B.E. (Civil Engineering) Third Semester (C.B.S.)
A
Notebook
Of
rd
B.E 3 Semester C.B.S
[Civil Engineering]
Subject:- Concrete Technology
Name:Class:Section:Roll No.:College:-
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Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
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Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Performance of charity is the key of attaining the estate of a philanthropist
Bachelor of Engineering (B.E)
In
( Civil Engineering )
3rd SEMESTER C.B.S
HELPFUL NOTES
Based On RTMNU, Nagpur Syllabus
Subject- Concrete Technology
BY
Md Shahjada Alam (Shah Sir)
B.E (Civil Engineering), M.Tech (Environmental Engineering)
Page | 3
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Disclaimer
This Helpful Notes does not claim any originality and cannot be used as a
substitute for prescribed textbooks. This Notes Complete done through with
the help of many sources (like Internet Sources, Textbook, My Engineering
Notes, Faculty Guidelines etc.). Specially, this Notes prepared for Job Seeker
Students & also a big treat for weak students. Further; this Notes Claims not
used for Commercial purposes.
यह सहायक नोट्स ककसी भी मौलिकता का दावा नह ीं करता है और इसे ननर्ााररत
पाठ्यपस्
ु तक के ववकल्प के रूप में उपयोग नह ीं ककया जा सकता है । यह नोट्स कई
स्रोतों (जैसे इींटरनेट स्रोत, पाठ्यपस्
ु तक, मेर इींजीननयररींग पस्
ु तक, सींकाय ददशाननदे श
आदद) की सहायता से परू ा ककया गया है । ववशेष रूप से यह नोट्स जॉब सीकर छात्रों के
लिए तैयार ककया गया है और कमजोर छात्रों के लिए एक बडा उपचार है । आगे की; इस
नोट्स का दावा वाणिज्ययक उद्दे श्यों के लिए नह ीं ककया गया है ।
About Writer
Md Shahjada Alam (Shah) former lecturer at Nuva College of Engineering &
Technology, Nagpur.
He completed his Graduation degree in Civil Engineering at the age of 20 years
from Nagpur University. (Batch 2014-18)
His Teaching style & hand written Notes are amazing & very helpful for
students. This achievement comes from his valuable students. Only at the age
of 14 years, he has been rewarded to Qualify Delhi-CET.
Page | 4
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Dedicated
To
My Respected Grandfather
Late Haji Mohammad Abbas
Page | 5
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
CONCRETE TECHNOLGY
(80/20 Marks)
Theories:- 80 Marks
Numericals:- 0 Marks
Syllabus
Unit – I
Cement: Chemistry of Cement, Main constituents of cement Hydration of cement, Water required,
Physical properties and testing of cement, Soundness test. Hardening and compressive strength
Grades and different types of cements. Ordinary Portland cement, Rapid Hardening Cement, B.B.
Blast furnace slag cement, Low heat Portland cement, Portland pozzolones cement, Portland flyash
cement, Sulphate resisting cement. Field test,
Aggregates : Sources of aggregates, classification and nomenclature. Coarse and fine aggregate,
normal weight (light and heavy weight aggregates). Aggregate characteristics and their significance
in strength, workability, placement and compartion of concrete.Sampling. Particle shape and
texture, Bond of aggregate, size & grading of aggregate strength of aggregates Mechanical
properties and test-Specific gravity, Bulk density, porosity absorption of aggregates, moisture
content of aggregate, bulking of sand abrasion test, impact value. Sieve analysisDeleterious
substances in aggregates, organic impurities class and other fine material etc.
Water : Quality of water for concrete mixing, suitability
Unit – II
Fresh concrete : Batching, Mechanical mixers, automatic batching and mixing plants. Efficiency of
mixing. Workability Measurement – Slump cont test, compacting factor test, flow table, Vee-Bee
consistometer, Factor affecting workability, setting time. W/C Law Significance of w/c ratio
cohesiveness.Segregation, bleeding, voids, permeability.Hot weather concreting.Underwater
concreting, Conveyance of concrete, Placing of concrete.Compaction-vibrators.
Curing of concrete Significance, methods of curing, Temperature effect on during& strength gain. IS
code on curing.Maturity of concrete.
Unit - III
Strength of concrete: Gain of strength, Wet ratio, Factor affecting compressive strength w/c ratio.
Type of cement, air entrainment, aggregates, mixing water, Admixtures, curing conditions. Tensile
and flexural strength.Relation between cracking in compression.Impact strength fatigue strength.
Shear strength, Bond between concrete & reinforcement. Modulus of elasticity, Poison’s ratio.
Testing of Hardness of Concrete: Compression test-cube strength & cylinder strength their relation,
effect of aspect ratio on strength. Flexural strength of concrete, Determination of tensile
strength.Indirect tension test.Splitting test.Abrasion resistance.Accelerated curing test.
Page | 6
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Unit – IV
Mix Design – Process, Statistical relation between mean & characteristic strength, Variance,
Standard deviation. Factor affection mix properties. Grading of aggregate, aggregate/ cement ration
etc. Degree of quality control. Design mix by Road note no. 4 (BS). IS:10262:2009.
Additives and Admixtures: Types of admixtures, Natural products-DietomaceousearthBy products
Pozzolones. Fly ash, silica fume, rice husk ash, , G.G. blast furnace slag. Admixturers-air encraining,
water reducing, acceletors, retarders, plasticizers & Super plasticizers, permeability reducing,surface
harderners.Corrosion inhibitors & water proofing agents.
Unit – V
Special concrete : Self compacting concrete, High performance concrete, fiber reinforced & polymer
concrete, Ferro cement, Shortcrete pumped concrete, Free flow concrete.
Shrinkage-Early volume changes, drying shrinkage, mechanism of shrinkage.Factor affecting
shrinkage. Influence of curing & storage conditions. Differential shrinkage.Carbonation
shrinkage.Creep-Factors influencing.Relation between creep & time, nature of creep, effect of creep.
Unit – VI
Durability of concrete-significance water as an agent of deterioration. Permeability of concrete,
Efflorescence. Distress in concrete structures and its causes, cuses of deterioration of concrete.
Cracks in concrete: Causes, types, prevention, repairs of craqcks – materials and methods Non
Destructive tests.
Instructions
1. For Topper Read All Questions.
2. For On paper Read All Compulsory & Semi-Compulsory Questions.
3. For Passing Read Only Compulsory Questions.
व्यावसाययक उपयोग के लिए कडाई से यिषिद्ध है
Page | 7
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Unit-01
(14 Marks)
Cement, Aggregates, Water
Theories:- 14 Marks
Ques No.01:- Give the oxide composition of cement & state the effect of each
on the properties of cement.
Or
Explain Bogue’s Compound Composition.
Or
What are the ingredients of the cement?
Or
Describe the cement composition.
Or
What are the functions of different cement ingredients?
(Compulsory For 7 Marks)
Ans:- Oxide composition of cement:
The raw materials used for the manufacture of cement consist mainly of lime, silica, alumina
and iron oxide. These oxides interact with one another in the kiln at high temperature to
form more complex compounds. The relative proportions of these oxide compositions are
responsible for influencing the various properties of cement; in addition to rate of cooling
and fineness of grinding.
Table 1: Approximate Oxide Composition Limits of Ordinary Portland Cement
S.No.
Oxides
Formula
Contents (%)
1.
Calcium oxide (lime)
CaO
60–67
2.
Silicon dioxide (silica)
SiO2
17–25
3.
Aluminum oxide
(alumina)
Iron oxide
Sulfur trioxide
Alkalies
(Potash And Soda )
Magnesium oxide
(Magnesia)
Calcium Sulfate
Al2O3
3.0–8.0
Fe2O3
SO3
( K2O, Na2O)
0.5–6.0
1.3–3.0
0.4–1.3
MgO
0.1–4.0
CaSO4
0.1-0.5
4.
5.
6.
7.
8.
Page | 8
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Functions of Cement Ingredients:The main features of these cement ingredients along with their functions and usefulness or
harmfulness are given below:
1. Lime: Lime is calcium oxide or calcium hydroxide.





Presence of lime in a sufficient quantity is required to form silicates and aluminates of
calcium.
Deficiency in lime reduces the strength of property to the cement.
Deficiency in lime causes cement to set quickly.
Excess lime makes cement unsound.
Excessive presence of lime cause cement to expand and disintegrate.
2. Silica: Silicon dioxide is known as silica, chemical formula SiO2.



Sufficient quantity of silica should be present in cement to dicalcium and tricalcium silicate.
Silica imparts strength to cement.
Silica usually presents to the extent of about 30 percent cement.
3. Alumina: Alumina is Aluminium oxide. The chemical formula is Al2O3.



Alumina imparts quick setting property to the cement.
Clinkering temperature is lowered by the presence of the requisite quantity of alumina.
Excess alumina weakens the cement.
4. Magnesia: Magnesium Oxide. Chemical formula is MgO.


Magnesia should not be present more than 2% in cement.
Excess magnesia will reduce the strength of the cement.
5. Iron oxide: Chemical formula is Fe2O3.




Iron oxide imparts color to cement.
It acts as a flux.
At a very high temperature, it imparts into the chemical reaction with calcium and aluminum
to form tricalcium alumino-ferrite.
Tricalcium alumino-ferrite imparts hardness and strength to cement.
6. Calcium Sulfate: Chemical formula is CaSO4 .


This is present in cement in the form of gypsum(CaSO4.2H2O)
It slows down or retards the setting action of cement.
7. Sulfur Trioxide: Chemical formula is SO3.


Should not be present more than 2%.
Excess Sulfur Trioxide causes cement to unsound.
Page | 9
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
8. Alkaline:


Should not be present more than 1%.
Excess Alkaline matter causes efflorescence.
Major Compounds of Portland Cement (Bogue’s Compound Composition):S.NO
NAME
Formula
Abbreviation
1.
2.
3.
4.
Tricalcium silicate
Dicalcium silicate
Tricalcium aluminate
Tetracalcium alumino
3CaO.SiO2
2CaO.SiO2
3CaO.Al2O3
4CaO.Al2O3
C 3S
C 2S
C 3A
C4AF
Properties of cement compounds:These compounds contribute to the properties of cement in different ways:
 Tricalcium aluminate, C3A:It liberates a lot of heat during the early stages of hydration, but has little strength
contribution. Gypsum slows down the hydration rate of C3A. Cement low in C3A is sulfate
resistant.
 Tricalcium silicate, C3S:This compound hydrates and hardens rapidly. It is largely responsible for portland cement’s
initial set and early strength gain.
 Dicalcium silicate, C2S:
C2S hydrates and hardens slowly. It is largely responsible for strength gain after one week.
 Ferrite, C4AF:
This is a fluxing agent which reduces the melting temperature of the raw materials in the kiln
(from 3,000o F to 2,600o F). It hydrates rapidly, but does not contribute much to strength of
the cement paste.
Characteristics of Hydration of the Cement Compounds:S.NO.
Compounds
Reaction
Rate
Amount of
Liberated
Strength
Heat
Liberation
1.
2.
C 3S
C 2S
Moderate
Slow
Moderate
Low
High
Low
3.
4.
C 3A
C4AF
Fast
Moderate
Very high
Moderate
High
Low initially,
high later
Low
Low
Page | 10
Concrete Technology
Very high
Moderate
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Ques No.02:- List different types of cements. Explain any two type in detail.
Or
Explain in brief "sulphate Resisting Portland Cement".
(Compulsory For 7 Marks)
Ans:- Cement:
Cement, any material that hardens and becomes strongly adhesive after application.
Types of Cement:Following are the different types of cement used in construction works:1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
13)
14)
15)
16)
Ordinary Portland Cement,
Rapid hardening cement,
Ultra-rapid hardening cement,
Low heat cement,
Quick setting cement,
High alumina cement,
Blast furnace slag cement,
Pozzolana cement,
White cement,
Hydrophobic cement,
Super sulfate cement,
Low alkali cement,
Water proof cement,
Air entraining cement,
Expansive cement,
Colored cement.
1. Ordinary Portland Cement:


In usual construction work, Ordinary Portland Cement is widely used. The composition of
Ordinary Portland Cement:
Argillaceous or silicates of alumina (clay and shale)
Calcareous or calcium carbonate (limestone, chalk, and marl)


Uses:
It is used for general construction purposes.
It is also used in most of the masonry works.
2. Rapid Hardening Cement:


It is also known as High-Early-Strength cement. It is manufactured with such adjustments in
the proportion of raw materials.
So that the cement produced attains maximum strength with-in 24-72 hours.
Rapid hardening cement is mostly used where rapid construction is needed like the
construction of pavement.
Page | 11
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)

Uses:
It is a special purpose cement. It is used in that types of projects, where quick hardening is
required.
3. Low Heat Cement:





It is that type in which a very low amount of heat or hydration is liberated during setting and
hardening. Mostly it is used in massive concrete structures like Dams etc.
The initial setting time shall not be less than 60 minutes. And the final setting time shall not
be less than ten hours.
Uses:
It is mostly used in mega projects construction like DAMS. If we use ordinary Portland
cement instead of low heat cement in such structures,
Cracks will develop in such structures due to the great amount of heat liberated during
setting and hardening.
And a DAM with cracks is a useless structure. But when low heat cement is used, this danger
(development of cracks) can be eliminated.
It is also used for the construction of chemical plants.
4. High Alumina Cement:





These Types of Cement contains alumina in considerably larger proportions (average 40
percent) than normal cement.
High Alumina cement is manufactured by calcining a well-proportioned mixture
of Limestone and Bauxite (Al 2O3, n H2O).
No other raw material is added, not even gypsum is mixed with the clinker during grinding.
The total Alumina content is generally above 32 percent.
Uses:
Unfortunately, it is more costly. Therefore it is used only in those situations where resistant
against corrosion is required.
It is commonly used in construction work near and along sea-shore.
5. White Cement:







It may also be defined as a special type of Portland cement when used it gives a milky or
snow-white appearance.
White cement is manufactured from pure limestone (chalk) and clay that are totally free
from iron oxides and any other pigments like manganese and chromium.
There strength and setting time is similar to ordinary Portland cement.
Uses:
White cement is the most favored material for use in making highways curbs and for a
variety of ornamental work.
They are also used widely for making cast stones of appealing appearance.
White cement is comparatively a costly cement type and is, therefore, used only selectively.
It is usually used in decorative work.
It can also use for traffic barriers, tile grouts, swimming pools, roof tiles patching materials
and terrazzo surfaces.
Page | 12
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
6. Air Entraining Cement:

This cement type is manufactured by adding some indigenous air entraining agents such as
glues, resins, sulfates, etc., during the grinding stage of clinker.
Uses:
They are used to improve the workability of concrete with smaller water-cement ratio and
they also improve the frost resistance of concrete.
7. Quick Setting Cement:



Quick setting cement is the cement which sets in a very short time. The initial setting time is
5 minutes and the final setting time is 30 minutes. The composition of Quick Setting Cement:
Clinker
Aluminium sulphate (1% to 3% by weight of clinker)
The aluminium sulphte increase the hydration rate of silicate.




