CE-201
ENGINEERING MATERIALS
What is Concrete?
Concrete is a mixture of cement, sand, gravel
(or crushed stone), and water. Sometimes,
special chemicals (admixtures) are added to
improve its properties. When mixed, it is soft
and moldable but hardens over time to become
E-mail: faruquegm@yahoo.com
strong and durable.
Lt Col G M Faruque, Engrs
CE Dept, MIST
Concrete
Concrete is a heterogeneous system of solid, discrete,
gradiently sized, inorganic mineral aggregates, usually
plutonic or sedimentary-calcareous in origin, embedded in a
matrix compounded of synthesized polybasic alkaline and
alkaloidal silicates held in aqueous solution and coprecipitate dispersion with other amphoteric oxides, this
matrix being originally capable of progressive dissolution,
hydration, re-precipitation, gelation and solidification
through a continuous and co-existent series of crystalline,
amorphous, colloidal and cryptocrystalline states and
ultimately subject to thermo-allotriomorphic alteration, the
system when first conjoined being plastic during which stage
it is impressed to a predetermined form into which it finally
consolidates, thus providing a structure relatively
impermeable and with useful capacity to transmit tensile,
compressive, and shear stresses.
Most Common Building Material – Used for buildings, roads, bridges, and dams.
Stronger Than Steel (by Volume) – More concrete is used than steel worldwide (about 10 times more).
Massive Global Use – Around 33 billion metric tons of concrete are used yearly!
Concrete
 Most widely used construction material
 In many countries of the world, the ration of concrete
consumption to steel consumption exceeds 10 to 1.
 It is estimated that the present consumption of con crete
in the world is of the order of 33 billion metric tonnes every
year.
 Reasons of widely use:
 Possesses excellent resistance to water. The use of plain
concrete for dams, canal linings and pavements is now a
common sight almost everywhere in the world.
 The ease with which structural concrete elements can be
formed into a variety of shapes and sizes.
 Usually the cheapest and most readily available material on
job. Water-Resistant – Ideal for dams, canals, and pavements.
Easily Shaped – Can be poured into different molds to create various structures.
Affordable & Available – Found almost everywhere and is cost-effective.
Concrete is composed mainly of cement (commonly Portland
cement), aggregate, water, and chemical admixtures.
Portland Cement
Coarse Aggregate
Fine Aggregate
Chemical Admixtures
Definition of PCC
 A mixture of:
 Portland Cement
 Fine Aggregate
 Coarse Aggregate
 Water
 Air
 Cement and water
combine, changing from a
moist, plastic consistency
to a strong, durable rocklike construction material
by means of a chemical
reaction called “hydration”
When cement and water mix, a chemical reaction
called hydration takes place.
Concrete has many applications and is used to make pavements, pipe,
structures, foundations, roads, bridges/overpasses, walls and footings for
gates.
Ingredients of Concrete
 Cement
 Water
 Aggregates
 Fine Agg
 Coarse Agg
 Admixtures
 Concrete is a composite
material that consists of a
binding medium
embedded with fine
aggregate and coarse
aggregate
 Water
 Drinking water is the best
 Admixtures
 Basic needs first
 Then spices
 Admixtures are spices to
satisfy the local conditions
 Spices increase taste?
 Mix Ratio (vol. or wt.) ?
 C : FA : CA
 1: 2 : 4
 1 : 3 : 6 Means water weight is 50%
of cement weight.
 w/c ratio = 0.5 (wt.) ?
Concrete ; Strongest; used in buildings, roads,
 Agg/cement = ?
bridges (Made of cement, sand, gravel, and water).
Mortar ; Used for bricklaying and plastering (Made of  Concrete >> Mortar >>
cement, sand, and water; no coarse aggregate).
Grout ;A flowable mixture used to fill gaps (Made of
cement, sand, water, and sometimes admixtures).
Grout?
Types of Concrete

Types of Concrete
Based on compressive strength
 Low-strength concrete: less than 20 MPa (3000 psi)
 Moderate-strength concrete: 20 to 40 Mpa (3000 to 6000 psi)
 High-strength concrete: more than 40 MPa (6000 psi)
Ingredients
Cement
255
356
510
Water
178
178
178
Fine Agg
801
848
890
Coarse Agg
1169
1032
872
Cement Paste Proportion
Percent by mass
18
22.1
28.1
Percent by volume
26
29.3
34.3
Water/cement by mass
0.70
0.50
0.35
Strength, MPa
18
30
60
Terminologies for fresh Concrete
How easily concrete can be mixed, placed, and compacted.
