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Concrete Technology
Unit- I
Q.1) Give the oxide composition of cement and state the effect of each on the properties of
cement.
Ans: -

The chemical composition of cement is made up of several oxides, which affect the properties of
cement. Here is a breakdown of the oxide composition and their effects on cement properties:

➢ Lime (CaO): 60-65%

i. Provides strength to cement
ii. Imparts color to cement
iii. Excess lime can cause cement to expand and disintegrate
➢ Silica (SiO2): 17-25%
i. Provides strength to cement
ii. Helps cement harden and set
iii. Excess silica can cause cement to be brittle and weak
➢ Alumina (Al2O3): 3-8%
i. Provides strength to cement
ii. Helps cement harden and set
iii. Excess alumina can cause cement to be brittle and weak
➢ Iron oxide (Fe2O3): 0.5-6%
i. Imparts color to cement
ii. Helps cement harden and set
iii. At high temperatures, reacts with calcium and aluminum to form tricalcium alumino-
ferrite, which imparts hardness and strength to cement
➢ Magnesia (MgO): 1-3%
i. Provides color to cement
ii. Provides hardness to cement
iii. Excess magnesia can cause cracks in mortar and produce unsound concrete
➢ Sulfur trioxide (SO3): 1-3%
Imparts soundness to cement
➢ Calcium sulfate (CaSO4.2H2O): 0.1-0.5%
i. Slows down or retards the setting action of cement

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ii. Helps regulate the setting time of cement

➢ Alkaline: 0-1%
i. Excess of alkali causes efflorescence in concrete
ii. Excess of alkali causes cracks in concrete.

Q.2) What are the field tests for judging the preliminary quality of cement?
Ans: -

There are several field tests that can be conducted to judge the preliminary quality of cement.
These tests are not very accurate but can provide a basic idea to the civil engineer regarding the
quality of the cement. Here are some of the field tests for cement quality:

a. Adulteration Test: Take a pinch of cement and feel (rub) between the fingers. It should
give a smooth feeling and not a gritty feeling.

b. Colour of Cement: The colour of the cement should be greenish grey and it should be
uniform in colour.

c. Presence of Lumps: There should not be any visible lumps. Thrust your hand into the
cement bag, there should not be any lumps inside. Any bags containing such lumps should
be rejected.

d. Temperature Test: When you insert your hand in the bag of cement, it should give you a
cool feeling.

e. Float Test: Take a sample of cement from the bag and throw it in a bucket full of water. It
should float for some time before it sinks.

f. Manufacturing Date of Cement: The strength of cement reduces with age, so the date of
manufacturing of cement bags should be checked.

g. Smoothness Test: When cement is touched or rubbed in between fingers, it should give a
smooth feeling. If it felt rough, it indicates adulteration with sand.

h. Shape Test: A 25mm × 25mm × 200mm (1”×1”×8”) block of cement with a smooth finish
should be prepared and immersed in water for 24 hours. It should not show any sign of
cracks or disintegration.

i. Strength Test: The strength of cement can be roughly ascertained by preparing a cement
paste and gauging it with the help of a vicat needle.

Amit Sir [M-Tech (STRUCTURE), BE, Diploma in Civil],

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Q.3) Give the classification of aggregates according to source, shape and size.
Ans: -

Aggregates can be classified based on their source, shape, and size. Here are the different
classifications of aggregates:
Classification of Aggregates Based on Source
a. Natural Aggregates
b. Artificial Aggregates
Classification of Aggregates Based on Shape
a. Rounded Aggregates
b. Irregular or Partly Rounded Aggregates
c. Angular Aggregates
d. Flaky Aggregates
e. Elongated Aggregates
Classification of Aggregates Based on Size
a. Coarse Aggregates
b. Fine Aggregates
Coarse aggregates are further classified based on their size:
a. Gravel: Coarse aggregates retained on the sieve of 4.75mm size
b. Crushed Stones: Coarse aggregates retained on the sieve of 4.75mm size up to 50% and
the remaining can be any size smaller than 4.75mm
c. Shingle: Coarse aggregates retained on the sieve of 4.75mm size up to 50% and the
remaining can be any size smaller than 10mm
d. Fine aggregates are also further classified based on their size:
e. Sand: Fine aggregates passing through the sieve of 4.75mm size and retained on the sieve
of 0.15mm size
f. Silt: Fine aggregates passing through the sieve of 0.15mm size and retained on the sieve
of 0.075mm size
g. Clay: Fine aggregates passing through the sieve of 0.075mm size.

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Q.4) Explain impact value test on Aggregate.

Ans: -

The impact value test is a measure of the resistance of aggregates to sudden impact or shock. It is
important in pavement design as the aggregates used in road construction should be strong enough
to resist abrasion, crushing, and impact load. Here is the procedure for the impact test on
aggregates:
i. The test sample consists of aggregates sized 10.0 mm and 12.5 mm.
ii. The aggregates may be dried by heating at 100-110°C for a period of 4 hours and cooled.
iii. Sieve the material through 12.5 mm and 10.0 mm IS sieves. The aggregates passing
through the 12.5 mm sieve and retained on the 10.0 mm sieve comprise the test material.
iv. A cylindrical metal measure with a diameter of 75 mm and a depth of 50 mm is used for
the test.
v. The test sample is filled in 3 layers, each layer being tamped with 25 strokes of a tamping
rod.
vi. The hammer of the impact testing machine is raised to a height of 380 ± 5 mm above the
upper surface of the aggregates in the cup.
vii. The machine is then allowed to fall freely on the aggregates.
viii. The test sample is subjected to a total of 15 such blows, each being delivered at an interval
of not less than one second.
ix. The crushed aggregate is removed from the test specimen and sieved through the 2.36 mm
IS sieve.
x. An impact value is measured as a percentage of aggregates passed through the 2.36 mm
sieve (W2) to the total weight of the sample (W1).
xi. The value of aggregate impact test should not be more than 45% by weight of aggregates
used for concrete other than the wearing surface. An impact value of 35% is permissible
for bituminous macadam. The maximum permissible impact value for the water-bound
macadam is 40%.

5) List various types of admixtures used in concrete. Explain plasticizers and super
plasticizers.
Ans: -
Admixtures are materials other than cement, water, and aggregates that are added to concrete to
enhance its properties. Here are various types of admixtures used in concrete:
i. Water-Reducing Admixtures
ii. Retarding Admixtures
iii. Accelerating Admixtures
iv. Air Entraining Admixtures

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v. Pozzolanic Admixtures
vi. Damp-proofing Admixtures
vii. Gas Forming Admixtures
viii. Air Detraining Admixtures
ix. Alkali Aggregate Expansion Preventing Admixtures
x. Anti-washout Admixtures
xi. Grouting Admixtures
xii. Corrosion Preventing Admixtures
xiii. Bonding Admixtures
xiv. Fungicidal, Germicidal, Insecticidal Admixtures
xv. Coloring Admixtures
Plasticizers are admixtures used in concrete to improve its plasticity or workability in the fresh
state. They are also called water reducers because they reduce the water content without affecting
the workability and water-cement ratio. Plasticizers are generally colorless liquids that are
relatively nonvolatile. They are added to the material to make it softer and more flexible.

Details about plasticizers:

i. Types of plasticizers include calcium, sodium, ammonium lignosulphonates, polyglycol
esters, and so on.
ii. They are used in the amount of 0.1% to 0.4% by weight of cement.
iii. When added, they get adsorbed on the cement particles and increase the slump of the
concrete mix.
iv. They have the capability of reducing water content up to an extent of 10%.
v. They improve the ability of pumping and maintain strength without affecting the structure.
Superplasticizers, also known as high-range water reducers, are chemical admixtures used in
making high-strength concrete or to place self-compacting concrete.

Details about superplasticizers:

i. Superplasticizers allow reduction in water content by 30% or more.
ii. They are employed at the level of a few weight percent.
iii. They are chemical compounds that enable the production of concrete with approximately
15% less water content.
iv. They are used to improve the workability of concrete without adding more water.
v. They are employed to reduce the water-cement ratio, which results in higher strength and
durability of concrete.

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vi. They are used to reduce the amount of cement needed in concrete, which reduces the cost
of concrete.
vii. They are classified into different types such as purified lignosulfonates, carboxylate
synthetic polymers, sulfonated synthetic polymers, and synthetic polymers with mixed
functionality cementitious materials.
viii. Compounds used as superplasticizers include sulfonated naphthalene formaldehyde
condensate, sulfonated melamine formaldehyde condensate, acetone formaldehyde
condensate, and polycarboxylate ethers.

6) Write short note on Accelerators and Retarders.

Ans: -
Accelerators and retarders are types of admixtures used in concrete to modify its setting time. Here
are some details about accelerators and retarders:

Accelerators:
i. Accelerating admixtures are used to reduce the initial setting time of concrete.
ii. They speed up the process of the initial stage of hardening of concrete.
iii. They are used to counteract the influence of cold weather, which slows down the curing
and setting process.
iv. Chemical compositions of accelerators include some of inorganic compounds such as
soluble chlorides, carbonates, silicates, fluosilicates, and some organic compounds such as
triethanolamine.
v. Examples of accelerators in concrete include calcium chloride, sodium chloride, and
triethanolamine.
vi. Calcium chloride is a common accelerator used to accelerate the time of set and the rate of
strength gain.
vii. Excessive amounts of calcium chloride in concrete mix may result in rapid stiffening,
increase in drying shrinkage, and corrosion of reinforcement.
viii. Accelerators are useful in eliminating the problems of quick setting in high-temperature
zones where concrete will set quickly.
Retarders:
i. Retarding admixtures delay the end of the dormant period and the start of setting and
hardening.
ii. They are used to extend the setting time of cement paste in concrete.
iii. They are helpful for concrete that has to be transported to long distances and placed at high
temperatures.
iv. They are also used to resist cracking.

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v. Most retarders also act as water-reducing agents, and some air may be added to the
concrete.
vi. Commonly used liquid accelerators are sodium silicate type, sodium aluminate type,
aluminum sulfate type, and aluminum potassium sulfate type accelerator.
vii. Concrete early-strength agent refers to an admixture that can increase the early strength of
concrete and has no significant effect on the later strength.

7) Explain the effect of Fly Ash on Fresh concrete & Hardened concrete.
Ans: -
Fly ash is a byproduct of coal combustion that can be used as a supplementary cementitious
material in concrete.

