Concrete is an artificially produced material formed by mixing binding material (cement, lime), aggregate (sand and gravel), water, and admixtures. Aggregates make up 60-75% of concrete by volume and include both fine and coarse particles. Concrete types include plain cement concrete, reinforced cement concrete, pre-stressed concrete, and special concretes like polymer concrete, fiber reinforced concrete, and air-entrained concrete. Aggregates provide strength, rigidity and fill volume in concrete and are generally inert materials derived from natural or artificial sources. Their physical, mechanical and chemical properties greatly influence the performance of concrete.

1. Concrete Technology
Introduction
It is an artificially produced material , formed by the hardening of a mixture of binding
material(Cement,Lime) , Aggregate(Sand and coarse aggregate) , water and an admixture
• Aggregate = 60 to 70%
• Cement = 14 to 21%
• Water = 7 to 15% (also can be described as 0.4 times the weight of
cement)
Water = 0.4 times weight of cement
0.23 Hydration of cement 0.17 remains in the voids of concrete
• Admixture = Gypsum + others used to enhance the properties of concrete
Types of Concrete
A. Based On Density
i. Light weight concrete : Specific weight 3KN/m3
to 18.5 KN/m3
.Made by adding light
weight aggregates like pumice etc
ii. Medium weight concrete: Specific weight 24 KN/m3
.
iii.Heavy weight concrete: Specific weight 32 KN/m3
. Made by adding heavy weight
aggregates like blast furnace slag,iron scrap etc
B. Based On Design
i. Plain Cement Concrete(PCC) : Made from the basic components of
concrete(Binding material , water and aggregate)
ii. Reinforced Cement Concrete(RCC) : Also called ferro concrete , made by adding
reinforcement (usually in the tensile zone) to increase the strength of concrete
iii.Pre-stressed Concrete : Intial compression is induced in concrete so that it can resist
tension with greater efficiency
iv.Special Concrete
• Polymer concrete composite:
▪ Polymer concretes are a type of concrete that use polymers to replace
lime-type cements as a binder. In some cases the polymer is used in
addition to Portland cement

2. ▪ Polymer concrete may be used for repairing of old concrete as the
adhesive properties of polymer concrete allow repair to be more
effective
• Fiber reinforced concrete
▪ Fiber-reinforced concrete (FRC) is concrete containing fibrous
material which increases its structural integrity. It contains short
discrete fibers that are uniformly distributed and randomly oriented.
Fibers include steel fibers, glass fibers, synthetic fibers and natural
fiber
▪ Use of fiber
• Improve structural strength
• Reduce steel reinforcement requirements
• Reduce crack widths and control the crack widths tightly, thus
improving durability
• Improve impact– and abrasion–resistance
▪ This type of concrete is being used as a replacement to conventional
type RCC and PCC in modern countries but not yet started in Nepal.
• Ferrocement concrete
▪ Contains a system of reinforced concrete reinforced by adding a thin
layer of metal mesh, woven expanded-metal or metal-fibers and
closely spaced thin steel rods such as rebar.
▪ It is used to construct relatively thin, hard, strong surfaces and
structures in many shapes such as hulls for boats, shell roofs,
combustion tanks and water tanks.
• Sawdust concrete
▪ sawdust is used as a partial replacement for fine aggregates in concrete
production.
▪ The increase in percentage of sawdust instead of sand in concrete led
to a corresponding reduction in compressive strength values.
▪ The optimum sawdust content is around 10% and its corresponding
compressive strength at 28 days is 7.41 N/mm2
▪ This concrete cannot be used for structural applications it is generally
used for panel walls , sound proofing etc
• Air-entrained concrete
▪ contains billions of microscopic air cells per cubic foot.
▪ These air pockets relieve internal pressure on the concrete by
providing tiny chambers for water to expand into when it freezes and
also increases workability
▪ Air-entrained concrete is produced using air-entraining Portland
cement, or by the introduction of air-entraining agents like aluminum
powder
▪ Air entrainment also increases workability

3. 1. For heat and sound insulation we shall use
a. Vacuum concrete
b. Air entrained concrete
c. Saw dust concrete
d. Both b and c
2. The concrete from which excess of air and water is removes after placing in position is
called
a. Vacuum concrete
b. Light weight concrete
c. Pre-stressed concrete
d. Saw dust concrete
3. The concrete made by mixing aluminum in it is called
a. Air entrained concrete
b. Cellular concrete
c. Aerated concrete
d. all
4. Light weight concrete is prepared by
a. Mixing cement with sawdust in
specified amount
b. Using coke bridge cinder slag as
aggregate
c. Mixing aluminum in concrete
d. None
5. In making precast units for wall partition and wall lining the concrete used is
a. Sawdust concrete
b. Air entrained concrete
c. Light weight concrete
d. Vacuum concrete
Answer
1.D 2.A 3.D 4.B 5.C
Concrete materials - Roles of different materials:
1. Aggregates:
• Major ingredient of concrete
• Chemically inert, inexpensive material distributed throughout the concrete so as to
produce large volume
• Acts as an economical space filler

4. • Provides rigidity, stability, durability and strength to concrete i.e. Aggregate properties
greatly influence performance of the concrete.
Types of Aggregate
A. Based on source
1. Natural aggregate : Aggregate derived from river bed , quarry etc. It is of following
type
i. Aggregate from igneous rock : Hard , tough , dense in nature , e.g. Basalt Granite
ii. Aggregate from sedimentary rock : Of varying quality , e.g. Sandstone
iii.Aggregate from metamorphic rock : e.g. Gneiss , Quarzite
2. Artificial aggregate : Created artificially of two types
• By product aggregate : Waste products of different insustrial processes turned
into aggregate
• Processed aggregate : Aggregate obtained from crusher
B. Based on size
• Coarse aggregates : Larger than 4.75mm and Smaller than 75mm IS Sieve
• Fine aggregates : Larger than 75 micron and Smaller than 4.75mm IS sieve
Although the maximum size of coarse aggregate is 75mm the actual maximum size that
can be used in the case of different structure is quite smaller than this and depends upon
• Thickness of section
• Mixing , Handling , Compacting capacity
• Spacing of reinforcements
C. Based on Shape
• Rounded aggregate : Fully formed by attrition e.g. water rock , sea sand etc
• Irregular aggregate : Partly formed by attrition e.g. Pit sand , shore gravel etc
• Flaky aggregate : If smallest dimension < 0.6 times the mean dimension then it
is called flaky aggregate
• Elongated aggregate : If largest dimension > 0.6 times the mean dimension then
it is called elongated aggregate
• Angular aggregate - Possesses sharp edges with angles

5. D. Based on surface texture
1. Smooth aggregate : Surface Smooth and uniformly coloured e.g. marble , shale ,
chert
2. Glossy aggregate : Having glossy patches e.g. Seashell , black flint
3. Granular aggregate : Surface showing granular structure e.g. Sandstone
4. Crystalline aggregate : Surface showing crystals e.g. Granite
5. Honeycombed aggregate : Surface shows lumpy cavities
6. Porous aggregate : Surface is made of numerous small pores
Type W/C Ratio
Smooth 0.54
Granular or angular 0.6
E. Based on surface moisture
1. Very very dry aggregate : No moisture is present in surface or pores
2. Dry aggregate (air dry aggregate) : Some moisture is present but surface is
completely dry
3. Saturated and surface dry aggregate : All pores are filled with moisture but there is
no moisture on the surface
4. Wet or moist aggregate : Moisture is present is voids as well as surface
When the same aggregate is oven dried & all of its moisture vanishes then it is said to be bone
dry aggregate.