 Workability
 Workability
 Consistence (Degree of
 Amount of useful
How wet or dry the concrete is.
wetness)
internal work necessary
 Factors
to produce full
 Water, agg, agg/cement
compaction
 Measurement of
 Workability is inverse
workability (e.g. Slump
test)
of energy required
 Energy/work is required
 Segregation
to overcome internal
 Opposite of Cohesion
friction between the
 Bleeding Water rises to the surface, individual particles
weakening concrete.
More workability = less effort needed to mix
 Or Water gain
and compact.
Strength ratio
10% reduction of
density leads to 50%
reduction of strength
Density ratio
Factor Affecting Workability of
Fresh Concrete
 Advise
 Pls read pp. 63-64 of
Concrete Technology
(by Neville and Brooks)
 Try to memorize with
understanding
 Effect of grading on
workability is best
described here
 Water content
 Aggregate
 Agg type
 Grading ***
 Agg/cement ratio
 Inverse relation
 Admixture
 Fineness of cement
 Factors are interacting.
 Why? How?
Effect of Grading of Aggregate
on Workability
 Four interacting factors
 Surface area,
 Agg/cement,
 Segregation potential,
 Amount of fines
 Surface Area
 Smaller particles need
more cement paste and
water
 But fine particle (less than
150 micron) act as
lubricant
Smaller particles have more surface area, needing
more cement paste and water to coat them.
 Agg/cement ratio
 Well graded agg and
cement paste exactly
necessary to coat the
particles  harsh and
unworkable mix
 Excess cement increase
workability
 Excess mortar improves
workability
Well-graded aggregates (balanced mix of sizes)
reduce cement demand. but may create a harsh,
unworkable mix.
Effect of Grading of Aggregate
on Workability
 Segregation Potential
 Well graded agg lead to a
dense concrete
 But small particles can
segregate in dry state
creating voids in agg
 What is the relation with
workability?
 Segregation leads to
less workable mix
Well-graded aggregates create dense concrete,
reducing segregation.
Too many fine particles can segregate when dry,
leaving voids
 Amount of fines in agg
 Less than 300 micron
For a satisfactorily workable mix
without harshness
Maximum
Absolute volume of
aggregate size fines as fraction of
(mm)
volume of concrete
8
0.165
16
0.14
32
0.125
63
0.11
True Slump
Slump Test
Disadvantage
• Lean Mix > Shear type or
collapse at low w/c ratio
Shear Slump
Collapse Slump
Degree of workability depends on w/c
within a range
Segregation
 For full compaction of
concrete, mix should be
cohesive
 Segregation is opposite of
cohesion
 Three forms of Segregation
 Remedies
 Proper gradation and
mix ratios
 Mixing, handling and
placing

 1. Coarser Particles travel long
distance

Happens when the mix is too dry or lean
Lean and dry mix
 2. Separation of grout

High w/c ratio
 3. Water gain or Bleeding
Excess water rises to the surface.
See figures in pp. 130-139
What is Bleeding?A type of segregation where water rises to the surface of concrete.
It happens when the mix is too watery and lacks cohesion.
Bleeding or Water Gain
 A form of segregation
of water from mix
 Measure settlement
per unit height of
concrete
 Causes
 Remedies
 high w/c ratio and/or
 High agg/cement ratio
 Or Lean mix
 Results
 Formation of weak layer
 Dusty surface on top
(laitance) Weakens concrete surface
 Reduction of strength
 Make rich mix
 Add Pozzolans or fly ash
in addition to cement
 Wait for evaporation
 Increase alkali content
(but)
 Increase C3A content
(but)
Strength of Concrete
 Factors affecting
strength of concrete
 w/c ratio, degree of
compaction
 Agg/cement ratio
 Agg properties
 Shape of agg
 Size and grading of
agg
 Age
 Primary factor is
 POROSITY
 The relative volume of
pores or voids in the
cement paste
More pores (air spaces) = weaker
 Thenconcrete.Less porosity = stronger,
denser conrete.