Effects of fly ash on fresh and hardened concrete:

Fresh Concrete:
i. Fly ash improves the workability of the concrete and reduces water demand.
ii. It must not be used like an additive; it has to take the place of cement.
iii. The use of fly ash in concrete can result in better workability, pumpability, cohesiveness,
finish, and durability.
iv. The fine particles in fly ash help to reduce bleeding and segregation and improve
pumpability and finishing, especially in lean mixes.
Hardened Concrete:
i. Fly ash enhances concrete's hardened properties by increasing long-term strength, lowering
permeability, and increasing overall durability.
ii. The use of fly ash can result in better workability, pumpability, cohesiveness, finish,
ultimate strength, and durability.
iii. The permeability of concrete reduces on the addition of fly ash to cement.
iv. Fly ash slightly improves the resistance of concrete to chemical attack.
v. Coarser fly ashes and those having high carbon content are more liable to increase drying
shrinkage than the finer fly ashes and those having low carbon content.
vi. Fly ash reduces the heat of hydration in concrete.
vii. Fly ash reduces the rate of hydration, thus low early compressive strength is observed.
After 7 days of curing, the compressive strength was observed to be lower than that of
concrete without fly ash.

Amit Sir [M-Tech (STRUCTURE), BE, Diploma in Civil],

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8) List important physical tests of cement? Explain any two in brief?

Ans: -
Important physical tests of cement include:
➢ Fineness Test: Fineness of cement is an essential parameter that affects the hydration
rate, early strength, workability, and durability of concrete. Increasing fineness causes an
increased rate of hydration, high strength, and high durability. Fineness can be determined
by using a sieve analysis test, air permeability test, or a sedimentation method.
➢ Soundness Test: The soundness of cement is the ability of cement to retain its volume
after it gets hardened. The soundness of cement is determined by the Le-Chatelier method.
This test measures the expansion of cement when it is mixed with water and kept in a mold.
The soundness of cement is important because if the cement is unsound, it can cause
cracking and other problems in the concrete.
➢ Consistency Test: The consistency of cement is the ability of cement to flow. The
consistency of cement is determined by the Vicat apparatus. This test measures the
penetration of a plunger into the cement paste. The consistency of cement is important
because it affects the workability of concrete.
➢ Strength Test: The strength of cement is the ability of cement to withstand the load. The
strength of cement is determined by the compressive strength test. This test measures the
strength of cement by applying a load to a cube of cement.
➢ Setting Time Test: The setting time of cement is the time taken by cement to set. The
setting time of cement is determined by the Vicat apparatus. This test measures the time
taken by cement to set by measuring the penetration of a plunger into the cement paste.
➢ Heat of Hydration Test: The heat of hydration of cement is the amount of heat
generated when cement reacts with water. The heat of hydration of cement is determined
by the calorimeter. This test measures the amount of heat generated by cement when it
reacts with water.

9) Explain in brief "Sulphate Resisting Portland Cement".

Ans: -
Sulphate Resisting Portland Cement (SRPC) is a type of Portland cement in which the amount of
Tricalcium Aluminate (C3A) is less than 5% and the amount of C3A and calcium aluminoferrite
(C4AF) together is less than 25%. SRPC is intended for the manufacture of concrete and concrete-
steel constructions having resistance to corrosion on exposure to media that are aggressive in their
Sulphate content. Here are some characteristics and uses of SRPC:

Characteristics:
i. Provides maximum resistance to chloride ions, minimizing the risk of corrosion of
reinforced steel.
ii. High level of concrete performance and structural integrity in aggressive environments.
iii. Resistant to Sulphate attack.
iv. Does not give much heat of hydration.
v. Preserves the durability of the structures in the areas prone to Sulphate attack.

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Uses:
i. SRPC is used in places where the concrete structure faces the risk of being damaged by
high amounts of Sulphate found in its immediate environment.
ii. The use of SRPC is recommended in places where the concrete is in contact with the soil,
groundwater, and seawater, and/or exposed to seacoast.
iii. SRPC is used where the prevailing temperature is below 40°C and in conditions where
concrete is exposed to deterioration due to Sulphate attack, such as concrete in contact with
soils or water.

10) What are the various Aggregates used in cement concrete work? Explain about the
surface Texture of Aggregates.
Ans: -
Aggregates are inert granular materials such as sand, gravel, or crushed stone that, along with
water and Portland cement, are an essential ingredient in concrete. The various aggregates used in
cement concrete work include:
a. Fine Aggregates: Fine aggregates generally consist of natural sand or crushed stone with
most particles passing through a 3/8-inch sieve. Fine aggregates are used in concrete mixes
to fill the voids between coarse aggregates and cement paste.
b. Coarse Aggregates: Coarse aggregates are larger than 4.75mm in size and are used in
concrete mixes to provide bulk and strength to the concrete. Gravel or broken stone
aggregates with rough and non-glassy texture are the best aggregates because they create
a good bond with the cement paste.
The surface texture of aggregates is an important factor that affects the properties of fresh concrete
more than hardened concrete. The surface texture of aggregates depends on rock hardness, grain
size, porosity, and previous exposure. The surface texture of aggregates affects the workability,
paste demand, and initial strength of concrete. Rough-textured and elongated particles require
more cement paste to produce workable concrete mixtures, thus increasing the cost. Porous
aggregates require more water compared to non-absorbent aggregates for achieving the same
degree of workability. The surface texture of aggregates can be classified into the following types:
a. Smooth and Rounded: Most natural sands and gravel from riverbeds or seashores are
smooth and rounded and are excellent aggregates. Concrete is more workable when smooth
and rounded aggregate is used instead of rough angular or elongated aggregate.
b. Rough and Angular: Rough and angular aggregates require more cement paste to
produce workable concrete mixtures, thus increasing the cost.
c. Flaky and Elongated: Flaky and elongated aggregates are not desirable for concrete
production because they reduce the workability of the concrete and increase the cement
paste demand.

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11) Explain in brief the Grading of coarse Aggregate and fine Aggregate.
Ans: -
Grading is the particle-size distribution of an aggregate as determined by a sieve analysis. The
proper grading of an aggregate produces dense concrete and needs less quantity of fine aggregate
and cement waste, therefore, it is essential that coarse and fine aggregates be well graded to
produce quality concrete. The grading curve of aggregates can be classified into the following
types:

Grading of Fine Aggregate:

i. Fine aggregates generally consist of natural sand or crushed stone with most particles
passing through a 3/8-inch sieve.
ii. Fine aggregates are divided into four zones according to the size of particles.
Grading of Course Aggregate:
i. Coarse aggregates are larger than 4.75mm in size.
ii. Coarse aggregates are divided into four zones according to the size of particles.
iii. Types of Grading of Aggregates:
iv. Dense-or well-graded aggregate – Has gradation close to the FWHA maximum density
grading curve.
➢ Gap-graded aggregate – Has only a small percentage of particles in the mid-size range.
➢ Uniformly graded aggregate – Composed mostly of particles of the same size.
➢ Open-graded aggregate – Contains only a small percentage of small-size particles.

12) Explain the four variable factors to be consider in connection with specifying a concrete
mix.
Ans: -
When specifying a concrete mix, there are four variable factors that need to be considered. These
factors are:
a. Compressive Strength: Compressive strength is one of the most important properties of
concrete and influences many other describable properties of the hardened concrete. The
mean compressive strength required after 28 days determines the nominal water-cement
ratio of the mix.
b. Workability: Workability is the ease with which concrete can be mixed, transported,
placed, compacted, and finished without segregation or bleeding. The adequate workability
necessary for full compaction, maximum water-cement ratio, and/or maximum cement
content to give adequate durability for site conditions, and maximum cement content to
avoid shrinkage cracking due to temperature in mass concrete are factors that need to be
considered.
c. Durability: Durability is the ability of concrete to resist weathering action, chemical
attack, and abrasion. The durability of concrete depends on the quality of the materials
used, the water-cement ratio, and the curing conditions.

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d. Water-Cement Ratio: The water-cement ratio is the ratio of the weight of water to the
weight of cement in a concrete mix. It is an important factor that affects the strength and
durability of concrete. The water-cement ratio should be kept as low as possible to achieve
the desired strength and durability of concrete.

13) Explain the test on specific gravity, bulk density & moisture content of aggregate.
Ans: -
Tests on specific gravity, bulk density, and moisture content of aggregate are important to
determine the suitability of the aggregate for use in concrete. Here are some details on each of
these tests:
a. Specific Gravity: Specific gravity is the ratio of the weight of a given volume of
aggregate to the weight of an equal volume of water. It is an important factor in determining
the suitability of an aggregate for use in concrete. Low specific gravity generally indicates
porous, weak, and absorptive materials, whereas high specific gravity indicates dense,
strong, and non-absorptive materials. The specific gravity of fine and coarse aggregates is
determined separately.
b. Bulk Density: Bulk density is the weight of aggregate required to fill a container of a
specified volume. It is an important factor in determining the yield of concrete per unit
volume of aggregate. The bulk density of an aggregate is affected by its specific gravity,
particle shape, and grading.
c. Moisture Content: Moisture content is the amount of water present in the aggregate. It
is an important factor in determining the water-cement ratio of the concrete mix. The
moisture content of the aggregate affects the workability of the concrete mix and the
strength and durability of the hardened concrete. The moisture content of the aggregate
should be determined before mixing the concrete.

14) Explain concrete Mix Design by Road Note No. 4 (BS).

Ans: -
Concrete Mix Design by Road Note No. 4 (BS) is a method of designing concrete mixes that was
developed specifically for concrete pavements. The method involves selecting suitable ingredients
of concrete and determining their relative quantities with the aim of achieving a desired
compressive strength at a specified age. Here are the steps involved in the Road Note No. 4 (BS)
method:
i. Determine the target compressive strength of the concrete at a specified age.
ii. Determine the water-cement ratio (W/C) required to achieve the target compressive
strength using the curves provided in Road Note No. 4.
iii. Determine the amount of cement required for the mix.
iv. Determine the amount of water required for the mix.
v. Determine the amount of fine aggregate required for the mix using the grading curve
provided in Road Note No. 4.
vi. Determine the amount of coarse aggregate required for the mix.

Amit Sir [M-Tech (STRUCTURE), BE, Diploma in Civil],

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15) Explain field test on cement? Also explain soundness test on cement.
Ans: -
Field test on cement is performed on-site to ensure the quality of cement before using it for
construction works.
The following are some of the field tests that can be conducted on cement:
a. Packaging Date on Cement Bag: Cement should be used within 3 months of its date of
manufacture.
b. Lumps in Cement Bag: No visible lumps should be present in the cement.
c. Color of Cement: The color of cement should be uniform and typical cement color, i.e.,
gray color with a light greenish shade.
d. Hard Lumps in Cement: Cement should be free from hard lumps formed by the
absorption of moisture from the atmosphere.
e. Glass Plate Test: A thick paste of cement with water is made on a piece of a glass plate
and it is kept under water for 24 hours. It should set and not crack.
Soundness test on cement is performed to determine the ability of cement to retain its volume after
setting.
The following are the steps involved in the soundness test:
i. A paste of cement and water is made and placed in a mold of a specified shape.
ii. The mold is placed in a steam cabinet for 3 hours.
iii. The mold is then removed from the steam cabinet and allowed to cool.
iv. The length of the mold is measured, and the difference between the original length and
the length after the test is calculated.