6. 1. What is the total percentage of aggregates in concrete by volume?
a) 50-60%
b) 60-75%
c) 85%
d) 50%
2. The light weight aggregates are obtained from
a) Sedimentary rocks
b) Metamorphic rocks
c) Igneous rocks
d) Volcanic source
3. Generally heavy weight aggregate obtained from ______________
a) Minerals ores
b) Palm oil shell
c) Sand
d) Crushed stone
4. An aggregate is called cyclopean aggregate if its size is more than
a.4.75 mm
b.30 mm
c.40 mm
d.75 mm
5. The minimum size of fine aggregate is
a.0.075 mm
b.0.0075 mm
c.0.75 mm
d.0.95 mm
6. For the construction of cement concrete dams the maximum size of aggregate is
a. 30mm
b. 40mm
c. 50mm
d. 60mm
7. For the construction of cement concrete floors the maximum size of aggregate is
a. 10mm
b. 20mm
c. 30mm
d. 40mm
8. For the construction of cement concrete lintels and band the maximum size of aggregate
is
a. 10mm
b. 15mm
c. 20mm
d. 40mm
9. The type of aggregate which contain the least amount of voids when compacted as
compared to other aggregate having same gradation are
a. Rounded aggregate
b. Angular aggregate
c. Irregular aggregate
d. Elongated aggregate

7. 10. The type of aggregate which is generally not preferred for use in concrete is the one with
following texture
a. Smooth aggregate
b. Glossy aggregate
c. Rough aggregate
d. Granular aggregate
Answers
1.B 2.D 3.A 4.D 5.A 6.B 7.A 8.B 9.A
10.B
Properties of Aggregate
A. Physical Properties
i. Grading :
• The process of determining the percentage by mass occupied by various size of
aggregate is called grading
• It is done by sieve analysis
• An example is given below

8. 1. Grading should be continuous for
a. Lean mix
b. Rich mix
c. Controlled mix
d. None
Answer : A
ii. Fineness Modulus :
• It is a numerical index to measure the average particle size of aggregates.
• 𝐹. 𝑀. 𝑜𝑓 𝑎𝑔𝑔𝑟𝑒𝑔𝑎𝑡𝑒𝑠 =
𝑆𝑢𝑚𝑚𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑐𝑢𝑚𝑢𝑙𝑎𝑡𝑖𝑣𝑒 % 𝑜𝑓 𝑤𝑡.𝑟𝑒𝑡𝑎𝑖𝑛𝑒𝑑 𝑜𝑛 𝐼.𝑆.𝑠𝑖𝑒𝑣𝑒
100
• Higher the F.M., higher will be coarser particles.
• Fineness modulus could be used as a yardstick to indicate the fineness of sand.
• The following limits may be taken as guidance
F.M. of Fine Sand: 2.2 – 2.6
F.M. of Medium Sand: 2.6 – 2.9
F.M. of Coarse Sand: 2.9 – 3.2
1. The fineness modulus of good sand shall be in the range of
a. 2-2.25
b. 2.5-3
c. 2-2.5
d. 3-3.2
2. The value of fineness modulus of fine sand ranges between
a. 1.1 to 1.3
b. 1.3 to 1.6
c. 1.6 to 2.2
d. 2.2 to 2.6
3. Sand requiring high water cement ratio belongs to
a. Zone I
b. Zone II
c. Zone III
d. Zone IV

9. 4. The fineness modulus of fine sand is between
a. 2-3.5
b. 3.5-5
c. 5-6
d. 6-7.5
Answer
1.B 2.D 3.A 4.A
iii. Specific gravity and Water absorption :
Let
W1 = Dry weight
W2 = Weight in water
W3 = Weight after draining water in external pores
V = Volume of vessel
Up thrust = W1 – W2 = Weight of displaced water
Volume of water = Volume of solids = Vn = Upthrust/Density of water
• Water absorption = (W3 – W1) / W1
• Specific gravity = Bulk Density / Density of water
= (W1 / V) /ρw
• Apparent Specific gravity = Apparent Density / Density of water
= (W1 / Vn) / ρw
1. The bulk density of aggregate depends upon
a. Shape of aggregate
b. Grading of aggregate
c. Compaction
d. All of above
2. The bulk density of aggregate is generally expressed as
a. Ton/m3
b. Kg/m3
c. Kg/lit
d. Gm/cm3
3. What is the range of water absorption of aggregates used in road?
a) 2.5-2.9
b) 0.1-2
c) 0.1-2.5
d) 2-2.9

10. 4. The density of aggregate does not depend upon
a. Shape and size of container
b. Specific gravity of aggregate
c. Grading of aggregate
d. Shape and size of container
Answers
1.D 2.C 3.B 4.D
B. Mechanical Properties
i. Strength
It is the resistance to compressive loads and is measured by aggregate crushing value test
AGGREGATE CRUSHING VALUE TEST
• The test specimen is cylindrical in shape of size 152 mm internal diameter and 125 mm
height.
• The aggregate is placed in the cylindrical mould and a load of 40 tonnes is applied
gradually through a plunger.
• The material crushed to finer than 2.36 mm is separated and expressed as a percentage of
original weight taken in the mould. This % is referred as aggregate crushing value.
• The crushing value of aggregate is restricted to 30% for concrete used for roads and
pavements and 45% may be permitted for other structures.
ii. Hardness
It is the resistance to wear and tear and is measured by LAA Test

11. LOS ANGELES ABRASION VALUE TEST (LAAVT)
• 5 to 10 kg of aggregate is placed in a cylindrical drum mounted horizontally with a shelf
inside.
• 11 spheres each of 11 to 14 kg are charged.
• The drum is rotated for about 500 cycles.
• The tumbling and dropping of the aggregate and of the balls result abrasion and attrition
of the aggregate.
• The proportion of broken material expressed as a percentage is measured.
iii.Toughness :
It is the resistance to impact and is measured by aggregate impact value test
AGGREGATE IMPACT VALUE (ATV)

12. • Weight of aggregate taken – 5 to 10 kg
• A sample of standard aggregate kept in a mould is subjected to 15 blows of a metal
hammer of weight 14 kgs falling from a height of 38 centimeters.
• The quantity of finer material (passing through 2.36 mm sieve) resulting from pounding
will indicate the toughness of the sample of aggregate.
• AIV – ratio of the weight of the fines formed to the weight of the total sample taken
iv. Bulking of sand
Bulking occurs when there is a change in volume due to the addition of water to the sand
particles.When water is added to dry sand, it forms a thin film around the particle which
causes them to separate and volume increases.After a certain limit the film begins to
break apart and thus again the volume starts to reduce.Therefore bulking is maximum at a
given water content, which can be shown from the following graph
Form the above graph it is clear that fine sands tend to bulk more than coarse sands due
to the small size of voids as result of which the articles are more susceptible to
separation.
Also it is seen that the bulking is maximum at water content of 4%.The relation between
bulking and moisture content for fine sand is as follows

13. Moisture
content
%
Bulking
2 15
3 20
4 25-30
5 22
Q. Bulking of coarse aggregate is
a. Less as compared to sand
b. More as compared to sand
c. 15% at 4% moisture content
d. Negligible
Answer: D
C. Chemical properties
i. Purity :
Aggregate shall be free from organic matter dust, chlorides and other chemical
impurities.
1. The sum of percentage of all deleterious material in aggregate shall not exceed
a. 5%
b. 10%
c. 15%
d. 20%
2. Sand generally contain salt if obtained from
a. Nala beds
b. River beds
c. Sea bed
d. All of above
3. The presence of salt in sand results in
a. Corrosion in reinforcement
b. Scaling
c. Pitting
d. All of above
Answers
1.A 2.C 3.D
2. Water:
Water is required for:
• Washing of ingredients
• Hydration of Cement
• Mixing the ingredients
• Curing of concrete