Uses:
It is used in underwater construction.
It is also used in rainy & cold weather conditions.
It is used a higher temperature where water evaporates easily.
Used for anchoring or rock bolt mining and tunnelling.
8. Hydrophobic Cement:


To resist the hydration process in the transportation or storage stage, clinkers are grinded
with water repellent film substance such as Oleic Acid or Stearic Acid. These chemicals form
a layer on the cement particle and do not allow water to mix and start the hydration
process. When cement and aggregate are thoroughly mixed in the mixer, protective layers
break and start normal hydration with some air-entrainment which increase workability.
Uses:
Usually, it is used in the construction of water structures such as dams, spillways, or other
submerged structures.
It is also used in the construction of underground structure like tunnel etc.
Sulphate Resisting Portland cement (SRC):
Sulphate Resisting Portland Cement is a type of Portland cement in which the amount of
Tricalcium aluminate (C3A) is restricted to lower than 5 % and (2 C3A + C4AF) is lower than
25%. SRC can be used for structural concrete wherever OPC or PPC or Slag Cement is usable
under normal conditions. The use of SRC is particularly beneficial in such conditions where
the concrete is exposed to the risk of deterioration due to sulphate attack.
The use of SRC is recommended for following applications:
1. Foundations, piles.
2. Basements and underground structures.
3. Sewage and Water treatment plants.
4. Chemical, Fertilizers and Sugar factories.
Page | 13
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
5. Food processing industries and Petrochemical projects.
6. Coastal works.
7. Also for normal construction works where OPC is used.
8. Construction of building along the coastal area within 50 km from sea.
Ques No.03:- List important physical tests of cement? Explain any two in
brief?
Or
What are the field tests for judging the preliminary quality of cement?
Or
Explain field test on cement? Also Explain soundness test on cement.
Or
Explain field test on cement & also list down the different types of lab test
conducted on cement.
(Compulsory For 7 Marks)
Ans:- Physical tests of cement:The physical tests which are generally performed to determine the acceptability of cement are:
1)
2)
3)
4)
5)
6)
7)
Fineness Test
Consistency Test
Setting time Test
Soundness Test
Strength Test
Heat of Hydration Test
Specific Gravity Test
1. Fineness Test:
Fineness is the mean size of cement grain. It is done to measure the mean size of cement
grain.

The finer the cement the surface area for hydration will be large and it increases the
strength of cement. But the fineness varies in different types of cement.
One of the Following three methods can be applied to test the fineness of cement:1) Sieve method
2) Air Permeability method
3) Sedimentation method
Importance of Fineness of Cement:1)
2)
3)
4)
It can decrease bleeding.
It can increase the final strength of cement.
Fineness can also affect workability.
Fineness test indirectly measures the surface area of the particles of cement per unit mass.
Page | 14
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
5) Fineness increases the strength development in the cement principally during its first seven
days.
6) It increases the rate of hydration. More is the fineness of cement particles more will be the
rate of hydration.
1. Sieving Method:Apparatus:
1)
2)
3)
4)
IS Sieve (90 µm) with lid.
A balance of 0.01 gm sensitivity.
A pure bristle or nylon brush.
Sieve Shaking Machine (optional).
Procedure:
1. Take 1000 grams (1 Kg) of cement for the test sample and name it as (w1).
2. Rub the cement particle well with your hands so that no lumps are left.
3. Now pour the 1 Kg cement content in the sieve and close it perfectly with the sieve lid.
4. If you have a sieve shaking machine then it’s awesome, now you just need to put the sieve in the
shaking machine and start the machine for 15 minutes.
 Anyway, if you don’t have the sieve shaking machine then no problem, you can shake it also
with your hands.
 But you need to make sure that the sieving operation is done in all the direction for a
minimum of 15 minutes.
5. Brush the sieve base gently with the bristle brush so that nothing is left on the sieve surface.
6. Now just weight the retained amount of cement on the sieve and note it as (w2).
7. Now you need to find the percentage of the weight of cement-retained on the 90 µm sieve.
8. For calculation the formula is;
Percent of cement retained on sieve = (w2/w1) x 100.
9. Repeat the test for at least three times to minimize the risk of errors.
Result:

According to Indian Standard, the amount of cement-retained on the 90 µm sieve shall
never exceed 10%.
2. Soundness Test:

Soundness of cement is the ability of a hardened paste to retain its volume after setting. A
cement is said to be unsound (i.e., having lack of soundness) if it is subjected to delayed
destructive expansion.
Unsoundness of cement is due to presence of excessive amount of hard-burned free lime or
magnesia.

Soundness of cement indicates quality to expand on the setting. Unsound cement expands
too much on setting and develops cracks in the structure.

The test used for determining soundness of cement is known as “Le chatelier apparatus
test.”
Page | 15
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)

By soundness of cement, it is understood that, its capacity to form a non-disintegrating, hard
uniformly strong mass on the setting.

The soundness of cement means it doesn’t undergo large volume change after setting. Large
changes in volume produce cracks, disintegration, and distortion, ultimately leading to
failure. So it is very important to test the soundness of cement.

This depends on its original composition, proper burning, and grinding. Presence of lime in
the free state, an excess of sulfate or magnesia and a very fine size may be the cause of
soundness in cement.

The Indian Bureau of Standards has specified the le chatelier apparatus test – the same as
adopted by British and American Standards for soundness test of cement.
To test the soundness two methods can be applied:1) Le-Chatelier method
2) Autoclave method
Le Chatelier Apparatus Test:Apparatus:


It consists of a small, split, metallic cylinder having an internal diameter of 30 mm. It is 30
mm in height, with the thickness of wall being 0.5 mm.
It is fixed with two indicators, one fixed on either side of the split. The distance from the end
of the indicator to the center of the cylinder is 165 mm.
Other apparatus used in the Le Chatelier Apparatus test are:
1)
2)
3)
4)
5)
6)
7)
8)
Balance.
Measuring box.
Water bath.
Caliper.
Le Chatelier Apparatus.
Glass Sheets.
Enamel Tray.
Trowel.
Specimen:

The cement to be tested is made into a paste of specified consistency. In common practice,
100 gm of neat cement is mixed with water calculated at 0.72 (P) where “P” is the
percentage of water required for making a paste of normal consistency.
Procedure:
1. Before commencing setting time test, do the consistency test to obtain the water required to give
the paste normal consistency (P).
2. Prepare a paste by adding 0.78 times the water required to give a paste of standard consistency
(i.e. 0.78P).
3. Lightly oil the Le-chatelier mold and place it on on a lightly oiled glass sheet.
Page | 16
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
4. The paste, of the known consistency, is filled in the cylindrical mold, covered with glass sheet and
kept under water (at 27 degrees to 32-degrees centigrade) for 24 hours.
5. After which the cylinder is taken out, and the distance between the two indicators is measured
(say it is x). It is again immersed in the water.
6. The water is then brought to the boiling point in 15-30 minutes and kept boiling for 1 hour after
which the distance between the two indicators is again measured (say it is now y).
7. The difference of y-x gives the expansion of the cement specimen on the setting.
8. It is specified that this distance shall not exceed 10 mm for the cement to qualify as SOUNDNESS
CEMENT.
Field Tests of Cement for Civil Engineers:1. Date of Manufacturing:
As the strength of cement reduces with age, the date of manufacturing of cement bags should be
checked.
2. Cement Color:
The color of cement should be uniform. It should be typical cement color i.e. gray color with a light
greenish shade.
3. Whether Hard Lumps are Formed:
Cement should be free from hard lumps. Such lumps are formed by the absorption of moisture from
the atmosphere.
4. Temperature Inside Cement Bag:
If the hand is plunged into a bag of cement, it should be cool inside the cement bag. If hydration
reaction takes place inside the bag, it will become warm.
5. 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.
6. Water Sinking Test:
If a small quantity of cement is thrown into the water, it should float some time before finally
sinking.
7. The smell of Cement Paste:
A thin paste of cement with water should feel sticky between the fingers. If the cement contains too
much-pounded clay and silt as an adulterant, the paste will give an earthy smell.
8. 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.
9. Block Test:
A 25mm × 25mm × 200mm (1”×1”×8”) block of cement with water is made. The block is then
immersed in water for three days. After removing, it is supported 150mm apart and a weight of 15kg
uniformly placed over it. If it shows no sign of failure the cement is good.
Page | 17
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Ques No.04:- What are the sources of aggregates. Explain the classification's
of Aggregate.
Or
Give the classification of aggregate according to their source, shape & size.
Or
What are the various Aggregates used in cement concrete work ? Explain
about the surface texture of Aggregates.
(Semi-Compulsory For 7 Marks)
Ans:- Aggregate:
Aggregates are the most widely used products during the construction. Aggregates are the
granular materials used as ingredients to make up the proportion of concrete. These
materials include gravel, sand, or crushed stone mixed with water which is all added to the
cement mixture to create concrete. The most common size of aggregate used in the
concrete mix is 20 mm for coarse aggregate and particle size less than 4.75 mm for fine
aggregate.

Aggregates are the important constituents of the concrete which give body to the concrete
and also reduce shrinkage. Aggregates occupy 70 to 80 % of total volume of concrete.
According to nature of the formation of aggregates, they are classified as:1) Natural Aggregates
2) Crushed Aggregates
1. Natural Aggregates:
Natural – Aggregates taken from natural sources, such as riverbeds, quarries and mines.

Sand, gravel, stone and rock are the most common, and these can be fine or coarse.
2. Crushed Aggregates:
Processed – Also called ‘artificial aggregates’, or ‘by-product’ aggregates, they are commonly
taken from industrial or engineering waste, then treated to form construction aggregates for
high quality concrete. Common processed aggregates include industrial slag, as well as burnt
clay.

Processed aggregates are used for both lightweight and high-density concrete mixes.
Aggregates are classified according to shape into the following types:1)
2)
3)
4)
5)
6)
Rounded aggregates
Irregular or partly rounded aggregates
Angular aggregates
Flaky aggregates
Elongated aggregates
Flaky and elongated aggregates
Page | 18
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
1. Rounded Aggregate:
The rounded aggregates are completely shaped by attrition and available in the form of
seashore gravel.

Rounded aggregates result the minimum percentage of voids (32 – 33%) hence gives more
workability.

They require lesser amount of water-cement ratio.

They are not considered for high strength concrete because of poor interlocking behavior
and weak bond strength.
2. Irregular Aggregates:
The irregular or partly rounded aggregates are partly shaped by attrition and these are
available in the form of pit sands and gravel.

Irregular aggregates may result 35- 37% of voids.

These will give lesser workability when compared to rounded aggregates.

The bond strength is slightly higher than rounded aggregates but not as required for high
strength concrete.
3. Angular Aggregates:
The angular aggregates consist well defined edges formed at the intersection of roughly
planar surfaces and these are obtained by crushing the rocks.

Angular aggregates result maximum percentage of voids (38-45%) hence gives less
workability.

They give 10-20% more compressive strength due to development of stronger aggregatemortar bond. So, these are useful in high strength concrete manufacturing.
4. Flaky Aggregates:
When the aggregate thickness is small when compared with width and length of that
aggregate it is said to be flaky aggregate.

Or in the other, when the least dimension of aggregate is less than the 60% of its mean
dimension then it is said to be flaky aggregate.
5. Elongated Aggregates:
When the length of aggregate is larger than the other two dimensions then it is called
elongated aggregate or the length of aggregate is greater than 180% of its mean dimension.
Page | 19
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
6. Flaky and Elongated Aggregates:
When the aggregate length is larger than its width and width is larger than its thickness then
it is said to be flaky and elongated aggregates.

The above 3 types of aggregates are not suitable for concrete mixing. These are generally
obtained from the poorly crushed rocks.
Aggregates are classified into 2 types according to size:1) Fine aggregate
2) Coarse aggregate
1. Fine Aggregate:
When the aggregate is sieved through 4.75mm sieve, the aggregate passed through it called
as fine aggregate.

Natural sand is generally used as fine aggregate, silt and clay are also come under this
category. The soft deposit consisting of sand, silt and clay is termed as loam.

The purpose of the fine aggregate is to fill the voids in the coarse aggregate and to act as a
workability agent.
According to sources, fine aggregates can be further classified as:a) Natural Sand:
It is the fine aggregate resulting from the natural disintegration of rock. It is deposited by
streams or glacial agencies.
b) Crushed Gravel Sand:
It is the fine aggregate which is produced by crushing hard gravel.
c) Crushed Stone Sand:
It is the fine aggregate which is produced by crushing natural stone.
2. Coarse Aggregate:
When the aggregate is sieved through 4.75mm sieve, the aggregate retained is called coarse
aggregate.

Gravel, cobble and boulders come under this category.

The maximum size aggregate used may be dependent upon some conditions. In general,
40mm size aggregate used for normal strengths and 20mm size is used for high strength
concrete. the size range of various coarse aggregates given below.
According to sources of coarse aggregates, it can be further classified as:
(a) Uncrushed Gravel or Stone:
It results from natural disintegration of rock.
Page | 20
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
(b) Crushed Gravel Stone:
It results from the crushing of gravel or hard stone.
Ques No.05:- Explain impact value test on Aggregate.
Or
Explain impact value test on Aggregate with diagram.
(Future For 7 Marks)
Ans:- Impact value test on Aggregate:
The property of a material to resist impact is known as toughness. Due to movement of
vehicles on the road the aggregates are subjected to impact resulting in their breaking down
into smaller pieces.

The aggregates should therefore have sufficient toughness to resist their disintegration due
to impact. This characteristic is measured by impact value test.

The aggregate impact value is a measure of resistance to sudden impact or shock, which may
differ from its resistance to gradually applied compressive load.
PURPOSE OF TEST:

Aggregate Impact Value test determines the Aggregate Impact Value (AIV) of aggregates
which provides a relative measure of the resistance of an aggregate to sudden shock or
impact.

Resistance of the aggregates to impact is termed as toughness. Aggregates used in the
pavement should be able to resist the effect caused by the jumping of the steel tyred wheels
from one particle to another at different levels causes severe impact on the aggregates.

Lower the aggregate crushing value greater will be the “resistance to to sudden shock or
impact (toughness)”.
Procedure to determine Aggregate Impact Value:1) The cup of the impact testing machine should be fixed firmly in position on the base of the
machine and the whole of the test sample placed in it and compacted by 25 strokes of the
tamping rod.
2) The hammer should be raised to 380mm above the upper surface of the aggregates in the
cup and allowed to fall freely onto the aggregates. The test sample should be subjected to a
total of 15 such blows, each being delivered at an interval of not less than one second.
APPLICATIONS OF AGGREGATE IMPACT VALUE:
Aggregate having AIV % less 50% is better to use in construction where as those having value
more than 50% are bad for construction.
Page | 21
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)

It is reliable to calculate the AIV % of the aggregate use as road construction as it will give us
the capacity of road to bear the load on it. Aggregate having AIV % equal or greater than 35
% is considered bad to use in road construction.
Diagram:-
RESULTS:
i) The sample should be removed and sieved through a 2.36mm IS Sieve. The fraction passing
through should be weighed (Weight ‘B’). The fraction retained on the sieve
should also be weighed (Weight ‘C’) and if the total weight (B+C) is less than the initial weight (A) by
more than one gram, the result should be discarded and a fresh test done.
ii) The ratio of the weight of the fines formed to the total
sample weight should be expressed as a percentage.
Aggregate impact value = B/A x 100%
Page | 22
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
iii) Two such tests should be carried out and the mean of the results should be reported.
A sample proforma for the record of the test results is given in the below table.
*****
Complete By
Shah Sir
(Civil Engineering Tutor)
Mob- +91 7888280720
Page | 23
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
SHAH ENGINEERING CLASSES
(A Classroom of Civil Engineering Department)
[Poly/B.E/B.Tech/M.Tech/JE Govt./GATE]
By
SHAH SIR
Weekly Classes Available
Venue:Trimurtinagar, Near Hingna T-Point, Nagpur
Contact Us:+91 7888280720 (SHAH SIR)
Page | 24
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Unit-02 (13 Marks)
Fresh concrete
Theories:- 13 Marks
Ques No.01:- What is workability and what are the factors affecting it?
Or
Explain various factors affecting workability of concrete.
Or
What is workability? List out the tests for workability measurements. compare
volume Batching & weight Batching.
Or
What do you mean by Workability of concrete? Is it necessary to determine
the workability of concrete. Explain.
Or
Define workability. Enlist various test to measure workability. Explain
compaction factor test in detail.
(Compulsory For 7 Marks)
Ans:- Workability:
Workability is a property of freshly mixed concrete. Concrete is a mixture
of cement, aggregates, water, and admixtures. The properties of concrete, whether in the
fresh state or hardened state, are affected by its ingredients and their proportions.