16) Write down the role of admixture as a component of concrete. Explain types of
admixtures and factors affecting admixture.
Ans: -
Admixtures are added to concrete mixtures to obtain certain properties such as accelerate setting,
early strength development, improve durability, enhance concrete cohesiveness for underwater
placement, decrease permeability, increase pumpability, reduce water content, and many more
desired properties. The role of admixture as a component of concrete is to modify the properties
of hardened concrete, ensure quality of concrete during mixing, transporting, placing, and curing,
and to overcome certain emergencies during concrete operations. Admixtures can be classified
into two main types: Chemical and Mineral.

Types of Admixtures:
A. Chemical Admixtures:
a. Air entrainers
b. Water reducers
c. Set retarders
d. Set accelerators
e. Superplasticizers

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B. Mineral Admixtures:
a. Fly ash
b. Silica fume
c. Ground granulated blast furnace slag
d. Metakaolin
Factors Affecting Admixture:
The effectiveness of an admixture depends on several factors including:
➢ Type and amount of cement
➢ Water content
➢ Mixing time
➢ Slump
➢ Temperatures of the concrete and air
➢ Aggregate shape, gradation, and size
➢ Chemical composition of the cement
➢ Admixture dosage and type

17) Explain metakaolin & Surkhi as admixture.

Ans: -
Metakaolin and Surkhi are two types of admixtures that can be used in concrete. Here is an
explanation of each:
➢ Metakaolin: Metakaolin is an anhydrous form of the mineral kaolin of clay. It is a
pozzolanic material that can be used in concrete as an admixture. Metakaolin has high
pozzolanic reactivity, enhances durability, reduces the risk of efflorescence, reduces the
risk of chemical attack to concrete, and reduces shrinkage. It is used to make concrete as
an admixture, to make high-performance lightweight concrete, to make precast concrete,
to manufacture ferrocement products, to make countertops, and in stucco. Metakaolin is
produced from kaolinite, a mineral found in kaolin clay. The material is purified to remove
compounds that could discolor concrete, and then calcined under controlled heat to create
an anhydrous form of the mineral.

➢ Surkhi: Surkhi is a type of admixture that is made by grinding burnt clay bricks or tiles.
It is a pozzolanic material that can be used in concrete as an admixture. Surkhi is used to
improve the workability of concrete, reduce the amount of cement required in the mix, and
increase the strength of the concrete. It is also used to make lime mortar for masonry work.
Surkhi is a cost-effective alternative to other admixtures and is readily available in many
parts of the world.

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Factors affecting admixture:

The effectiveness of an admixture depends on several factors, including:

i. Type and amount of cement
ii. Water content
iii. Mixing time
iv. Slump
v. Temperatures of the concrete and air
vi. Aggregate shape, gradation, and size
vii. Chemical composition of the cement
viii. Admixture dosage and type.

18) What are the objective of concrete mix design? Draw a flow chart for concrete mix
design. Why mix design is registered?
Ans: -
The objective of concrete mix design is to determine the proportions of the constituent materials
that will produce a concrete mix that meets the desired properties and performance requirements.
The following are the objectives of concrete mix design:
i. To achieve the desired strength and durability of concrete.
ii. To ensure that the concrete is workable and can be placed and compacted easily.
iii. To minimize the cost of concrete by using the most economical combination of materials.
iv. To ensure that the concrete is durable and resistant to environmental factors such as freeze-
thaw cycles, chemical attack, and abrasion.
Flow chart for concrete mix design.

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Why mix design is registered:

Mix design is registered to ensure that the concrete mix meets the desired properties and
performance requirements. It is important to register the mix design to ensure that the concrete
produced is consistent and meets the specified requirements. The registered mix design serves as
a reference for future projects and helps to ensure that the quality of the concrete is maintained. It
also helps to ensure that the concrete is durable and resistant to environmental factors such as
freeze-thaw cycles, chemical attack, and abrasion.

19) Describe in details the ways to control Alkali aggregate reaction.

Ans: -
Alkali aggregate reaction (AAR) is a chemical reaction between alkalis in the concrete and reactive
components of the aggregates. This reaction can cause expansion and cracking over a period of
many years. Here are some ways to control alkali aggregate reaction:
a. Use low-alkali cement: The use of low-alkali cement can help to reduce the risk of
AAR. Low-alkali cement contains less than 0.6% alkali content.
b. Use non-reactive aggregates: The use of non-reactive aggregates can help to reduce the
risk of AAR. Non-reactive aggregates are those that do not contain reactive silica or
carbonate minerals.
c. Use pozzolanic admixtures: The use of pozzolanic admixtures such as fly ash, silica
fume, or metakaolin can help to reduce the risk of AAR. These admixtures react with the
alkalis in the concrete and form a non-expansive gel.
d. Limit the amount of alkali in the mix: Limiting the amount of alkali in the mix can
help to reduce the risk of AAR. This can be done by reducing the amount of cement in the
mix or by using a cement with a lower alkali content.
e. Use a protective coating: Applying a protective coating to the concrete surface can help
to reduce the risk of AAR. The coating can prevent moisture from penetrating the concrete
and reacting with the aggregates.
f. Monitor the concrete: Regular monitoring of the concrete can help to detect AAR at an
early stage. This can be done by visual inspection, petrographic analysis, or by using
specialized testing methods.
g. Use air-entraining agents: The use of air-entraining agents can help to reduce the risk of
AAR. These agents create small air bubbles in the concrete, which can help to reduce the
amount of moisture that comes into contact with the aggregates.
h. Limit the amount of moisture: Limiting the amount of moisture that comes into contact
with the concrete can help to reduce the risk of AAR. This can be done by using proper
drainage systems, applying waterproof coatings, or by using a concrete mix with a lower
water-cement ratio.

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20) Explain how the fineness of cement affects the strength of cement.
Ans: -
The fineness of cement has a significant impact on the strength of cement. Here are some ways in
which the fineness of cement affects the strength of cement:
a. Hydration rate: The fineness of cement affects the rate at which cement hydrates. Finer
cement particles have more surface area to react with water, which leads to a faster rate of
hydration. This results in faster strength development.
b. Setting time: The fineness of cement affects the setting time of cement. Finer cement
particles have a higher surface area, which leads to a faster rate of reaction with water. This
can cause the cement to set faster, which can affect the workability of the concrete.
c. Heat of hydration: The fineness of cement affects the heat of hydration of cement. Finer
cement particles have a higher surface area, which leads to a faster rate of reaction with
water. This can cause the temperature of the concrete to rise, which can affect the strength
of the concrete.
d. Workability: The fineness of cement affects the workability of the concrete. Finer
cement particles require more water to achieve the same workability as coarser particles.
This can affect the water-cement ratio, which can affect the strength of the concrete.
e. Surface area: The fineness of cement affects the surface area of cement particles. Finer
cement particles have a higher surface area, which leads to a higher rate of reaction with
water. This can affect the strength of the concrete.

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Unit- II
1) What is workability and explain various factors affecting workability of concrete.
Ans: -

Workability of concrete refers to the ease with which the concrete can be mixed, transported,
placed in forms, and compacted. It is an important property of concrete that affects its strength,
durability, and appearance. The following are the various factors affecting the workability of
concrete:
a. Water content: The amount of water in the concrete mix is a critical factor affecting
workability. The higher the water content, the more workable the concrete will be.
However, excessive water content can lead to bleeding, segregation, and reduced strength.
b. Cement content: The amount of cement in the concrete mix affects the workability of
concrete. A higher cement content can lead to a stiffer mix, which can be more difficult to
work with.
c. Aggregate size and shape: The size and shape of the aggregate affect the workability of
concrete. Larger aggregates require more water to achieve the same workability as smaller
aggregates. Angular and rough aggregates require more water than smooth and rounded
aggregates.
d. Aggregate grading: The grading of the aggregate affects the workability of concrete. A
well-graded aggregate mix can improve the workability of concrete.
e. Admixtures: The use of admixtures can affect the workability of concrete. Admixtures
such as plasticizers and superplasticizers can improve the workability of concrete.
f. Mixing time: The mixing time affects the workability of concrete. Over mixing can
cause the concrete to become stiff and difficult to work with.
g. Temperature: The temperature of the concrete affects the workability of concrete.
Higher temperatures can cause the concrete to set faster, which can affect the workability
of the concrete.
h. Humidity: The humidity of the environment affects the workability of concrete. High
humidity can cause the concrete to set faster, which can affect the workability of the
concrete.

2) Write a short note on hot weather concreting and underwater concreting.

Ans: -

Hot weather concreting and underwater concreting are two specialized techniques used in concrete
construction. Here is a short note on each of them:

Hot weather concreting:

i. Hot weather concreting refers to the process of mixing, placing, and curing concrete in
high-temperature conditions.
ii. Hot weather conditions can lead to problems in mixing, placing, and curing hydraulic
cement concrete that can adversely affect the properties of the concrete.

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iii. The success of hot weather concreting operations depends on the steps taken to slow the
cement hydration reactions within the concrete and to minimize the rate of evaporation of
moisture from the freshly mixed concrete.
iv. Potential concrete problems in hot weather are likely to include increased water demand,
increased rate of slump loss, increased rate of setting, and increased tendency for plastic-
shrinkage cracking.
v. Some precautions that can be taken during hot weather concreting include using cool water
in the mix, shading the concrete from direct sunlight, and using windbreaks to reduce wind
speed.
Underwater concreting:
i. Underwater concreting refers to the process of placing and curing concrete underwater.
ii. Underwater concreting is used in the construction of structures such as dams, bridges, and
underwater tunnels.
iii. The process of underwater concreting involves the use of specialized equipment such as
tremie pipes, which are used to place the concrete underwater.
iv. The concrete mix used in underwater concreting is designed to be highly workable and to
have a low water-cement ratio to ensure that the concrete can be placed and compacted
underwater.
v. The curing of underwater concrete is done by keeping the concrete wet for a period of time
to allow the concrete to gain strength.
vi. Some precautions that can be taken during underwater concreting include ensuring that the
concrete is placed in a continuous pour to prevent cold joints, using a tremie pipe to place
the concrete, and using a sealant to prevent water from entering the concrete.

3) What is curing? Explain various types of curing with their suitability?