Cracks or
 Flaws and
weak spots
reduce
 Discontiuities
strength.
 Stress concentration is
the mechanism
High stress at certain points can cause cracks.
Fully compacted
concrete
Concrete
10% reduction of
density leads to 50%
reduction of strength
Porosity in Concrete
 Three forms of H2O in Concrete
 Combined Water >> 23% dry cement mass Permanently bonded in concrete.
 Gel Water >> 28% of cement gel volume Helps in strength development.
 Capillary Water >> minimum 18.5% of dry cement vol.
 Combined water: combined physically or chemically with
C-S-H Gel Combined water becomes a part of the solid structure during the hydration
reaction.
 Gel water: held physically or adsorbed on surfaces of C-S-H
Gel, gel pore dia = 2 nm Gel water is held in very tiny pores inside the C-S-H
gel.These gel pores are very small, so they don’t
significantly weaken the concret
 Capillary water: dry cement vol + H2O vol > C-S-H Gel >>
minimum capillary pore = 18.5%; capillary pore dia = 1000
nm Capillary Water (Minimum 18.5% of dry cement volume)
Leftover water that doesn't react with cement.
Creates capillary pores (1000 nm in size), reducing strength.
More capillary water = more porosity = weaker concrete.
Porosity (%)
Total porosity
Degree of
Hydration
Capillary porosity
W/C ratio
Concrete
27
Concrete
Mix proportion =
1:2:4
w/c = 0.55
70% hydration
Concrete
Some Facts about Porosity
 Cement paste contains an interconnected system of
pores, when partially hydrated
 >> lower strength, higher permeability >> vulnerable to
chemical, freezing-thawing
 Pore system become segmented/isolated when
degree of hydration is sufficiently high
Agg/Cement Ratio
 C : FA : CA
 1:1.5:3
 1:2:4
 1:3:6
 Agg/cement=?
Shape of Aggregates ,Smooth (rounded) gravel = Cracks form easily under stress.Angular (crushed)
aggregates = Crack growth is blocked, improving flexural strength.
Smooth aggregates need less water for the same workability, but overall, both types give similar
strength.
Aggregate Properties
SHAPE
 Smooth gravel leads to
cracking at lower stresses
than rough and angular
crushed aggregates
 Propagation of cracking is
obstructed in angular agg,
so more flexural strength
 Smooth and round agg
provide same workability
with less w/c ratio
 So two effects are
compensated and both agg
leads similar strength
Maximum Agg Size
• Larger agg >> smaller
surface area >> w/c ratio
can be reduced by
maintaining same
workability and agg/c ratio
>> more strength
• However, excessively large
agg provide less bond area,
discontinuity and voids >>
less strength
• Segregation potential is
more for larger particles
during stockpiling
Maximum Aggregate Size
Larger aggregates = Less surface area, so less cement paste is needed, which increases strength.
But too large aggregates = Poor bonding, more voids, and discontinuities, leading to lower strength.
Larger particles can also cause segregation (separation of materials), especially during handling.
Effect of Max Size of Agg
Effect of aging on concrete
Compressive strength
over time concrete:
Sets (becomes hard),
Gains strength, and Becomes less porous (less water
can pass through it).But these things only happen if:
The concrete is kept warm enough, and There is
enough moisture for the chemical reactions to
continue.
What happens if conditions are not right?
If the concrete is kept too cold, or all water is
removed:
These good changes won’t happen, no matter how
much time passes
Concrete
Age (days)
Effect aging or something else?
If one means merely the effect caused by the passage of
time, has no effect on concrete.
Of course concrete sets, hardens, gains strength, and
exhibits reduced permeability with the passage of time,
but it is not the passage of time alone that causes these
things to happen.
If the concrete is kept very cold, none of this will happen.
If all moisture is removed, none of this will happen.
Many or even most concretes are confronted with
potential deteriorative service conditions. If the concrete
has not been provided with immunity against these
influences, it may well slowly deteriorate as time passes,
but not simply because time passes. Concrete need not
deteriorate.
