Concrete Properties Guide

Unit1
Properties of Concrete
Fresh concrete
Workability
Flowability
Consistency
Segregation
Bleeding
Setting time
Air entrain
Hard concrete
 Compressive Strength
 Tensile & flexural
 Shrinkage & creep
deformations
 Permiability &
durability
 Stress-strain
 Response to
temperature variations

1.Workablity
As per IS 6461-1973(Part-7) workability of fresh
concrete is defined as the ease & homogeneity
with which concrete can be mixed, transported,
placed in form work, compacted & finished.
The workability is associated with the following four
concepts:
1.Ease of flow (internal friction)
2.Prevention of segregation
3.Prevention of harshness
4.Prevention of bleeding
Workable concrete have a uniform colour, the
aggregates will be lubricated with sufficient paste, so
that it can be easily poured into formwork.
2

Workability Vs Consistency
Consistency:Amount of work required to be done in
order to compact the concrete
Stiff Normal Flowing
Vee Bee Comp.Factor & slump Slump-flow
Workability is ease and homogeneity with which
concrete can work in different part.
3
Rheometer is instrument to use to measure viscosity
& yield stress of concrete, which includes all above.

Factors Affecting Workability
1. W/C ratio-Amount of water content
2. Size & shape of aggregate
3. Grading & surface texture of aggregate
4. Quantity and characteristics of cementing
materials
5. Quantity and characteristics of admixtures
6. Amount of entrained air
7. Mix proportion & ambient air temperature
8. Method and duration of transportation

1. W/C ratio-Amount of water content-higher water
content per cubic meter higher is the workability.
lower water content means low slump. Hence water
should be optimum for required slump.
2. Size & shape of aggregate-
 Bigger size aggregate –less surface area-less
water for wetting aggregate-less paste require-reduce
friction gives more workability.
 More fine aggregate-more surface area-more
paste and water demand.
 rounded aggregate –less surface area-less void-
required less paste-more workability.
 Angular, elongated results less void ratio-more
paste-less workability-harsh concrete.

3.Grading of aggregate & Surface texture - Rough
surface texture-more surface area-more friction-
less workability. Smooth surface particle-less
internal friction-high workability.
Well graded aggregate concrete gives less void
ratio for given volume due to which more paste
available-mix is cohesive and prevent
segregation-less internal friction-high workability
4.Quantity & use of admixture- plasticizers & super
plasticizers improves workability at low water
content. pozzolana, air entraining agents
improve workability. Dose of admixture depends
on type of cement, temp. and site conditions.

Rounded particles –
better workability
Angular particles –
poor workability

5.Air entrained concrete-more workability
6.Temperature & environmental condition-
Hot weather-more evaporation-reduce water
content-low workability.
Cold weather-Low temperature -frozen water
reduces workability.
7.Transportation-Workability-slump-reduces as
time increases. plasticizers control workability
8.Mix proportion-higher aggregate-cement ratio
leaner is the concrete-in lean mix less paste
quantity available for lubrication.
Lower aggregate-cement ratio-rich cohesive
mix-more quantity of paste available-better
workability

Workability test on fresh concrete-
Slump cone test
Compaction factor test
Vee-bee test
Flow table test
10

10
cm
20
cm
30
cm
The slump cone is filled in 3 layers. Every
layer is evenly rodded tamping rod of
16mm dia & 60 cm length about 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.
1.Slump cone test

Slump cone test-if the frustum just settle down
called true slump
12

Slump cone test-most common test on site
13

Amount of Mixing Water
Relationship between slump and water content
is non-linear

% Loss of Slump
Slump decreases with time
•Hydration
•Evaporation
•Rate increases with
increase in
ambient
Temp.

2.Compacting factor apparatus-slump cone
test will not give good results in case of stiff or harsh
concrete then this test suit.
Wt. of partially compacted concrete
Compaction factor=
Wt. of fully compacted concrete
16
Compaction factor test not suitable for
low workability (compacted by
vibrations)concrete or low slump
concrete. As per IS compaction factor for
low slump concrete should be between-
0.75 to 0.8

Degree of
workability
Slump in
mm
Compaction
factor
Placing conditions
Very low 0-25 0.78 Blinding concrete, shallow
sections, pavement pavers-
vibrated by power machines
Low 25-50 0.85 Mass concrete, light
reinforcement section, slab,
beam, canal lining, strip
footings
Medium 50-100 0.92 Manually compacted flat slab,
normal RCC & heavily
reinforced sections with
vibrations
High 100-150 0.96 Congested reinforcement,
pumped concree, tremie
placing, Trench filling, in situ
piling