Workability is a purely physical property of freshly mixed concrete. Workability of concrete
simply means the ability to work with concrete. Fresh concrete is said to be workable if it
can be easily transported, placed, compacted, and finished without any segregation. The
ease of placing, compacting, and finishing of concrete in the desired manner is called its
workability.

ACI (American Concrete Institute) defines it as ‘that property of freshly mixed concrete or
mortar which determines the ease and homogeneity with which it can be mixed, placed,
consolidated and finished’.

ASTM (American Society for Testing and Materials) defines it as “that property determining
the effort required to manipulate a freshly mixed quantity of concrete with minimum loss of
homogeneity”.
Page | 25
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Elaborating More a Concrete is Said to be Workable If:
1) It can be placed without loss of homogeneity. i.e. concrete ingredients never get dispersed
while placing and remain uniformly distributed across cross section.
2) It can be handled without segregation. i.e. concrete ingredients never get separated during
transport or placing.
3) It can be compacted with specified effort. i.e. with a normal vibrator or even rodding with
bamboo or a rod.
4) It can be finished easily.
Workability Vs. Strength of Concrete:The following figure explains the relation between workability and compressive strength of
concrete:
(Fig: Workability Vs. Strength of Concrete)
Factors Affecting Workability of Concrete:1) Water content: The increase in water content increases the fluidity of the concrete thus
providing greater lubrication. This helps to increase the workability of the concrete.
Increasing the water content should be the last resort to improve the workability in the
concrete as this will seriously affect the strength of the concrete. Even if more amount of
water is to be added, more cement also should be added so that the water/ cement ratio
remains the same and hence the strength of the concrete remains unaffected.
2) Size of aggregates: The surface area of bigger aggregates is less and hence less amount of
water is required for lubricating the surface to reduce the friction. Thus the concrete having
large sized aggregate is more workable (of course, within certain limits).
3) Mix proportions: Aggregate/ cement ratio is the measure of how lean or rich the concrete
is. If aggregate/ cement ratio is higher, the concrete becomes leaner. In lean concrete less
paste is available for the lubrication of the aggregate, while in rich concrete with low a/c
ratio, more paste is available which makes the mix more cohesive and hence provides better
workability.
Page | 26
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
4) Shape of aggregates: Rounded aggregates have considerably less surface area and less voids
in comparison to angular or flaky aggregates which provide better possibility of overcoming
the frictional resistance. Further, angular and flaky aggregates make concrete very harsh.
5) Surface texture of aggregates: The aggregates having smooth or glossy texture have less
surface area compared to rough textured aggregates. This provides better workability as less
amount of water is required for lubricating effect. But, taking into account the poor
interlocking action provided by the glossy textured aggregate, its use is generally
discouraged in high strength concrete.
6) Grading of aggregates: Well graded aggregate is the one with least amount of voids in a
given volume. If the grading of aggregate is good, the voids will be less and hence higher the
workability.
7) Use of admixtures: Use of admixtures in concrete is the major factor that affects the
workability. The use of plasticizers and super-plasticizers amply increase the workability of
the concrete. Air entraining agents produce air bubbles which act as rollers between
particles and provide better mobility thus improving the workability.
8) Time and temperature: Fresh concrete gets stiffened as the time flows. This is because
some of the water used to mix the concrete gets evaporated and some gets absorbed by the
aggregates. Thus the workability of concrete reduces with time. This loss of workability with
time is known as slump loss. The effect of temperature on workability of concrete is
noteworthy. As the temperature increases, the workability of the mix reduces.
DIFFERENT TEST METHODS FOR WORKABILITY MEASUREMENT:Depending upon the water cement ratio in the concrete mix, the workability may be determined
by the following three methods:1) Slump Test
2) Compaction Factor Test
3) Vee-bee Consistometer Test
1. SLUMP TEST:
It is the most common method for measuring the workability of freshly mixed concrete. It
can be performed both in lab and at site. Uniformity of the concrete regarding workability
and quality aspects can be assessed from batch to batch by observing the nature in which
the concrete slumps. It is not very suitable for very wet or very dry concrete.

A steel mould in the form of frustum of cone is used in slump test which has the top
diameter of 100 mm, bottom diameter of 200 mm and the height is 300 mm. According to
Indian standard specification, the maximum size of the aggregate in concrete that can be
used to perform slump test is restricted to 38 mm.
The mould is cleaned and freed from any surface moistures and then the concrete is placed
in three layers. Each layer is tamped 25 times with a standard tamping rod (16 mm dia, 0.6
meter length). Immediately after filling, the cone is slowly lifted and the concrete is allowed
to subside. The decrease in the height of the center of the slumped concrete is called slump
and is measured to the nearest 5mm.

Page | 27
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)

If the concrete subsides evenly all round, the slump measured is true slump. If one half of
the cone slides down an inclined plane, a shear slump is said to have taken place and the
test has to be repeated. Too wet mix shows collapsible nature of slump.
SUITABILITY:

This method is suitable only for the concrete of high workability.

This test is carried out with a mould called slump cone whose top diameter is 10 cm, bottom
diameter is 20 cm and height is 30 cm.
Diagram:-
Page | 28
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
PROCEDURE:
The test is performed in the following steps:
1) Place the slump mould on a smooth flat and non-absorbent surface.
2) Mix the dry ingredients of the concrete thoroughly till a uniform colour is obtained and then
add the required quantity of water in it.
3) Place the mixed concrete in the mould to about one-fourth of its height.
4) Compact the concrete 25 times with the help of a tamping rod uniformly all over the area.
5) Place the mixed concrete in the mould to about half of its height and compact it again.
6) Similarly, place the concrete upto its three-fourth height and then up to its top. Compact
each layer 25 times with the help of tamping rod uniformly. For the second and subsequent
layers, the tamping rod should penetrate into underlying layer.
7) Strike off the top surface of mould with a trowel or tamping rod so that the mould is filled to
its top.
8) Remove the mould immediately, ensuring its movement in vertical direction.
9) When the settlement of concrete stops, measure the subsidence of the concrete in
millimeters which is the required slump of the concrete.
LIMITATIONS OF SLUMP TEST:Following are the limitations:
1)
2)
3)
4)
Not suitable for concrete containing aggregates larger than 40 mm.
Not suitable for concrete of dry mix.
Not suitable for very wet concrete.
Not reliable because slump may be of any shape.
2. COMPACTION FACTOR TEST:
According to this test, the workability may be defined as the amount of applied work
required to compact the concrete to its maximum density.
Page | 29
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
SUITABILITY:

This method is adopted for determining the workability of concrete mix in laboratories. It
gives fairly good results for concrete of low workability.
Diagram:-
Page | 30
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
PROCEDURE:
1)
2)
3)
4)
The test is performed in the following steps:
Clean and dry the internal surface of the mould.
With the help of hand scoop, place the concrete in upper hopper A.
Open the trap door of hopper in order to facilitate the falling of the concrete into lower
hopper B. the concrete sticking to the sides of the hopper A, should be pushed downward
with the help of a steel rod.
5) Open the trap door of the hopper B and allow the concrete to fall into cylinder C.
6) Remove the surplus concrete from the top of the cylinder with the help of a trowel. Wipe
and clean the outside surface of the cylinder.
7) Weigh the cylinder with partially compacted concrete nearest to 10 g.
8) Fill in the cylinder with fresh concrete in layers not exceeding 5 cm in thickness and compact
each layer till 100 percent compaction is achievd.
9) Wipe off and clean the outside surface of the cylinder and weigh the cylinder with fully
compacted concrete nearest to 10 g.
10) Calculate the value of compaction factor using the following formula.
Compaction factor = weight of partially compacted concrete/weight of fully compacted concrete
ADVANTAGES OF COMPACTION FACTOR TEST:Following are the advantages:
1)
2)
3)
4)
Suitable for testing workability in laboratories
Suitable for concrete of low workability
Suitable to detect the variation in workability over a wide range
Its results are more precise and sensitive.
Ques No.02:- What is batching ? Compare Volume Batching and Weight
Batching.
(Future For 6 Marks)
Ans:- The following steps are involved in the concreting:1. Batching
2. Mixing
3. Transporting
4. Placing &
5. Compacting.
Batching:
In general batching is the process of measuring and combining the ingredients of concrete
(cement, water, sand, aggregates)…as per the mix design.

Batching is the process of measuring and combining required ingredients of concrete by
either by weight or by volume as per the mix design and introducing them into a mixture to
produce a uniform quality of concrete.

The proper and accurate measurement of all the material used in concrete making is
necessary to ensure uniformity of proportions in succeeding batches.
Page | 31
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Compare Volume Batching and Weight Batching:S.No.
1.
Volume Batching
The concrete ingredients are
batched / proportioned based on
volume.
Batching by volume achieved by
using a constructed gauge boxes
(Farmas) for proportioning the
materials according to various mix
proportions and based on the
quantity of material needed per
batch.
In small works gamellas are also
used for batching. But it is not
recommended for batching of
concrete.
3.
Nominal mix is batched by mass
using regularly maintained and
well-calibrated equipment,
therefore high degree of
uniformity in proportion of the
fresh and hardened state concrete
can be achieved.
4.
Materials batched by mass are
exact in measurement taking
cognisance of the differences in
the material properties.
Water for mixing is weighed out
precisely as a function of the
weight of cement used for each
mix proportion. Hence
uniform water-cement ratio can be
maintained, which plays an
important role in achieving
strength of concrete.
Each batch is weighed which
makes it easy to detect overruns
or incorrect dosages.
The slump of concrete batched by
mass is higher than batched by
volume for same mix proportion
and water cement ratios. i.e.
slump varies from medium to very
high slump.
For same mix proportion, the
compressive strength of concrete
batched by mass is higher than
that batched by volume at all w/c
ratios and for curing ages 7 to 28
days.
When batching by volume is used,
possible sources of error could
lead to variation in the amount of
aggregate in a specific volume and
errors in measured volume. These
errors often lead to variations in
the fresh and hardened properties
of concrete as against specified
characteristics properties.
Variations in quantity are very
much likely for materials.
Ultimately affect strength of
concrete.
The volume of water required for
mixing is not often specified.
Sometime extra water is added to
make concrete workable.
This makes concrete non uniform
and reduces the strength.
2.
5.
6.
7.
8.
Page | 32
Weight Batching
The concrete ingredients are
batched/ proportioned based on
weight.
Batching by mass is achieved by
using weigh batching machine/
plant.
Concrete Technology
Difficult to detect overruns or
incorrect dosages.
Slump varies from low to high.
For same mix proportion, the
compressive strength of concrete
batched by volume is lower than
that batched by mass at all w/c
ratios and for curing ages 7 to 28
days.
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)

Batching can be done by two methods, volume batching and weight batching. Batching
should be done properly to get quality concrete mix.
Ques No.03:- What is curing? Explain various types of curing with their
suitability?
Or
Why curing is necessary ? Explain various methods of curing.
Or
Explain significance of concrete curing? Also explain maturity of concrete.
Or
What is curing of concrete? How do you decide the period of curing. Explain.
(Semi-Compulsory For 7 Marks)
Ans:- Curing:
The curing of concrete is the process of keeping the concrete damp or moist and warm after
the initial setting of concrete or removal of formwork. Proper curing of concrete maintains
the satisfactory moisture content and favorable temperature inside the concrete so that
hydration of cement may continue until the desired properties are developed.

The curing of concrete must be continued for a reasonable period of time to achieve its
desire strength and durability.

Curing of Concrete is a method by which the concrete is protected against loss of moisture
required for hydration and kept within the recommended temperature range. Curing
will increase the strength and decrease the permeability of hardened concrete. Curing is
also helps in mitigating thermal and plastic cracks, which can severely impact durability of
structures.

A curing practice involves keeping the concrete damp or moist until the hydration of
concrete is complete and strength is attained. Curing of concrete should begin soon after
initial setting time of concrete or formwork/shuttering is removed and must continue for a
reasonable period of time as per the specified standards, for the concrete to achieve its
desired strength and durability.

It is important to make sure an uninterrupted hydration of PCC & RC after concrete is placed
and finished in its position. Uniform temperature ought to be maintained throughout the
concrete-section depth to avoid thermal shrinkage cracks.
Why Curing of Concrete is Necessary:1)
2)
3)
4)
Enhance Hydration of Concrete to achieve desired Strength
Improved durability of concrete by reducing cracks
Higher serviceability performance by increasing abrasion resistance
Improved microstructure by developing better hydrate gels and solid mass.
Page | 33
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Significance of concrete curing:
Curing has a strong influence on all properties of concrete and therefore it should not be
taken lightly. Properly cured concrete has better surface hardness and can better withstand
surface wear and abrasion apart from the basic strength.

Curing also makes concrete more impermeable, which prevents moisture and water-borne
chemicals from entering into the concrete, thereby increasing durability and service life.

Proper curing helps to prevent crazing, dusting, surface disintegration and scaling.Adequate
curing reduces shrinkage, gives better resistance to wear and improves long-term
appearance.

Without proper curing, the chemical process of hydration is not complete. Without proper
curing, you will never be able to get the designed strength of concrete and please note that
this is a loss of strength for a lifetime and there is no easy alternative to strengthen such
poorly cured weak concrete. So always be careful and cure with care.
METHODS USED FOR CURING OF CONCRETE:There are various methods of curing. The adoption of a particular method will depend upon the
nature of work and the climatic conditions.
The following methods of curing of concrete are generally adopted:
1)
2)
3)
4)
5)
6)
7)
Shading concrete work
Covering concrete surfaces with hessian or gunny bags
Sprinkling of water
Ponding method
Membrane curing
Steam curing
Spraying or Fogging Method
1. SHADING OF CONCRETE WORK:
The object of shading concrete work is to prevent the evaporation of water from the surface
even before setting. This is adopted mainly in case of large concrete surfaces such as road
slabs. This is essential in dry weather to protect the concrete from heat, direct sun rays and
wind. It also protects the surface from rain. In cold weather shading helps in preserving the
heat of hydration of cement thereby preventing freezing of concrete under mild frost
conditions. Shading may be achieved by using canvas stretched on frames. This method has
a limited application only.
2. COVERING CONCRETE SURFACES WITH HESSIAN OR GUNNY BAGS:
This is a widely used method of curing, particularly for structural concrete. Thus exposed
surface of concrete is prevented from drying out by covering it with hessian, canvas or
empty cement bags. The covering over vertical and sloping surfaces should be secured
properly. These are periodically wetted. The interval of wetting will depend upon the rate of
Page | 34
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
evaporation of water. It should be ensured that the surface of concrete is not allowed to dry
even for a short time during the curing period. Special arrangements for keeping the surface
wet must be made at nights and on holidays.
3. SPRINKLING OF WATER:
Sprinkling of water continuously on the concrete surface provides an efficient curing. It is
mostly used for curing floor slabs. The concrete should be allowed to set sufficiently before
sprinkling is started. The spray can be obtained from a perforated plastic box. On small jobs
sprinkling of water may be done by hand. Vertical and sloping surfaces can be kept
continuously wet by sprinkling water on top surfaces and allowing it to run down between
the forms and the concrete. For this method of curing the water requirement is higher.
4. PONDING METHOD:
This is the best method of curing. It is suitable for curing horizontal surfaces such as floors,
roof slabs, road and air field pavements. The horizontal top surfaces of beams can also be
ponded.