Mixing, Handling, Placing and
Compacting CONCRETE
Control of Segregation
Mixing, Handling, Placing and
Compacting CONCRETE
Control of Segregation
Mixing, Handling, Placing and
Compacting CONCRETE
Control of Segregation
Mixing, Handling, Placing and
Compacting CONCRETE
Control of Segregation
Mixing, Handling, Placing and
Compacting CONCRETE
Control of Segregation
Mixing, Handling, Placing and
Compacting CONCRETE
Control of Segregation
Mixing, Handling, Placing and
Compacting CONCRETE
Control of Segregation
Mixing, Handling, Placing and
Compacting CONCRETE
Control of Segregation
Tremie
Control of
Erosion and
Segregation
44
Mixing, Handling, Placing and
Compacting CONCRETE
Shrinkage in concrete is the reduction in volume over time, which can cause cracks.
Types of Shrinkage:
Plastic Shrinkage – Occurs before the concrete hardens due to rapid water loss from the surface.
Drying Shrinkage – Happens after the concrete hardens as moisture evaporates from the concrete.
Thermal Shrinkage – Occurs when the concrete cools down after setting.
Using Vibrator
Autogenous Shrinkage – Caused by internal chemical reactions during hydration.
Proper curing, a good mix design, and the use of shrinkage-reducing admixtures can help reduce the
risk of cracking
Shrinkage is the reduction in volume of concrete over time, which can cause cracks
Types of Deformation
Concrete deforms (changes shape) due to external loads and environmental conditions, often leading to cracks.
 Deformation in concrete which often lead to cracking, occur as
a result of the material’s response to external load and
environment.
 When freshly hardened concrete is exposed to the ambient
temperature and humidity, it generally undergoes thermal
shrinkage (shrinkage strain associated with cooling) and drying
shrinkage (shrinkage strain associated with moisture loss).
 Which one of the two shrinkage strains will be dominant
under a given condition depends, among other factors, on the
size of the member, characteristics of concrete making
materials, and the mix proportions.
 Generally, with massive structures (e.g., nearly 1 m or more
thickness), the drying shrinkage is less important a factor than
the thermal shrinkage.
Creep of Concrete
 Elastic deformations occur immediately after the concrete
is subjected to a given load, according to Hooke's Law.
 Inelastic deformations increase with time as the concrete
experiences a sustained load.
 This inelastic deformation of structure under sustained
load, also known as creep, increases at a decreasing rate
during the loading period.
 Basically, long term pressure or stress on concrete can
make it change shape.
 This deformation usually occurs in the direction the force is
being applied. Like a concrete column getting more
compressed, or a beam bending.
Creep of Concrete refers to the gradual deformation (change in shape) of concrete when it is under constant load for
a long time.
Elastic Deformation happens immediately after applying a load, where concrete stretches or compresses but returns
to its original shape once the load is removed.
Inelastic Deformation (creep) continues to increase over time under a sustained load, even though it happens at a
slower rate as time goes on.
Shrinkage of Concrete refers to the decrease in volume of concrete as it hardens, mainly due to the loss of moisture.
Shrinkage of Concrete
 Concrete is subjected to changes in volume either autogenous or
induced. Volume change is one of the most detrimental properties of
concrete.
 Shrinkage is defined as the contracting of a hardened concrete
mixture due to the loss of capillary water.
 This shrinkage causes an increase in tensile stress, which may lead to
cracking, internal warping, and external deflection, before the concrete
is subjected to any kind of loading.
 Concrete slabs can shrink as much as 1/2 inch per 100 feet.
 This shrinkage causes forces in the concrete. Cracks are the end result
of these forces.
Types of Shrinkage in Concrete
Occurs before the concrete hardens, usually due to rapid
 Plastic Shrinkage moisture loss from the surface (like in hot weather), leading
to cracks.
 Drying Shrinkage – Happens after concrete hardens as moisture evaporates over
time.
 Autogeneous Shrinkage Occurs because of internal chemical reactions during hydration
 Carbonation Shrinkage Results from the chemical reaction of concrete with carbon dioxide in the
air, which can cause shrinkage over time.
Difference between Creep and Shrinkage
 This time-dependent strain is termed as creep.
 Drying shrinkage (often, simply shrinkage) is the
reduction in volume of hardened concrete due to loss of
moisture by evaporation.