•This lab test is a extension of slump cone test
•Perform slump test in cylinder first.
•Turn glass plate, start vibrator and stop watch.
•Record the time required when concrete has fully acquired
cylindrical shape.
•That time is known as vee-bee degree. Method is suitable for
low slump (stiff)concrete.
3.Vee-Bee consistometer Test

19
Degree of workability w.r.t. Vee-Bee
Seconds
S.NO. Time in seconds Degree of
workability
1.
2.
3.
4.
5.
20-40
10-20
7-10
3-7
1-3
Very low
Low
Medium
High
Very High

4.Workability by flow table
20
•Method is suitable for high slump concrete(Self Compacting
Concrete).
•Cone size-17,25cm dia & 12cm ht.

Segregation can be defined as the
separation of the constituent material of fresh
concrete, resulting in a non-uniform mix.
Sp.Gr. Size
Cement 3-3.15 5-90 m
C.Agg. 2.4-2.8 4.75-40 mm
F.Agg. 2.4-2.8 <4.75 mm
SEGREGATION
 The primary causes of
segregation are differences
in specific gravity and size of
constituents of concrete.
Moreover, improper mixing,
improper placing and
improper consolidation also
lead to segregation.

Segregation occurs in 3 forms-
1.The coarse aggregate settles down in the matrix
2.The matrix paste separates from the coarse
aggregate
3.Water (slurry)separates out from other
ingredients.
SEGREGATION

Causes of Segregation:
1. Wrong proportion or bad proportion mix-
insufficient paste available
2. Insufficient mixing with excess water
3. Dropping of concrete more than 1m,in case of
columns
4. Badly designed mixer and continuous
vibrations for long time.
5. Transportation by conveyor belt, wheel borrow
at long distance
6. Discharge of concrete at dense reinforcements
SEGREGATION

Factors affecting segregation:
1. Larger maximum particle size (25mm)
and proportion of the larger particles.
2. High specific gravity of coarse
aggregate.
3. Decrease in the amount of fine
particles.
4. Particle shape and texture.
5. Water/cement ratio.
SEGREGATION

 Bleeding is the form of segregation in which water
comes up to the top of concrete or tendency of water
to rise to the surface of freshly placed concrete.
 It is also called as water gain , form of segregation
Bleedıng

27
Causes of bleeding.
(i) presence of excess water.
(ii) Deficiency of fine aggregate.
(iii) Too much finishing.
Bleedıng
Prevention of bleeding.
bleeding can be prevented by:
1. Controlling the water- content ratio
2. Proper proportioning and uniform mixing.
3. Providing finer grading of fine aggregates.
4. Using finely ground cement.
5. Controlling compaction.
6. The air-entraining agents should be used to prevent
bleeding.
Bleeding is not harmful when rate of evaporation is high.

The tendency of concrete to bleeding
depends largely on properties of
cement.
It is decreased by:
 Increasing the rate of hydration (C3S,
C3A and alkalies)
 Adding pozzolans
 Reducing water content
 Proper uniform mixing
Bleedıng

Properties of Hardened Concrete
Compressive Strength
Tensile & flexural
Shrinkage & creep deformations
Permiability & durability
Stress-strain
Response to temperature variations
29

Following are important factors which affect strength:
1. Water -cement ratio, Abram’s law
2. Gel -space ratio
3. Aggregate cement ratio
4. Aggregate size, grading
5. Age of concrete
6. Degree of hydration & consolidation, Temperature
7. Specimen parameters ; loading parameters
Factors affecting strength of Concrete

Factors Affecting Strength of Concrete:
Water -cement ratio, Abram’s law
1. W/C is defined as ratio of weight of water added
at the time of mixing to the weight of concrete
mix.
2. W/C ratio affect strength of concrete directly.
3. Strength of concrete depends upon strength of
paste. strength of paste increases with increase
in cement & decreases with water & air contents.

Water -cement ratio, Abram’s law
 But by proper compaction of
concrete pores can be
reduced & strength can be
improves.
 It can be seen that lower
w/c ratio could be used
when concrete is vibrated to
achieve high strength,
comparatively higher w/c
ratio required when
concrete is hand
compacted.
 The graph shows hyperbolic
shape which is difficult to
interpolate.