In the ponding method, small rectangular or square artificial ponds are built with using
bunds of clay or lean mortar or sand across and along the concrete surface. Water is filled in
small rectangular or square ponds two or three times per day depending upon the
atmospheric conditions. This method is very efficient but the amount of water required is
huge.
Page | 35
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
5. MEMBRANE CURING:
The method of curing described above come under the category of moist curing. Another
method of curing is to cover the wetted concrete surface by a layer of water proof material,
which is kept in contact with the concrete surface of seven days. This method of curing is
termed as membrane curing. A membrane will prevent the evaporation of water from the
concrete. The membrane can be either in solid or liquid form. They are also known as sealing
compounds. Bituminised water proof papers, wax emulsions, bitumen emulsions and plastic
films are the common types of membrane used.

Whenever bitumen is applied over the surface for curing, it should be done only after 24
hours curing with gunny bags. The surface is allowed to dry out so that loose water is not
visible and then the liquid asphalt sprayed throughout. The moisture in the concrete is thus
preserved. It is quite enough for curing.

This method of curing does not need constant supervision. It is adopted with advantage at
places where water is not available in sufficient quantity for wet curing. This method of
curing is not efficient as compared with wet curing because rate of hydration is less.
Moreover the strength of concrete cured by any membrane is less than the concrete which
is moist cured. When membrane is damaged the curing is badly affected.
6. STEAM CURING:
Steam curing and hot water curing is sometimes adopted. With these methods of curing, the
strength development of concrete is very rapid.

These methods can best be used in pre cast concrete work. In steam curing the temperature
of steam should be restricted to a maximum of 750C as in the absence of proper humidity
(about 90%) the concrete may dry too soon. In case of hot water curing, temperature may
be raised to any limit, ay 1000C.

At this temperature, the development of strength is about 70% of 28 days strength after 4 to
5 hours.

In both cases, the temperature should be fully controlled to avoid non-uniformity. The
concrete should be prevented from rapid drying and cooling which would form cracks.
7. Spraying or Fogging Method:
Curing by spraying of water or fogging is one of the conventional methods of curing concrete
in the construction industry.

It can be an efficient method for curing by supplying additional moisture during hot weather.

By using nozzles or sprayers, water is sprayed on the concrete members, which are to be
cured.
Page | 36
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
What is the Right Time for Concrete Curing?
The right time of curing of concrete depends on several factors. Like, temperature, the evaporation
rate, moisture content in the air, etc.
According to ACI-308, three phases of concrete curing should be done:
(1) Initial Curing:





This process is also called Bleeding of Concrete. After placing of concrete, the water starts
bleeding from concrete and rises from its pores.
After rising of water, evaporation take place, and the water starts disappearing from the
surface due to evaporation.
Bleeding of concrete depends on many factors like thickness, length, temperature, etc.
So, to reduce the loss of water and prevent shrinkage, initial curing of concrete is required.
Evaporation reducers can be used for this process.
(2) Intermediate Curing of Concrete:


This process is done when finishing work is finished before the final setting of cement.
As you know, water plays an important role in the strength of concrete. Therefore, the
intermediate curing of concrete is required.
(3) Final Concrete curing:

After the final setting of concrete, it should be cured so that to prevent the loss of more
water and increase the strength of concrete.
Ques No.04:- Explain in Brief segregation, Bleeding & Water Cement ratio.
Or
Explain significance of water cement ratio. What is segregation and bleeding
in concrete.
Or
What are various causes of bleeding and segregation in concrete ?
(Compulsory For 7 Marks)
Ans:- Segregation:
Segregation is the “Separation of constituent materials in concrete.”

Segregation of concrete is the separation of cement paste and aggregates of concrete from
each other during handling and placement. Segregation also occurs due to over-vibration or
compaction of concrete, in which cement paste comes to the top and aggregates settles at
the bottom.

Segregation of concrete affects strength and durability in structures. In a good concrete, all
concrete aggregates are evenly coated with sand and cement paste and forms a
homogeneous mass.
Page | 37
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Diagram:-
In concrete technology, segregation is of three types:1) Separation of Coarse aggregate from the concrete mixture,
2) Separation of Cement pastes from the concrete during its plastic stage.
3) Separation of water from the concrete mix (Bleeding in concrete)
Causes of Segregation of Concrete:a) Use of high water-cement ratio in concrete. This general happens in case of concrete mixed
at site by unskilled workers.
b) Excessive vibration of concrete with mechanical needle vibrators makes heavier particles
settle at bottom and lighter cement sand paste comes on top.
c) When concreting is done from height in case of underground foundations and rafts, which
causes concrete to segregate.
How to minimize segregation in concrete:1) Segregation can be controlled by maintaining proper proportioning the mix.
2) By proper handling, placing, transporting, compacting and finishing of concrete.
3) Adding air entraining agents, admixtures and pozzolanic materials in the mix segregation
controlled to some extent.
Page | 38
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Bleeding:
Bleeding is a form of segregation in which water present in the concrete mix is pushed
upwards due to the settlement of cement and aggregate. The specific gravity of water is low,
due to this water tends to move upwards. Bleeding ordinarily occurs in the wet mix of
concrete.

The Prime factor for bleeding in concrete is the high dosage of Water cement ratio. Higher
water-cement ratio weakens concrete and leads to excessive bleeding.

The bleeding in concrete is not harmful if the rate of evaporation of water is equal to the
rate of bleeding. Normal bleeding is quite good, and it enhances the workability of concrete.
When the concrete is fully plastic, bleeding may not cause much harm. However, concrete is
still in the plastic stage later it is subsidized and compacted.
Causes of bleeding in Concrete:a) High water-cement ratio leading to highly wet mix.
b) Badly proportioned and insufficiently mixed concrete.
How the bleeding in concrete is controlled:a) Bleeding in concrete is controlled by Adding minimum water content in the concrete mix.
b) Encouraging the use of air en-training admixtures in the mix.
c) By adding more cement in the mix.
Effects Of Bleeding:a) Due to bleeding concrete loses its homogeneity.
b) Bleeding is responsible for causing permeability in concrete.
c) As far as safety is concerned, water that accumulates below the reinforcing bars, reduces
the bond between the reinforcement and concrete.
d) In the process of bleeding the accumulation of water creates a water voids and reduces
bond between the aggregate and cement paste.
e) Due to bleeding pumping ability of concrete is reduced.
f) Increase in the water-cement ratio at the top.
g) The accumulation of water at the top, results in delayed surface finishing.
Water Cement ratio:
Water-Cement Ratio - The ratio of the amount of water to the amount of cement by weight
is termed the water-cement ratio. The strength and quality of concrete depend on this ratio.
The quantity of water is usually expressed in litre per bag of cement. if water required for
one bag of cement is 30 litres, the water-cement ratio is equal to 30/50 = 0.6.

Water cement ratio can be defined as the ratio of the volume of water to the volume
of cement used in a concrete mix. Water has a great role on the strength and workability of
concrete. After lots of experiments it has been found that for a specific proportion of
materials in a concrete mix, there is a certain amount of water that gives maximum strength.
Page | 39
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)

A slight change in the amount of water causes much more differences in the strength of
concrete. If less water is used, the resultant concrete will be nearly dry, hard to place in the
form and may create difficulties in compaction. Besides this, with less water proper setting
will not be guaranteed and thus the strength of concrete get reduced considerably.

On the other hand, if water is used more, it may develop larger voids and honey-combing in
the set concrete, in this way decreasing its density, durability, and strength. Hence, water
cement ratio attends an important role in producing concrete of required strength. The
lower the ratio, the greater is the strength of concrete.
Duff Abrams’ Law for Water-Cement Ratio:
American Researcher Duff Abrams’ gave a concept on water/cement ratio which known is as
“Abrams’ water/cement ratio law”.

As per Duff Abrams’ law strength of concrete is inversely related to the W/C ratio. If w/c
ratio increases, the strength of concrete decreases.

Compaction of concrete is also important because, If concrete is not properly compacted it
contains large voids, which leads to porosity. Thus, at a low water/cement ratio, where fully
compacting is hard to achieve, Abrams’ law is not valid.

Decrease in compressive strength with an increase in water/cement ratio illustrated
graphically below,

Water-cement ratio is the most important factor which affects the properties of concrete.
Selection of water-cement ratio depends on various factors like requirements of strength,
workability, concreting techniques, nature of work etc. General criteria why the low watercement ratio is recommended are as below.
Page | 40
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Following reasons why high water-cement ratio is not recommended:
1)
2)
3)
4)
5)
6)
7)
8)
Chances of segregation and bleeding
Less durability
Development of voids
Decrease in strength of concrete
Decrease in life of structure
Leakage and chances of corrosion
Increased carbonation due to voids and hence reduce life
Freeze-thaw effect etc.
Following major reasons why the low water-cement ratio is recommended:
1)
2)
3)
4)
5)
6)
Increase in strength
Increase in durability
Lower permeability
No leakage or dampness
Greater freeze-thaw durability
Better bond with reinforcement etc.
Ques No.05:- Write a short note on hot weather concreting and underwater
concreting.
Or
Explain under water concreting by the use of Tremie Pipe method.
Or
Explain hot whether concreting & underwater concreting.
Or
Explain hot weather concreting.
(Compulsory For 7 Marks)
Ans:- Under water concreting by the use of Tremie Pipe method:
The degradation of concrete under water is a serious and troublesome matter. Underwater
concreting is necessarily adopted in marine works and in deep foundations. Due to the
continuous loss of cement and segregation of concrete, placing of concrete under water
becomes very difficult to unreinforced construction.

There are several methods to carry out underwater concreting such as tremie method,
pumping methods, preplaced aggregate concrete etc.

The underwater concreting techniques designed mostly to prevent cement washout. These
methods did not obtain the full purpose of avoiding cement wash out at early stages of using
under water concreting apart from cases where large masses of concreting were employed.
Methods of Underwater Concreting:Following are the methods of underwater concreting:
Page | 41
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
1)
2)
3)
4)
5)
6)
7)
8)
9)
Tremie method
Pumping technique
Hydro valve method
Pneumatic valve method
Skip method
Tilting pallet barge method
Preplaced aggregate concrete
Toggle bags method
Bagged concrete method
1. Tremie Method of Underwater Concreting:
Tremie method is one of the most common methods that is used for concreting under
water. In this method, a long steel pipe (named as tremie) having a diameter of 15 to 30 cm
is inserted vertically into the water. The pipe should be long enough that it reaches to the
bed of water keeping its one end above the water level.

The tremie is then fitted with a hopper at the upper end for pouring concrete inside the
pipe. The lower end of the tremie pipe must be closed with a check valve before inserting it
into the water. After that, freshly mixed concrete is poured with the help of hopper. When
the concrete is poured, it displaces the air and water present in the pipe and finally reaches
to the bed.
Diagram:-
Page | 42
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Advantages:
If the work is executed properly, this method has the following advantages:
1. The concrete is not affected by the flowing water, except the top layer. The top layer may be cut
off to remove the affected concrete at the end of the whole operation.
2. Under water concrete dos not need compaction as concrete automatically gets compacted by the
hydrostatic pressure of water.
3. The concrete is of such a high consistency which normally does not require compaction.
Disadvantage:

Concreting by tremie method requires high water/cement ratio for obtaining high
consistency, which reduces the strength of concrete. But now, with the use of some
plasticizer a concrete with as low w/c ratio as 0.3 or even less can be placed by tremie
method.
Hot weather concreting:
We know that cement possesses faster rate of hydration in hot weather. The rate of
hydration of cement increases with the increases in temperature. Generally, 10° C – 27° C is
considered as most suitable for hydration.

At higher temperature, the concrete may start to set before placing and compacting in
position. Therefore the concrete should be placed as fast as possible after mixing. During
concreting in hot climatic condition, the concrete may have to be cooled to protect from ill
effects. To achieve this, cooled water and aggregates can be used while preparing the
concrete.

The concrete placed at an atmospheric temperature above 40C is considered as hot weather
concreting.At this temperature certain special problems are usually encountered.
They are:
1)
2)
3)
4)
5)
6)
7)
8)
Rapid rate of hydration of cement, quick setting and early stiffening
Rapid evaporation of mixed water.
Greater plastic shrinkage.
Less time for finishing.
Reduced relative humidity.
Absorption of water from the concrete by the sub grade andformwork.
Difficulty in continuous and uninterrupted curing.
Difficulty in incorporation of Air entertainment.
Precautions:
1) Aggregate should be stack piled in shade frequent sprinkling of water should be done to
lower the temperature.
2) Cold water may be used to lower the temperature and concrete or use of ice can be done
while mixing.
3) Reinforcement formwork and subgrade should be wetted with cold water prior to planning.
Page | 43
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
4) It is better to do the concreting operations during the evening time when temperature is
low.
5) Continuous wet curing is necessary