 Second, the strain-time curves of both the phenomenon
are very similar. The factors that effect creep also effects
shrinkage.
 In practice, creep during drying is inseparable from
shrinkage. The rate of creep increases with the rate of
change of pore humidity (i.e., relative vapor pressure in the
pores).
 For small specimen thickness, the creep during drying
greatly exceeds the sum of the drying shrinkage at no load
and the creep of a loaded sealed specimen.
Stages of producing concrete
Difference Between Creep and Shrinkage
 Batching
 Mixing
 Transportation
 Placing
 Compaction
 Curing
 Finishing
Difference Between Creep and Shrinkage in Concrete
Creep is the gradual deformation (change in shape) of concrete
under a constant load over time. Shrinkage is the reduction in
volume of concrete due to moisture loss, even without any load.
Similarities and Differences:
Both creep and shrinkage cause time-dependent strain (change in
size or shape).
The factors affecting creep also affect shrinkage (e.g., moisture
content, mix design, and curing conditions).
.
When concrete dries, the rate of creep increases because moisture
loss affects the internal structure.
In thin concrete elements, creep can be much higher than
shrinkage alone, especially during drying.
Proper curing, moisture control, and mix design help minimize both
creep and shrinkage.
Batching
Batching (Measuring Materials for
Concrete)
(1) Volume Batching
 Volume batching is not a good method.
 Moist sand in loose condition weights less than the
materials by volume, leading to inaccuracy.
same volume of dry sand. Measures
Moist sand takes up more space than dry sand.
Used only for small works.
 Practiced for small work.
 For quality work weight batching is practiced.
(2) Weight Batching
 Weight batching is correct method.
 Facilitates accuracy, flexibility and simplicity.
 Different batching machines are available:
(a) Manual, for regular works.
(b) Automatic, for large works.
Mixing
(Combining Materials for Concrete)
Mixing of cement, fine aggregate and coarse
aggregate should ensure that
 The mass is homogeneous
 Uniform in color
 Consistent
Types
 Manual mixing. For small works
 Machine mixing.
 Medium & large scale works.
 Mixing is efficient, economical & produce quality concrete.

Types
 Batch mixer. Batch by batch with time interval.
 Continuous mixer. Continuously mix & discharge.
Concrete Mixer
Types
Pan type
Drum type
 Tilting: 85T, 100T, 140T, 200T
Non-Tilting: 200NT, 280NT, 375NT, 500NT
 Reversing: 200R, 280R, 375R, 500R, 1000 R

Tilting Mixer
 Internal blades lift and tumble the ingredients onto
itself.
 Two primary types exist:
 Horizontal. One end has an opening for charging
and another end has opening for discharging.
 Single drum. Materials are charged and discharged
through a single opening.
Sequence of Charging Drums
 First half quantity of coarse aggregate is placed in skip
 Over it half quantity of sand
 On that full quantity of cement
 Over it balance quantity of fine and coarse aggregate in
place
 This prevents spillage of cement in air while discharging in
drum
 25% water is placed in drum and then mix from skip is
discharged in drum
 This prevents sticking of cement on blades
 75% water is immediately poured after placing mix material
(cement, sand etc.) in drum
Mixing Time
 In small machine mixing time varies between 1-2 minutes.
 In Ready Mix Concrete mixer 15-30 seconds.
 RPM of Drum 15-20
 Compressive strength of concrete increases with increase
in mixing time but after 2 minutes increase in compressive
strength is not significant.
 If concrete is not used after mix it may set.
 But when concrete is agitated on time to time in drum
setting time rule does not follow.
Small Machine Mixing: 1-2 minutes
Ready-Mix Concrete (RMC) Mixing: 15-30 seconds
Drum Speed: 15-20 RPM
Effects of Mixing Time:
Longer mixing improves strength, but after 2 minutes, the improvement is minimal.
If not used in time, concrete may start setting.
Agitating (stirring) the mix in the drum prevents early setting.
Retempering of Concrete
 Sometime concrete for RMC plant is delivered to site due to
traffic congestion.
 Concrete becomes stiff and unworkable.
 Site engineers can reject the concrete is delay is more.
 If it can be used then small volume of water is added and
again agitated in the drum.
 This is called Retempering of Concrete.