Gel-space ratio
The strength of concrete at any w/c ratio depends upon
hydration of cement & air content in case of air entrain
concrete. Therefore instead of relating w/c ratio, the strength
can be related to the solid product of hydration of cement &
space available to form these product-Gel Space Ratio.
It is better approach as it take into account-
1.Degree of hydration
2.Chemical & physical properties of cement
3.Temperature at which hydration takes place.
4.Air entrain in case of air entrain concrete
5.Effect of w/c ratio
33

Gel-space ratio
As water/cement ratio increases- gel / space ratio decreases
●
As gel/space ratio decreases concrete porosity increases
●
As concrete porosity increases its strength decreases.
●
If we focus on gel/space ratio and it increases -concrete
porosity decreases and concrete gives better strength.
●
Strength obtained by W/C ratio is depend on age whereas
strength obtained by Gel- space ratio is independent of age.
34

Gel-space ratio
Gel- space ratio is the ratio of the volume of hydrated cement
paste to the sum of volumes of the hydrated cement paste and
the capillary pores.
Volume of gel
Gel space ratio=-------------------------------
Space available (vol. of hydrated cement gel+vol. of
capillary pores)
35

Gel-space ratio Powers & Brownyard
established relationship
between strength & gel-
space ratio.
Power experiment found the
relationship 240 x³ where x
is the gel-space ratio & 240 is
the inherent strength of the
gel in Mpa.
Gel-space ratio can be
calculate at any age & any
fraction of hydration of
cement. As gel space ratio
increases strength increases.
36

Aggregate-cement ratio
Aggregate cement ratio is a secondary factor which
affect strength.
A large amount/quantity of aggregate absorb more
quantity of water & reduce w/c ratio. Thus it affects the
strength indirectly.
For economy consideration ,aggregate-cement ratio
should be high but as higher the aggregate-cement
ratio will reduces strength.
37

Size of Aggregates
Larger the size of aggregate
lesser the surface area available
for development of gel bonds
which is responsible for lower
strength of concrete.
Larger size aggregate causes
more heterogeneity in concrete
which will prevent uniform
distribution of load under
stressed.
Large size aggregate, due to
internal bleeding, resulting
weaker transition zone and
micro cracks are developed.
38
The influence of maximum
size of aggregate on
compressive strength of
concrete

Size of Aggregates
High strength concrete effected
by large size aggregates & use
of lower size aggregate give
high strength.
In lean mixes large size
aggregates give highest
strength.
39
Influence of maximum size of aggregate on
28 day compressive strength of concrete of
different richness

Age of concrete
Concrete develops strength with
age due to continued hydration.
Initially rate of gain of strength is
fast which reduces as time
increases.
As per IS456-2000 –there is
gain of strength beyond 28
days. The quantum of increase
depends upon grade, type of
cement, curing, environmental
conditions. The design based on
28 days strength.
40
Gain of strength with time Vs different W/C ratio

Age of concrete
Maturity of concrete/strength gain also depends on temperature.
Maturity= (time +temperature)
Ʃ
Hydration of concrete is continue up to -11°C.Hence it is datum temp.
Concrete cured at 18°C for 28days consider as fully maturated.
Plowman give the constants (A,B)to calculate maturity in eq.
Comp. strength=A+B log 10 (Maturity/1000) 41

42
Age of concrete
 Concrete develops strength due
to 4 Bouge compounds.C3S &
C2S plays major part.
 Fineness of particles plays also
role-
 5-7 micron- contribute in first 1-
2 days strength
 20-25 micron- contribute in first
7 days strength
 More than 30 micron- contribute
in first 28 days strength

Rise in temp. speed up rate of hydration
resulting strength in early ages.
But higher temp. during placing & setting
will effect poor physical structure, more
porous, less strength.
43
Temperature

Maturity concept
 Since the degree of cement hydration depends on
both time and temperature, the strength of concrete
may be evaluated from the concept of maturity,
which is expressed as a function of the time and
the temperature of curing.
 It is assumed that batches of the same concrete
mixtures of same maturity will attain the same
strength regardless of the time-temperature
combinations leading to that maturity.
 Maturity = ∑ (time x temperature)
44

Maturity concept
 Datum temperature for calculating maturity of concrete is -11ºC
 The rate of strength development at early ages is related to the
rate of hydration of cement.
 Heat generated from the hydration reaction will be recorded as a
temperature rise in the concrete.
 The main advantage of the maturity method is that it uses the
actual temperature profile of the concrete in the structure to
estimate its in-place strength.
 The maturity concept is governed by the underlying assumption
that concrete samples of a given mixture will have the same
strength when they have the same maturity index.
 For example, concrete cured at a temperature of 50°F (10°C) for 7
days may have the same maturity index as concrete cured at 80°F
(27°C) for 3 days and therefore would have similar strengths.
45

