

35. opaline is a man-made
'crystal'
Diatomaceous earth deposit

36. (f) QUICK SETTING CEMENT:
When concrete is to be laid under water, quick
setting cement is to used. This cement is manufactured
by adding small %age of aluminum sulphate (Al2SO4)
which accelerates the setting action. This cement can
also be produced by not adding gypsum to OPC The
setting action of such cement starts with in 05 minutes
after addition of water and it becomes stone hard in less
than half an hour.
(h) LOW HEAT CEMENT:
In this cement the heat of hydration is reduced by
tri calcium aluminate (C3A ) content. It contains less
%age of lime than ordinary port land cement. It is used
for mass concrete works such as dams etc.

37. WHITE CEMENT:
This cement is called snowcrete. As iron
oxide gives the grey colour to cement, it is
therefore necessary for white cement to
keep the content of iron oxide as low as
possible. Lime stone and china clay free from
iron oxide are suitable for its manufacturing.
This cement is costlier than O.P.C. It is mainly
used for architectural finishing in the
buildings.

38. Tests on Cement
 Field Test
 Laboratory test
Field Test
(a) Date of Manufacture
(b) One feels cool by thrusting one’s hand in the cement
bag.
(c) It is smooth when rubbed in between fingers.
(d) A handful of cement thrown in a bucket of water
should float.

39. Laboratory test
(Self Study)
(1) Fineness Test. (why?)
(2) Consistency test. (why?)
(3) Setting Time Test. (why?)
(4) Soundness test. (why?)
(4) Compressive strength test. (why?)

40. Q? How would you differentiate
between Coarse Aggregate and fine
aggregate.
Aggregate

41. Aggregate
What size of aggregate should be used?
 The nominal maximum size of coarse aggregate in no case
greater than one-fourth of the minimum thickness of the
member, provided that the concrete can be placed
without difficulty so as to surround all reinforcement
thoroughly and fill the comers of the form.
 For heavily reinforced concrete members as in the case of
ribs of main beams, the nominal maximum size of the
aggregate should usually be restricted to 5 mm less than
the minimum clear distance between the main bars or 5
mm less than the minimum cover to the reinforcement
whichever is smaller.

42. • Generally represent 60 to 75% of the total
volume of concrete  strong influence on the
properties, proportioning, cost and the
performance of the concrete mixtures.
• Generally divided in two groups:
• Fine aggregates: natural or manufactured
sand. Generally, sand particles almost
entirely pass the 4.75mm sieve and are
predominantly retained on the 75µm sieve.
• Coarse aggregates: natural gravel or
manufactured material. The particles are
predominantly retained on the 4.75mm
sieve.
Aggregates

43. Properties of aggregate
 Inherited Properties
 Chemical and mineral composition
 Specific gravity
 Hardness
 Strength
 Color etc.
 Acquired properties
 Shape
 Size
 Surface texture
 Water absorption

45. IMPORTANCE OF ANGULARITY NUMBER
 The normal aggregate which are suitable
for making concrete may have angularity
number anything from 0 to 11.
 Angularity number 0 represents the most
practicable rounded aggregate
 Angularity number 11 indicates the most
angular aggregate that could be used for
making concrete.

46. Flaky and elongated particles may have adverse effects on
concrete. For instance, flaky and elongated particles tend to lower
the workability of concrete mix which may impair the long-term
durability.
Flakiness Index is It is the percentage by weight of flaky particles in a
sample.
Elongation Index is the percentage by weight of elongated particles
in a sample.

53. Effort should be made to use minimum
volume of paste in the concrete. It should
just be sufficient to fill the voids left out by
the aggregates.
This can be achieved by using well graded
aggregates so that the voids are minimum.

54. Grading of aggregate

55. Type of Sand
Fineness Modulus
Range
Fine Sand 2.2 – 2.6
Medium Sand 2.6 – 2.9
Coarse Sand 2.9 – 3.2
WHY TO DETERMINE FINENESS
MODULUS?
•Fineness modulus is generally used to get an idea of how coarse
or fine the aggregate is. More fineness modulus value indicates that
the aggregate is coarser and small value of fineness modulus
indicates that the aggregate is finer.
•Fineness modulus of different type of sand is as per given below.
•Generally sand having fineness modulus more than 3.2 is not used
for making good concrete.

56. Fineness Modulus = 246/100 = 2.46

57. Bulking of sand
 The volume increase of fine aggregate due to
presence of moisture content is known as
bulking.
 Bulking increases with increase in moisture
content up to a certain limit and beyond that
the further increase in moisture content results in
decrease in volume.
WHAT CAUSES BULKING OF AGGREGATE?
The moisture present in aggregate forms a film around each particle.
These films of moisture exert a force, known as surface tension, on
each particle. Due to this surface tension each particles gets away
from each other. Because of this no direct contact is possible among
individual particles and this causes bulking of the volume.
Bulking of aggregate is dependent upon two factors,
Percentage of moisture content
Particle size of fine aggregate

59. WHY TO DETERMINE PERCENTAGE OF BULKING?
Due to bulking, fine aggregate shows completely unrealistic volume.
Therefore, it is absolutely necessary that consideration must be given
to the effect of bulking in proportioning the concrete by volume.