14. Requirement of water
1. The silt content should be less than 2000 ppm. It affects setting and hardening of concrete
, organic content shall be less than 500 ppm and inorganic content shall be less than 3000
ppm
2. Water may be unsuitable as mixing water when the water has a high concentration of
sodium or potassium.
3. As a rule, any water with a pH of 6.0 to 8.0 i.e. which does not taste saline or brackish is
suitable for use.
4. Water should be free from wild acids, alkalies and organic matter.
5. Alkali carbonates and bicarbonates in water should not exceed 1000 ppm.
1. The internal friction between the ingredients of concrete is reduced by
a. Adopting coarse aggregate
b. Using more water
c. Reducing surface area
d. All of above
2. The presence of …………. In water has adverse affect on setting time
Or
The impurity of water which adversely affects the setting time of concrete is
a. Sodium carbonate and
bicarbonate
b. Sodium chloride
c. Sodium sulphate
d. Calcium chloride
3. The presence of calcium chloride in mixing water
a. Accelerates setting
b. Accelerates hardening
c. Causes little effect on quality
d. All of above
4. Smaller size of coarse aggregate require ………. Water for hydration
a. More
b. Less
c. Same
d. None
5. The vegetable oil if present in mixing for concrete
a) Improves strength
b) Reduces strength
c) Gives more slump
d) Gives a smooth surface
6. The mineral oil if present in mixing for concrete
a) Improves strength
b) Reduces strength
c) Gives more slump
d) Gives a smooth surface

15. 7. The presence of salt in mixing water causes
Or
If sea water is used it causes
a. Reduction in strength
b. Corrosssion of steel
reinforcement
c. Causes efflorescence
d. All of above
Answers
1.D 2.A 3.B 4.A 5.B 6.A 7.D
1. Admixture
They are compounds which when added to concrete enhances properties like strength ,
hardness , durability etc. They are of following types
A. Chemical Admixture :
• They are admixtures having formulated chemical composition and are added
to concrete in order to modify a specific property like strength, durability ,
hardness , water requirement etc
• They are generally added during the manufacture of concrete and are added
in very small amount
• Any small excess can cause adverse effects on the properties of concrete
• These type of admixtures work through chemical interaction with cement or
by modifying the physical properties of water like viscosity, surface tension
etc.
• The different type of chemical admixtures are as follows
a) Plasticizers (Water-reducing Admixtures)
• To achieve a higher strength by decreasing the water cement ratio at the same
workability as an admixture free mix.
• These admixtures disperse the cement more actively in the concrete matrix thereby
reducing the lubrication requirements
• To achieve the same workability by decreasing the cement content so as to reduce the
heat of hydration in mass concrete.
• To increase the workability so as to ease placing in accessible locations.

16. • Reduces water content for given workability upto 15%
• e.g. Ligno – sulpahate , Hydro carbolic acid
b) Super plasticizer
These are more recent and more effective type of water reducing admixtures also known
as high range water reducer. The main benefits of super plasticizers can be summarized
as follows:
Increased Fluidity:
• Flowing
• Self-leveling
• Self-compacting concrete
• Penetration and compaction around dense reinforcement
Increased strength
• Very high early strength, > 200% at 24 hours or earlier
• Very high later age strengths, > 100 MPa is possible through application of HRWR
• Reduced shrinkage, especially if combined with reduced cement content.
• Improved durability by removing water to reduce permeability and diffusion.
Water reduction: Upto 30%
Dosage: Low (0.6 to 2 % on cement)
Examples of commonly used super plasticizers are Sulphonated Melamine
Formaldehyde condensates (SMF), Sulphonated Naphthalene Formaldehyde
condensates (SNF) and Prolycarboxylate Ether super plasticizer (PCE).
c) Accelerator
• It is an admixture which when added to concrete, mortar or grout, increases the rate of
hydration of hydraulic cement, shortens the time of set in concrete or increases the rate
of hardening or strength development.
• It accelerates the action of C3S and C2S

17. • Earlier hardening of concrete is useful in several situations such as early removal of
formwork, less period of curing, emergency repair works, for constructions in low
temperature regions etc.
• Triethenolamine, calcium formate, silica fume, calcium chloride, finely divided
silica gel Thiocynate etc. Calcium chloride (CaCl2) is the cheap and commonly
used accelerating admixture.
d) Retarders
• It increases the setting time of cement by suspending the action of C3A and C3S
• Used for large and continuous batching of concrete to prevent the formation of cold
joints
• e.g. Gypsum , Glucose , Sugar , starch, cellulose
e) Set Retarders
The function of retarder is to delay or extend the setting time of cement paste in concrete.
When water is first added to cement there is a rapid initial hydration reaction, after
which there is little formation of further hydrates for typically some time , the exact time
depends mainly on the cement type and the temperature. This is called the dormant
period when the concrete is plastic and can be placed. At the end of the dormant period,
the hydration rate increases and a lot of calcium silicate hydrate and calcium hydroxide
is formed relatively quickly. This corresponds to the setting of the concrete.
Retarding admixtures delay the end of the dormant period and the start of setting and
hardening. This is useful when used with plasticizers to give workability retention. Used
on their own, retarders allow later vibration of the concrete to prevent the formation of
cold joints between layers of concrete placed with a significant delay between them.
These are helpful for concrete that has to be transported to long distance, and helpful in
placing the concrete at high temperatures or when there is significant ga between batches
of concrete
e.g. Calcium Ligno-sulphonates, Carbohydrate derivatives

18. f) Water proofer
Used to slow down the ingression of water i.e. to make the concrete water proof. e.g. :
Vegetable oil , tar, water etc . These materials acts as pore fillers thereby preventing the
flow of water into the sample. The pore filling materials might be chemically active pore
fillers like silicate of soda, aluminums, zinc sulphates and calcium chloride or
chemically inactive mineral fillers like chalk, fullers earth and talc. And aluminums is
active filling material. Chemically active ingredients lead to increase in strength while
chemically inactive ingredients leads to improvement in workability
e.g. zinc sulfate, aluminum chloride, silicate of soda etc.
g) Air entraining admixture
These agents are added in concrete to induce air it it. Air entrainment increases
workability and also eliminates the chances of frost action. It also reduces bleeding ,
laitance , segregation , porosity etc. e.g. Aluminum powder , commercial products like
vinsol resin, darex, Teepol, Cheecol etc. which are of natural wood resins, alkali salts,
animal and vegetable fats and oils etc.
h) Corrosion inhibiting admixture
These agents coats the concrete mass and prevents the ingression of corroding agents
and prevents corrosion.
i) Air removing admixture
Used to remove excess of air from air entrained concrete in order to enhance the strength
e.g. tributyl phosphate, silicones, water insoluble alcohols etc.
j) Bonding Admixture
Used to increase the bond strength in new concrete or to make bond in new and old
concrete
e.g. natural rubber, synthetic rubbers, polymers like poly vinyl chloride, polyvinyl
acetate etc.
k) Alkali Aggregate Expansion Preventing Admixtures
Alkali aggregate expansion in concrete is happened by the reaction of alkali of cement
with the silica present in the aggregates. It forms a gel like substance and cause
volumetric expansion of concrete which may lead to cracking and disintegration.

19. Use of pozzolanic admixtures will prevent the alkali-aggregate reaction and in some
cases air-entraining admixtures are also useful. Aluminum powder and lithium salts can
also be used for this purpose
Some of the corrosion preventing admixtures used in reinforced concrete are sodium
benzoate, sodium nitrate, sodium nitrite etc.
B. Mineral Admixture
• These admixtures do not have formulated chemical composition and are added to
concrete in order to modify more than one property
• They are added to concrete in large amount and are added to cement during
manufacture.
• Any small excess will not have adverse effects on the properties of concrete
• The different type of mineral admixtures are as follows
These are generally of two types:
• Cementing Admixture
These enhance the cementing properties of concrete. e.g. Ground Granulated Blast
Furnace Slag (GGBFS)
• Pozzolanic Admixture
A pozzolana is a material which, when combined with calcium hydroxide (lime),
exhibits cementitious and other properties. Pozzolans are commonly used as an
addition (the technical term is "cement extender") to Portland cement concrete
mixtures to increase the long-term strength and other material properties of Portland
cement concrete and in some cases reduce the material cost of concrete. Examples
are
• Fly Ash
Coal from mines is generally contaminated with clay. When this coal is grinded to
fine size and then burnt in thermal power plant, it turns into carbon dioxide. The
clay contaminants form ash mainly of silica and alumina. The larger ash settles on
the bottom whereas the finer ones called fly ash fly above.

