Concrete

Concrete
• Cement & its Constituents
• Types of Cement
• Concrete Constituents
• Grades of Concrete
• Normal & High Density Concrete
• Concrete Mix
• Temperature Controlled Concrete
• Batching Plant
• Self Compacting Concrete
1

Concrete
• Concrete is the most widely used man-made
construction material due to the fact that from the
common ingredients, namely, cement, aggregate and
water (and sometimes admixture), it is possible to tailor
the properties of concrete so as to meet the demands of
any particular situation.
2

Concrete
• Concrete and steel are most commonly used structural
materials.
• Steel is manufactured under carefully controlled
conditions and properties are well defined and designers
need to specify only relevant standard.
• On the contrary Concrete is totally different. To some
extent quality of cement is guaranteed by manufacturer
in a manner similar to steel.
• The quality of concrete depends on workmanship of
making & placing of concrete and properties &
proportioning of ingredients other than cement, if a
suitable cement is chosen . 3

Concrete Ingredients
• Chief constitutes of concrete are cement, fine aggregate,
coarse aggregate, and water.
• A fourth ingredient called ‘admixture’ is used to modify
certain specific properties of the concrete mix in fresh
and hardened states.
4

Cement
• Cement is the most important constituent of concrete.
• Made out of naturally occurring raw materials and
sometimes blended or interground with industrial wastes,
cements come in various types and chemical
compositions.
• It is a bonding material used with aggregates, sand,
bricks etc for constructional purpose. The cements used
in the concrete have property of setting and hardening
under water by virtue of chemical reaction called
hydration.
5

Cement
• Among the various types, ordinary Portland cement is
perhaps the most common.
• Ordinary Portland cement is obtained by intimately
mixing together a calcareous material such as limestone
or chalk, and an argillaceous material (that is, silica,
alumina and iron oxide bearing material), for example,
clay or shale, burning them at a temperature of 1400 to
1450 deg.C and grinding the resulting clinker with
gypsum.
• Since the raw materials consist mainly of lime, silica,
alumina and iron oxide, these form the major elements in
cement also. 6

Cement
Cement constituents
• The typical ranges of these elements in ordinary
Portland cement may be expressed as below:
• Lime (CaO) 60 to 67 %
• Silica (SiO2) 17 to 25 %
• Alumina (Al2O3) 3 to 8 %
• Iron oxide (Fe2O3) 0.5 to 6 %
• MgO, Alkalies, SO3 etc. 1 to 8 %
7

Cement
Major compounds of cement
Tricalcium Silicate C3S } Major Strength
Dicalcium Silicate C2S } at a later date.
Tricalcium Aluminate C3A ] Immediate setting
Tetracalcium Aluminoferrite C4AF ] At initial stages.
8

Types of Cement
The cement shall be any of the following and the type
selected should be appropriate for the intended use:
• 33 / 43 / 53 Grade ordinary Portland cement
• Rapid hardening Portland cement
– Higher C3S – Fine grinding up to 325 M2/Kg – Higher rate of
heat development – Not recommended for mass concrete - 3
days strength is equal to 7 days of OPC.
• Extra Rapid Hardening Portland Cement :
– CaCl2 is added (not more than 2%) – Not recommended for RCC
works in order to avoid corrosion.
9

Types of Cement
• Portland slag cement
• Portland pozzolana cement (fly ash based)
• Portland pozzolana cement (calcined clay based)
• Hydrophobic cement
• Low heat Portland cement
– Low C3S & C3A – 60 Cal/gram of cement in 7 days & 70
Cal/gram in 28 days – Slower development of strength but
ultimate strength is same as OPC.
10

Types of Cement
Ground Granulated Blast Furnace Slag
– Waste product in the production of Pig Iron, a mixture of lime,
silica & alumina.
Ultra High Early Strength Cement.
– Fineness is 700 to 900 M2/Kg - 1 days strength is equal to 7
days of OPC.
Sulphate Resistance Cement.
– Due to sulphate attack, there will be disintegration of cement due
to increase in volume as C3A reacts with Sulphate and forms
calcium Sulpho aluminate – Hence Low C3A
11