Ans: -

Curing is the process of maintaining satisfactory moisture content and temperature in freshly cast
concrete for a definite period of time immediately following placement. The purpose of curing is
to ensure that the concrete develops the desired properties in terms of strength and durability. Here
are the various types of curing with their suitability:
a. Water curing: Water curing involves keeping the concrete surface continuously wet for
a period of time. This can be done by spraying water on the surface or by covering the
surface with wet burlap or other materials. Water curing is suitable for all types of concrete.
b. Membrane curing: Membrane curing involves covering the concrete surface with a
membrane to prevent moisture loss. This can be done using plastic sheets, curing
compounds, or other materials. Membrane curing is suitable for horizontal surfaces such
as floors and pavements.
c. Steam curing: Steam curing involves exposing the concrete to high-temperature steam
to accelerate the curing process. This is suitable for precast concrete elements and other
applications where rapid strength gain is required.

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d. Chemical curing: Chemical curing involves the use of chemical compounds to

accelerate the curing process. This is suitable for applications where rapid strength gain is
required.
e. Carbonation curing: Carbonation curing involves exposing the concrete to carbon
dioxide to accelerate the curing process. This is suitable for precast concrete elements and
other applications where rapid strength gain is required.

4) What is mean by maturity of concrete?

Ans: -

Concrete maturity is an index value that represents the progression of concrete curing. It is a real-
time approach to estimating the compressive strength of in-place concrete, and relating it to the
effects of temperature and time. The maturity of concrete is determined by the relationship
between concrete temperature, time, and strength gain. Here are some key points about concrete
maturity:
i. Maturity is the relationship between concrete temperature, time, and strength gain.
ii. Maturity is represented by an index value that can be measured in real time in the field.
iii. The maturity of concrete is determined by the sum of the product of age and temperature
(curing).
iv. The maturity method is a way of evaluating new concrete’s in-place strength by relating
time and temperature measurements to actual strength values.
v. The standard practice for measuring maturity is designated ASTMC1074.
vi. The maturity method allows evaluation of concrete strength at a specific time – it is a
precise and time-sensitive method of measuring concrete strength.
vii. The maturity of concrete is important in determining when formwork can be removed,
when post-tensioning can be applied, and when the concrete can be loaded.

5) What are the factors affecting compressive strength of concrete.

Ans: -
The compressive strength of concrete is an important property that determines the ability of
concrete to withstand compressive loads. Here are the factors affecting the compressive strength
of concrete:
a. Water-cement ratio: The water-cement ratio is one of the most important factors
affecting the strength of concrete. A lower water-cement ratio leads to higher strength of
concrete. Generally, the water-cement ratio of 0.45 to 0.60 is used.
b. Quality of cement: The quality of cement used in concrete structures affects the
compressive strength of concrete.
c. Quality of aggregates: The strength of concrete depends upon the strength of
aggregates. Low-quality aggregates reduce the strength of concrete.

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d. Compaction of concrete: Compaction of concrete increases the density of the concrete,

which makes the concrete compact and dense. The presence of air voids in concrete greatly
reduces its strength.
e. Curing: Proper curing of concrete is essential for achieving the desired compressive
strength. The curing process should be done for a sufficient period of time and at the
appropriate temperature.
f. Age of concrete: The compressive strength of concrete increases with age. The strength
gain is rapid in the first 28 days, but it continues to increase for a longer period.
g. Type of cement: The type of cement used in the concrete mix affects the compressive
strength of concrete. Different types of cement have different strength properties.
h. Admixtures: The use of admixtures can affect the compressive strength of concrete.
Admixtures such as plasticizers and superplasticizers can improve the workability and
strength of concrete.
i. Alkali content: The alkali content of cement affects the compressive strength of
concrete. Cements with a high alkali content produce concretes with lower compressive
strength.

6) Explain Modulus of elasticity of concrete.

Ans: -
Modulus of elasticity of concrete (Ec) is defined as the ratio of the applied stress to the
corresponding strain within the elastic limit. It is a measure of the stiffness of concrete and reflects
the ability of concrete to deflect elastically.

Key points about the modulus of elasticity of concrete:

i. The modulus of elasticity of concrete is sensitive to aggregate and mixture proportions of
concrete.
ii. The value of elastic modulus is higher for stiffer materials.
iii. The modulus of elasticity of concrete can be defined as the slope of the line drawn from
stress of zero to a compressive stress of 0.45f’c.
iv. The strength of concrete is dependent on the relative proportion and modulus of elasticity
of the aggregate.
v. The modulus of elasticity of concrete is important in the design of concrete structures as it
is used to calculate the deflection of concrete members under load.
vi. The modulus of elasticity of concrete can be determined through laboratory testing or by
using empirical formulas provided by different codes.

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7) Explain the following.

i) Effect of height/diameter ratio on strength.
ii) Compression test.
Ans: -
i) Effect of height/diameter ratio on strength: -

The height/diameter ratio can have an effect on the strength of a material

i. The compressive strength of concrete increases as the height/diameter ratio decreases.

ii. The compressive strength of high-performance concrete specimens increases with

decreasing height/diameter ratio.

iii. The compressive strength of cylindrical concrete specimens increases as the

height/diameter ratio decreases.

iv. The unconfined compressive strength of a clayey soil increases with the increase of the
height/diameter ratio.
v. The loading rate and height/diameter ratio are important factors affecting the compression
characteristics of aviation alloys.

ii) Compression test: -

i. Compression testing is a mechanical test that is used to determine how a product or material
responds when it is compressed, squashed, crushed, or flattened.
ii. The test measures fundamental parameters that determine the specimen behavior under a
compressive load.
iii. The purpose of a compression test is to evaluate the static compressive strength
characteristics of materials, products, and components.
iv. The test is used to determine the behavior or response of a material while it experiences a
compressive load by measuring fundamental variables such as strain, stress, and
deformation.
v. The test is performed by loading a standardized specimen under compressive stress until it
breaks or until a first crack appears.
vi. Compression testing is a fundamental mechanical test, similar in nature to tensile and bend
tests.
vii. The test is used to assess the strength of components such as automotive and aeronautical
control switches, compression springs, bellows, keypads, package seals, PET containers,
PVC/ABS pipes, solenoids, etc.
viii. Compression testing is also used to characterize the compressive properties of materials
such as foam, metal, PET, and other plastics and rubber.
ix. The benefits of compression testing include providing data on the integrity and safety of
materials, components, and products, helping manufacturers ensure that their finished
products meet the required standards.

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8) Short note on indirect tension test with its advantages.

Ans: -
The indirect tensile test (ITT) is a method of testing the tensile strength of materials that involves
applying a force to a specimen in a manner that is not directly along the axis of the specimen. The
ITT is performed by placing a cylindrical specimen between two platens and applying a
compressive force to the platens. The force is then transferred to the specimen, which is subjected
to tensile stress.
Advantages:

i. A strength of a selected plane is able to determine.

ii. The ITT has been adopted by researchers for fatigue testing of bituminous mixes.

iii. The ITT can better replace the direct tensile test at low temperatures and diminish the
deviation of the test data.

iv. The ITT is useful for testing the tensile strength of stabilized materials.
v. The ITT is useful for testing the tensile behavior and properties of asphalt mixtures.

9) Define and classify Shrinkage in concrete. How it can be controlled?

Ans: -
Concrete shrinkage is the decrease in length or volume of concrete caused by changes in moisture
content or chemical reactions. There are four categories of shrinkage seen in concrete: Drying
Shrinkage, Chemical Shrinkage, Plastic Shrinkage, and Autogenous Shrinkage.

❖ Drying Shrinkage: This is the significant shrinkage mechanism in most concrete.

Moisture lost during drying shrinkage is evaporated into the environment as the concrete
dries out, and if not properly managed, it can lead to wide joint openings, cracking from
internal stresses, and slab curling.

❖ Chemical Shrinkage: This is the shrinkage due to the chemical reaction between cement
and water during the hydration process.

❖ Plastic Shrinkage: This is the shrinkage that occurs when the concrete is still in its plastic
state and is caused by the evaporation of water from the surface of the concrete.

❖ Autogenous Shrinkage: This is the shrinkage due to the self-desiccation of the cement
paste as it hardens.
To control concrete shrinkage, the following measures can be taken:
i. Reduce water quantity in the concrete mix.

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ii. Use shrinkage-reducing admixtures that compensate for concrete shrinkage by creating
expansive crystals.
iii. Use water-reducing admixtures that reduce water content and concrete shrinkage.
iv. Use aggregates with low shrinkage potential.
v. Control the relative humidity of the atmosphere at which the concrete specimen is kept.
vi. Adjust the concrete mixture and use proven construction techniques to control plastic
shrinkage.

10) What do you understand by Creep? What are various factors affecting it?
Ans: -
Creep is the time-dependent deformation below the strength of the material yield of a material
under constant stress. It is the tendency of a solid material to undergo slow deformation while
subject to persistent mechanical stresses. Creep can occur as a result of long-term exposure to high
levels of stress that are still below the yield strength of the material. Creep is more severe in
materials that are subjected to heat for long periods and generally increases as they near their
melting point.
Factors affecting creep:

a. Temperature: Creep is more severe in materials that are subjected to heat for long periods
and generally increases as they near their melting point.

b. Stress level: Creep occurs as a result of long-term exposure to high levels of stress that are
still below the yield strength of the material.

c. Time: Creep is a time-dependent deformation under a certain applied load.

d. Material composition: The temperature at which creep begins depends on the alloy
composition.

e. Microstructure: The microstructure of a material can affect its creep behavior.

To control creep, the following measures can be taken:

i. Reduce the stress level on the material.
ii. Reduce the temperature of the material.
iii. Use materials with a lower susceptibility to creep.
iv. Modify the microstructure of the material to make it more resistant to creep.

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11) Explain under water concreting by the use of Tremie Pipe method.
Ans: -
Underwater concreting by the use of Tremie Pipe method is a process of placing concrete
underwater using a tremie pipe. The tremie pipe is a long steel pipe with a diameter of 15 to 30 cm
that is inserted vertically into the water. The pipe should be long enough that it reaches the bottom
of the water body. The tremie pipe is used to deliver the concrete to the desired location
underwater.
Procedure for concreting by Tremie Pipe method:
i. Place the tremie pipe to the concrete placement point.
ii. After the tremie pipe reaches the desired depth, fit a funnel in the top end for concrete
pouring.
iii. Pour the concrete with high slump into the funnel until the tremie pipe is filled.
iv. Lower the tremie pipe slowly into the water to the desired depth.
v. Start the concrete pouring by lifting the plug at the bottom of the tremie pipe.
vi. Continue the concrete pouring until the tremie pipe is completely emptied.
vii. After the concrete pouring is completed, slowly lift the tremie pipe to avoid the formation
of voids.
Advantages of Tremie Pipe method:

i. It is the only satisfactory method for underwater concreting.

ii. It is convenient for pouring large amounts of high flowable concrete.

iii. It prevents intermixing of both concrete and water.