20. Thus, fly ash is the finely divided residue resulting form the combustion of ground
or powdered coal. Fly ash is generally captured from the chimneys of coal-fired
power plants.
Fly ash increases cementitious property. One of the most important fields of
application for fly ash is PCC pavement, where a large quantity of concrete is used
and economy is an important factor in concrete pavement construction.
Silica Fume
• By-product of semiconductor industry.
• Because of its extreme fineness and high silica content, Silica Fume is a highly
effective pozzolanic material. Silica Fume is used in concrete to improve its
properties. It has been found that Silica Fume improves compressive strength,
bond strength, and abrasion resistance; reduces permeability of concrete to
chloride ions; and therefore helps in protecting reinforcing steel from corrosion,
especially in chloride-rich environments such as coastal regions.
Rice Husk Ash
• This is a bio waste from the husk left from the grains of rice. It is used as a
pozzolanic material in cement to increase durability and strength.
• The silica is absorbed from the ground and gathered in the husk where it makes a
structure and is filled with cellulose. When cellulose is burned, only silica is left
which is grinded to fine powder which is used as pozzolana.
• Concrete becomes cohesive and more plastic and thus permits easier placing and
finishing of concrete. It also increases workability of concrete.
1. Setting time of cement decreases by adding
a. Gypsum
b. Hydrogen peroxide
c. Calcium chloride
d. Sodium oxide
2. Calcium chloride as accelerator is not recommended for use with
a. OPC
b. High alumina cement
c. RHPC
d. None of above
3. Admixture is generally added during
a. Grading of cement
b. Mixing of cement
c. After pouring
d. None of above

21. 4. Accelerator shortens all except
a. Setting time
b. Curing period
c. strength
d. Period of removal of framework
5. Retarder decreases the following except
a. Rate of hydration
b. Water cement ratio
c. Workability and comp strength
d. Rate of development of strength
6. An admixture
a. Accelerate initial setting
b. Increases strength
c. Improves workability
d. All of above
7. What is the amount used of plasticizers in cement by weight?
a) 0
b) .1-.4%
c) 1%
d) 1-2%
8. At normal temperatures addition of sugar _____________ per cent have little effect on the
rate of hydration
a) .5-1
b) 1-2
c) .05-1
d) .1-.2
9. Mid-range water reducers result in at least _________ %.
a) 2
b) 4
c) 6
d) 8
Qns 1 2 3 4 5 6 7 8 9
Ans c b b c d d b c d
Manufacture of concrete
1. Batching :
• Process of accurate measurement of all concrete materials for uniformly and
desirable properties are called batching. It can be done through
a) Weight batching: in which the different materials are weighted according to their
proportions. It can be done through spring dial ,platform weighing machine,
portable weight batchers, done for large jobs
b) Volume batching: the volume of one bag of cement is taken as 35 liter and the
other ingredients are added as per their ratio in terms of volume
1. For batching 1:2:4 concrete by volume the ingredients required per bag of cement
are
a. 50 kg c: 70 kg FA: 140 kg CA
b. 50 kg c: 70 lit fine aggregate:140 lit CA
c. 50 kg concrete:100 kg fine aggregate:20 kg course aggregate
d. 50 kg concrete :100 lit fine aggregate:200 lit course aggregate

22. 2. The inner dimension of 50 liter forma is
a. 25x25x40
b. 29x29x48
c. 30x30x50
d. 31x31x52
3. The dimension of 35 litre forma for measuring aggregation by volume are
a. L=30 B=25 H=30
b. L=39 B=25 H=32
c. L=27 B=27 H=32
d. L=22 B=25 H=40
4. In batching the materials should be measured with respect to the standard amount
with a maximum tolerance,
a. +1.o
b. +2.0
c. +3.0
d. +4.0
Answers
1.B 4.C
2. Mixing
The process of throught mixing of the materials of concrete to obtain a uniform
mixture can be done by
a. Manual mixing
b. Machine mixing
-Continuous plant
-Interminnent plant
• Tilting
• Non tilting
The capacity of mixture is designated by the amount in liters which it can produce
in each batch.
The speed of rotation in mixture is 15 to 20 per minute, 25-30 complete rotations
are required for well designed mixture. some standard recommendations are as
follow
Capacity Natural aggregate Man made or processed aggregate
<1 m3
1.25 min 1.5 min
1-2 m3
1.5 min 2 min
>2 m3
2 min 2.5 min
1. The process of mixing some mortar in the mixer at the beginning of first batch is
called

23. a. Buttering
b. Burrowing
c. Initiating
d. Acceleration
2. In case of hand mixing the extra cement to be added is
a. 5%
b. 10%
c. 15%
d. 20%
3. During manufacture of concrete minimum period for which mixing is done is in
mixer for manufactured crushed aggregate is
a. 1 min
b. 2 min
c. 2.5 min
d. 3 min
Answers
1.A 2.B 3.C
3. Transportation
The processs of bringing concrete to the place of application. Transportation can be
done by various methods like
a. Iron pans b. wheel barrows c. pumps d. trucks e. conveyors etc
1. Transport of concrete by pump is done for a distance of
a. 100 m
b. 200 m
c. 300 m
d. 400 m
2. For transportation by pump
a. water cement ratio shall be
between 0.5 to 0.55
b. Slump shall be between 50-80
mm
c. None
d. Both (a) and (b)
Answers
1.D 2.D
4. Placing
The process of putting the concrete in desired place.following precautions shall be taken
a. Concrete should not be thrown from height more than 1m
b. Placing is optimum at 27+2o
c and shall not be done in very cold surface

24. 5. Compaction
It is the process of removing excess of air void so as to make the concrete dense and
strong compaction may be done
a. Manually
b. Mechanically
For roads surface Screed vibrator
For RCC dams beams columns Needle vibrator or internal vibrator
For one way or PCC Form vibrator or external vibrator
1. For mechanical compaction the slump should not exceed
a. 2.5 cm
b. 5cm
c. 7.5 cm
d. 10 cm
2. screed vibrator can only be used when the thickness of section does not exceed
a. 100 mm
b. 150 mm
c. 200 mm
d. 250 mm
3. Concrete is unsuitable for compaction by vibrator if it is
a. Dry
b. Plastic
c. Semi-plastic
d. Earth moist
Answer
1.B 2.V 3.B
6.Finishing
Finishing is the process of forming dense concrete with smooth and plain surface
Best finishing is obtained when slumb is 50 mm
Finishing is done in following stages
• Screeding: it is the process of removal of humps and hollows and give a true and
uniform surface
• Floating: the process of removing of irregularities left from screeding
• Trowelling: it is the final stage, it produces a smooth and dense surface
1. The process of mixing, transportation, placing and compacting should be completed
within
a. 30 minutes
b. 60 minutes
c. 90 minutes
d. 120 minutes
Answer : A