Types of Cement
White Cement
– Using very little MgO & Fe2O3 – Used for architectural works like
marble flooring, plastering etc.
High Alumina Cement
– 40% each of Alumina and Lime are mixed – 80% strength in 24
hours – setting is slow – initial setting 4 –5 hours and final set
after another half an hour – High rate of heat development i.e., 9
cal/g/hour in comparison with RHPC which is only 3.5 cal/g/hour
– Used as refractory materials – can withstand upto 18000C.
12

Cement
Setting of Cement
• Stiffening – Fluid state to rigid state.
• Initial Setting Time – Not less than 30 minutes
• Final Setting Time - Not more than 600 minutes.
Hardening of Cement
• Gain of strength of set cement paste.
Fineness of Cement
• Measured in specific area M2/Kg. Finer the cement ,
rapid is the hydration of cement.
13

Cement
Heat of Hydration
• Hydration of cement is Exothermic and around 120
cal/gm of cement is being liberated.
Soundness
• Measure of change in volume of cement i.e., to know the
quantity of unburnt/free lime .
Strength of Cement :
• It is measured using 1:3 cement – sand mortar on
70X70mm cubes with a water – cement ratio of 0.40.
• Depending on the strength of cement cubes at 28 days,
OPC is categorized as OPC 33, 43 and 53 grade i.e.,
compressive strength being 33 N/mm2, 43 N/mm2 and 53
N/mm2 respectively.
14

Aggregates
• Aggregates (fine as well coarse aggregates) occupy
nearly 70 to 75 per cent volume of concrete are inert
ingredients in more than one sense.
• However, it is now well recognized that physical,
chemical and thermal properties of aggregates
substantially influence the properties and performance of
concrete.
• Proper selection and use of aggregates are important
considerations, both economically as well as technically.
• Aggregates are generally cheaper than cement and
imparting greater volume stability and durability to
concrete. 15

CLASSIFICATION OF
AGGREGATES
• General classification of aggregates can be on the basis
of their sizes, geological origin, soundness in particular
environments, unit weight or on many other similar
considerations.
• Fine aggregates are those most of which pass through
4.75 mm IS sieve.
• Aggregates, retained on 4.75 mm IS sieve are termed as
‘coarse’ aggregates.
16

Size of Aggregates
• The nominal maximum size of coarse aggregate should
be as large as possible within the limits specified but 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 corners of the form.
• For most work, 20 mm aggregate is suitable. Where
there is no restriction to the flow of concrete into
sections, 40 mm or larger size may be permitted.
• In concrete elements with thin sections, closely spaced
reinforcement or small cover, consideration should be
given to the use of 10 mm nominal maximum size.
17

Grading of Aggregates
• The grading of aggregate should be controlled by
obtaining the coarse aggregate in different sizes and
blending them in the right proportions.
• The grading of coarse and fine aggregate should be
checked as frequently as possible, the frequency for a
given job being determined by the engineer-in-charge to
ensure that the specified grading is maintained.
18

Aggregates
Bonding of Aggregate :
• Bond between cement paste and aggregate is mainly due to
interlocking of the aggregate and cement paste owing to the
roughness of the surface of the aggregates. Crushed particles give
better bonding.
Strength of aggregate :
• The strength of the aggregate is obtained indirectly either from
crushing strength of prepared rock samples, crushing value of bulk
aggregates or from performance of aggregates in concrete. Good
average crushing strength of aggregate is around 200 MPa.
Specific Gravity :
• The range of specific gravity for natural aggregates is between 2.6
to 2.7. This is mainly used in the calculations of quantities in design
mix of concrete.
19

Aggregates
Porosity and Adsorption of Aggregate :
• The porosity of aggregate influences the bond between
aggregates and cement paste. Saturated condition and
surface dry is said, when all pores in the aggregates are
full. Bone dry is called when no moisture content is
present when dried in an oven. Air dry is called when
aggregates are dried in natural air wherein some of the
moisture is evaporated. Water adsorption of aggregates
is percentage increase in weight of bone dry aggregates
when immersed in water for 24 hours.
20