Hot weather has a significant effect on all stages of concrete production and placement
procedures such as increasing rate of hydration and movement of moisture from within
and surface of the concrete. It affects long term strength and durability. Hot weather along
with relative humidity and wind speed also have a significant influence.
Basic Guides for Hot Weather Concreting:1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
Plan in advance. Have equipment and materials ready before the hot weather arrives.
Keep the subgrade and forms moist so they do not absorb water from the mix.
Keep sunshades and windbreaks available and use them whenever possible.
Have everything prepared before the ready-mix truck arrives. Don’t make the truck wait for
you.
Keep in constant communication with the ready-mix concrete provider. Coordination
between the contractor and the producer is key.
Concrete should be placed, struck off and darby immediately.
Use evaporation retardants, fogging or misting with water, or cover with a vapor-proof sheet
after screeding. This will help prevent rapid drying, crusting, plastic shrinkage and rubber
sets.
Temporary covers, like continuously moistened burlap, may be placed over the fresh
concrete and removed in small sections immediately ahead of the finishers.
Substituting a burlap drag or broom finish will eliminate other high-risk finishing practices,
such as smooth trowel finish.
Curing should take place when the surfaces are hard enough to resist marring.
Seal with a good, quality sealer for a minimum of 30 days after placing and curing.
Remember to protect the crew in high temperatures. Drink plenty of fluids and be careful
with long exposure to the sun.
*****
Complete By
Shah Sir
(Civil Engineering Tutor)
Mob- +91 7888280720
Page | 44
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
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Page | 45
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Unit-03
(13 Marks)
Strength of concrete, Testing of Hardness of Concrete
Theories:- 13 Marks
Ques No.01:- What are the factors which affect the strength of concrete?
Explain one of them in brief.
Or
Explain factor affecting strength of concrete.
Or
Explain the various properties which affect the quality of concrete.
(Semi-Compulsory For 7 Marks)
Ans:- Factors which affect the strength of concrete:1) Water – Cement Ratio: Water cement ratio is one of the most important factors which
govern the strength of concrete. Water cement ratio is the weight of water in proportion to
weight of cement expressed in terms of percentage. Workability increases if more water is
added. But if large amount of water is added then paste will become dilute and it will not
gain its strength. Adequate amount of water should be added so as to attain high workability
and strength.
2) Size of Aggregates Used: For large size aggregates, the surface area is less and less cement
paste is required to cover the surface area. But if extra-large size aggregates are used then
cracks may appear.
3) Shape of Aggregates: Rounded aggregates give more workability to concrete. Angular or
pointed aggregates make concrete harsh.
4) Mix Proportion: High mixes of concrete give more workability to concrete as more cement
gives more paste of cement for lubricating the concrete.
5) Admixtures: Presence of admixtures such as pozzolana or plasticizers increases the
workability and strength of concrete.
6) Grading of Aggregates: If proper grading of aggregates is done then presence of void is
reduced. Therefore aggregates must be properly graded and then used so as to increase the
workability and strength of concrete.
7) Surface Texture of Aggregates: Aggregates having irregular or hard surface require more
cement to cover them. Hence aggregates must be smooth so as to give proper covering of
cement to aggregates and provide workability to concrete.
8) Quality of Aggregates: Good quality aggregates prevents the concrete from creep.
Page | 46
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
9) Creep: Creep of concrete is the permanent strain induces in concrete due to sustained load
over a long period of time. Poor mix proportion shows more creep and water-cement ratio is
the major factor which affects creep in concrete.
10) Age of Concrete: With age of concrete the rate of creep also increases in concrete due to
sustained load for a long period of time.
11) Segregation: Segregation is the separation of constituent materials of concrete. Segregation
may appear due to bad quality of aggregates used or due to voids present in cement paste.
12) Bleeding: Bleeding is a form of segregation in which water comes at top of the concrete.
Bleeding is also called water gain and is more problematic in wet mixes.
13) Shrinkage: Concrete shrinks in volume due to loss of water or absorption of water. Major
cause of shrinkage is bleeding due to which water from surface evaporates rapidly causing
shrinkage cracks or uneven surface finish. Shrinkage can also appear due to hydration
reaction.
Ques No.02:- Explain Poison's ratio of concrete.
(Compulsory For 4 Marks)
Ans:- Poison's ratio of concrete:
The ratio of the relative contraction strain (transverse, lateral or radial strain) normal to
the applied load - to the relative extension strain (or axial strain) in the direction of the
applied load.

Poisson's ratio varies between 0.1 for high strength concrete and 0.2 for weak mixes. It is
normally taken as 0.15 for strength design and 0.2 for serviceability criteria.
Poisson's Ratio can be expressed as;
μ = - εt / εl
where;
μ = Poisson's ratio
εt = transverse strain (m/m, ft/ft)
εl = longitudinal or axial strain (m/m, ft/ft)
Ques No.03:- Explain Modulus of elasticity of concrete.
(Future For 4 Marks)
Ans:- Modulus of elasticity of concrete:
Modulus of elasticity (also known as elastic modulus, the coefficient of elasticity) of a
material is a number which is defined by the ratio of the applied stress to the corresponding
strain within the elastic limit. Physically it indicates a material’s resistance to being deformed
when a stress is applied to it.

Modulus of elasticity also indicates the stiffness of a material. Value of elastic modulus is
higher for the stiffer materials.
Page | 47
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)

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. As concrete is a heterogeneous material. The
strength of concrete is dependent on the relative proportion and modulus of elasticity of the
aggregate.

Modulus of elasticity of concrete(Ec) is defined as the ratio of the applied stress to the
corresponding strain. Not only does it demonstrate the ability of concrete to withstand
deformation due to applied stress but also its stiffness. In other words, it reflects the ability
of concrete to deflect elastically. Modulus of elasticity of concrete is sensitive to aggregate
and mixture proportions of concrete.

It is defined as the ratio between the normal stress to normal strain below the proportional
limit of a material called modulus of elasticity Ec.

Modulus of elasticity = unit stress/unit strain

With the compressive strength test on the concrete specimen (cylinder of 15 cm diameter
and 30 cm length having a volume 15 cm cube), the modulus of elasticity of concrete is
calculated with the help of stress and strain graph.
According to ACI codes, the modulus of elasticity of concrete can e measure with the formula,
And with normal density or weight of concrete, these two relationships can be simplified as,
#Where
Ec = Modulus of elasticity of concrete.
f’c = Compressive strength of concrete.
Ques No.04:- Write short notes on Accelerated curing test.
(Compulsory For 4 Marks)
Ans:- Accelerated curing test:
Accelerated Curing Method is used to get early high compressive strength in concrete. This
method is also used to find out 28 days compressive strength of concrete in 28 hours. (As
per IS 9013-1978-Method of making, curing and determining compressive strength of
accelerated cured concrete test specimens).
OBJECTIVE:

Normally, the strength of concrete is found out after 7 days and 28 days. For some
construction activities, it may be too late and need to know the strength earlier.
Page | 48
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
REFERENCE STANDARDS:

IS: 9013-1978-Method of making, curing and determining compressive strength of
accelerated cured concrete test specimen.
EQUIPMENT & APPARATUS:
1) Accelerated curing tank
2) Compression Testing Machine
PROCEDURE:
1) Prepare the specimen and store it in moist air of at least 90% relative humidity and at a
temperature of 27+2 0C for 23 hrs + 15 minutes.
2) Lower the specimen, into a curing tank with water at 100 0C and keep it totally immersed
for 3 ½ hours + 5 minutes
3) The temperature of water shall not drop more than 3 0C after the specimens are placed and
should return to boiling within 15 minutes.
4) After curing for 3 ½ hours + 5 minutes in the curing tank, the specimen shall be removed
from the moulds and cooled by immersing in cooling water 27+2 0C for a period of at least
one hour.
5) Read my post compressive strength test of concrete for further steps.
CALCULATION:

The corresponding strength at 28 days can be found out from the following correlation. (It is
however suggested that a new specific correlation should be developed for the specific
concrete used at site.)
R28 (Strength at 28 days) = 8.09 + 1.64 Ra
Where,
Ra = Accelerated Curing Strength in MPa.
SAFETY & PRECAUTIONS:
1) Use hand gloves, safety shoes, while removing containers from curing tank after switching
off the curing tank & place sample in machine properly.
2) Equipment should be cleaned thoroughly before testing & after testing.
*****
Complete By
Shah Sir
(Civil Engineering Tutor)
Mob- +91 7888280720
Page | 49
Concrete Technology
By SHAH SIR (7888280720)
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Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Unit-04
(13 Marks)
Mix Design, Additives and Admixtures
Theories:- 13 Marks
Ques No.01:- Explain concept of Mix design & Factor affecting mix
proportion.
Or
Enlist various methods of mix design and discuss various factors affecting
mix proportions.
Or
Explain mix design process ? What are the factors affecting mix properties ?
Also explain aggregate cement ratio.
Or
What are the objective of concrete mix design? Draw a flow chart for concrete
mix design. Why mix design is required?
(Compulsory For 7 Marks)
Ans:- Concrete mix design:
Cement concrete is a very useful constructional material whose properties can be modified
readily at will. The desired properties of concrete can be obtained by using ingredients in a
certain proportion. Thus determining the relative amount of materials is known as mix
design. Hence mix design can be defined as the process of selecting suitable ingredients of
concrete and determining their relative quantities for producing concrete of certain
minimum properties as strength, durability and consistency etc., as economically as possible.
Objective of concrete mix design:Following are the objectives of concrete mix design:a)
b)
c)
d)
e)
f)
g)
h)
To achieve a specified compressive strength for a specified grade.
To maintain workability of concrete mix throughout work.
For achieving durability.
To achieve economy by selecting appropriate concrete ingredients.
To obtain maximum possible yield per bag of cement.
To avoid honey combing and bleeding.
To comply with various standards.
To reduce wastage of concrete by correct proportioning.
Page | 51
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Advantages of Concrete Mix Design:1)
2)
3)
4)
5)
Required Proportions of Each ingredient
Quality Concrete Mix
Economical Concrete Mix
Best Use of Locally Available Material
Desired Properties of Mix
Requirements of concrete mix design:The requirements which form the basis of selection and proportioning of mix ingredients are :
1) The minimum compressive strength required from structural consideration
2) The adequate workability necessary for full compaction with the compacting equipment
available.
3) Maximum water-cement ratio and/or maximum cement content to give adequate durability
for the particular site conditions
4) Maximum cement content to avoid shrinkage cracking due to temperature cycle in mass
concrete.
Factors Affecting the Choice of Mix Proportion:According to IS 456-1978 and IS-1345-1980, the design of concrete should be based on the
following factors:
1)
2)
3)
4)
5)
6)
7)
8)
Grade designation
Type of cement
Max nominal size of aggregate
Grading of combined aggregates
Water-cement ratio
Workability
Durability, and
Quality control.
Methods of Mix Design:There are various methods of mix design as follows:1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
Arbitrary method
Minimum void method
Maximum density method
Water-cement ratio method
Fineness modulus method
Standard deviation method
American method of mix design
Graphic or Road Note 4 method of mix design
Indian Road Congress IRC-44 method
High strength concrete mix design
Mix design based on flexural strength
ACI committee 211-1 method
Page | 52
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
13)
14)
15)
16)
Department of Environment (DOE) mix design method
Mix design for pumpable concrete
Indian standard recommended (IS 10262-1982) method, and
Rapid method of mix design.
Nowadays out of the above methods following methods are commonly used:
1)
2)
3)
4)
ACI committee 211 method
DOE method
Indian Standard method, and
Rapid method of mix design.
Aggregate cement ratio:
Aggregate cement ratio is the ratio of weights of aggregate to the weight of cement. If this
ratio is more, that implies aggregates are more and cement is less and if this ratio is less,
that implies weight of aggregate is less and weight of cement is more (relatively).

When the weight of cement is more, i.e. aggregate cement ratio is less, the concrete has
more cement paste required to coat aggregates and fill the voids between them. This more
cement paste makes the concrete relatively easy to mix, place and compact as it reduces
the friction between aggregates and allows its smooth movement. Thus the workability of
concrete increases.

When the weight of cement is less, i.e. aggregate cement ratio is more, then there will be
very less cement paste to coat aggregate surfaces and fill the voids, thus, mixing, placing and
compacting of concrete will be more harder than previous case. This implies, the workability
of concrete will be less than previous case.
Ques No.02:- What are admixtures ? Explain air entrained concrete.
Or
List various types of Admixtures used in concrete ? Explain plasticizers and
superplasticizers.
Or
Write a short note on Air entraining admixtures ,plasticizers and super
plasticizers.
Or
Types of admixtures and factors affecting admixture (any two).
Or
Write down the role of admixture as a component of concrete & Explain
plasticizers.
Or
Explain various admixtures used to improve workability of concrete.
Or
Write short note on Accelerators and Retarders.
(Compulsory For 7 Marks)
Page | 53
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Ans:- Admixtures:

As per BIS (IS – 9103: 1999) Page No.1, Concrete Admixture is defined as a material other
than water, aggregates and hydraulic cement and additives like Pozzolana or slag and fiber
reinforcement, used as on ingredient of concrete or mortar and added to the batch
immediately before or during its mixing to modify one or more of the properties of concrete
in the plastic or hardened state.
A material other than water, aggregates, or cement that is used as an ingredient of concrete
or mortar to control setting and early hardening, workability, or to provide additional
cementing properties.

Admixtures of concrete are generally used to alter the properties of concrete (such as
increased workability or reduced water content, acceleration or retardation of setting time,
acceleration of strength development, and improved resistance to weather and chemical
attacks) to make it more suitable for a particular purpose.

For example, calcium chloride can be used to accelerate strength development in mass
concrete during winter. Air-entraining admixtures (inexpensive soaps, detergents, etc.)
entrained air which greatly improves the workability of concrete and thus permits the use of
harsher and more poorly graded aggregates and also those of undesirable shapes.
When Concrete Admixtures Used?
1)
2)
3)
4)
5)
When properties cannot be made by varying the composition of basic material.
To produce desired effects more economically.
Unlikely to make a poor concrete better.
Not a substitute for good concrete practice.
Required dose must be carefully determined and administered
Types of Concrete Admixtures:Concrete admixtures are of different types and they are as follows:
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
13)
14)
15)
Water Reducing Admixtures (Plasticizers)
Retarding Admixtures
Accelerating Admixtures
Air entraining concrete admixture
Pozzolanic Admixtures
Damp-proofing Admixtures
Gas forming Admixtures
Air detraining Admixtures
Alkali Aggregate Expansion Inhibiting Admixtures
Anti-washout Admixtures
Grouting Admixtures
Corrosion Inhibiting Admixtures
Bonding Admixtures
Fungicidal, Germicidal, Insecticidal Admixtures
Coloring Admixtures
Page | 54
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
1. Water Reducing Admixtures (Plasticizers):
Water reducing admixtures, the name itself defining that they are used to minimize the
water demand in a concrete mix. Workability is the important property of concrete which is
improved with the addition of water but if water is added more than required the strength
and durability properties of concrete gets affected.

In addition to increase in workability it also improves the strength of concrete, good bond
between concrete and steel, prevents cracking, segregation, honeycombing, bleeding etc.

Water reducing admixtures are also called as plasticizers and these are classified into three
types namely plasticizers, mid-range plasticizers and super plasticizers. Normal plasticizer
reduces the water demand up to 10%, mid-range plasticizers reduce the water demand up
to 15% while super plasticizers reduce the water demand up to 30%.

Calcium, sodium and ammonium lignosulphonates are commonly used plasticizers. Some of
the new generation super plasticizers are acrylic polymer based, poly carboxylate,
multicarbovylatethers etc.
Applications of Retarding Concrete Admixture:1) Where long transportation of ready mixed concrete is required then premature setting can
be usefully avoided by this type admixture.
2) When concrete is being placed or transported under conditions of high ambient
temperature.
3) In case of large concrete pours
4) Concrete construction involving sliding formwork
2. Retarding Admixtures:
Retarding admixtures slow down the rate of hydration of cement in its initial stage and
increase the initial setting time of concrete. These are also called as retarders and used
especially in high temperature zones where concrete will set quickly.

The quick setting in some situations may lead to discontinuities in structure, poor bond
between the surfaces, creates unnecessary voids in concrete etc. Retarders are useful to
eliminate this type of problems.

Commonly used retarding admixture is calcium sulphate or gypsum. Starch, cellulose
products, common sugar, salts of acids are some other retarders. Most of water reducing
admixtures are also acts as retarding admixtures and they are called as retarding plasticizers.
3. Accelerating Admixtures:
Accelerating admixtures are used for quicker setting times of concrete. It provides higher
early strength development in freshly cast concrete.