25. 7. Curing
The process of wetting the concrete with water so as to make it able to gain strength
sufficiently is called curing
It can be done through
• Ponding
• Member curing
• Steam curing
• Chemical curing (chemicals reduces moisture loss and absorb moisture from
environment)
1. Curing shall commence after _____ from the time of finishing
a. 24 hr
b. 7 days
c. 14 days
d. 21 days
2. Steam curing is used for
a. Columns
b. Long slabs and columns
c. Mass production of precast
concrete
d. All
3. Steam curing cannot be used for
a. OPC
b. High alumina cement
c. RHPC cement
d. All
4. Curing period is minimum for
a. RHPC
b. High alumina cement
c. PPC
d. OPC
Answer
1.A 2.C 2.B 4.B
Stripping of form
Concrete is supported by framework, till it gains sufficient strength, after this formwork
can be removed. Some recommendation for removal of formwork are
Vertical sides of column: 1-2 days
Beam soffits: 2 days to 7 days
14 days for slabs upto 4.6 m else 7 more
21 Days for beams 6m span else 14
Deflects of concreting
Bleeding: appearance of water on surface
Segregation: separation of particles from concrete
Laitance: watery scum on surface

26. Mix Design
It is the process of determining the proportion of different materials to be added in the
concrete
Types of concrete mix based in design
i. Nominal Mix
Those mixes of fixed cement-aggregate ratio which ensures adequate strength are termed nominal
mixes.These mixes provide adequate strength even in the worst condition of aggregate and cement,
Therefore are conservative in their nature.Some commonly used nominal mixes are
M10 1:3:6
M15 1:2:4
M20 1:1.5:3
M25 1:1:2
ii. Design Mix
Those mixes for which the proportion are determined by performing detailed design based
in the exact properties of the aggregate and cement are called design mix.
1. For mass concreting in piers and abutements the grade of concrete mix used is
a. 1:1:2
b. 1:1.5:3
c. 1:2:4
d. 1:3:6
2. For highly loaded column the concrete mix used is
a. 1:1:2
b. 1:1.5:3
c. 1:2:4
d. 1:3:6
3. The concrete in which no preliminary test is performed during its design is called
a. Rich concrete
b. Ordinary concrete
c. Controlled concrete
d. Lean concrete
4. The concrete in which number of preliminary test are performed during its design is
called
a. Rich concrete
b. Ordinary concrete
c. Controlled concrete
d. Lean concrete
5. For preliminary testing the concrete shall be placed in a mould in Layers of
equal volume
a. one
b. two
c. three
d. five
6. The minimum quantity of cement for controlled concrete is
a. 120 kg/m3
b. 160 kg/m3
c. 220 kg/m3
d. 280 kg/m3
Answer :
1.D 2.A 3.C 4.B 5.C 6.C

27. Philosophy of Mix design
The results of testing of a large sample of test specimens will show a scatter or a distribution
of strengths about the mean strength. This can be shown by a histogram, which can be
approximated by the dashed curve
It can be seen that the curve is symmetrical about the mean value and extends to plus and
minus infinity. In practice, these very low and very high values of strength do not occur in
concrete but these extremes can be ignored because most of the area under the curve (99.6
%) within ±3s and can be taken to represent all the strength values of concrete. For mix
design we take the the range in which 95% sample falls
It is clear from the above graph that if the mix is designed for (fck) then the lowest value of
strength is lower than charactetstic strength(fck) for the range of 95% , therefore we shall
target a value of strength as a mean for which the lowest value of strength is equal to the (fck)
this value of mean strength for which the design shall be targeted is called Target strength
(ft)
We have for normal distribution
fck = ft – KS
ft = fck - KS
Where fck = Characteristic Strength
ft = Target Strength
K = factor based on the accuracy
S = Standard deviation

28. Properties of Concrete
A. Fresh Stage :
(i)Water cement ratio
It is the ratio of weight of water to the weight of cement. Generally water equal to 1/5th
(20%) of the weight of cement is sufficient for for complete hydration , of cement. But in
the case of concrete only about half of the used water is utilized for hydration and the rest
remains in the voids of concrete. Therefore, about 40 %(38% to be exact) water is to be
added to concrete in order to ensure complete hydration of concrete.
Despite this a minimum water cement ratio of 0.45 is necessary to prohibit the phenomena
of honeycombing.
Similarly the range of water cement ratio to be maintained for different grades of concrete
are as follows
M10 = 0.6 to 0..65
M15 = 0.55 to 0.6
M20 = 0.5 to 0.55
M25 = 0.45 to 0.5
For concrete of higher strengths further lower value of water cement ratio is not permissible
therefore plasticizer is to be used
Water cement ratio vs. strength
The relation between strength and water cement ratio is given by
Upto a certain water cement ratio the strength of concrete is not attained due to honeycombing
(Generally 0/45).Beyond this water content, in the case of machine compacted concrete the strength
of concrete decreases with increase in water content. In the case of hand compacted concrete the
strength initially increases on addition of water due to increased ease of compaction , but after a
certain point when full compaction is possible the strength decreases with increase in water content.
This phenomena of variation in strength of concrete with change in water content was first observed
by duff Abrahams. Based on his findings stated thar “The strength of concrete is only dependent
upon water/cement ratio provided the mix is workable.” This is called Abrams water/cement
ratio law.

29. 1. For concrete exposed to a very aggressive environment the w/c should be lower than
a) 1
b) .5
c) .4
d) .8
Answer : 1.C
(ii)Workability
It is the property of freshly prepared concrete which determines the ease and homogeneity
with which it can be mixed, placed , compacted and finished. Higher is the workability greater
is the ease for these processes
The following are the factors which affect the workability of concrete
• Water content: With increase in water content the workability increases
• Size of aggregate: Concrete with larger size of aggregate is more workable for given
aggregate
• Shape of aggregate : Concrete with rounded aggregate is most and with angular
aggregate is least workable provided other conditions remain same
• Surface texture of aggregate : Smooth and glossy aggregate have lower workability
while granular and porous aggregate have lower workability
• Air entrainment : Air entrainment increases workability
• Temperature : Workability reduces at high temperature, because in high temperature the
concrete dries too quickly and has to be placed and compacted soon which decreases the
ease of working
Workability Tests
Slump Test

30. Tools and Apparatus used for Slump Test:
1. Standard Slump Cone (100 mm top diameter x 200 mm bottom diameter x 300 mm
height)
2. Bullet-nosed road (600 mm long x 16 mm diameter)
3. Slump Plate (500 mm x 500 mm)
Procedure:
i. The mould in the form of a frustum of a cone is placed on a smooth surface with the
smaller opening at the top and filled with concrete in three layers.
ii. Each layer is tamped 25 times with a standard 16 mm φ steel rod.
iii. The top surface is struck off by means of a screeding and rolling motion of the tamping
rod.
iv. The mould must be firmly held against its base during the entire operation; this is
facilitated by handles or foot-rests brazed to the mould.
v. Immediately after filling, the cone is slowly lifted and the unsupported concrete will now
slump. The decrease in the height of the centre of the slumped concrete is called slump.
Precautions:
• The inside of the mould and its base should be moistened at the beginning of every test.
• The test should be repeated in case a shear slump is observed.
• Slump Test is not suitable for too wet or too dry concrete.

31. 1. Compacting Factor Test
This test uses the inverse approach i.e. while workability is defined in terms of ratio of
compaction achieved by standard free fall to the compaction obtained in fully compacted
concrete
Compacting Factor =
Density actually achieved in the test
Density of the same concrete fully compacted
For higher workability CF is higher and vice versa
Tools and Apparatus required:
1. Two hoppers, each a frustum of a cone
2. One cylinder
The hoppers have hinged doors at the bottom. All inside surfaces are polished to reduce friction.
Procedure:
i. The upper hopper is filled with concrete, this being placed gently so that, at this stage,
no work is done on the concrete to produce compaction.
ii. The bottom door of the hopper is then released and the concrete falls into the lower
hopper. This lower hopper is smaller than the upper one.
iii. The lower hopper is filled to overflowing and thus always contains approximately the
same amount of concrete in a standard state.
iv. The bottom door of the lower hopper is released and the concrete falls into the
cylinder.
v. The net mass of concrete in the known volume of cylinder is determined.