Aggregates
Moisture Content
• Surface or free moisture present in the aggregates
specially fine aggregates expressed as percentage on
the weight of the saturated and surface dry aggregate is
called as moisture content and this needs to be adjusted
while batching the materials for concrete. In the case of
sand at a particular range of moisture content, there will
be increase in volume due to the water film and is called
bulking of sand. This is to be considered while doing
volume batching. It is observed that around 5-8%
moisture content increases the volume by 20 to 30%.
21

Aggregates
Soundness of Aggregate :
• Ability of aggregate to resist excessive changes in
volume as a result of changes in physical conditions like
alternate wetting & drying, freezing & thawing, thermal
changes etc. If aggregates change in volume in these
conditions, then considered as unsound resulting in
deterioration of concrete.
22

Aggregates
Alkali-Aggregate Reaction :
• It is deleterious chemical reaction between surrounding
cement paste and aggregate. Active silica in aggregate
and alkali in cement paste react and results in a gel of
unlimited swelling type. This results increase in volume
and internal pressures will cause expansion, cracking
and disruption of cement paste. Most harmful to the
concrete. Mortar-bar test is conducted to determine
whether this reaction is exists in aggregates or not.
Crushed aggregates and cement with minimum 0.6%
alkali content bars are prepared and if expansion is more
than 0.05% after 3 months or 0.1% after 6 months, then
the aggregate under test is harmful.
23

Aggregates
Fineness Modulus :
• Fineness modulus is sum of cumulative percentage
retained on sieves of standard 150, 300, 600, 1.18, 2.36
and 4.75 mm. More the fineness modulus, more coarser
the aggregate.
• Other properties of aggregates like Flakiness Index (max
20%), Elongation Index (max. 20%), Impact Value (max.
45%), Abrasive value (max. 50% & 30% for road work),
Soundness (max. 12% with sodium sulphate & 18% with
Magnesium Sulphate) etc., are also important for
concrete.
24

Water
• Water used for mixing and curing shall be clean and free
from injurious amounts of oils, acids, alkalis, salts, sugar,
organic materials or other substances that may be
deleterious to concrete or steel.
• Only potable water is required to be used for mixing of
concrete.
25

Mineral Admixtures
• Pozzolanic materials conforming to relevant Indian
Standards may be used with the permission of the
engineer-in-charge, provided uniform blending with
cement is ensured.
• Fly ash conforming to IS may be used as part
replacement of ordinary Portland cement provided
uniform blending with cement is ensured.
26

Mineral Admixtures
• Silica fume conforming to IS standard approved by the
deciding authority may be used as part replacement of
cement provided uniform blending with the cement is
ensured.
• Rice husk ash giving required performance and
uniformity characteristics may be used with the approval
of the deciding authority.
27

Admixtures
• Present day concrete often incorporates a fourth
ingredient called admixture, in addition to cement,
aggregates and water.
• Admixtures are added to the concrete mix immediately
before or during mixing, to modify one or more of the
specific properties of concrete in the fresh or hardened
states.
• These are used mainly to improve the workability of
concrete and thereby reduce the water demand for a
given workability.
28

Admixtures
• The different types of admixtures are:
• Accelerating admixtures
• Retarding admixtures,
• Water-reducing admixtures, and
• Air-entraining admixture
29

Admixtures
• ACCELERATING ADMIXTURES – These are
substances which when added to concrete increase the
rate of hydration of cement, shorten the setting time and
increase the rate of strength development.
• RETARDING ADMIXTGURES – A delay in the setting of
concrete is achieved by the use of retarding admixtures.
Regarding admixtures are used in hot weather when
normal setting time of cement gets reduced due to high
temperature,mainly to avoid cold joints
30