60. • The grading, the shape and the texture of
aggregates can significantly influence concrete
workability.
• The amount of water required for a target
workability is related to aggregate properties:
 Nominal maximum size of the coarse
aggregate.
 Shape and texture of particles of fine
and coarse aggregates.
 Grading of coarse aggregate.
Some Properties of Aggregates
Affecting Fresh Concrete Properties

61. Properties of Aggregates Affecting
Fresh Concrete Properties
• Angular sand (manufactured sand) can
significantly increase the water demand and
the cement content for a required
workability.
• Very coarse sands and coarse aggregates
can produce harsh, unworkable mixes.
• Changes in grading (or the shape / texture)
of the aggregates can cause changes in the
water demand of concrete, segregation and
affect uniformity of concrete from batch to
batch.

62. • The shape and grading of the fine
aggregate can have significant effect on
the bleeding and the finishing properties
of concrete  the finer the sand, the
lower the bleeding.
• The temperature of aggregates can
strongly impact on the setting time of the
concrete (T° ↑  setting time ↓).
Properties of Aggregates Affecting
Fresh Concrete Properties

63. • For concrete with compressive strengths
< 20 MPa, the strength ↑ with ↑ maximum
size of the coarse aggregate.
• For concrete of higher compressive
strengths, there is an optimum maximum
size fraction for each strength level. For
high-performance concrete, the maximum
coarse aggregate size is often limited to
10 – 14 mm.
Properties of Aggregates Affecting
Hardened Concrete Properties

64. • Generally,
• The modulus of elasticity of concrete ↑ with
↑ modulus of elasticity of the aggregates;
• With ↑ modulus of elasticity of the
aggregate, the creep of concrete ↓.
• For similar compressive strength levels,
better flexural strengths are obtained
when using aggregates with higher
angularity and good surface roughness.
Properties of Aggregates Affecting
Hardened Concrete Properties

65. Some Aggregate Characteristics Affecting Concrete
Properties
Specific gravity
and bulk
density
Mix proportioning calculations and
concrete density
Size and
grading,
particle shape,
surface texture
Workability of fresh concrete,
economy (mixture proportioning),
strength, bleeding, finish-ability,
pumping
Absorption and
surface
moisture
Affect the net water content in
concrete  workability, strength will
vary
High absorption could reduce
durability (freezing and thawing)
Cleanness Dirty aggregates  poor fresh and
hardened (aggregate – paste bond)
concrete properties

66. Aggregate Characteristics Affecting Concrete Properties
Hardness,
toughness and
wear
resistance
Affects the mechanical properties
Abrasion resistance of concrete 
function of aggregate type. Hard
aggregates with good micro- and
macrotextures are better (related to
mineralogy).
Soundness Durability, resistance to weathering
Particle
strength and
elasticity
Resistance to abrasion, creep &
shrinkage; the effect is generally
relatively limited for conventional
(normal) strength concrete
Volume
stability
Drying shrinkage  aggregates with
high absorption properties may
have high shrinkage properties on
drying (e.g. sandstone, shale, slate,
greywacke)

67. Requirements of water used in concrete
 Water used for mixing and curing shall be clean and free
from injurious amounts of Oils, Acids, Alkalis, Salts, Sugar,
Organic materials
 Potable water is generally considered satisfactory for mixing
concrete
 Mixing and curing with sea water shall not be permitted.
 The pH value shall not be less than 6

69. The permissible limits for solids in water
Solids Permissible Limits (Max)
Organic 200 mg/lit
Inorganic 3000 mg/lit
Sulphates (SO4) 500 mg/lit
Chlorides (Cl) 500 mg/lit
Suspended matter 2000 mg/lit
Requirements of water used in concrete
What if water does not meet the above
requirements????

70. Effect of Sea Water
 Salinity of sea water is approximately 3.5%. If sea
water is used, the main concern will be the
corrosion of steel and reduction in strength.
 In addition, it also accelerates the setting time of
cement, causes efflorescence and persistent
dampness. Therefore use of sea water should be
avoided for concrete works.

71. Hydration
Concrete achieves its strength through a
chemical process called Hydration.
Hydration is a complex process but in
simple terms, is the reaction between water
and the cement in the mix.

72. Water/Cement Ratio and Strength
The most important indicator of strength
Lower the w/c ratio, the higher the final concrete strength
Concept was developed by Duff Abrams
A reduction in the water-cement ratio generally results in an increased quality of concrete, in
terms of density, strength, impermeability, reduced shrinkage and creep, etc.