Accelerating admixtures are used to reduce the initial setting time of concrete. They speed
up the process of initial stage of hardening of concrete hence they are also called as
Page | 55
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
accelerators. These accelerators also improves the strength of concrete in it early stage by
increasing the rate of hydration.

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.

Some of the accelerating admixtures are triethenolamine, calcium formate, silica fume,
calcium chloride, finely divided silica gel etc. Calcium chloride is the cheap and commonly
used accelerating admixture.
Disadvantages of Accelerating Concrete Admixtures:1)
2)
3)
4)
It has increased drying shrinkage
It offers reduced resistance to sulphate attack
CaCl2 high risk of corrosion of steel – not permitted in reinforced concrete
It is more expensive and less effective
Main uses of Accelerating Concrete Admixtures:1) These admixtures are suitable for concreting in winter conditions
2) During any emergency repair work
3) In case of early removal of formwork
4. Air Entraining Concrete Admixture:
Air entraining admixtures are one of the most important inventions in concrete technology.
Their primary function is to increase the durability of concrete under freezing and thawing
conditions. When added to concrete mix, these admixtures will form millions of noncoalescing air bubbles throughout the mix and improves the properties of concrete.

Air entrainment in concrete will also improve the workability of concrete, prevents
segregation and bleeding, lower the unit weight and modulus of elasticity of concrete,
improves the chemical resistance of concrete and reduction of cement or sand or water
content in concrete etc.

Most used air entrainment admixtures are vinsol resin, darex, Teepol, Cheecol etc. These
admixtures are actually made of Natural wood resins, alkali salts, animal and vegetable fats
and oils etc.
5. Damp-proofing Admixtures:
Damp proofing or water proofing admixtures are used to make the concrete structure
impermeable against water and to prevent dampness on concrete surface. In addition to
water proof property, they also acts like accelerators in early stage of concrete hardening.

Damp proofing admixtures are available in liquid form, powder form, paste form etc. The
main constituents of these admixtures are aluminum sulfate, zinc sulfate aluminum chloride,
calcium chloride, silicate of soda etc. which are chemically active pore fillers.
Page | 56
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
6. Super Plasticizers or High Range Water-Reducing Admixtures in
Concrete:
These are the second generation admixture and also called as Superplasticizers. These are
synthetic chemical products made from organic sulphonates of type RSO3, where R is
complex organic group of higher molecular weight produced under carefully controlled
condition.
The commonly used superplasticizer are as follows:
a) Sulphonated melamine formaldehyde condensate (S M F C)
b) Sulphonated napthalene formaldehyde condensate (S N F C)
c) Modified ligno-sulphonates and other sulphonic esters, acids etc.,
Advantages of Super Plasticizer Admixtures:1) The concrete using this admixture can be placed with little or no compaction and is not
subject to excessive bleeding or segregation.
2) They can be used as high dosages became they do not markedly change the surface tension
of water.
3) It does not significantly affect the setting of concrete except that when used the cements
having a very low C3A content.
4) They do not influence shrinkage, creep modulus of elasticity or resistance to freeing to
thawing.
Disadvantage:1) The only real disadvantage of superplasticizer is their relatively high cost.
Applications of Super Plasticizer Admixtures:2) In very heavily reinforced sections, in inaccessible areas in floor or road slabs.
3) Where very rapid placing is desired.
Ques No.03:- Explain in detail concrete mix Design by IS : 10262 : 2009.
Or
Explain I. S. method of concrete Mix Design.
Or
Write the step by step procedure adopted for the method of mix design as per
IS.
Or
Explain concrete mix design procedure as per IS:10262.
(Compulsory For 6 Marks)
Ans:- Concrete mix Design by IS : 10262 : 2009:
Procedure for concrete mix design calculation as per IS 10262-2009 based on strength and
durability, workability, economy . To produce concrete of required strength and properties,
selection of ingredients and their quantity is to be found which is called concrete mix design.
Page | 57
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Concrete Mix Design Procedure as per is 10262 – 2009:Procedure for concrete mix design requires following step by step process:1)
2)
3)
4)
5)
6)
7)
8)
Calculation of target strength of concrete
Selection of water-cement ratio
Determination of aggregate air content
Selection of water content for concrete
Selection of cement content for concrete
Calculation of aggregate ratio
Calculation of aggregate content for concrete
Trial mixes for testing concrete mix design strength
Step 1: Calculation of Target Strength of Concrete:
Target strength is denoted by ft which is obtained by characteristic compressive strength of concrete
at 28 days (fck) and value of standard deviation (s)
ft = fck + 1.65 s
Standard deviation can be taken from below table:
Grade of concrete
Standard deviation (N/mm2)
M10
M15
M20
M25
M30
M35
M40
M45
M50
3.5
3.5
4.0
4.0
5.0
5.0
5.0
5.0
5.0
Step 2: Selection of Water-Cement Ratio:
Ratio of the weight of water to weight of cement in the concrete mix is water-cement ratio. It is the
important consideration in concrete mix design to make the concrete workable. Water cement ratio
is selected from the below curve for 28 days characteristic compressive strength of concrete.
(Fig: Selection of Water-Cement Ratio for Concrete Mix Design)
Page | 58
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)

Similarly, we can determine the water-cement ration from the 7-day concrete strength, the
curves are divided on the basis of strength from water cement ratio is decided. Which is
observed from the below graph.
(Fig: Concrete Compressive Strength vs. Water Cement Ratio)
Step 3: Determination of Aggregate Air content:
Air content in the concrete mix is determined by the nominal maximum size of aggregate used.
Below table will give the entrapped air content in percentage of volume of concrete.
Nominal maximum size of aggregate
10mm
20mm
40mm
Air content (% of volume of concrete)
5%
2%
1%
Step 4: Selection of Water Content for Concrete:
Select the water content which is useful to get required workability with the help of nominal
maximum size of aggregate as given in below table. The table given below is used when only angular
shaped aggregates are used in concrete as well as the slump should be 25 to 50mm.
Nominal maximum size of aggregate
10mm
20mm
40mm
Page | 59
Concrete Technology
Maximum water content
208
186
165
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
If the shape of aggregate or slump value is differing from above, then some adjustments are
required as follows.
Condition
Adjustment
Sub angular aggregate
Gravel with crushed stone
Rounded gravel
Using plasticizer
Using superplasticizer
For every increment of 25mm slump
Reduce the selected value by 10%
Reduce the selected value by 20kg
Reduce the selected value by 25kg
Decrease the selected value by 5-10%
Decrease the selected value by 20-30%
Increase the selected value by 3%
Step 5: Selection of Cement Content for Concrete:
Water – cement ratio is determined in step2 and quantity of water is determined in step -4. So, we
can easily calculate the quantity of cement from these two conditions. But, the value obtained
should satisfy the minimum conditions as given in the below table. The greater of the two values is
decided as quantity of cement content.
Cement Content for Plain Cement Concrete:
Exposure
Mild
Moderate
Severe
Very severe
Extreme
Plain Cement Concrete (P.C.C)
Minimum Cement
Max Free Water –
Content Kg/m3
Cement Ratio
220
0.6
240
0.6
250
0.5
260
0.45
280
0.4
Minimum Grade of
Concrete
–
M15
M20
M20
M25
Cement Content for Reinforced Concrete:
Exposure
Mild
Moderate
Severe
Very
severe
Extreme
Reinforced Cement Concrete (RCC)
Minimum Cement
Max Free Water –
Content Kg/m3
Cement Ratio
300
0.55
300
0.5
320
0.45
340
0.45
Minimum Grade of
Concrete
M20
M25
M30
M35
360
M40
0.4
Step 6: Calculation of Aggregate Ratio:
For the given nominal maximum size of aggregate, we can calculate the ratio of volumes of coarse
aggregate and volume of total aggregates for different zones of fine aggregates from the below table
Page | 60
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Nominal maximum
size of aggregate
10mm
20mm
40mm
Ratio of volume of coarse aggregate and volume of total
aggregate for different zones of fine aggregate
Zone – 1
Zone – 2
Zone – 3
Zone – 4
0.44
0.46
0.48
0.50
0.6
0.62
0.64
0.66
0.69
0.71
0.73
0.75
Step 7: Calculation of Aggregate Content for Concrete:
We already determine the coarse aggregate volume ratio in the total aggregate volume. So, it is very
easy that, 1 – volume of coarse aggregate will give the volume of fine aggregate. Alternatively, there
are some formulae to find the volume of fine and coarse aggregates as follows.
Mass of fine aggregate is calculated from below formula:
Similarly, mass of coarse aggregate is calculated from below formula:
Where,
V = volume of concrete
W = water content
C = cement content
Gc = sp. Gravity of cement
P = aggregate ration obtained in step6
F.A & C.A = masses of fine and coarse aggregates
Gf & Gca = sp. Gravities of fine and coarse aggregates.
Step 8: Trial Mixes for Testing Concrete Mix Design Strength:
Based on the values obtained above, conduct a trail test by making at least 3 cubes of 150mm size as
per above standards. Test that cubes and verify whether the required strength is gained or not. If
not, redesign the mix with proper adjustments until required strength of cube occurs.
The following points should be remembered before proportioning a concrete mix a per IS-102622009:a) This method of concrete mix proportioning is applicable only for ordinary and standard
concrete grades.
b) The air content in concrete is considered as nil.
c) The proportioning is carried out to achieve specified characteristic compressive strength at
specified age, workability of fresh concrete and durability requirements.
******
Page | 61
Concrete Technology
By SHAH SIR (7888280720)
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10 Days Workshop (Starts from 28th Oct to 10th Nov)
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Fees:M-3 @3000/M-3+SOM @5000/With
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Page | 62
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Unit-05
(13 Marks)
Special concrete, Shrinkage, Creep
Theories:- 13 Marks
Ques No.01:- Explain in brief self compacting concrete and high
performance concrete.
Or
What is high performance concrete. Also explain its procedure. Why this
concrete is used in the field.
Or
Write short notes on:i) Self compacting concrete
ii) High performance concrete
(Compulsory For 7 Marks)
Ans:- Self compacting concrete:
Self compacting concrete (SCC) can be defined as fresh concrete that flows under its own
weight and does not require external vibration to undergo compaction. It is used in the
construction where it is hard to use vibrators for consolidation of concrete. Filling and
passing ability, segregation resistance are the properties of self compacting concrete.

SCC possess superior flow ability in its fresh state that performs self compaction and
material consolidation without segregation issues.
Advantages of Self Compacting Concrete:The main advantages of self compacting concrete are:
a)
b)
c)
d)
e)
f)
g)
The permeability of the concrete structure is decreased
SCC enables freedom in designing concrete structures
The SCC construction is faster
The problems associated with vibration is eliminated
The concrete is placed with ease, which results in large cost saving
The quality of the construction is increase
The durability and reliability of the concrete structure is high compared to normal concrete
structures
h) Noise from vibration is reduced. This also reduce the hand arm vibration syndrome issues
Page | 63
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Disadvantages of Self Compacting Concrete:SCC construction face the following limitations:
a)
b)
c)
d)
e)
There is no globally accepted test standard to undergo SCC mix design
The cost of construction is costlier than the conventional concrete construction
The use of designed mix will require more trial batches and lab tests
The measurement and monitoring must be more precise.
The material selection for SCC is more stringent
Applications of Self Compacting Concrete:The major applications of self compacting concrete are:
a)
b)
c)
d)
Construction of structures with complicated reinforcement
SCC is used for repairs, restoration and renewal construction
Highly stable and durable retaining walls are constructed with the help of SCC
SCC is employed in the construction of raft and pile foundations
High performance concrete:
High performance concrete is a concrete having high strength, high durability, high
resistance to chemical attack and high workability. In other words all the mechanical
properties of concrete are superior in a high performance concrete.

High performance concrete is a concrete mixture, which possess high durability and high
strength when compared to conventional concrete. This concrete contains one or more of
cementious materials such as fly ash, Silica fume or ground granulated blast furnace slag and
usually a super plasticizer. The term ‘high performance’ is somewhat pretentious because
the essential feature of this concrete is that it’s ingredients and proportions are specifically
chosen so as to have particularly appropriate properties for the expected use of the
structure such as high strength and low permeability. Hence High performance concrete is
not a special type of concrete. It comprises of the same materials as that of the conventional
cement concrete. The use of some mineral and chemical admixtures like Silica fume and
Super plasticizer enhance the strength, durability and workability qualities to a very high
extent.

High Performance concrete works out to be economical, even though it’s initial cost is
higher than that of conventional concrete because the use of High Performance concrete in
construction enhances the service life of the structure and the structure suffers less damage
which would reduce overall costs.
ADVANTAGES OF HPC:a)
b)
c)
d)
e)
Reduction in size of the columns
Speed of construction
More economical than steel concrete composite columns
Workability and pumpability
Most economical material in terms of time and money
Page | 64
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
f)
g)
h)
i)
j)
k)
l)
m)
n)
o)
p)
Increased rentable\useful floor space
Reduced depth of floor system and decrease in overall building height
Higher seismic resistance, lower wind sway and drift
Improved durability in aggressive environment
Wearing resistance, abrasion resistance
Durability against chloride attack
Increased durability in marine environment
Low shrinkage and high strength
Service life more than 100 years
High tensile strength
Reduced maintenance cost
LIMITATIONS OF HPC:a) High Performance Concrete has to be manufactured and placed much more carefully than
normal concrete.
b) An extended quality control is required
c) In concrete plant and at delivery site, additional tests are required. This increases the cost
d) Some special constituents are required which may not be available in the ready mix concrete
plants.
Ques No.02:- Write short notes on :(i) Ferrocement.
(ii) Shotcrete.
Or
Explain shotcrete pumped concrete.
(Semi-Compulsory For 6 Marks)
Ans:- (i) Ferrocement:
Ferrocement is a construction material consisting of wire meshes and cement mortar.
Applications of ferrocement in construction is vast due to the low self weight, lack of skilled
workers, no need of framework etc.

“Ferro cement is a type of thin wall reinforced concrete, commonly constructed of hydraulic
cement mortar, reinforced with closely spaced layers of continuous and relatively small size
wire mesh. The mesh may be made of metallic or other suitable materials”.
Properties of Ferrocement:a) Highly versatile form of reinforced concrete.
b) It’s a type of thin reinforced concrete construction, in which large amount of small diameter
wire meshes uniformly throughout the cross section.
c) Mesh may be metal or suitable material.
d) Instead of concrete Portland cement mortar is used.
e) Strength depends on two factors quality of sand/cement mortar mix and quantity of
reinforcing materials used.
Page | 65
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Constituent Materials for Ferrocement:a)
b)
c)
d)
e)
f)
g)
h)
Cement
Fine Aggregate
Water
Admixture
Mortar Mix
Reinforcing mesh
Skeletal Steel
Coating
Advantages and Disadvantages of Ferrocement:Advantages:
a)
b)
c)
d)
e)
f)
g)
h)
High ductility
High resistance to cracking width
Ability to undergo large deflection
Improved impact resistance and toughness
Good fire resistance
Good impermeability
Low strength to weight ratio
Low maintenance costs
Disadvantages:
a)
b)
c)
d)
e)
f)
Structures made of it can be punctured by collision with pointed objects.
Corrosion of the reinforcing materials due to the incomplete coverage of metal by mortar.
It is difficult to fasten to Ferrocement with bolts, screws, welding and nail etc.
Large no of labors required.
Cost of semi-skilled and unskilled labors is high.
Tying rods and mesh together is especially tedious and time consuming.
Process of Ferrocement Construction:a)
b)
c)
d)
Fabricating the skeletal framing system.
Applying rods and meshes.
Plastering.
Curing
Applications of Ferrocements in Construction:a)
b)
c)
d)
e)
f)
g)
h)
Marine applications
Water supply and sanitation
Agricultural
Residential buildings
Rural energy
Other structures
Boats, fishing vessels, barges, cargo tugs, catamarans, yachts and flotation buoys
Key criteria for marine applications: light weight, impact resistance, thickness and water
tightness
Page | 66
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
(ii) Shotcrete:
Shotcrete is defined as “mortar or concrete pneumatically projected at high speed onto a
surface” (American Concrete Institute, 1990). There are two basic types of shotcrete—dry
mix and wet mix. In dry mix shotcrete, the dry cement, sand, and coarse aggregate, if used,
are premixed with only sufficient water to reduce dusting.