Admixtures
• WATER REDUCING ADMIXTURES – These admixtures
increase the setting time by about 2 to 6 hours during
which concrete can be vibrated, revibrated and finished.
This is particularly important in hot weather conditions or
where the nature of construction demands a time gap
between the placing of successive layers of concrete.
Used for improving strength of concrete with desired
workability.
• AIR-ENTRAINING ADMIXTURES- These admixtures
cause air to be incorporated in the form of minute
bubbles in the concrete during mixing, usually to
increase workability and resistance to freezing and
thawing. They control the amount of air in fresh concrete
and disperse properly sized air bubbles through the
concrete. 31

Superplasticizers
• High range water-reducers - Mainly used for higher
strength at lower water-cement ratios with proper
workability of concrete. Mainly used for High
Performance Concrete, Heavily reinforced and also
requiring pumping of concrete.
32

Classification of Concrete
• Concrete can be classified by its
• Density (light weight, normal weight or heavy weight
concrete)
• Workability (flowing or pumpable concretes)
• Durability in specific environments (sulphate-resisting
concrete or its resistance to fire).
• Grade of Concrete
33

Grades of Concrete
• Among the many properties of concrete, its compressive
strength is considered to be the most important and has
been held as an index of its overall quality.
• Many other Engineering properties of concrete appear to
be generally related to its compressive strength.
• Concrete is, therefore, mostly graded according to its
compressive strength.
34

Grades of Concrete
• Different grades of concrete viz., M20, M30, etc. ‘M’
stands for mix and number 20 or 30 etc., stands for
characteristic compressive strength of concrete cubes of
size 150mm taken after 28 days of casting the cubes in
N/Sqmm.
• It is 95% probability that results will not fall below these
specified values.
• The tensile strength of concrete is very low and concrete
is never designed to resist any direct tension.
35

Heavy Concrete
• High density concrete
• Used for radiation shielding
• Called as biological shield
• Slows down gamma rays
• Concrete density – 3200 kg/cum to 4500
kg/cum
• Obtained by using haematite, magnetite
ore etc.
36

Reinforced Cement Concrete
• Plain cement concrete is mainly used as a sub base to
foundations, bed blocks, sub base to floors, etc.,
• As concrete is very weak in tension, Reinforcement
mostly in the form of steel bars is used to with stand
tension in the structural members and the concrete is
called as Reinforced Cement Concrete.
• The mild steel or tor steel has got good bonding with
concrete
• The coefficient of thermal expansion of both concrete
and steel are almost equal and hence behave as a
homogeneous material.
37

Workability
• From the stage of mixing till it is transported, placed in
the formwork and compacted, fresh concrete should
satisfy a number of requirements which may be
summarized as follows:
– The mix should be stable, in that it should not segregate during
transportation and placing. The tendency of bleeding should be
minimized.
– The mix should be cohesive and mobile enough to be placed in
the form around the reinforcement and should be able to cast
into the required shape.
• The ease with which the concrete can be mixed,
transported, placed, compacted and finished is termed
as workability.
38

Compaction
• Compaction is very important from the strength &
durability point of view of the concrete.
• The compaction is required to eliminate the entrapped
air from fresh concrete until as close as a configuration
as possible for a given concrete mix is achieved. Water
content is the major factor affecting the workability.
• The workability is measured either by Slump cone test or
Compaction Factor test or Flow test or Vebe Test etc.
39

Water – Cement Ratio
• Strength of concrete is most valuable property of the
concrete and it depends on water/cement ratio in
addition to degree of compaction.
• Compressive strength of the concrete is inversely
proportional to the water/cement ratio.
• Lesser the water content, more is the strength of the
concrete but workability decreases.
• Hence optimum amount of water needs to be added
using number of trail mixes.
40

Water – Cement Ratio
• It is important to maintain the water-cement ratio
constant at its correct value.
• To this end, determination of moisture contents in both
fine and coarse aggregates shall be made as frequently
as possible, the frequency for a given job being
determined by the engineer-in-charge according to
weather conditions.
• The amount of the added water shall be adjusted to
compensate for any observed variations in the moisture
contents.
41