8) To increase resistance to chemical attack,
corrosion of steel
9) To reduce segregation and improve pump
ability, finish.
10) To increase bonding between steel & concrete
11) To produce colour concrete
12) To increase bonding between old & new
concrete
13) To reduced cost of concrete
47
Functions of Admixtures
In concrete

Classification of Admixtures
• Mineral Admixture-
A)Natural pozzolana-
Clay & shale
Opalinc cherts
Diatomaceous earth
Volcanic tuffs &
Pumicites
B)Artificial pozzolana-
Fly ash
Blast furnace slag
Silica Fumes
Rice husk ash
Metakaoline
surkhi
• Chemical Admixture
Plasticizers
Super plasticizers
Accelerators
Retarders
Air entraining agents
Grouting
Waterproofing agents
Corrosion resisting
Bonding agents
Colouring admixtures
48

Mineral Admixtures and Properties

Fly Ash: How it work in concrete?
50

Advantages of fly ash
1) To reduce heat of hydration & thus reduce thermal cracks &
improve soundness of concrete.
2) To improve workability & pump ability
3) It convert released lime from hydration of OPC into additional
cementations material-contribute strength improvement.
4) Due to reaction between fly ash & liberated lime improves
permeability (pore refinement)
5) To reduce requirement of cement for same strength & reduce cost
of concrete.
6) Concrete using fly ash is generally show reduced segregation and
bleeding

Silica Fume
Properties
1. It is also referred as “microsilica”. It is an artificial pozzolanic admixture.It
is a by-product during the manufacture of silicon or Ferro silicon alloy.
2. Spherical shape. Extremely fine ( particle size < 1 micron)
3. 100 times smaller than avg. cement particles.
4. Specific surface area 20000 m2/kg. Silica fume, is a highly active
pozzolan and has cement properties because of fine nature.
5. Water demand increase, workability reduce. Concrete with micro silica
causes produce more heat of hydration & initial plastic shrinkage.
6. Reduce bleeding & no segregation.
7. With silica fume concrete become resistant to corrosion, increase
in strength & durability, control permeability.
52

Plasticizers-(water reducers)
 Plasticizes is an admixtures used in concrete to improve
workability by reducing water content.
 They gives-
1. Better workability without increasing water
2. Which gives easy placement of concrete in poor locations
without vibrations.
3. True shutter finish for highly reinforced member.
4. Reduction in cement content
Typical water reducers reduce the water content by
approximately 5% to 15%.

Plasticizers-(water reducers)
54
Cement particles are deflocculated & dispersed.
When they deflocculated water trapped in flocs get released.

Super plasticizers :(High-Range Water
Reducers HRWR)
• These admixtures are added to concrete for
production of flowing, self levelling, self
compacting and for production of high strength,
high performance concrete.
• They reduce water content upto 30%
• Dosage -1 to 2% by weight of cement
• workable concrete that can be placed with little
or no vibration or compaction while still free of
excessive bleeding or segregation.

Retarding Admixtures
1. Retarder is an admixture that slows down the
chemical process of hydration(rate of hydration)
2. Concrete remain in plastic & workable for long time.
We can place it without structural discontinuities.
3. They use to overcome the accelerating effect of high
temperature ,high humidity on concrete in hot
weather. ex. grouting oil wells.
4. Retarders do not decrease the initial temperature of
concrete.
5. They delay initial setting by forming a thin coating on
the cement particles & slow down their reaction with
water .

Accelerating Admixtures
 They added to concrete to accelerate or increase
the rate of early strength development in concrete
and shorten the setting time-
1.For earlier removal of formwork
2.Reduce period of curing
3.Structure can be place in service in advance
4.Compensate retarding effect of low temperature
during cold weather concreting-add calcium
chloride.
5.In emergency repair work- highway, bridge
6.Plugging leakage

Air-Entraining Admixtures
Increased resistance to freezing and thawing.
Improvement in workability.
Reduction in strength.
Reduces the tendencies of segregation.
Reduces the bleeding and laitance.
 Decreases the permeability.
Increases the resistance to chemical attack.
Permits reduction in sand content.
Improves place ability, and early finishing.
Reduces the cement content, cost, and heat of hydration.
Reduces the unit weight.
Permits reduction in water content.
Reduces the modulus of elasticity.