Shotcrete is a method of applying concrete projected at high velocity primarily on to a
vertical or overhead surface. The impact created by the application consolidates the
concrete. Although the hardened properties of shotcrete are similar to those of
conventional cast-in-place concrete, the nature of the placement process results in an
excellent bond with most substrates, and rapid or instant capabilities, particularly on
complex forms or shapes.

The shotcrete process requires less formwork and can be more economical than
conventionally placed concrete. Shotcrete is applied using a wet- or dry-mix process. The
wet-mix shotcrete process mixes all ingredients, including water, before introduction into
the delivery hose. The dry-mix shotcrete process adds water to the mix at the nozzle.
Shotcrete is used in new construction and repairs and is suitable for curved and thin
elements (ACI 506R).

Shotcrete, also called (trademark) Gunite, concrete applied by spraying. Shotcrete is a
mixture of aggregate and portland cement, conveyed by compressed air to the nozzle of
a spray gun, where water is added. The wet mixture is then sprayed in place and may be
carved or troweled almost immediately.

For structural uses, shotcrete is usually applied over a framework of reinforcing bars
and steel mesh. Because it can take any shape, is easily coloured, and can be sculptured
after application, shotcrete is used for a variety of fancy concrete structures, including
artificial rock walls, zoo enclosures, canopy roofs, refractory linings, pools, and dams. It is
sometimes used in tunneling to bind the walls of the tunnel to prevent leaks and
fragmentation.

Shortcreting is define as pneumatically applied concrete or motor placed directly on to the
surface. Shortcreting can be placed by either the dry mix or wet mix process.
Page | 67
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Dry mix process consist of :a)
b)
c)
d)
Thoroughly mixing the dry material.
Feeding of these material into mechanical feeder or gun.
Carrying the material by compress air through a nose to special nozzle.
Introducing water at nozzle point and immediately mixing it with other ingredient at the
nozzle.
e) Jetting the mixture from the nozzle at high velocity on to the surface to receive the
shortcrete.
Wet mix process shall be consist of :a)
b)
c)
d)
Thoroughly mixing all ingredient with the expecting of the accelerating admixture if used.
Feeding the mixture into the delivery equipment.
Delivering the mixture by positive displacement or compressed air to nozzle.
Setting the mixture from the nozzle at high velocity on the surface to receive the shortcrete.

If specification fibre at steel polypropylene or other material as may be specified could also
be used together with the admixture to modify the structural properties at the concrete
motor being placed in position.
Ques No.03:- Explain in brief polymer concrete & fibre reinforced concrete.
Or
Write a short note on:i) Fiber Reinforced & Polymer concrete.
(Future For 6 Marks)
Ans:- Fibre reinforced concrete:
Fiber Reinforced Concrete can be defined as a composite material consisting of mixtures of
cement, mortar or concrete and discontinuous, discrete, uniformly dispersed suitable fibers.
Fiber reinforced concrete are of different types and properties with many advantages.
Continuous meshes, woven fabrics and long wires or rods are not considered to be discrete
fibers.

Fiber is a small piece of reinforcing material possessing certain characteristics properties.
They can be circular or flat. The fiber is often described by a convenient parameter called
“aspect ratio”. The aspect ratio of the fiber is the ratio of its length to its diameter. Typical
aspect ratio ranges from 30 to 150.

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
fibers. Within these different fibers that character of fiber reinforced concrete changes with
varying concretes, fiber materials, geometries, distribution, orientation and densities.

Fibre-reinforcement is mainly used in shotcrete, but can also be used in normal concrete.
Fibre-reinforced normal concrete are mostly used for on-ground floors and pavements, but
can be considered for a wide range of construction parts (beams, pliers, foundations etc)
either alone or with hand-tied rebars.
Page | 68
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Necessity of Fiber Reinforced Concrete:a)
b)
c)
d)
It increases the tensile strength of the concrete.
It reduce the air voids and water voids the inherent porosity of gel.
It increases the durability of the concrete.
Fibres such as graphite and glass have excellent resistance to creep, while the same is not
true for most resins. Therefore, the orientation and volume of fibres have a significant
influence on the creep performance of rebars/tendons.
e) Reinforced concrete itself is a composite material, where the reinforcement acts as the
strengthening fibre and the concrete as the matrix. It is therefore imperative that the
behavior under thermal stresses for the two materials be similar so that the differential
deformations of concrete and the reinforcement are minimized.
f) It has been recognized that the addition of small, closely spaced and uniformly dispersed
fibers to concrete would act as crack arrester and would substantially improve its static and
dynamic properties.
Polymer concrete:
Polymer concrete is an ordinary concrete produced with OPC ( Ordinary portland cement)
wet cured and inseminated with liquid or vaporous chemical compound (Methyl
methacrylate monomer) and polymerized by gamma radiation or with chemical initiated
implies, i.e by utilizing thermal catalytic method (Adding 3% Benzoyl peroxide) to the
monomer as a catalyst. The impregnation is helped by drying the concrete at an extreme
temperature by evacuations and absorbing the monomer under limited pressure.
TYPES OF POLYMER CONCRETE:
Polymer concrete can be classified in following three categories:
a) Polymer impregnated concrete (PIC).
b) Polymer cement concrete (PCC).
c) Polymer concrete (PC).
ADVANTAGES OF POLYMER CONCRETE:
a)
b)
c)
d)
It has high impact resistance and high compressive strength.
Polymer concrete is highly resistant to freezing and thawing.
Highly resistant to chemical attack and abrasion.
Permeability is lower than other conventional concrete.
APPLICATION OF POLYMER CONCRETE:
Polymer concrete is broadly utilizing in several circumstances as following:
a)
b)
c)
d)
e)
f)
Nuclear power plants.
Kerbstones.
Prefabricated structural element.
Precast slabs for bridge decks.
Roads.
Marine Works.
Page | 69
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
g)
h)
i)
j)
k)
Prestressed concrete.
Irrigation works.
Sewage works.
Waterproofing of buildings.
Food processing buildings etc.
Ques No.04:- Explain in detail shrinkage of concrete.
Or
Define Shrinkage ? Explain in brief various classification of shrinkage.
Or
Define and classify Shrinkage in concrete. How it can be controlled?
Or
Different types of shrinkage and factors affecting shrinkage.
Or
Explain the factors affecting creep and shrinkage of concrete.
Or
Explain Differential shrinkage.
Or
Explain plastic shrinkage and drying shrinkage.
(Compulsory For 7 Marks)
Ans:- Shrinkage:
The volumetric changes of concrete structures due to the loss of moisture by evaporation is
known as concrete shrinkage or shrinkage of concrete. It is a time-dependent deformation
which reduces the volume of concrete without the impact of external forces.

Concrete is subjected to changes in volume either autogenous or induced. Volume change is
one of the most detrimental properties of concrete, which affects the long-term strength
and durability.

To the practical engineer, the aspect of volume change in concrete is important from the
point of view that it causes unsightly cracks in concrete and called concrete shrinkage.
TYPES OF SHRINKAGE:
The types of concrete shrinkage are listed below:
1. PLASTIC SHRINKAGE:
Plastic shrinkage occurs very soon after pouring the concrete in the forms. The hydration of cement
results in a reduction in the volume of concrete due to evaporation from the surface of concrete,
which leads to cracking.
2. DRYING SHRINKAGE:
The shrinkage that appears after the setting and hardening of the concrete mixture due to loss of
capillary water is known as drying shrinkage.
Drying shrinkage generally occurs in the first few months and decreases with time.
Page | 70
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
3. CARBONATION SHRINKAGE:
Carbonation shrinkage occurs due to the reaction of carbon dioxide (Co2) with the hydrated cement
minerals, carbonating Ca(Oh)2 to CaCO3.
The carbonation slowly penetrates the outer surface of the concrete. This type of shrinkage mainly
occurs at medium humidities and results increased strength and reduced permeability.
4. AUTOGENOUS SHRINKAGE:
Autogenous shrinkage occurs due to no moisture movement from concrete paste under constant
temperature. It is a minor problem of concrete and can be ignored.
FACTORS AFFECTING SHRINKAGE:
The shrinkage of concrete depends on several factors which are listed below.
1. WATER-CEMENT RATIO:
shrinkage is mostly influenced by the water cement ratio of concrete. It increases with the increases
in the water-cement ratio.
2. ENVIRONMENTAL CONDITION:
It is one of the major factors that affect the total volume of shrinkage. Shrinkage is mostly occurred
due to the drying condition of the atmosphere. It increases with the decrease in the humidity.
3. TIME:
The rate of shrinkage rapidly decreases with time. It is found that 14-34% of the 20 years shrinkage
occurs in two weeks, 40-80% shrinkage occurs in three months and the rest 66-85% shrinkage occurs
in one year.
4. TYPE OF AGGREGATE:
Aggregates with moisture movement and low elastic modulus cause large shrinkage. The rate of
shrinkage generally decreases with the increase of the size of aggregates. It is found that concrete
made from sandstone shrinks twice than the concrete of limestone.
5. ADMIXTURES:
The shrinkage increases with the addition of accelerating admixtures due to the presence of calcium
chloride (CaCl2) in it And it can be reduced by lime replacement.
Other Factors:
a)
b)
c)
d)
e)
The type and quantity of cement.
Granular and microbiological composition of aggregates.
The strength of concrete.
The method of curing.
The dimension of elements etc.
Page | 71
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Ques No.05:- Define creep. Explain various factors affecting creep.
Or
Define creep and write down the factor affecting creep.
Or
What do you understand by Creep? What are various factors affecting it?
Or
What do you mean by creep in harden concrete? Describe the relation
between creep & age of concrete.
(Compulsory For 7 Marks)
Ans:- Creep:
Concrete creep is defined as: deformation of structure under sustained load. Basically, long
term pressure or stress on concrete can make it change shape. This deformation usually
occurs in the direction the force is being applied. Like a concrete column getting more
compressed, or a beam bending.

Creep does not necessarily cause concrete to fail or break apart. When a load is applied to
concrete, it experiences an instantaneous elastic strain which develops into creep strain if
the load is sustained.
FACTORS AFFECTING CREEP OF CONCRETE:
The factors that affect creep of concrete are similar to the factors affecting shrinkage, which are as
following:
1. WATER-CEMENT RATIO:
The rate of creep is increased with increasing water cement ratio.
2. HUMIDITY:
It is influenced by humidity and drying condition of the atmosphere.
Page | 72
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
3. AGE OF CONCRETE:
The rate of creep rapidly decreases with time. The time taken by a concrete structure to attained
creep is 5 years.
4. AGGREGATE:
Aggregates with moisture movement and low elastic modulus cause a large amount of creep. The
rate of creep generally decreases with the increase of the size of aggregates.
5. ADMIXTURES:
Some admixtures (mainly accelerators) are also responsible for causing creep in concrete.
6. OTHER FACTORS:
a) Types of cement:
Fineness of cement affects the strength development at early ages & thus influence of
creep.
b) Entrained air.
c) Concrete strength.
******
Complete By
Shah Sir
(Civil Engineering Tutor)
Mob- +91 7888280720
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Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
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Page | 74
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Unit-06
(14 Marks)
Durability of concrete, Cracks in concrete
Theories:- 14 Marks
Ques No.01:- Explain permeability of concrete.
(Compulsory For 7 Marks)
Ans:- Permeability of concrete:
Concrete is a composite material comprising of Cement, Sand & coarse aggregate. Every
material has pores, which contains voids in it. Aggregates have a more substantial void
ranging from 1mm to 10mm which cement paste fills these. Even cement has voids ranging
from 1micron to 10micron. Due to this interconnected and continuous link to fill one void by
other material concrete is prone to permeate fluid or gases into it.

In simple words, Presence of voids in concrete makes permeable which in turn allows water
or gas to flow into it. The permeability of concrete is the ability of concrete to resist the
water flow or any other substance into it when the external force is applied.

Permeability of concrete is defined as the property that controls the rate of flow of fluids
into a porous solid. It largely depends on the size of pores, connectivity of pores, and how
tortuous the path is for the permeating fluid.

Permeability is the ease with which liquids or gases can travel through concrete.
The coefficient of permeability, K, of concrete (simply called as “permeability” in concrete
technology) for steady-state flow of water through a sample of concrete is determined from
Darcy’s expression:
dq/dt = K (A . ∆h/L)
Where;
dq/dt = rate of flow of water through the sample
A = cross-sectional area of the sample
∆h= drop in hydraulic head through the sample
L= thickness of the sample
Significance:a) Permeability of concrete plays an important role in durability because it controls the rate of
entry of moisture that may contain aggressive chemicals and the movement of water during
heating or freezing. Higher the permeability lesser will be the durability
Page | 75
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
b) Permeability of concrete is of interest also in relation to the water-tightness of liquidretaining structures. Higher the permeability lesser will be the water-tightness
Factors Influencing Concrete Permeability:There are three major factors that influence the permeability of concrete :
1. Water-Cement ratio:
Excessive water is added to the concrete mix to increase the workability of concrete. This additional
mixing of water, more than required increases the porosity in concrete and degrades the durability
of concrete. To resist the entry of water into the concrete 0.4 water-cement ratio is adopted.
Experiments proved that taking a water-cement ratio of 0.4 makes concrete impermeable.
2. Improper compaction of concrete:
Improper compaction in concrete is the major problem for porosity in concrete. Concrete should be
adequately compacted using hand compaction method or machine compaction methods. Poorly
compacted concrete leads to the formation of honeycomb which ultimately makes steel to corrode
and forms surface cracks.
3. Improper Curing:
Concrete should be adequately cured by considering the atmospheric weather. Improper curing in
concrete leads to the formation of cracks and in turn, it increases the permeability of concrete.
Ques No.02:- Explain in brief non destructive test of concrete.
Or
Explain in brief the following Non-Destructive testing of concrete.
i) Rebound Hammer method.
ii) Ultrasonic Pulse velocity testing method.
Or
Describe ultra sonic pulse velocity test. its suitability & its significance.
Or
Explain ultra sonic pulse velocity test on concrete.
(Compulsory For 14 Marks)
Ans:- Non destructive test of concrete:
Non destructive test is a method of testing existing concrete structures to assess the
strength and durability of concrete structure. In the non destructive method of testing,
without loading the specimen to failure (i.e. without destructing the concrete) we can
measure strength of concrete. Now days this method has become a part of quality control
process. This method of testing also helps us to investigate crack depth, micro cracks and
deterioration of concrete.