Segregation
• Segregation i.e., separation of constituents of concrete
mix so that their distribution is not uniform. Depending on
the water content more or less, cement paste segregates
from the mix and coarser particles segregates from finer
particles.
42

Bleeding
• Bleeding is a form of segregation in which some of water
in the mix tends to the surface of freshly laid concrete.
• This is manly due to inability of solids of the mix to hold
mixing water.
• Bleeding concrete should not be superimposed by
another concrete as porous, weak, and non-durable
concrete results.
• One must wait for the water to get evaporated before
finishing is started.
• On the other hand, if evaporation of water is faster than
bleeding rate plastic shrinkage cracks occur.
43

Curing
• Curing is the procedure used for promoting the hydration
of cement, and consists of a control of temperature and
of the moisture movement from and into the concrete.
• This is a must in the earlier stages of hardening.
• Water loss by evaporation must be prevented.
• Concrete looses strength to almost half, if not cured
when compared with 14 days moist cured strength.
44

Concrete Mix
• By judicious use of available materials for concrete
making and their proportioning, concrete mixes are
produced to have the desired properties in the fresh and
hardened states, as the situation demands.
• The mix should be amenable to proper and thorough
compaction as possible in the situation of placing and
with the facilities of compaction.
• It should be possible to obtain a satisfactory surface
finish.
• Concrete has to have satisfactory properties both in the
fresh and hardened states.
45

Concrete Mixing
• Concrete shall be mixed in a mechanical mixer
• The mixing shall be continued until there is a uniform
distribution of the materials and the mass is uniform in
colour and consistency.
• For guidance, the mixing time shall be at least 2 min.
For other types of more efficient mixers, manufacturers
recommendations shall be followed.
46

CONCRETE MIX
PROPORTIONING
• The mix proportions shall be selected to ensure the
workability of the fresh concrete and when concrete is
hardened, it shall have the required strength, durability
and surface finish.
• The determination of the proportions of cement,
aggregates and water to attain the require strength be
made as follows:
• By designing the concrete mix; such concrete shall be
called ‘Design mix concrete’, or
• By adopting nominal concrete mix; such concrete shall
be called ‘Nominal mix concrete’.
47

CONCRETE MIX
PROPORTIONING
• Design mix concrete is preferred to nominal mix. If
design mix concrete cannot be used for any reason on
the work for grades of M 20 or lower, nominal mixes may
be used with the permission of engineer-in-charge,
which, however, is likely to involve a higher cement
content.
48

CONCRETE MIX
PROPORTIONING
• The proportioning of concrete mixes is accomplished by
the use of certain relationships established from
experimental data, which afford reasonably accurate
guide to select the best combination of ingredients so as
to achieve the desirable properties. The following basic
assumptions are made in design of plastic concrete
mixes of medium strength:
• The compressive strength of concrete is governed by its
water- cement ratio, and
• For a given aggregate characteristics, the workability of
concrete is governed by its water content.
49

CONCRETE MIX
PROPORTIONING
• For high strength concrete mixes of low workability,
considerable interaction occurs between these two
criteria and validity of such assumptions may become
limited. Moreover, there are various other factors which
affect the properties of concrete, for example, the quality
and quantity of cement, water and aggregates;
procedures of batching, mixing, placing, compaction and
curing, etc.
• Therefore, the specific relationships that are used in
proportioning concrete mixes should be considered only
as a basis for trial mixes. Further modifications are
necessary at the site based on the situation as well as
specific materials available.
50

Factors in the Choice of Mix
Design
Design of concrete mix be based on the following factors:
• Grade designation,
• Type of cement,
• Maximum nominal size of aggregates,
• Minimum water-cement ratio,
• Workability, and
• Minimum cement content.
51