32. vi. The density of the fully compacted concrete is obtained by actually filling the cylinder
with concrete in four layers, each tamped or vibrated. Thus, the compacting factor can
be calculated.
2. Vee Bee Consistometer Test
A – Slump Cone (20 cm lower dia., 10 cm
upper dia., 30 cm height)
B – Container
C – Clear Plastic Disk/Transparent Rider
(2.75 kg) (held by moving vertical rod)
D – Vebe Table (260 mm x 260 mm)
• Developed by V. Bahrner of Sweden
The Vebe time test is a more scientific test for workability than the Slump test, in that it measures
the work needed to compact the concrete. The freshly mixed concrete is packed into the slump
cone in a standard manner. The cone stands within a special container on a platform, which is
vibrated with an eccentric weight rotating at 50 Hz so that the vertical amplitude of the table is
approximately ±0.35 mm. Vibration is performed after the cone has been lifted off the concrete.
The time taken for the concrete to be compacted is measured. Compaction is assumed to be
complete when the transparent rider is totally covered with concrete and all cavities on the
surface of the concrete have disappeared. This is judged visually.
It is assumed that the input of energy required for full compaction is a measure of workability of
the mix, and this is expressed Vebe seconds. Greater is the vebed time in seconds lower is the
workability and vice versa
The different types of concrete based on workability are as follows

33. Workability
Test
Very low Low Medium Good
Slump 0-25 25-50 50-75 75-100
Compaction
factor test
<0.85 0.85 – 0.90 0.90 – 0.95 >0.95
Vee bee test 10-20 5-10 2-5 0-2
Q1. Workability of concrete can be improved by addition
a) Iron
b) Sodium
c) Zinc
d) Sulphur
Q2 Which test used for fiber reinforced concrete?
a) Slump test
b) Compacting factor test
c) Flow table test
d) VeBe test
Q3 Which test Used for high workable concretes?
a) Slump test
b) Compacting factor test
c) Flow table test
d) VeBe test
Q4What is the compaction factor for medium degree of workability?
a) .78
b) .85
c) .92
d) .95
Q5What is the compaction factor for low degree of workability?
a) .78
b) .85
c) .92
d) .95
Answer: 1.c 2.c 3.c 4.C 5.b
B. Hardened stage
1. Strength of concrete and grades
Strength of concrete is measured in terms of compressive strength, flexural strength, bond
strength and shear strength. Out of these the most frequently used parameter to
denote the strength is the compressive strength of the concrete sample.
A. Compressive strength: The compressive strength of concrete is defined as the the
compressive stress induced in the sample at the verge of failure. The magnitude of this
strength is time dependent and increases with time. Generally 28 day strength of
concrete is taken as the compressive strength of concrete.
In general the variation in strength of concrete with respect to the 28day strength can be
shown by the following table
Day 3 7 21 28 90 180 360
Percentage of 28
day strength
40 65 90 100 115 120 130

34. Furthermore the percentage of strength not only depends on the time but also depends on
the product of time and temperature called Maturity
Strength = f(Σ timeX temperature) = f(maturity)
Percentage of 28 days strength = A + B log10(
𝑀𝑎𝑡𝑢𝑟𝑖𝑡𝑦
103
)
Factors on which strength depends
The following are the main factors on which the strength of concrete depends
a. Water cement ration : Strength decreases with increase in water cement ratio
b. Gel space ratio : it is the ratio of volume of hydrated cement past to the volume of
concrete(i.e. the sum of colume of hydrated cement paste and pores)
According to Mr. Power (or powers law)
Strength = 2400 Χ3
Kgf/cm2
Where X = Gel space ratio =
0.657𝐶
0.319𝐶+𝑊𝑤
C = Weight of cement
Ww = weight of water
c. Size of aggregate : As size of aggregate increases the strength of concrete increases
d. Admixture : Strength increases when admixture is added
e. Air entrainment : Air entrainment decreases strength
f. Age : The strength of concrete increases with age.
Grades of concrete
Concrete are designated on the basis of their 28days compressive strength, this designation of
concrete is called grade of concrete. The grade of concrete is defined by the letter M
followed by the 28days compressive in MPa for e.g. If concrete is graded as M20 its 28day
compressive strength is 20MPa(200kg/cm2
)
The different grades of concrete can be shown form the following table
S.N. Types of Concrete Grade Designation Characteristic Strength (N/mm2
)
1. Ordinary Concrete M10 10
M15 15
M20 20
2. Standard Concrete M25 25
M30 30
M35 35
M40 40

35. M45 45
M50 50
M55 55
3. High Strength Concrete M60 60
M65 65
M70 70
M75 75
M80 80
1. The minimum strength of high strength concrete is
a. 40 MPa
b. 50 MPa
c. 60 MPa
d. 70 MPa
2. As per IS 456 : 1978 the concrete mixes are designated into
a. 4 Grade
b. 5 Grade
c. 7 Grade
d. 10 Grade
3. Which of the following grades of concrete is not recommended by Is code
a. 20 MPa
b. 35 MPa
c. 25MPa
d. 55 MPa
Answers
1.C 2.C 3.D
B. Shear strength
The amount of shear at which failure occurs is called shear strength , it is generally 12% of
compressive strength for PCC
As per the IS 456 :2000 the maximum shear that reinforced concrete can resist depends on
the grade of concrete
Concrete Grade M15 M20 M25 M30 M35 M40
Shear Strength
(N/mm2)
1.6 1.8 1.9 2.2 2.3 2.5
C. Bond Strength
It is defined as the stress induced in the concrete sample while pulling the bars at which the
slipping of reinforcement occurs
Bond strength can be increased by 60% for deformed bars and 25% for steel in compression
According to IS code the bond strength of concrete is as follows
Concrete Grade M20 M25 M30 M35
Bond Strength
(N/mm2)
1.2 1.4 1.6 1.8

36. D. Direct Tensile strength
It is approximately equal to 1/10th of the compressive strength
As per Standards
Fct = 0.35√𝑓𝑐𝑘
Where
Fct = Direct tensile strength
Fck = Characteristic compressive strength
E. Flexural Tensile strength
It is equalt to the bending stress induced in the extreme tension fiber at the verge of failure.
It is also called modulus of rupture. We have
Modulus of Rupture fcr= 0.7√𝑓𝑐𝑘
Fck = Characteristic compressive strength
Testing Of Concrete
1. Cube Test
Specimen is cast in Iron or steel moulds of size 150X150X150 mm. The cube is filled in 3
layers and well compacted. After compaction the top surface is made smooth. The finished
sample is left undisturbed for 24 hours at room temperature then the mould is removed
and specimen is stored in water for further curing.For research purspose Cubes are tested
at 3,7,14,28,90 days while in field cubes are tested at 28days only and a minimum 3 cubes
are required
Compressive Strength =
𝐹𝑜𝑟𝑐𝑒 𝑎𝑡 𝐹𝑎𝑖𝑙𝑢𝑟𝑒
𝐴𝑟𝑒𝑎
2. Cylinder test
The standard cylinder mould is of 150mm diameter and 300mm height and is made of cast
iron or steel. The cylinders are also filled with three layers of concrete and compacted in the
same manner as cube
In reality the experiments shows that there is no relation between the cube strength and
the cylinder strength but the cube strength is always greater than the cylinder strength.
Some general codal provisions are as follows
H/D Ratio
Strength correction factor
American standard British Standard
2 1 1
1.75 0.98 0.98
1.5 0.96 0.96
1.25 0.93 0.94
1 0.87 0.92