Disadvantages of Tremie Pipe method:

i. It requires a large amount of equipment and labor.

ii. It is a time-consuming process.

iii. It requires a high degree of skill and experience to perform correctly.

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12) Explain the various stages of manufacture of concrete.

Ans: -
The manufacture of concrete involves several stages, which are as follows:
a. Batching: The first step involves gathering the ingredients necessary to produce the
particular type of concrete. The measurement of materials like aggregates, cement, water
necessary for preparing different grades of concrete is batching. It is by two processes. One
is volume and other is weight batching. The volume batching is by mixing materials with
its volume. And weight batching is by the self-weight ratio of materials.
b. Mixing: Mixing is to produce uniform, quality concrete. The mixing process involves
adding water to the dry mix of cement and aggregates and then mixing them thoroughly
until they form a consistent, plastic-like mass. Generally, mixing is done by three ways:
hand mixing, machine mixing, and ready-mix concrete.
c. Transporting: The mixed concrete is transported to the construction site by various
means like trucks, dumpers, and conveyors.
d. Placing: The concrete is placed in the formwork or molds at the construction site. The
formwork is designed to hold the concrete in place until it hardens.
e. Compacting: The concrete is compacted to remove any air pockets or voids that may
have formed during the placement process. This is done to ensure that the concrete is dense
and strong.
f. Curing: The concrete is allowed to cure or harden for a specific period. During this time,
the concrete gains strength and durability. The curing process can be done by various
methods like water curing, steam curing, and chemical curing.

13) Explain the various properties which affect the quality of concrete.
Ans: -
The quality of concrete depends on various properties that affect its strength, durability, and
appearance. Here are some of the properties that affect the quality of concrete:
a. Workability: Workability is the property of freshly mixed concrete that determines the
ease and homogeneity with which it can be mixed, placed, consolidated, and finished. It
directly impacts strength, quality, appearance, and even the cost of labor for placement and
finishing operations. Workability is affected by factors such as water-cement ratio, cement
content, aggregate size and shape, and use of admixtures.
b. Setting time: Setting time is the time required for the concrete to harden after mixing. It
is affected by factors such as water-cement ratio, temperature, and type of cement.
c. Bleeding: Bleeding is the separation of water from the concrete mix. It can affect the
strength and durability of the concrete.
d. Segregation: Segregation is the separation of coarse aggregates from the concrete mix. It
can affect the strength and durability of the concrete.
e. Hydration: Hydration is the chemical reaction that occurs between cement and water,
which causes the concrete to harden. It is affected by factors such as water-cement ratio,
temperature, and curing.
f. Air entrainment: Air entrainment is the process of adding small air bubbles to the
concrete mix. It can improve the durability of the concrete by reducing the effects of freeze-
thaw cycles.

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g. Density: Density is the mass per unit volume of the concrete. It affects the strength and
durability of the concrete.
h. Water-cement ratio: Water-cement ratio is the ratio of the weight of water to the weight
of cement in the concrete mix. It affects the strength and durability of the concrete.
i. Cement content: Cement content is the amount of cement in the concrete mix. It affects
the strength and durability of the concrete.
j. Aggregate properties: Aggregate properties such as size, shape, and grading affect the
workability and strength of the concrete.

14) Write a detailed note on water cement ratio and bond strength between cement & steel
reinforcement.
Ans: -
Water-cement ratio and bond strength between cement and steel reinforcement are two important
factors that affect the quality of concrete.

Water-Cement Ratio:
i. The water-cement ratio is the ratio of the weight or volume of water to the weight of cement
in a concrete mixture.
ii. It is a critical factor in determining the strength, workability, and durability of concrete.
iii. A lower water-cement ratio results in higher strength and durability of concrete, while a
higher water-cement ratio results in lower strength and durability.
iv. The water-cement ratio affects the workability of concrete, which is the ease with which it
can be mixed, placed, consolidated, and finished.
v. The water-cement ratio also affects the porosity of concrete, which is the amount of voids
or empty spaces in the concrete.
vi. A good concrete must be prepared with as little water as possible, but with enough water
to hydrate the cement minerals and to properly handle it.
vii. The water-cement ratio varies from 0.4 to 0.6 for normal concrete, and 0.7 for pumped
concrete.
viii. The selection of the water-cement ratio depends on the requirement of workability in
different exposure conditions and nature of work.
Bond Strength between Cement and Steel Reinforcement:
i. The bond strength between cement and steel reinforcement is the ability of the concrete to
adhere to the steel reinforcement.
ii. It is an important factor in determining the strength and durability of reinforced concrete
structures.
iii. The bond strength is affected by factors such as the surface condition of the steel
reinforcement, the diameter of the reinforcement, the cover thickness, and the quality of
the concrete.

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iv. The surface of the steel reinforcement should be free from rust, mill scale, and other
contaminants that can reduce the bond strength.
v. The diameter of the reinforcement affects the bond strength, with larger diameter
reinforcement having higher bond strength.
vi. The cover thickness is the distance between the surface of the concrete and the surface of
the steel reinforcement. A thicker cover results in lower bond strength.
vii. The quality of the concrete affects the bond strength, with higher quality concrete having
higher bond strength.
viii. The bond strength can be improved by using deformed reinforcement, which has a rough
surface that provides better adhesion to the concrete.

15) Compare volume batching & weight Batching.

Ans: -
Sr. No. Weight Batching Volume Batching
• • The concrete ingredients are batched
The concrete ingredients are batched/
1
proportioned based on weight. / proportioned based on volume.
• • Difficult
Each batch is weighed which makes it to detect overruns or
2 easy to detect overruns or incorrect incorrect dosages.
dosages.
• • Admixtures are difficult to batch at
Admixtures can be dosed at any stage of
3 batching and in multiple dumps- thereby certain stages of the batching
achieving optimal performance. sequence.
4 • More precise method. • Less precise method.
5 • Need skilled labours • No need to required skilled labours.
6 • Operation difficult. • Easy to operate.
• Speed of construction is high. • Speed of construction is slower than
7
weigh batching.
8 • Maintenance cost is practically nil.
Maintenance cost is high.
• This method is expensive. • This method is cheaper and
9
economical.

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16) Explain Relation between creep & time.

Ans: -
Creep is a time-dependent deformation under a certain applied load. The relation between creep
and time can be explained as follows:
a. Creep curve: The creep curve is generally divided into three stages: instantaneous creep,
primary creep, and secondary creep. The primary creep stage is characterized by a
decreasing creep rate, while the secondary creep stage is characterized by a constant creep
rate.
b. Time-dependent deformation: Creep is the effect due to which concrete undergoes
continuous deformation under sustained loading applied for a considerable time. The
deformation-induced for a specimen under sustained loading increases with time and can
be many times greater than its initial immediate value.
c. High temperature: Creep generally occurs at high temperature (thermal creep), but can
also happen at room temperature.
d. Load: The deformation under creep is induced due to sustained loading applied for a
considerable time. The creep deformation rate increases with time under sustained load.
e. Creep and shrinkage: Creep and shrinkage are time-dependent effects that can cause
continuous deformation and contraction in concrete, respectively. Shrinkage is
independent of applied loads, while creep is induced due to sustained loading.

17) Explain plastic shrinkage and drying shrinkage.

Ans: -
Plastic shrinkage and drying shrinkage are two types of shrinkage that occur in concrete.

Plastic Shrinkage:
i. Plastic shrinkage occurs when water is lost from the surface of the concrete while it is still
in a semi-fluid (plastic) state.
ii. This type of shrinkage generally occurs within the first few hours after the concrete is
placed.
iii. Plastic shrinkage can cause cracks on the surface of the concrete, which can be unsightly
and reduce the durability of the concrete.
iv. The main reason for shrinkage cracks under plastic shrinkage is due to the water absorption
from the concrete by the aggregate.
Drying Shrinkage:
i. Drying shrinkage occurs when moisture is lost from the concrete after it has hardened.
ii. This type of shrinkage can occur over a period of months or even years after the concrete
is placed.
iii. Drying shrinkage is the most significant shrinkage mechanism in most concrete.
iv. Moisture lost during drying shrinkage is evaporated into the environment as the concrete
dries out, and if not properly managed, it can lead to wide joint openings, cracking from
internal stresses, and slab curling.

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18) What is compaction, Explain different method's in compaction.

Ans: -
Compaction is a process of increasing soil density and removing air, usually by mechanical means.
It is an important process in construction, as it improves the strength and stiffness of soil.
There are different methods used in compaction, which are explained below:
a. Static force: This method uses the pressure of a weight to physically and continuously
compact soil. It is the most common method used in compaction.
b. Manipulation: This method involves kneading or shearing the soil in alternating
movements to compact soil at greater depths.
c. Dynamic force: This method involves adding a vibrating mechanism to the compactor to
apply dynamic force to the soil.
d. Impact force: This method involves dropping a weight onto the soil to compact it.
e. Rolling: This method involves using a roller to compact soil. It is commonly used in road
construction.
f. Tamping: This method involves using a tamping machine to compact soil. It is
commonly used in small-scale construction projects.
The degree of compaction is measured by dry unit weight and depends on the water content and
compactive effort. The maximum dry unit weight occurs at an optimum water content. Compaction
is employed in the construction of road bases, runways, earth dams, and other structures that
require a stable foundation.

19) Explain the relation between compression and tensile strength in concrete.
Ans: -
i. The relationship between compression and tensile strength in concrete is not a direct
proportionality.
ii. The theoretical compressive strength of concrete is eight times larger than its tensile
strength, but the ratio of tensile to compressive strength is lower for higher compressive
strengths.
iii. The rate of increase of tensile strength is of decreasing order with higher compressive
strength.
iv. The tensile strength of concrete is relatively low, about 10 to 15% of the compressive
strength, occasionally 20%.
v. The tensile strength of concrete is more sensitive to improper curing than its compressive
strength.
vi. The inferior quality of gel due to improper curing may be the reason for the lower tensile
strength of concrete.
vii. The relation between the flexure strength and compressive strength depends on the type of
coarse aggregate used, except in high strength concrete.
viii. Concrete is made of 'little' stones, which means that it always has microscopic cracks in its
body.
ix. When tensile forces are applied to concrete, these cracks become elongated and eventually
the concrete breaks apart.

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20) Explain in Brief segregation, Bleeding & Water Cement ratio.

Ans: -
Segregation, bleeding, and water-cement ratio are important concepts in concrete technology.