Design Mix Concrete
• Concrete mix design is mainly based on the concept that
voids in the coarse aggregates are filled with fine
aggregates and voids in fine aggregates are filled with
cement particles thereby forming a cohesive concrete
mix.
• The target strength for design mix is selected based on
the required standard deviation/degree of control and
water-cement ratio is selected for this desired strength.
• Mixing water based on the required slump & maximum
size of aggregate is selected. Based on these
parameters, cement content is calculated.
52

Design Mix Concrete
• Water content is adjusted based on moisture content in
aggregate.
• Trial mixes are made and checked for slump &
cohesiveness. Cubes of size 150mm are cast and
strength at 7 and 28 days are determined and checked
with target strength. In 7 days, the strength will be
between 65 to 75% to that of 28 days.
• Design mix concrete is required to be used for all
Reinforced cement concrete works.
53

Design Mix Concrete
• Concrete mix design for required workability, strength
and durability is to be carried out as per the relevant
standards.
• All the ingredients of the concrete must be prequalified
as per the Q.A plans and standards.
54

Design Mix Concrete
• The concrete mix design shall be supported with
minimum 30 numbers of trial mix results and statistical
analysis for the required concrete strength.
• Minimum cement content and maximum water content
ratio from the durability considerations shall be
specifically recommended in the mix design based on
relevant Indian Standards.
• The approved concrete mix design shall be verified in
case of any change of ingredients either in source/type.
55

Batching
• To avoid confusion and error in batching, consideration
should be given to using the smallest practical number of
different concrete mixes on any sites or in any one plant.
In batching concrete, the quantity of both cement and
aggregate shall be determined by mass; admixture may
however be measured in volume or mass; water shall be
weighed or measured by volume in a calibrated tank
• Ready-mixed concrete supplied by ready-mixed concrete
plant shall be preferred.
56

Batching
• Proportion/ type and grading of aggregates shall be
made by trial in such a way so as to obtain densest
possible concrete. All ingredients of the concrete should
be used by mass only.
• Volume batching may be allowed only where weigh-
batching is not practical and provided accurate bulk
densities of materials to be actually used in concrete
have earlier been established.
57

Temp. Controlled Concrete
• To reduce temperature stresses
• 190c, 230c, 250c etc.
• Obtained by replacing water with cool
water / ice flakes
• Must for mass concrete
• Based on the thickness of concrete
section, type of cement, volume of
concrete temp. is arrived at.
58

250 TPH
Capacity
Aggregate Crushing Plant
59

Self-Consolidating /
Compacting Concrete

Topics Covered
• Brief Introduction to SCC
• Limitations
• Research Effort
• Opportunities and Challenges

Traditional Concrete
Construction
• Vibration necessary
• Labor intensive
• Skill dependent
• Quality varies

Self-Compacting/Consolidating
Concrete
• No vibration needed
• Less noise
• Better working
environment
• Faster construction
• Improved quality
and durability

Motivations
– Decreasing Skill Labor
– Quality without Vibration
– Durable Structures
– Reduce Repair

Further developed SCC
– Non-vibrated Concrete
– Super Quality Concrete
– Super Workable Concrete
– Neuro-Crete

SCC Demonstration
• Filling ability
• Passing ability
Double click on picture to show video.

Experiment with Free Fall
• Test for
resistance
to segregation

Three Key Characteristics of
SCC
• Ability to flow into forms
• Ability to pass through reinforcement
• Resistance to segregation

SCC Prestressed Girders
Used in Japan

Applications of SCC
• Cast time reduced by 35–40%
• Labor reduced by 50%
• No repair for defects

Sodra Lanken Project
(US$800 million)
Reasons for SCC:
• Heavy reinforcement
• Uneven rock surfaces
• Manual vibration not feasible

SCC Deck Pour

Precast SCC Railing
In Spokane, WA

Excellent Surface Finish
SCC in Walls
Labor reduced from 6 to 2
Placement time reduced
from 2 hours to 1 hour
No voids to repair.

I-4 Pedestrian Overpass
Heathrow, Florida

In Search of Standard Tests
• Slump flow test
• J-Ring
• L-box test
• Others

Slump Flow Test
J-Ring
Column Segregation

Concrete

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