37. 3. Tensile Strength Test
Since concrete is very weak in tension it is not expected to bear the tensile stresses due to
external loads. However as a result of restrained condition and temperature effects little
amount of tensile stresses are induced in concrete which have to be resisted by it.Tensile
strength can be measures in two ways
(a) Direct tension test
In this method the tensile strength is measured by applying uniaxial tensile loads th the
specimen.Since it is very difficult to apply uniaxial tensile loads, this method is rarely
used
Fct = 0.35√𝑓𝑐𝑘
Where
Fct = Direct tensile strength
Fck = Characteristic compressive strength
4. Modulus of rupture (Rupture test)
This is the tensile strength under bending. In the flexural test the maximum tensile stress is
reached in the bottom fiber of the test beam. This value of tensile strength is called
modulus of rupture
The two cases are
Central Point Loading
L/2 L/2
d/2
𝑀
𝐼
=
𝑓
𝑦
f =
𝑀
𝐼
∗ 𝑦
f =
𝑃𝐿/4
𝐼
∗
𝑑
2
f =
𝑃𝐿/4
𝑏𝑑3/12
∗
𝑑
2
f =
3𝑃𝐿
2𝑏𝑑2
Two Point Loading /Third point Loading
L/3 L/3 L/3
d/2

38. 𝑀
𝐼
=
𝑓
𝑦
f =
𝑀
𝐼
∗ 𝑦
f =
𝑃𝐿/6
𝐼
∗
𝑑
2
=
𝑃𝐿/6
𝑏𝑑3/12
∗
𝑑
2
=
𝑃𝐿
𝑏𝑑2
1. Tensile strength is ………….. the flexural strength
a. Twice
b. Thrice
c. Half
d. Equal
2. The surface area of cube used for finding the compressive strength of concrete is
a. 225 cm2
b. 2250 mm2
c. 0.225 m2
d. All of above
3. In cylindrical specimen failure plane makes an angle with the horizontal
a. 30®
b. 45®
c. 60®
d. 75®
4. The cube strength exceeds the cylinder strength by
a. 10 to 15 %
b. 15 to 20%
c. 20 to 25%
d. 25 to 30%
5. If engineer in charge approves 10cm cubes then they may be used provided that the
maximum size of aggregate do not exceed
a. 10 mm
b. 15 mm
c. 20 mm
d. 25 mm
6. The compressive test is repeated for preliminary concrete if difference in the cube
strength exceeds
a. 5 kg/cm2
b. 8 kg/cm2
c. 10 kg/cm2
d. 15 kg/cm2
7. The 28 days cube strength of mass concrete using aggregate of maximum size 5cm for
gravity dams should be
a. Between 150 kg/cm2 and 300 kg/cm2
b. Between 350 kg/cm2 and 600 kg/cm2
c. Between 150 kg/cm2 and 500 kg/cm2
d. Below 200 kg/cm2
Answers
1.A 2.D 3.C 4.C 5.C 6.D 7.D

39. Shrinkage , Creep and Relaxation
Shrinkage :
The strain induced at zero stress is called shrinkage. It is caused due to withdrawl of
moisture from the fresh concrete
Creep :
The additional strain at prolonged stress is called creep
Relaxation
The reduction in stress at constant strain is called relaxation
Factors affecting shrinkage
a. Water cement ration: More water cement ratio means more amount of water will be
dried from the concrete and thus shrinkage is more for higher water cemnent ratio
b. Richness: Richness is the amount of cement per m3 of concrete.With increase in richness
i.e. the amount of cement shrinkage increases
c. Age : Shrinkage increases non-linearly with age
2 weeks = 75% of total
3 months = 80% of total
1 Year = 85% of total
Factors affecting creep
a. Concrete mix proportion: Creep is inversely proportional to the richness of the mix i.e.
richer the mix lesser will the creep be
b. Properties of aggregate: Aggregate with higher modulus of elasticity show less creep.
Also light weight aggregate show higher creep
c. Age of loading: Quality of gel improves with loading therefore the amount of creep
decreases with delay in loading
d. Curing of concrete: Curing prevents rapid evaporation and therefore improves the
strength which reduces creep in concrete
e. Cement quality: finer cement will cause higher creep
f. Stress: Higher load induces more amount of creep
1. Durability is proportional to
Or Shrinkage is proportional to
a. Sand content
b. Water cement ratio
c. Aggregate Ration
d. Cement aggregate ratio
2. Shrinkage in concrete
a. Is proportional to water cement
ration
b. Is proportional to cement
content

40. c. Increases with age d. All
3. Shrinkage in concrete is directly proportional to
a. Water content
b. Sand content
c. Aggregate content
d. Aggregate cement ratio
4. The rate of creep rapidly ________ with time.
a) Increase
b) Decrease
c) Doesn’t affect
d) Depends on the temperature
5. Shrinkage is propotional to
a. Cement content
b. Sand content
c. Aggregate content
d. Temperature of water
6. ____ exhibits creep upon application of load on a concrete specimen.
a) Aggregates
b) Water
c) Cement paste
d) Admixtures
Answers
1.D 2.D 3.A 4.B 5.A 6.C
Moduli of Elasticity
Loading
unloading
Slope of the relationship between stress and strain is called modulus of elasticity but Young’s modulus is
applied strictly for linear categories only.
If the load is applied extremely rapidly, the strains ate greatly reduced and the curvature of strain stress
curve becomes very small.An increase in loading time from 5 seconds to 2 minutes can increase the
strain upto 15%.An increase in loading within the range of 2 minutes to 10 minutes , strain increases
non-linearly. Modulus of elasticity is the measurement of stiffness or resistance to deformation.
Types of Modulus of Elasticity
a) Static modulus of elasticity
The value of modulus of elasticity determined by actual loading of concrete is static modulus of
elasticity. It is given by the slope of stress-strain curve for concrete under uniaxial loading. Since
Such a curve is non-linear for concrete, following methods are used to determine the modulus of
elasticity.
I) Initial tangent modulus: The tangent of the curve at origin.
II) Tangent modulus: The slope of the line drawn from the origin to any point on the curve.

41. III) Secant modulus: Slope of the line drawn from the origin to the point on the curve corresponding to
40% stress of the failure load.
IV) Chord modulus: The slope of line drawn between the two points of the stress-strain curve.
Specimen.
Tangent Modulus
Secant Modulus
Strain Initial tangent modulus
Chord Modulus
Stress
b) Dynamic modulus of elasticity
Due to several cycles of loading and unloading reduce the sufficient creeps show that the stress
strain curve on the sufficient loading exhibits only a small curvature. This slope of curve is called
dynamic modulus. The dynamic modulus of elasticity corresponding to a very small
instantaneous Strain approximately given by the initial tangent modulus and it is calculated by:
Ed= K 𝑥 𝑛2
𝑥 𝐿2
𝑥 ρ
Where, Ed= Dynamic modulus of elasticity
K= constant
n= resonant frequency
L= length of specimen
ρ = Density of sample
Poisson’s ratio(μ):
It is the ratio of the lateral to linear strain
Poisson’s ratio(μ) =
𝐿𝑎𝑡𝑒𝑟𝑎𝑙 𝑠𝑡𝑟𝑎𝑖𝑛
𝐿𝑜𝑛𝑔𝑖𝑡𝑢𝑑𝑖𝑡𝑖𝑜𝑛𝑎𝑙 𝑠𝑡𝑟𝑎𝑖𝑛
1. The poisons ratio of concrete reduces by using
a. Rich mix
b. Poor mix
c. Constant all
d. All
2. Poissons ratio for concrete ranges between
a. 0.11 to 0.21
b. 0.20 to 0.25
c. 0.25 to 0.30
d. 0.30 to 0.35
3. IS 456 of 2000 gives the modulus of elasticity as _______
4.
a) Ec = 5000 fck.5
b) Ec = 5000 fck2
c) Ec = 5000 fck3
d) Ec = 5000 fck1/