73. Water/Cement Ratio and
Strength

74. (w/c) Ratio 0.40 0.50 0.60 0.70 0.80
Probable Strength(%) 100 87 70 55 44
Factors Low w/c ratio High w/c ratio
Strength High Low
Permeability Low High
Shrinkage Low High
Water/Cement Ratio and Strength

75. Adding extra water to concrete!!!
 Adding more water creates a diluted paste that is weaker and
more susceptible to cracking and shrinkage
 Shrinkage leads to micro-cracks (zones of weakness)
 Once the fresh concrete is placed, excess water is squeezed
out of paste by weight of aggregate and cement
 The excess water bleeds out onto the surface.
 The micro channels and passages that were created inside the
concrete to allow that water to flow become weak zones

76. Adding extra water to concrete!!!
 This affects the compressive, tensile and flexural
strengths, the porosity and the shrinkage
 Loss of Inherent good qualities like Cohesiveness
and Homogeneity
 Harmful to Strength and Durability
 Sowing the seed of Cancer in concrete
It is an Abuse, It is a Criminal act, Un-engineering ----
--------------(M.S.Shetty, Eminent Author)

77. * Increased strength.
* Lower permeability.
* Increased resistance to weathering.
* Better bond between concrete and
reinforcement.
* Reduced drying shrinkage and cracking.
* Less volume change from wetting and drying.
Advantages of low
water/cement ratio

78. Workability
 The ease with which freshly mixed concrete can be
transported, placed and finished without
segregation
 Influencing factors
 Size, Shape, Texture and grading of aggregate
 Water Content

79. ADMIXTURE
 It is an optional ingredient of concrete which is
added to modify the properties of fresh as well as
hardened concrete and grout material as per
some specific requirements.
 Addition of admixture may alter workability,
pumping qualities, strength development,
appearance etc. in fresh concrete and
permeability, strength, durability etc. in hardened
concrete.
 Use of chemical admixture is a must for producing
high grade concrete.

80. Admixture types
Admixtures to enhance workability
 Mineral (Fly ash, Silica fume, GGBFS)
 Chemical
 Air entraining
Chemical and Air-entraining admixtures are
Covered by IS:9301-1999
a) Accelerating admixtures
b) Retarding Admixtures
c) Water-reducing admixtures (plasticizers)
d) Air-entraining admixtures and
e) Super-plasticizing admixtures

81. Water-reducing admixtures
 An admixture which either increases workability of
freshly mixed mortar or concrete without increasing
water content or maintains workability with a
reduced amount of water
 Role of water reducers is to deflocculate the cement
particles agglomerated together and release the
water tied up in these agglomerations
 Can be categorized according to their active
ingredients
 salts and modifications of hydroxylized carboxylic acids
(HC type)
 salts and modifications of lignosulfonic acids and
 Polymeric materials (PS type)
 Reduces water demand 7-10%
 Example: PolyHeed 997 -BASF, FLOCRETE N-Don
chemicals

82. Air-entraining admixtures
 Which causes air to be incorporated in the
form of minute bubbles in the concrete or
mortar during mixing, usually to increase
workability and resistance to freezing and
thawing and disruptive action of de-icing salts
 Reduces bleeding and segregation of fresh
concrete
 Can be categorized into four groups:
 salts of wood resins
 synthetic detergents
 salts of petroleum acids,
 fatty and resinous acids and their salts
 MB-AE 90-BASF, Airalon® 3000-Grace

83. Super-plasticizing admixtures
 Which imparts very high workability or allows a
large decrease in water content for a given
workability
 Reduce water content by 12 to 30 percent
 The effect of superplasticizers lasts only 30 to
60 minutes and is followed by a rapid loss in
workability
 Superplasticizers are usually added to
concrete at the jobsite
 Example : Glenium-BASF, Supaflo-Don
Chemicals

84. Production of Concrete:
 Material
 Activity related to material are there selection and
Proportions
 Process
 Mixing
 Transportation
 Placement
 Compaction
 Curing

85. Proportioning of concrete
 Nominal Mix
The Nominal mixes of grades M10, M15, M20
and M25 correspond approximately to the mix
proportions (1:3:6), (1:2:4), (1:1.5:3) and (1:1:2)
respectively.
 Design Mix

86. Q? Why we are proportioning
Concrete
 The goal is to provide the desired strength and
workability at minimum expense.

96. Curing methods
1. Water curing 2. Steam curing 3. Curing
compounds
Water curing
 Sea water shall not be used for curing
 Seawater shall not come into contact with
concrete members unless it has attained
adequate strength
 Exposed surface of concrete shall be kept
continuously in a damp or wet condition by
ponding or by covering with a layer of sacks,
canvas, Hessian or similar materials and shall be
kept constantly wet for a period of not less than
14 days from the date of placing of concrete.
Curing