Segregation:
i. Segregation is the separation of constituent materials (cement paste and aggregates) of
concrete from each other during handling and placement.
ii. Segregation can be of three types: cement paste separated from the concrete during its
plastic stage before hardening, separation of coarse aggregate from the concrete mixture,
and water separate from the concrete mix.
iii. Segregation affects the structural strength and durability of structures. A good concrete is
one in which all the ingredients are properly distributed to make a homogeneous mixture.
iv. The primary cause of segregation in concrete is the differences in specific gravity of the
concrete material (fine, coarse aggregate, and cement). Other factors causing segregation
in concrete include transporting concrete mixes for long distances, poorly proportioned
mix, dropping concrete from more than 1m, and vibrating concrete for a long time.
v. Segregation can be controlled by maintaining proper proportioning of the mix, peculiar
handling, placing, transporting, compacting, and finishing of concrete, and adding air
entraining agents, admixtures, and fibers.
Bleeding:
i. Bleeding is the tendency of the water to rise to the surface of freshly laid concrete. This
results from the inability of the solid material of concrete to hold all the water mixed for
preparation.
ii. Bleeding is a form of segregation.
iii. Bleeding can cause surface scaling, dusting, and reduced durability of concrete. It can also
lead to the formation of voids and honeycombing in the concrete.
iv. Bleeding can be minimized by reducing the water-cement ratio, using a well-graded
aggregate, and using admixtures such as air-entraining agents and plasticizers.
Water-Cement Ratio:
i. The water-cement ratio is the ratio of the weight of water to the weight of cement in a
concrete mix.
ii. It is an important factor in determining the strength and durability of concrete.
iii. A lower water-cement ratio results in higher strength and durability of concrete.
iv. However, a lower water-cement ratio can also result in decreased workability and increased
risk of cracking.
v. The water-cement ratio should be carefully controlled to achieve the desired strength and
durability of concrete.

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21) What do you mean by M5, M10, M15, M20, M25 concrete? Give its proper ratio. Is
concrete is necessary. Explain why?
Ans: -
i. Concrete is a mixture of cement, sand, and aggregates in a specific ratio.
ii. The ratio of these materials determines the strength and durability of the concrete.
iii. The strength of concrete is measured in terms of its compressive strength, which is the
maximum load it can bear before it fails.
iv. The different grades of concrete are classified into M5, M7.5, M10, M15, M20, M25,
M30, M35, M40, M45, M50, M55, M60, M65, M70, M75, and M80.
a. M5 Grade of Concrete: It is an ordinary grade of concrete with a compressive strength of
5 N/mm2. The mix ratio is 1:5:10 (Cement: Sand: Aggregates).
b. M10 Grade of Concrete: It is an ordinary grade of concrete with a compressive strength
of 10 N/mm2. The mix ratio is 1:3:6 (Cement: Sand: Aggregates).
c. M15 Grade of Concrete: It is an ordinary grade of concrete with a compressive strength
of 15 N/mm2. The mix ratio is 1:2:4 (Cement: Sand: Aggregates).
d. M20 Grade of Concrete: It is a standard grade of concrete with a compressive strength of
20 N/mm2. The mix ratio is 1:1.5:3 (Cement: Sand: Aggregates).
e. M25 Grade of Concrete: It is a standard grade of concrete with a compressive strength of
25 N/mm2. The mix ratio is 1:1:2 (Cement: Sand: Aggregates).

22) Write short notes on Split Cylinder Test.

Ans: -
The Split Cylinder Test is a type of indirect tensile test used to determine the tensile strength of
concrete. In this test, a standard test cylinder of concrete specimen is placed horizontally between
the loading surfaces of a compression testing machine. The compression load is applied
diametrically and uniformly along the length of the cylinder until the failure of the cylinder along
the vertical diameter. The cylinder splits into two halves along this vertical plane due to indirect
tensile stress generated by Poisson's effect. The test is performed in accordance with ASTM C496.
i. The Split Cylinder Test is also known as the Splitting Tensile Strength Test or the Brazilian
Test.
ii. The test is performed on a cylindrical specimen of concrete.
iii. The test is an indirect method of testing the tensile strength of concrete because it is difficult
to apply true axial load to a concrete specimen.
iv. The test is performed by applying a compressive load diametrically and uniformly along
the length of the cylinder until the failure of the cylinder along the vertical diameter.
v. The cylinder splits into two halves along this vertical plane due to indirect tensile stress
generated by Poisson's effect.
vi. The test is performed to determine the tensile strength of concrete.
vii. The test is performed in accordance with ASTM C496.

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viii. The test is useful in determining the quality of concrete and its ability to resist tensile
stresses.
ix. The test is performed on a standard test cylinder of concrete specimen (300 mm X 150mm
diameter).
x. The test is performed by placing the cylinder horizontally between the loading surfaces of
a compression testing machine.
xi. The test is performed by applying a compressive load diametrically and uniformly along
the length of the cylinder until the failure of the cylinder along the vertical diameter.
xii. The cylinder splits into two halves along this vertical plane due to indirect tensile stress
generated by Poisson's effect.
xiii. The test is performed by using strips of plywood between the specimen and loading platens
of the testing machine to allow the uniform distribution of the applied load and to reduce
the magnitude of the high compressive stresses near the points of application of this load.

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Unit- III
1) Explain concrete mix design procedure as per IS: 10262:2009.
Ans: -
The concrete mix design procedure as per IS: 10262:2009 involves the following steps:
i. Calculation of target strength of concrete based on the type of structure, exposure
conditions, and durability requirements.
ii. Selection of water-cement ratio based on the target strength and the type of cement used.
iii. Determination of aggregate air content based on the maximum size of aggregate and the
type of aggregate used.
iv. Selection of water content for concrete based on the aggregate air content and the water-
cement ratio.
v. Selection of cement content for concrete based on the water content and the water-cement
ratio.
vi. Calculation of aggregate ratio based on the water content, cement content, and water-
cement ratio.
vii. Calculation of aggregate content for concrete based on the aggregate ratio and the cement
content.
viii. Trial mixes for testing concrete mix design strength.

2) What are the significance of fly-ash & pozzolana in view of quality of concrete?
Ans: -
Fly ash and pozzolana are supplementary cementitious materials that are used in the production of
concrete.

Significance of Fly Ash:

i. Fly ash is a by-product of coal combustion and using it as a pozzolan helps reduce the
environmental impact of concrete construction.
ii. Fly ash is a supplementary cementitious material that contributes to the properties of the
hardened concrete through hydraulic or pozzolanic activity, or both.
iii. Fly ash improves the workability, pumpability, cohesiveness, finish, ultimate strength, and
durability of concrete.
iv. Fly ash reduces cracking, permeability, and bleeding, creating a dense, high-durability
concrete that is resistant to environmental factors.
v. Fly ash can be used to replace a portion of the cement in concrete, which reduces the overall
impact on the environment and recycles hazardous waste.
vi. Fly ash can continue to hydrate for six months or longer, leading to much higher ultimate
strength than concrete without fly ash.

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vii. Significance of Pozzolana:

viii. Pozzolana is a naturally occurring or synthetic material that reacts with calcium hydroxide
in the presence of water to form cementitious compounds.
ix. Pozzolana improves the workability, durability, and strength of concrete.
x. Pozzolana reduces the heat of hydration, which reduces the risk of thermal cracking in
concrete.
xi. Pozzolana reduces the permeability of concrete, which improves its resistance to
environmental factors.
xii. Pozzolana can be used to replace a portion of the cement in concrete, which reduces the
overall impact on the environment and recycles hazardous waste.

3) Explain mix design by Road Note No. 4 (BS).

Ans: -

Mix design by Road Note No. 4 (BS) is a method of concrete mix design that was developed in
the UK.
i. Determine the target strength of the concrete based on the type of structure, exposure
conditions, and durability requirements.
ii. Determine the water-cement ratio based on the target strength and the type of cement used.
iii. Determine the aggregate-cement ratio based on the type of aggregate used.
iv. Determine the aggregate grading based on the maximum size of aggregate and the type of
aggregate used.
v. Determine the amount of entrained air based on the exposure conditions and the type of
aggregate used.
vi. Determine the amount of water to be added based on the water-cement ratio and the amount
of entrained air.
vii. Determine the amount of cement to be added based on the water-cement ratio and the
aggregate-cement ratio.
viii. Determine the amount of fine aggregate and coarse aggregate to be added based on the
aggregate grading and the water-cement ratio.
ix. Adjust the mix proportions based on the trial mixes and the results of laboratory testing.

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4) Explain Mix Design process? What are the factors affecting mix properties? Also explain
aggregate cement ratio.
Ans: -

Mix design is the process of selecting suitable ingredients of concrete and determining their
relative amounts with the objective of producing a concrete of the required workability, strength,
and durability as economically as possible. The mix design process involves various steps,
calculations, and laboratory testing to find the right mix proportions.
i. Calculation of target strength of concrete based on the type of structure, exposure
conditions, and durability requirements.
ii. Selection of water-cement ratio based on the target strength and the type of cement used.
iii. Determination of aggregate air content based on the maximum size of aggregate and the
type of aggregate used.
iv. Selection of water content for concrete based on the aggregate air content and the water-
cement ratio.
v. Selection of cement content for concrete based on the water content and the water-cement
ratio.
vi. Calculation of aggregate ratio based on the water content, cement content, and water-
cement ratio.
vii. Calculation of aggregate content for concrete based on the aggregate ratio and the cement
content.
viii. Trial mixes for testing concrete mix design strength.
Factors affecting mix properties:
❖ Type of cement used
❖ Type and size of aggregate used
❖ Water-cement ratio
❖ Air content
❖ Admixtures used
❖ Mixing time and method
❖ Curing conditions
Aggregate-cement ratio:

Aggregate-cement ratio is the ratio of the weight of aggregate to the weight of cement in a concrete
mix. It is an important factor in determining the strength and durability of concrete. The aggregate-
cement ratio depends on the type of aggregate used, the maximum size of aggregate, and the water-
cement ratio. The aggregate-cement ratio should be selected based on the target strength and the
type of structure. A lower aggregate-cement ratio results in a higher strength and durability of
concrete, but it also results in a higher cost.

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5) Write a short note on corrosion inhibitors and water proofing agents.

Ans: -
Corrosion inhibitors and waterproofing agents are chemical products used to protect concrete
structures from damage caused by corrosion and water penetration.