42. Answers
1.A 2.A 3.A
Cold weather concreting
The effects of cold weather concreting are:
• Hydration will be hampered
• Setting time will be prolonged
• Low workability
• Disruption in strength gaining of freshly placed concrete because of freezing
• Freezing and thawing effect
• Improper curing
• Workmanship is affected
• Deicing effect.
The precautionary measures to take for concreting in cold weather are:
• Using hot water
• Providing enclosure i.e. covered area.
• Using air entraining agents.
• Scheduling concreting.
• Using admixtures accelerators such as calcium chloride.
• Use of type III or high early strength cement i.e. cements containing more C3S and C3A.
• Using sufficient amount of cement.
• Concreting shouldn't be done in frozen surfaces.
1. Concreting shall be stopped when the temperature falls below
a. 4.5® C
b. 15® C
c. 20® C
d. 25® C
2. At freezing point of water concrete
a. Sets slowly
b. Sets freely
c. Sets rapidly
d. Does not set
3. The datum temperature by plowman is
a. 23® C
b. 0® C
c. -5.6® C
d. -11.7® C
4. Concrete is not recommended to be placed at a temperature below __________o
C.
a) 2
b) 3
c) 4
d) 5

43. 5. Concrete is not recommended to be placed at a temperature below __________o
C.
a) 2
b) 3
c) 4
d) 5
Answers
1.A 2.D 3.D 4.D 5.C
Hot weather concreting
• At higher temperature a fresh concrete results in accelerated setting time and may reduce
long term strength.
• The rapid hardening of concrete before compaction accelerated chemical activity result in
rapid setting and rapid evaporation of mixing water.
• Due to rapid evaporation, plastic shrinkage in concrete occurs and would cause cracking.
• Increases in tendency to cracking. The precautionary measures to take for concreting in
hot weather are:
o The temperature of concrete may be kept as low as possible by shading aggregate and
mixture.
o The temperature of aggregate may be lowered by sprinkling water over them.
o Rapid hardening is also reduced by working at night.
o For curing moisture retaining materials are used.
PRE-STRESSED CONCRETE
Pre-stressing is a method in which compression force is applied to the reinforced concrete
section. The effect of pre stressing is to reduce the tensile stress in the section to the point till the
tensile stress is below the cracking stress. Thus the concrete does not crack.
1. A pre-stressed concrete member is
a. Made of concrete
b. Made of reinforced concrete
c. Is stressed after casting
d. Possesses internal stress
2. In pre-stressed concrete the steel is under
a. Compression
b. Tension
c. Shear
d. Torsion
3. In Pre-stressed concrete structure, the pre-stressing of concrete is done to compensate
the stress caused by
a. Dead Load
b. Working Load
c. Live Load
d. Dynamic Load
Answers
1.D 2.B 3.B

44. Principle of Pre-stressing:
There are basically two principles of pre-stressing of concrete
1. Pre-stressing is applied at the c.g of the section
2. Pre-stressing is applied eccentrically with respect to the c.g of the section.

45. 1. The net effect due to pre-stress in pre-stressed concrete beam is usually
a. Tension
b. Compression
c. Bending and Tension
d. Bending and Compression
2. If the maximum dip of a parabolic tendon carrying tension ‘p’ is ‘h’ and the effective
length of the pre-stressed beam is ‘L’ the pressure ‘w’ shall be
𝑎.
8𝑝ℎ
𝐿
𝑏.
8𝑝ℎ
𝐿2
𝑐.
8𝐿ℎ
𝑝
𝑑.
8ℎ𝐿
𝑃2
Answers
1.D 2.B
Pre-stressed profile of the tendon is similar to the shape of BMD of the UDL
1. If the loading on a pre-stressed rectangular beam is uniformly distributed, the tendon to
be provided should be
a. Straight below centroidal axis
b. Parabolic with convexity downwards
c. Parabolic with convexity upwards
d. Straight above centroidal axis

46. Pre-stressed Concrete: Methods
There are two basic methods of applying pre-stress to a concrete member
Pre-tensioning: In Pre-tension, the tendons are tensioned against some abutments before the
concrete is place. After the concrete hardened, the tension force is released. The tendon tries to
shrink back to the initial length but the concrete resists it through the bond between them, thus,
compression force is induced in concrete. Pretension is usually done with precast members
Post tensioning: In post tension, the tendons are tensioned after the concrete has hardened.
Commonly, metal or plastic ducts are placed inside the concrete before casting. After the
concrete hardened and had enough strength, the tendon was placed inside the duct, stressed, and
anchored against concrete. Grout may be injected into the duct later. This can be done either as
precast or cast-in-place.
Advantages: Disadvantages
Take full advantages of high strength concrete
and high strength steel
Need less materials
Smaller and lighter structure
No cracks
Use the entire section to resist the load
Very effective for deflection control
Better shear resistance
Need higher quality materials
More complex technically
More expensive
Harder to re-cycle
Requirements of Pre-Stressed Concrete
1. High Grade of concrete: Higher grade concrete allows for smaller section thus smaller
shrinkages and is preferred
Pre Tensioned > M40
Post Tensioned > M35
2. Pre Stressing Tendon = 1200 – 2700 MPa
Methods of Pre-Stressing
1. Pre Tensioned Concrete
a. Hover system or long line system
Two bulk heads are anchored to the ground and wires are stretched between the supports.
Concrete is placed in mould enclosing the wires. The wires are loosened after the concrete has
gained sufficient strength. Using this method several members can be produced at a time ,
therefore this method is more preferred for the mass production of pre tensioned pre-stressed
concrete.
b. Shorer system:
In this system a central tube of high strength carries the pre-stress from the surrounding wires.
The entire assembly is placed in position and concrete is poured, after the concrete has gained
sufficient strength, the tube is removed and the void is filled with grout.

47. 2. Post Tensioned Concrete
a. Freyssinet system
High strength steel wires are grouped into a tendon (usually 8 , 12 , 16 , 24) all tendon are
stretched at one
b. Mangel Blaton System:
High strength steel wires are grouped into a tendon (usually 8 , 12 , 16 , 24) two tendon are
stretched at once
c. Gifford Udal System:
High strength steel wires are grouped into a tendon (Any number of wires can be grouped to
form a cable). Each wire is stretched independently using a double acting jack,
d. Lee Mc. Call system:
In this system pre-stress is given by means of steel bars of diameter 12 to 28mm After stretching
the bars with threads are jointed to plates by means of nuts thus pre-stressing is possible
1. The minimum clear horizontal spacing between the groups of cables or ducts in grouped
cables shall be greater of
a. 30mm or 5mm more than the maximum size of aggregate
b. 40mm or 5mm more than the maximum size of aggregate
c. 30mm or maximum size of aggregate
d. 40mm or maximum size of aggregate
2. The minimum clear vertical spacing between the groups of cables or ducts in grouped
cables shall be greater of
a. 30mm
b. 40mm
c. 50mm
d. None of above
3. The minimum clear spacing of non grouped cables or large bars should be
a. 40mm
b. Maximum size of cable or bar
c. 5mm plus maximum size of aggregate
d. All of above
Answer
1.B 2.C 3.D
Losses of Pre-Stress
Pre Tensioning System
Total loss = 20%
Post Tensioning System
Total loss = 15%
1. Elastic shortening of concrete
2. Relaxation of steel in concrete 1. Relaxation of steel in concrete
3. Shrinkage of concrete 2. Shrinkage of concrete
4. Creep of concrete 3. Creep of concrete
4. Friction loss
1. For the pre-stressed concrete to be feasible the total loss in the system shall not exceed
a. 15%
b. 20%
c. 25%
d. 30%
Answer : C