Retempering is the process of adding a small amount of water to stiffened concrete and mixing it again
to restore workability.
Concrete from a Ready-Mix Plant (RMC) may arrive late due to traffic.
It becomes stiff and hard to work with.
Solution:
If too much time has passed, the engineer may reject it.
If still usable, a small amount of water is added, and the mix is stirred again in the drum.
This process is called Retempering of Concrete.
Transportation of Concrete
Precaution:
 Homogeneity of concrete mass is maintained.
 Movement of hand trolley or truck on rough road surface
makes vibrations.
 This results in deposition of heavy aggregates at bottom of
trucks.
 Water and cement slurry comes on top.
Methods:
Mortar Pan
Wheel barrow
Truck mixers & Dumpers
Crane, bucket & ropeway
Belt conveyors
Chutes.
Pump & pipelines. etc
Placing of Concrete:
Concrete should be placed within 30 minutes after
adding water.
It must be transported quickly using pans,
wheelbarrows, pumps, or cranes.
Always place concrete in thin layers and compact each
layer before adding the next.
Avoid dropping concrete from a height to prevent
separation of materials.
If too much water is present or thick layers are placed, a
weak top layer (laitance) may form.
Placing of Concrete
 After mixing of concrete is should be placed within 30
minutes of adding water.
 It should be quickly transported to the place of lying by
means of iron pans manually, in wheel barrows, by
pumping or by cranes.
 In placing, concrete should be laid in thin layers. Each layer
being thoroughly consolidated, before the next one is laid.
 Concrete should not be dropped from a height as it would
cause segregation of aggregates.
 In case concrete has more of water or it has been laid in
thick layers, then on compaction water and fine particles
comes forming a layer of weak substance known as
laintance.
Compaction of Concrete
Compaction of Concrete:
Proper compaction removes air voids and improves strength, durability, and water resistance.
 Compaction of concrete is very important in developing
qualities like strength, durability, imperviousness by
making the concrete dense and free from voids.
 In case of RCC compaction is done by pinning with an iron
rod or even with trowel blade.
 Excess temping should be avoided as otherwise water,
cement and finer particles would come to the surface and
results in non uniform concreting.
 In case of important and big works, compaction of concrete
In RCC work, compaction is done using an iron rod or trowel.
is done with vibrator. Too much tamping can bring water and fine particles to the
surface, leading to poor quality.
 Use of vibrator is best and most efficient way of
compacting concrete. It produces very dense concrete.
 Care should be taken not to make excessive use of vibrators
otherwise the concrete becomes non-homogeneous.
Vibrators are used for large projects as they make the concrete dense and strong.Excessive vibration
can cause concrete to become non-uniform
Curing of Concrete
 The process of keeping concrete wet to enable it to attain
full strength is known as curing.
 The objective of curing is to prevent loss of moisture from
concrete due to evaporation or because of any other reason.
 Curing should be done for a period of 3 (three) weeks but
not less than 10 (ten) days.
 In case of important and big works, compaction of concrete
is done with vibrator.
 Use of vibrator is best and most efficient way of
compacting concrete. It produces very dense concrete.
 Care should be taken not to make excessive use of vibrators
otherwise the concrete becomes non-homogeneous.
Curing means keeping concrete wet so it gains full strength.
It prevents moisture loss, which is important for proper hardening.
Curing should be done for at least 10 days, but 3 weeks is ideal.
This ensures concrete becomes strong and durable.
Curing of Concrete
 What is meant by
 Disadvantage of
curing of concrete?
membrane curing?
 Effect of curing
 Why is curing
temperature on strength
important?
 Durability of concrete is  Typical steam curing cycle
is maturity rule?
dependent on length of  What
What is the limitation of
curing. How?
maturity rule?
 Types of curing
 Normal curing
 Spraying, ponding, covering
with wet materials,
membrane curing
 Steam curing
 Autoclaving?
Cement Paste
Concrete
28
7
Curing temp
During first 24
Hours = 10Ạ C
3
Maturity Rule
 M = ∑ T.dt
 Limitation
 Adverse
effect of
early high
temp could
not be
counted
This rule helps estimate
concrete strength based on
temperature and time.