Corrosion resistancing
• The chlorides can cause corrosion of steel
reinforcement in concrete.
• Ferrous oxide and ferric oxide form on the
surface of reinforcing steel in concrete.
• Ferrous oxide reacts with chlorides to form
complexes that move away from the steel to
form rust. The chloride ions continue to
attack the steel until the passivating oxide
layer is destroyed.

Shrinkage-Reducing
Admixtures
• Shrinkage cracks,
such as shown on this
bridge deck, can be
reduced with the use
of good concreting
practices and
shrinkage reducing
admixtures.

Coloring admixtures
(Pigments)
• Red and blue
pigments were
used to color this
floor

What is Green Concrete?
• A concrete that uses less energy in
its production & produces less
carbon dioxide than normal
concrete is green concrete.
• Green Concrete is taken to mean
environment-friendly concrete.
• Fly ash used for partial replacement
of cement called as green concrete.

• The main ingredient in concrete is cement and it
consists of Limestone (Calcium Carbonate
CaCO3).
• During manufacture of cement, its ingredients are
heated to about 800 - 1000C.
• During this process the Carbon Dioxide is driven
off.
• Approximately 1kg of cement releases about
900gms of Carbon Dioxide into the atmosphere.
• Therefore, green concrete came into existence to
reduce the emission of carbon dioxide.
What is Green Concrete?

Materials for Green Concrete
• Locally available: Construction materials,
components, and systems found locally or
regionally, saving energy and resources in
transportation to the project site.
• Salvaged, re-furnished, or re-
manufactured: Includes saving a material from
disposal and renovating, repairing, restoring, or
generally improving the appearance,
performance, quality, functionality, or value of a
product.
• Reusable or recyclable: Select materials that
can be easily dismantled and reused or recycled
at the end of their useful life.

Materials for Green concrete
• Fly ash
• Ground Granulated Blast-Furnace Slag (GGBS)
• Silica Fume (SF)
• Rice Husk Ash (RHA)
• Silpozz(made from RHA)
2. Use of Recycled Material
Concrete Debris
• Post –Consumer Glass
• Foundry Sand
• Cupolas Slag
• Wood Ash

How green concrete help in achieving the
sustainable construction
1. Increased dependence on recycled materials: Effective use of recycle
material ,industrial byproducts etc. can help in reducing the
dependence on virgin material.
2. Effective use of supplementary cementitious material: Partial
replacement of cement can be done by the byproducts of industrial
processes, such as fly ash and slag as the production of Portland of
cement is responsible for generation of CO2 and huge energy is
consumed.
3. Improved mechanical properties: Proper use of recycle material can
help in improving the mechanical properties.
4. Reuse of wash water: The recycling of wash water can be seen
practice by the most of the construction industry and required by law in
some countries.

IMP points in Mix Design
• Optimizes void space between
aggregates by optimizing particle
proportions and packing of materials.
This makes more effective use of the
cement binder. Less W/C and W/B ratios.
• Aggregates replace excess cement paste
to give improved stability, less shrinkage
and increase in strength & durability.
• Less cement also generates less heat of
hydration.

Example: Fly Ash concrete
• Fly ash is the by-product during the operation of coal
fired power plants. Its divided in coal ash & pond ash
• Fly ash particles are round and fine, act as ball bearing
in concrete mix provided lubricant effect. Which
improve concrete workability & pumping ability.
• By using 20% fly ash water demand reduces approx.
10% hence lower w/c ratio possible with high
workability.
• Replacement for cement, fly ash reduce the heat of
hydration.
• Increased durability & lower permeability.
• Fly ash reacts with available lime & alkali in concrete,
produces additional C-S-H gel
• It improves latter age strength of concrete
• Decrease in water content with production of additional

Advantages of Green concrete
• High use of industrial waste about 20% , Green
Concrete uses local and recycled materials in
concrete.
• Reduce CO2 emissions about 30%.
• Reduce energy consumption during
manufacturing process
• User-friendly, no environmental pollution during
production
• Optimized mix designs mean easier handling,
better consistency, workability and easier
finishing
• Low heat of hydration & reduction in shrinkage &
creep.
• Less maintenance & better compressive, flexural
strength than traditional concrete

Limitations
• Increase in reinforcement cost
consumption
• It has lesser split tension when it is
compared to the conventional types
of concrete.
• Durability study is essential, as green
concrete have comparatively less life
in aggressive environment

Concrete Properties Guide

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Concrete Properties Guide