Corrosion inhibitors:
i. Corrosion inhibitors are chemical compounds that slow down the rate of corrosion in
metals or alloys that come into contact with fluids.
ii. They are classified as anodic, cathodic, film-forming, and oxygen-absorbing agents
depending on their mode of action.
iii. The effectiveness of most corrosion inhibitors is significantly affected by the water’s
chemical properties and by physical conditions such as temperature and flow velocity.
iv. Corrosion inhibitors can be used in industry and also found in over-the-counter products,
typically in spray form in combination with a lubricant and sometimes a penetrating oil.
v. They may be added to water to prevent leaching of lead or copper from pipes.
vi. A common mechanism for inhibiting corrosion involves formation of a coating, often a
passivation layer, which prevents access of the corrosive substance to the metal.
Water proofing agents:
i. Waterproofing agents are chemical products that prevent water penetration into concrete
structures.
ii. They can be applied to the surface of concrete structures or added to the concrete mix
during production.
iii. Waterproofing agents can be classified as integral or surface-applied agents.
iv. Integral waterproofing agents are added to the concrete mix during production to improve
the water resistance of the concrete.
v. Surface-applied waterproofing agents are applied to the surface of concrete structures to
prevent water penetration.
vi. Surface-applied waterproofing agents can be further classified as coatings, sealers, and
membranes.
vii. Coatings and sealers are applied to the surface of concrete structures to form a protective
layer that prevents water penetration.
viii. Membranes are applied to the surface of concrete structures to form a waterproof barrier
that prevents water penetration.

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6) Explain the four variable factors to be consider in connection with specifying a concrete.
mix.
Ans: -
When specifying a concrete mix, there are four variable factors that need to be considered. These
factors are:
a. Water-cement ratio: The water-cement ratio is the ratio of the weight of water to the
weight of cement in a concrete mix. It is an important factor in determining the strength
and durability of concrete. The water-cement ratio should be selected based on the target
strength and the type of structure.
b. Cement content: The cement content is the amount of cement used in a concrete mix. It
is an important factor in determining the strength and durability of concrete. The cement
content should be selected based on the water-cement ratio and the type of aggregate used.
c. Relative proportion of fine and coarse aggregates: The relative proportion of fine and
coarse aggregates is the ratio of the weight of fine aggregate to the weight of coarse
aggregate in a concrete mix. It is an important factor in determining the workability and
strength of concrete. The relative proportion of fine and coarse aggregates should be
selected based on the maximum size of aggregate and the water-cement ratio.
d. Admixture content: Admixtures are chemical products added to concrete to improve its
properties. The admixture content is the amount of admixture used in a concrete mix. It is
an important factor in determining the workability and strength of concrete. The admixture
content should be selected based on the type of admixture used and the target strength of
concrete.

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Unit- IV
1) Write short note on
a) Fiber reinforced concrete
b) Shotcrete pumped concrete.
Ans: -
a) Fiber reinforced concrete.
Fiber reinforced concrete (FRC) is a composite material consisting of cement, mortar or concrete
and discontinuous, discrete, uniformly dispersed suitable fibers. The fibers used in FRC include
steel fibers, glass fibers, synthetic fibers, natural fibers, and others.

Types of fibers:
a. Steel fibers: These fibers are generally used for providing tensile strength and toughness
to concrete.
b. Glass fibers: Glass fiber reinforced concrete (GFRC) has been predominantly used in
architectural applications and modified cement-based panel structures.
c. Synthetic fibers: Most are manufactured from polypropylene, polyethylene, polyester,
nylon, and other synthetic materials, such as carbon, aramid, and acrylics. Micro-synthetic
fibers are used for the control and mitigation of plastic shrinkage cracking.
Natural fibers: Natural fibers such as sisal, jute, coir, bamboo, and hemp are used in FRC
d.
to provide tensile strength and toughness.
Advantages of FRC:
i. Improved durability and toughness
ii. Reduced permeability and bleeding of water
iii. Improved freeze-thaw resistance
iv. Reduced cracking due to plastic shrinkage and drying shrinkage
v. Increased resistance to plastic shrinkage during curing
vi. Improved mix cohesion, improving pumpability over long distances
Applications of FRC:
a. Industrial projects: Macro-synthetic fibers are used to improve concrete’s durability.
Made from synthetic materials, these fibers are long and thick in size and may be used as
a replacement for bar or fabric reinforcement.
b. Architectural applications: GFRC is predominantly used in architectural applications and
modified cement-based panel structures.
c. Pavements and roads: FRC is used in pavements and roads to improve their durability
and toughness.
d. Precast concrete products: FRC is used in precast concrete products to improve their
strength and durability.

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b) Shotcrete pumped concrete.

Shotcrete is a type of concrete that is sprayed onto a surface, as opposed to being poured.
It is typically made of Portland cement, water, and aggregates such as sand and gravel.
Shotcrete is applied at a high velocity, which allows it to form a strong bond with whatever it is
applied to.

Types of shotcrete:
a. Dry mix process: In this process, water is added at the nozzle while spraying the concrete
or mortar mix.
b. Wet mix process: In this process, water is added to the concrete or mortar mix before
placing it in the shotcreting equipment.
Applications of shotcrete:
i. Shotcrete is used for rapid concrete construction, such as repair of damaged buildings,
underground construction, and new constructions.
ii. Shotcrete is used for stabilization and support for structures, such as tunnels and reservoirs.
iii. Shotcrete is used to fill gaps and holes, seal cracks, and create a smooth surface.
Advantages of shotcrete:
i. Shotcrete saves money and time compared to traditional concrete pouring methods.
ii. Shotcrete produces better-quality concrete.
iii. Shotcrete can be used in remote areas where traditional concrete pouring methods are not
feasible.
iv. Shotcrete can be used to repair and strengthen existing structures.

2) Define Shrinkage? Explain in brief various classification of shrinkage and factors affecting
shrinkage.
Ans: -
Shrinkage in concrete is the change in volume over time that decreases the dimensions of the
concrete.
Shrinkage can be classified into different types, including:
a. Plastic shrinkage: This type of shrinkage occurs when the concrete is still in its plastic
state and is caused by the rapid evaporation of surface moisture due to high temperatures,
low humidity, and wind.
b. Drying shrinkage: This type of shrinkage occurs after the concrete has hardened and is
caused by the loss of moisture from the concrete due to evaporation. Drying shrinkage is
the most common type of shrinkage and can cause cracks in the concrete.
c. Autogenous shrinkage: This type of shrinkage occurs due to the self-desiccation of the
cement paste during the hardening process. Autogenous shrinkage is caused by the
chemical reaction between the cement and water and can cause cracks in the concrete.

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d. Carbonation shrinkage: This type of shrinkage occurs due to the reaction between
carbon dioxide in the air and the calcium hydroxide in the concrete. Carbonation shrinkage
can cause the concrete to lose strength and durability.
Factors affecting shrinkage:
a. Water-cement ratio: A higher water-cement ratio can increase the amount of shrinkage
in the concrete.
b. Type of cement: Different types of cement have different shrinkage properties.
c. Aggregate type and size: The type and size of the aggregate used in the concrete can affect
the amount of shrinkage.
d. Temperature and humidity: High temperatures and low humidity can increase the
amount of shrinkage in the concrete.
e. Curing conditions: Proper curing can reduce the amount of shrinkage in the concrete.

3) Define creep? Explain various factors affecting creep.

Ans: -
Creep in concrete is defined as the deformation of a structure under sustained load. It is a time-
dependent deformation that occurs when a load is applied to concrete, and it experiences an
instantaneous elastic strain which develops into creep strain if the load is sustained. Creep is
factored in when concrete structures are designed.
a. Aggregate: The type and size of the aggregate used in the concrete can affect the amount
of creep. A higher aggregate content can reduce the amount of creep.
b. Mix proportions: The proportion of cement, water, and aggregate used in the concrete
can affect the amount of creep. A higher cement content can increase the amount of creep.
c. Age of concrete: The age of the concrete can affect the amount of creep. Creep tends to
decrease with age.
d. Temperature: The temperature of the concrete can affect the amount of creep. Higher
temperatures can increase the amount of creep.
e. Moisture content: The moisture content of the concrete can affect the amount of creep.
Higher moisture content can increase the amount of creep.
f. Stress level: The magnitude of the applied stress can affect the amount of creep. Higher
stress levels can increase the amount of creep.

4) Explain in brief self - compacting concrete.

Ans: -
Self-consolidating concrete (SCC), also known as self-compacting concrete, is a highly flowable,
non-segregating concrete that spreads into place, fills the formwork, and encapsulates
reinforcement without any bleeding or segregation.

Advantages of self-compacting concrete:

i. Reduced labor required to place and finish the concrete
ii. Elimination of mechanical vibration and reduction of screeding

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iii. Decreased noise in precast production settings

iv. Improved durability and strength due to the elimination of voids
v. Improved surface finish and appearance
vi. Increased safety due to the elimination of vibration
Applications of self-compacting concrete:
i. Architectural concrete
ii. Various horizontal elements
iii. Precast concrete elements with dense reinforcement
iv. Highly reinforced precast concrete elements with spacing greater than 1.5 inches.
Factors affecting self-compacting concrete:
a. Mix design: The mix design of self-compacting concrete is critical to its performance. The
mix design should be optimized to achieve the desired flowability and strength.
b. Aggregate: The type and size of the aggregate used in the concrete can affect its flowability
and strength.
c. Admixtures: Admixtures such as superplasticizers and viscosity modifiers can be used to
improve the flowability and workability of self-compacting concrete.
d. Curing: Proper curing is important to ensure the strength and durability of self-compacting
concrete.

5) Explain in brief polymer concrete.

Ans: -
Polymer concrete is a type of concrete that uses a polymer as a binder instead of traditional cement
hydrate binders.

Composition:
i. Polymer concrete uses a polymer such as epoxy, polyester, or vinyl ester as a binder instead
of traditional cement hydrate binders.
ii. Polymer concrete may be used for new construction or repairing of old concrete.
Types of polymer concrete:
a. Polymer cement concrete (PCC): The polymer is used in addition to Portland cement to
form PCC.
b. Polymer modified concrete (PMC): The polymer is mixed with ordinary cement to form
PMC.

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Advantages of polymer concrete:

i. High compressive strength
ii. Fast curing
iii. High specific strength
iv. Corrosion resistance
v. Low permeability
vi. Adhesive properties that allow repair of both polymer and conventional cement-based
concretes.
Applications of polymer concrete:
i. Repair to corrosion-damaged concrete
ii. Prestressed concrete
iii. Nuclear power plants
iv. Electrical or industrial construction
v. Marine works
vi. Swimming pools
vii. Sewer structure applications
viii. Drainage channels
ix. Electrolytic cells for base metal recovery
x. Other structures that contain liquids or corrosive chemicals.
Factors affecting polymer concrete:
a. Type of polymer: Different types of polymers have different properties that can affect the
performance of polymer concrete.
b. Mix design: The mix design of polymer concrete is critical to its performance. The mix
design should be optimized to achieve the desired strength and durability.
c. Curing: Proper curing is important to ensure the strength and durability of polymer
concrete.