Steam Curing
 Mainly used for precast concrete
 High early strength development
 Steam curing with high pressure = autoclaving
Symptoms: White deposits, cracks, and surface peeling.
Cause: Sulphates react with C3A (Tricalcium Aluminate) in cement, forming compounds that expand and
damage concrete.
Durability of Concrete
Effect: Expansion leads to cracks and weakens concrete.
Sulphate Attack.
Severity: More damage occurs if sulphate concentration is high and concrete is permeable (allows water
in).

Symptoms: Whitish appearance, cracking and spalling
of concrete
 Mechanism: formation calcium sulphate and calcium
sulpho-aluminate (from C3A + sulphate), products
volume is greater than reactants, resulting expansion
and disruption of concrete
 Damage extent depends on concentration of sulphate
and permeability of concrete
Remedy.
 Use of blast furnace slag cement and Portland-pozzolan
cement
Prevention:
 Compaction, curing, clear cover >> durable concrete
Use sulphate-resistant cement (blast furnace slag or pozzolan cement).
Ensure good compaction, curing, and proper cover for durability.
Testing of Concrete
Measures how much load concrete can withstand before crushing.
 Compressive strength
 Tensile strength
Measures concrete’s ability to resist pulling forces.
 Flexure test
Measures how concrete resists bending
 Splitting test
Measures indirect tensile strength.

Tensile splitting strength
= 2P/(π Ld)
This test helps determine how well concrete resists cracking under tension.
Effect of Platen Restraint
Platen restraint occurs due to friction between the testing
machine’s steel plates and the concrete sample, restricting
lateral expansion.
This creates lateral shearing stress, affecting failure patterns.
Lateral shearing stressIdeal failure: Cone or pyramid-like cracks.
Types of failure other than these are regarded as
unsatisfactory and indicate a probable fault in the
testing machine
Compressive Strength
 When h/d ratio
increases, the influence
of platen restraint
decreases in the central
part of specimen
 Cube strength = 1.25 *
cylinder strength
 Merits and demerits of
cylinder and cube test?
Merits & Demerits:
Cube: Higher strength, easy to handle but less
realistic.
Cylinder: More accurate for structures but lower
strength.
h= height
d= diameter
Effect of h/d ratio on cylinder
strength
Types of Concrete
 There are various types of concrete for different applications that
are created by changing the proportions of the main ingredients.
 The mix design depends on the type of structure being built, how
the concrete will be mixed and delivered, and how it will be
placed to form the structure.
Examples include:
 Regular concrete
 Pre-Mixed concrete
 High-strength concrete
 Stamped concrete
 High-Performance concrete
 UHPC (Ultra-High Performance
Concrete)
 Self-consolidating concretes
 Vacuum concretes
 Shotcrete
 Cellular concrete
 Roller-compacted concrete
 Glass concrete
 Asphalt concrete
 Rapid strength concrete
 Rubberized concrete
 Polymer concrete
 Geopolymer or Green
concrete
 Limecrete
 Gypsum concrete
 Light-Transmitting Concrete
Basic Composition for Main Concretes
Regular Concrete
Cement, Aggregate, and water
Geopolymer (Green concrete)
Fly Ash and Regular
Concrete
High Strength Concrete
Silica Fume
Strong Aggregates
Ultra High Performance Concrete (UHPC)
Cement
Coarse/Fine Aggregate
Air
Silica Fume
Polypropylene Fibers
Concrete Testing
Non-Destructive
Testing
Concrete
Destructive
NDT-Importance
 Whether concrete is hardened properly and gained its
designed strength ?
 NDT is for both old and New Structures
 Exercise this without damaging the Structure…….
Purpose: To check if the concrete has hardened properly and gained its intended strength
without damaging the structure.
For New & Old Structures: NDT is useful for both.
Cost Effectiveness
Destructive Testing: Expensive, as it requires taking samples and testing them.
NDT: Simple, cost-effective, and allows multiple tests to be done at the same cost of one
sample.
Cost Effectiveness
 Destructive testing
 Huge Cost initially has to put in for taking sample and
then to test it.