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Unit- V
1) Explain permeability of concrete & Sulphate Attack.
Ans: -
Permeability of concrete refers to the property that governs the rate of flow of a fluid into a porous
solid. The presence of aggressive fluids and their transport is the most important factor controlling
the durability of cement-based composites.
i. Permeability is defined as the property of a material that it cannot be pervaded by water or
other liquids.
ii. A dense pore structure limits the penetrability through the concrete matrix, thereby
improving the durability of the material and extending its service life.
iii. Concrete is by design a porous material and water can pass through it by hydrostatic
pressure, water vapor gradient, or capillary action.
iv. Waterproofing is required to eliminate deterioration to the concrete that can occur from
exterior and interior chemicals that are present at the building site.
v. Permeability to asphaltic-s and gases varies considerably with different concretes. Even
the best concrete has some small degree of permeability.
vi. Permeability increases rapidly with increasing water-cement ratio and with decreasing
moisture-curing time.
Sulphate attack is a chemical reaction that occurs when sulphate ions in groundwater or soil react
with the components of concrete.
i. Sulphate attack can cause the concrete to crack, spall, and lose strength.
ii. Sulphate attack can occur in both reinforced and unreinforced concrete.
iii. Sulphate attack can be classified into two types: external and internal.
iv. External sulphate attack occurs when the concrete is exposed to sulphate ions in
groundwater or soil.
v. Internal sulphate attack occurs when the concrete contains excess sulphate ions that react
with the components of the concrete.
vi. Sulphate attack can be prevented by using low-permeability concrete, reducing the water-
cement ratio, and using Sulphate-resistant cement.
vii. Sulphate attack can be mitigated by using protective coatings, surface treatments, and
cathodic protection.

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2) What are types of cracks in concrete? Explain various causes of cracks in concrete.
Ans: -

There are different types of cracks in concrete, and they can be classified into two categories:
structural cracks and non-structural cracks. Structural cracks are those that result from incorrect
design, faulty construction, or overloading and may endanger the safety of a building and its
occupants. Non-structural cracks are those that occur mostly due to internally induced stresses in
building materials and do not endanger the safety but may look unsightly, create an impression of
faulty work, or give a feeling of instability.

Types of cracks in concrete:

a. Plastic shrinkage concrete cracks: These cracks occur when the concrete is still in its
plastic state (before hardening) and is caused by rapid drying due to high temperatures, low
humidity, or wind.
b. Drying shrinkage cracks: These cracks occur due to the loss of moisture from the
concrete after it has hardened.
c. Thermal cracks: These cracks occur due to temperature differences within a concrete
structure that result in differential volume changes.
d. Chemical reaction cracks: These cracks occur due to deleterious chemical reactions that
cause cracking of concrete.
e. Corrosion cracks: These cracks occur due to the corrosion of reinforcement in concrete.
f. Overload cracks: These cracks occur due to excessive loads on the concrete structure.
Causes of cracks in concrete:
a. Poor construction practices: Poor construction practices such as inadequate compaction,
improper curing, and insufficient reinforcement can cause cracks in concrete.
b. Errors in design and detailing: Errors in design and detailing such as inadequate
thickness, improper joint spacing, and inadequate reinforcement can cause cracks in
concrete.
c. Weathering: Weathering due to exposure to freeze-thaw cycles, chemical attack, and
abrasion can cause cracks in concrete.
d. Settlement: Settlement due to soil consolidation, subgrade failure, or inadequate
foundation design can cause cracks in concrete.
e. Thermal stresses: Thermal stresses due to temperature differences within a concrete
structure can cause cracks in concrete.
f. Chemical reactions: Deleterious chemical reactions due to materials used to make the
concrete or objects that come into contact with it after it has hardened can cause cracks in
concrete.
g. Corrosion of reinforcement: Corrosion of reinforcement due to exposure to moisture and
chloride ions can cause cracks in concrete.
h. Overloads: Overloads due to excessive loads on the concrete structure can cause cracks in
concrete.

Amit Sir [M-Tech (STRUCTURE), BE, Diploma in Civil],

7020059691/7385990691
 Amit Sir’s
CIVIL ENGINEERING CLASSES

3) Explain in brief the following non -destructive tests on concrete.

a. Rebound hammer method
b. Ultrasonic pulse velocity method.
Ans: -
a. Rebound hammer method.
The rebound hammer test is a non-destructive testing method used to assess the quality and
strength of concrete. It provides a convenient and rapid indication of the compressive strength of
the concrete.
i. The rebound hammer test is also called the Schmidt hammer test, and it has been around
since the late 1940s.
ii. The rebound hammer test is based on the principle that the rebound of an elastic mass
depends on the hardness of the concrete surface against which the mass strikes.
iii. The rebound hammer test involves striking the surface of the concrete with the hammer
and measuring the rebound distance of the hammer.
iv. The rebound hammer test provides a rapid indication of the compressive strength of the
concrete, but it is not a substitute for a laboratory test.
v. The rebound hammer test can be used to estimate the compressive strength of concrete in
situ, to compare the qualities of one particular element to those of another element, and to
distinguish between the portions of the construction that are acceptable and those that are
problematic.
vi. The rebound hammer test has some advantages, such as being non-destructive, easy to use,
and providing a quick indication of the compressive strength of the concrete. However, it
also has some disadvantages, such as being affected by the surface condition of the
concrete, the moisture content of the concrete, and the presence of reinforcing steel.

b. Ultrasonic pulse velocity method.

The ultrasonic pulse velocity (UPV) test is a non-destructive testing method used to examine the
homogeneity, quality, cracks, cavities, and defects in concrete.
i. The UPV test is an in-situ, non-destructive test to check the quality of concrete and natural
rocks.
ii. The UPV test assesses the strength and quality of concrete or rock by measuring the
velocity of an ultrasonic pulse passing through a concrete structure or natural rock
formation.
iii. The UPV test is conducted by passing a pulse of ultrasonic through concrete to be tested
and measuring the time taken by the pulse to get through the structure.
iv. Higher velocities indicate good quality and continuity of the material, while slower
velocities may indicate concrete with many cracks or voids.

Amit Sir [M-Tech (STRUCTURE), BE, Diploma in Civil],

7020059691/7385990691
 Amit Sir’s
CIVIL ENGINEERING CLASSES

v. The UPV test can be used to evaluate the quality and homogeneity of concrete materials,
identify voiding, honeycombing, cracking, and other defects, and define the size and shape
of a defect by using multiple test paths.
vi. The UPV test requires two-sided access for direct-path testing and can test around corners
when complex geometry precludes direct-path testing, such as at beam intersections.
vii. The UPV test has some advantages, such as being non-destructive, easy to use, and
providing a quick indication of the quality of concrete. However, it also has some
disadvantages, such as being affected by the surface condition of the concrete, the moisture
content of the concrete, and the presence of reinforcing steel.

4) Write a note on Distress in concrete structures and its causes.

Ans: -
Distress in concrete structures refers to the loss of materials and decrease in integrity of concrete,
which can lead to cracking, surface disintegration, and other forms of damage.

Causes of distress in concrete structures:

a. Poor curing: Improper curing can lead to various types of cracking and surface
disintegration in concrete.
b. Improper location of joints: Improper location of joints can lead to cracking due to the
lack of control over the location and direction of the cracks.
c. Overloading: Overloading can cause excessive stress on the concrete structure, leading to
cracking and other forms of damage.
d. Corrosion of reinforcement: Corrosion of reinforcement can lead to cracking and spalling
of concrete due to the expansion of the corroded steel.
e. Freeze-thaw cycles: Freeze-thaw cycles can cause cracking and spalling of concrete due
to the expansion of water as it freezes and contracts.
f. Chemical attack: Chemical attack can cause cracking and spalling of concrete due to the
reaction of chemicals with the concrete.
g. Alkali-silica reaction: Alkali-silica reaction can cause cracking and spalling of concrete
due to the reaction of alkalis in the concrete with reactive silica minerals in the aggregates.
h. Shrinkage: Shrinkage can cause cracking in concrete due to the loss of moisture during
the drying process.

Amit Sir [M-Tech (STRUCTURE), BE, Diploma in Civil],

7020059691/7385990691
 Amit Sir’s
CIVIL ENGINEERING CLASSES

5) Explain the material and methods of Repairs of cracks in concrete.

Ans: -

There are several methods for repairing cracks in concrete structures. The selection of a suitable
method depends on the evaluation of the crack in the structure for its causes. Once the cause is
known and the type of crack is established, a suitable method can be selected.
a. Epoxy injection: This method involves injecting epoxy into the cracks to bond the
concrete back together. It is suitable for cracks with an opening greater than or equal to
0.05 mm.
b. Routing and sealing: This method involves cutting a groove in the concrete along the
length of the crack and filling it with a sealant. It is suitable for cracks with an opening
greater than 0.1 mm.
c. Grouting: This method involves injecting a cementitious or resinous grout into the
cracks to fill them. It is suitable for cracks with an opening greater than 0.1 mm.
d. Stitching: This method involves drilling holes on either side of the crack and inserting
metal staples or stitching wires across the crack to hold the concrete together. It is suitable
for cracks with an opening greater than 0.1 mm.
e. Drilling and plugging: This method involves drilling holes across the crack and filling
them with a suitable non-shrink construction grout or epoxy grout. It is suitable for vertical
cracks formed on concrete walls.
f. Gravity filling: This method involves pouring a suitable non-shrink grout into the crack
and allowing it to flow into the voids. It is suitable for narrow cracks with an opening less
than 0.1 mm.

6) Explain water as an agent of deterioration of concrete.

Ans: -
Water is one of the most destructive agents of concrete structures and components. Here are some
ways water attacks concrete structures:
a. Carbonation: Carbon dioxide in the air reacts with the calcium hydroxide in concrete to
form calcium carbonate, which reduces the alkalinity of the concrete and makes it more
susceptible to corrosion.
b. Chloride attack: Chlorides dissolved in water can permeate through sound concrete or
reach the steel through cracks, causing corrosion of the reinforcement bars.
c. Sulfate attack: Sulfates in water can react with the calcium aluminate in concrete to
form expansive compounds that can cause cracking and spalling of the concrete.
d. Alkali-aggregate reaction (AAR): Certain aggregates can react with the alkali
hydroxides in concrete over time to cause a slow deterioration of the concrete through
expansion and cracking. This may cause significant damage outright, and the resulting
cracking is an invitation for the ingress of water to cause corrosion of the rebar.
e. Calcium leaching: Water infiltration can cause calcium to leach out of the concrete,
which can weaken the structure.

Amit Sir [M-Tech (STRUCTURE), BE, Diploma in Civil],

7020059691/7385990691