 NDT
 Its very easy and simple process and a lot many tests can
be performed on concrete less than single amount
require for sampling of concrete
Where to use NDT
 Quality control of Construction , in situ
 Confirming Workmanship
 Determining position of reinforcement
 Location of Cracks/Joints/Honeycombing
Signs of Distress
 Cracks
NDT is a method used to inspect and test concrete without
damaging it. It helps evaluate the condition and quality of the
concrete without affecting its ability to function.
Purpose of NDT
Measure Strength and Durability: Check how strong and
durable the concrete is.
 Spalling
Quality Control: Ensure the concrete is properly hardened
and of good quality.
 Dis-integration Crack and Deterioration Monitoring: Detect cracks, microcracks, and any damage that might be developing.
 Color change
Properties Measured by NDT;;;
Hardness
 Weathering
Resistance to penetration
Resonant frequency
 Staining
Ability to pass ultrasonic pulses
Common NDT Methods
 Surface blemishesSurface Hardness: Measures how hard the surface of the
concrete is.
 Lack of Uniformity
Penetration Resistance: Tests how resistant the concrete is
to penetration.
Pull-out Resistance: Assesses how strongly embedded
elements resist being pulled out.
 Pop-outs
Non-destructive test of Concrete (NDT)
Non-destructive testing (NDT) is defined as the method of
inspecting, testing, or evaluating materials, components or
assemblies without destroying the serviceability of the part or
system.
NDT is conducted to:
 Measure the strength & durability of concrete.
 Assessing & controlling quality of hardened concrete.
 Helps to measure Crack depth, Micro crack and progressive
deterioration.
Measures properties of concrete such as:
 Hardness.
 Resistance to penetration.
 Resonant frequency
 Ability to allow ultrasonic pulse
Non-destructive test of Concrete (NDT)
Common NDT methods:
Resonant Frequency: Checks the
concrete's vibrational characteristics.
 Surface hardness method
Maturity Test: Measures the age and
 Penetration resistance method temperature history of the concrete.
 Pull-out resistance method
Permeation Test: Assesses how easily
fluids pass through concrete.
 Pull-off resistance method
 Resonant frequency test methodUltrasonic Pulse Velocity: Uses sound
waves to assess the concrete’s condition.
 Maturity test method
Impact-Echo Method: Tests the concrete's
 Permeation test method
structural integrity by applying an impact.
 Ultrasonic pulse velocity methodCorrosion of Reinforcement: Detects the
corrosion level of steel reinforcement
 Impact-echo method
inside the concrete.
 Corrosion of reinforcement method
Rebound Hammer Test
Rebound Hammer Test
 Surface hardness test
 Rebound of elastic mass depends on hardness of
surface
 Relation between rebound number and strength of
surface
The Rebound Hammer Test measures the surface hardness of concrete by checking how much
a spring-loaded hammer bounces back when it strikes the surface. The rebound number (how
much it bounces) indicates the surface strength of the concrete. A higher rebound number
suggests a stronger surface, while a lower number suggests a weaker surface. It's a quick way
to estimate concrete strength but doesn’t give exact values.
Components of Hammer
Rebound Hammer
Device
Measuring
Direction
Original
Schmidt
Hammer
Impact
Used for the non-destructive
direction
measurement of the
perpendicular concrete/mortar compressive
to the surface
strength characteristics
900 g
Silver
Schmidt
Hammer
independent
of impact
direction
600 g
Applications
Suitable for testing a wide
variety of concrete, mortar
and rock
Weight
Limitation
a) Smoothness of surface under test
b) Size , shape and rigidity of the specimen
c) Age of specimen
d) Surface and internal moisture condition of the
The surface must be smooth.
concrete
The concrete’s age can influence readings.
content on or inside the concrete
e) Type of coarse aggregate Moisture
impacts the rebound.
f) Type of cement
g) Type of mould
Different types of cement and aggregates give
different results.
The type of mould used during casting can
affect strength.
h) Carbonation of concrete surface
Carbonation (a chemical reaction on the
concrete surface) can alter results.
Procedure
Rebound Hammer & strength of Concrete
Horizontal
hammer
WET
Non-destructive test of Concrete (NDT)
 Schmidt hammer / Rebound hammer / Impact
hammer test
 Rebound number >> comp strength
 10-12 readings are necessary for one spot
 Plunger must be normal to surface of concrete
Section of Rebound Hammer
Calibration of Rebound Hammer
Concrete