Non destructive testing of concrete is a very simple method of testing but it requires skilled
and experienced persons having some special knowledge to interpret and analyze test
results.
Page | 76
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Purposes of Non-destructive Tests:1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
Estimating the in-situ compressive strength
Estimating the uniformity and homogeneity
Estimating the quality in relation to standard requirement
Identifying areas of lower integrity in comparison to other parts
Detection of presence of cracks, voids and other imperfections
Monitoring changes in the structure of the concrete which may occur with time
Identification of reinforcement profile and measurement of cover, bar diameter, etc.
Condition of prestressing/reinforcement steel with respect to corrosion
Chloride, sulphate, alkali contents or degree of carbonation
Measurement of Elastic Modulus
Condition of grouting in prestressing cable ducts
Methods of Non-Destructive Testing of Concrete:Following are different methods of NDT on concrete:
1)
2)
3)
4)
5)
Penetration method
Rebound hammer method
Pull out test method
Ultrasonic pulse velocity method
Radioactive methods
i) Rebound Hammer method:
Rebound Hammer test is a Non-destructive testing method of concrete which provide a
convenient and rapid indication of the compressive strength of the concrete. The rebound
hammer is also called as Schmidt hammer that consist of a spring controlled mass that slides
on a plunger within a tubular housing.

The operation of rebound hammer is shown in the fig.1. When the plunger of rebound
hammer is pressed against the surface of concrete, a spring controlled mass with a constant
energy is made to hit concrete surface to rebound back. The extent of rebound, which is a
measure of surface hardness, is measured on a graduated scale. This measured value is
designated as Rebound Number (rebound index). A concrete with low strength and low
stiffness will absorb more energy to yield in a lower rebound value.
Objective of Rebound Hammer Test:1) To determine the compressive strength of the concrete by relating the rebound index and
the compressive strength
2) To assess the uniformity of the concrete
3) To assess the quality of the concrete based on the standard specifications
4) To relate one concrete element with other in terms of quality
Page | 77
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
(Fig.1.Operation of the rebound hammer)
Principle of Rebound Hammer Test:
Rebound hammer test method 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. The
operation of the rebound hammer is shown in figure-1. When the plunger of rebound
hammer is pressed against the concrete surface, the spring controlled mass in the hammer
rebounds. The amount of rebound of the mass depends on the hardness of concrete
surface.

Thus, the hardness of concrete and rebound hammer reading can be correlated with
compressive strength of concrete. The
rebound value is read off along a graduated scale and is designated as the
rebound number or rebound index.

The compressive strength can be read directly from the graph provided on the body of the
hammer.
Advantages and Disadvantages of Rebound Hammer Test:The advantages of Rebound hammer tests are:
1)
2)
3)
4)
Apparatus is easy to use
Determines uniformity properties of the surface
The equipment used is inexpensive
Used for the rehabilitation of old monuments
Page | 78
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
The disadvantages of Rebound Hammer Test:
1) The results obtained is based on a local point
2) The test results are not directly related to the strength and the deformation property of the
surface
3) The probe and spring arrangement will require regular cleaning and maintenance
4) Flaws cannot be detected with accuracy
ii) Ultrasonic Pulse velocity testing method:
Ultrasonic testing of concrete or ultrasonic pulse velocity test on concrete is a nondestructive test to assess the homogeneity and integrity of concrete.
With this ultrasonic test on concrete, following can be assessed:
1) Qualitative assessment of strength of concrete, its gradation in different locations of
structural members and plotting the same.
2) Any discontinuity in cross section like cracks, cover concrete delamination etc.
3) Depth of surface cracks.

Ultrasonic pulse velocity test consists of measuring travel time, T of ultrasonic pulse of 50 to
54 kHz, produced by an electro-acoustical transducer, held in contact with one surface of the
concrete member under test and receiving the same by a similar transducer in contact with
the surface at the other end.
With the path length L, (i.e. the distance between the two probes) and time of travel T, the
pulse velocity (V=L/T) is calculated.

Higher the elastic modulus, density and integrity of the concrete, higher is the pulse
velocity. The ultrasonic pulse velocity depends on the density and elastic properties of the
material being tested.

Ultrasonic pulse velocity tests have a great potential for concrete control, particularly for
establishing uniformity and detecting cracks or defects. Its use for predicting strength is
much more limited, owing to the large number of variables affecting the relation between
strength and pulse velocity.
Procedure for Ultrasonic Pulse Velocity:i) Preparing for use:
Before switching on the ‘V’ meter, the transducers should be connected to the sockets marked
“TRAN” and ” REC”.
The ‘V’ meter may be operated with either:
1) The internal battery,
2) An external battery or
3) The A.C line.
Page | 79
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
ii) Set reference:
A reference bar is provided to check the instrument zero. The pulse time for the bar is engraved on
it. Apply a smear of grease to the transducer faces before placing it on the opposite ends of the bar.
Adjust the ‘SET REF’ control until the reference bar transit time is obtained on the instrument readout.
iii) Range selection:
For maximum accuracy, it is recommended that the 0.1 microsecond range be selected for path
length upto 400mm.
iv) Pulse velocity:
Having determined the most suitable test points on the material to be tested, make careful
measurement of the path length ‘L’. Apply couplant to the surfaces of the transducers and press it
hard onto the surface of the material.
Do not move the transducers while a reading is being taken, as this can generate noise signals and
errors in measurements. Continue holding the transducers onto the surface of the material until a
consistent reading appears on the display, which is the time in microsecond for the ultrasonic pulse
to travel the distance ‘L’.
The mean value of the display readings should be taken when the units digit hunts between two
values.
Pulse velocity=(Path length/Travel time)
v) Separation of transducer leads: It is advisable to prevent the two transducer leads from coming
into close contact with each other when the transit time measurements are being taken.

If this is not done, the receiver lead might pick-up unwanted signals from the transmitter
lead and this would result in an incorrect display of the transit time.
Table: 1 – Concrete Quality based on Ultrasonic Pulse Velocity Test
PULSE VELOCITY
CONCRETE QUALITY
>4.0 km/s
3.5 – 4.0 km/s
3.0 – 3.5 km/s
<3.0 km/s
Very good to excellent
Good to very good, slight porosity may exist
Satisfactory but loss of integrity is suspected
Poor and los of integrity exist.
Ques No.03:- What are the different types of cracks. Occur in concrete also
Explain its causes? Explain the procedure of repairs.
Or
What are types of cracks in concrete ? Explain various causes of cracks in
concrete.
Or
Explain various causes of cracks in concrete.
Or
Explain the methods on repairs of crack in concrete.
Or
Page | 80
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
Explain the material and methods of Repairs of cracks in concrete.
Or
Explain Repairs of cracks – materials & methods.
(Compulsory For 7 Marks)
Ans:- Types of cracks in concrete:1)
2)
3)
4)
5)
6)
Plastic shrinkage concrete cracks
Expansion concrete cracks
Heaving concrete cracks
Settling concrete cracks
Concrete cracks caused by overloading the slab
Concrete cracks caused by premature drying
1. Plastic shrinkage concrete cracks:

Plastic shrinkage cracking (Fig.1) occurs when subjected to a very rapid loss of moisture
caused by a combination of factors which include air and concrete temperatures, relative
humidity, and wind velocity at the surface of the concrete.

These factors can combine to cause high rates of surface evaporation in either hot or cold
weather.” When moisture evaporates from the surface of freshly placed concrete faster
than it is replaced by bleed water, the surface concrete shrinks.

Since plastic shrinkage cracking is due to a differential volume change in the plastic concrete,
successful control measures require a reduction in the relative volume change between the
surface and other portions of the concrete.

These measures include the use of fog nozzles to saturate the air above the surface and the
use of plastic sheeting to cover the surface between finishing operations.
(Fig.1: Typical Plastic Shrinkage Cracks in Concrete)
Page | 81
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
2. Settlement Cracks in Concrete:
After initial placement, vibration, and finishing, concrete has a tendency to continue to
consolidate. During this period, the plastic concrete may be locally restrained by reinforcing
steel, a prior concrete placement, or formwork. This local restraint may result in voids
and/or cracks adjacent to the restraining element (Fig.2).

When associated with reinforcing steel, settlement cracking increases with increasing bar
size, increasing slump, and decreasing cover (Dakhil et al. 1975). The use of the lowest
possible slump, and an increase in concrete cover will reduce settlement cracking.
(Fig.2: Settlement Cracks in Concrete)
3. Expansion Cracks:

It is so apparent that in hot weather a concrete slab, the same as anything else, will
enlarged. Expansion in concrete is another reason for concrete cracking. This can cause great
stress on a slab. As the concrete expands, it pushes against any object in its path, such as a
brick wall or an adjacent slab of concrete. If neither has the ability to flex, the resulting force
will cause something to crack. Two separate surfaces can be subdivided by an isolation joint
or expansion joint as a boarder. Its entire depth is filled with some type of compressible
material such as tar-impregnated cellulose fiber, closed-cell poly foam, or even lumber.
Various causes of cracks in concrete:Common cause of cracking in concrete is restrained drying shrinkage.
1)
2)
3)
4)
5)
6)
7)
8)
Shrinkage
Temperature Change
Cracks due to Thermal Stresses.
Cracks due to Chemical Reaction.
Weathering Cracks. ...
Corrosion of Reinforcement.
Poor Construction Practices.
Construction Overloads.
Page | 82
Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
9) Errors in Design and Detailing.
10) Elastic Deformation and creep
1. SHRINKAGE:
Shrinkage is one of the major causes of cracking in hardened concrete. In drying shrinkage, the
volume of concrete is gradually decreased and if the component is restrained against free
movement, tensile stresses are developed which causes cracks.
2. TEMPERATURE CHANGES:
The temperature variation in concrete results in the differential volume change. When the tensile
strain capacity of concrete exceeds due to the differential volume change, it will crack.
3. CHEMICAL REACTION:
Due to the alkaline nature of cement, it reacts with the carbon dioxide (CO2) present in the
atmosphere resulting in an appreciable increase in the volume of the materials which finally leads to
cracking.
4. POOR CONSTRUCTION PRACTICES:
Poor construction practices such as adding excessive water to the mix, lack of curing, poor
compaction, using low-grade materials, unreasonable placements of construction joints etc. are also
responsible for cracking in concrete.
5. ERRORS IN DESIGN & DETAILING:
Errors in design and detailing such as an inadequate amount of reinforcement, improper design of
foundation, precast members and slabs, improper selection of materials, lack of sufficient
contraction joints etc may result in excessive cracking.
6. CONSTRUCTION OVERLOADS & EARLY FORMWORK REMOVAL:
The load induced in the structure during construction can also lead to cracking especially at the
younger stage when the formwork is removed earlier.
7. ELASTIC DEFORMATION AND CREEP:
The different components of the building such as wall, column, beam. slab etc undergo elastic
deformation when loaded. The deformation of concrete depends on the type of building materials
used in the construction such as bricks, cement concrete blocks etc. This unusual deformation of
concrete results in cracking.
8. CORROSION OF CONCRETE:
The corrosion of steel develops a huge amount of iron oxides and hydroxide that have a much
greater volume than the volume of metallic iron. Hence the volume is increased and cracks.
Various methods on repairs of crack in concrete:
There are several methods of concrete crack repair such as epoxy injection, routing and
sealing, grouting, stitching, drilling and plugging, gravity filling of cracks in concrete.
1. Stitching of Concrete:

In this technique, the crack is bridged with U-shaped metal units called stitching dogs before
being repaired with a rigid resin material. A non- shrink grout or an epoxy resin based
adhesive should be used to anchor the legs of the dogs. Stitching is suitable when tensile
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Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
strength must be re -established across major cracks. Stitching dogs should be of variable
length and orientation.
(Fig. Concrete Crack Repair by Stitching)
Benefits Of Cracked Stitching:
1)
2)
3)
4)
Quick, simple, effective and permanent.
The grout combination provides an excellent bond within the substrate.
Masonry remains flexible enough to accommodate natural building movement.
Non-disruptive structural stabilization with no additional stress
2. Epoxy Injections:

Epoxy injection method of concrete crack repair may be used to bond the cracks having
greater than or equal to 0.05mm opening. This method is not suitable for crack is active and
if the cracks are large in number, or when the water leakage cannot be controlled.

In this method, the cracks on exposed concrete surfaces are sealed by injecting epoxy under
the concrete crack. But, it is essential to find and fix the major cause of cracks before
injecting the epoxy into the cracks otherwise the cracks will keep on emerging again and
again. Problems such as leakages and silt contamination damage the efficiency of epoxy,
therefore it is recommended to fix these issues before injecting the epoxy to make it last
longer.

Epoxy injection method of crack repairing requires a lot of discipline and skillful execution so
you need to be sure that the person executing the repairs knows his work.
3. Drilling and Plugging Method:

Drilling and plugging a crack consists of drilling down the length of the crack and grouting it
to form a key (Fig.6).
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Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
(Fig.6: Concrete Crack Repair by Drilling and Plugging)

This technique is only applicable when cracks run in reasonable straight lines and are
accessible at one end. This method is most often used to repair vertical cracks in retaining
walls. A hole [typically 2 to 3 in. (50 to 75 mm) in diameter] should be drilled, centered on
and following the crack.

The grout key prevents transverse movements of the sections of concrete adjacent to the
crack. The key will also reduce heavy leakage through the crack and loss of soil from behind
a leaking wall.

If water-tightness is essential and structural load transfer is not, the drilled hole should be
filled with a resilient material of low modulus in lieu of grout. If the keying effect is essential,
the resilient material can be placed in a second hole, the fiat being grouted.
Ques No.04:- Write a note on distress in concrete structure and its cause.
(Future For 7 Marks)
Ans:- Distress in concrete structure:
Distress in concrete members occurs with age due to corrosion in reinforcement, loading,
settlement of foundations etc. This distress in in building can be found by development of
cracks in concrete members such as slabs, beams, columns etc.
The cracking of concrete in building is developed in three stages:
1. Stage – I: Volume of rust formed due to corrosion of reinforcement is increased about 2.5 times
the volume of steel. With the result of corroded reinforcement bar presses the concrete outwards.
Since concrete is poor in tension, longitudinal cracks are developed along the reinforcement bar.
2. Stage – II: Longitudinal cracks in RCC provide wide access to oxygen, carbon dioxide, and moisture
with result excessive carbonation starts and structural damages starts. Fear in the mind of users
starts.
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Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
3. Stage – III: In this stage cover comes out and causes danger to the life of structure and structure
becomes unserviceable.
Remedial Measures for Distressed Concrete:
1. At design stage:
1) Adequate cover to concrete should be planned.
2) Adequate thickness of structural members particularly non-structural members e.g. chajjas,
parapets, pergolas and fins etc. should be provided.
3) Proper detailing of reinforcement specially at junctions should be designed to avoid
congestion and to ensure smooth placement of concrete.
2. At the construction stage:
1) Concrete should be workable with minimum water cement ratio (< 0.45). It should be well
compacted by vibrator. Thus we should try to achieve highest density with minimum void.
2) Ensure proper grading and quality of aggregate free from deleterious material.
3) Use potable water only.
4) Leak proof and properly designed from work should be used. Ensure proper mixing,
placement, compaction and curing of concrete. No segregation, honeycombing is allowed.
5) Use of plasticizers and super-plasticizers to achieve workability for controlled water-cement
ratio in placement of concrete in congested conditions.
6) Binding wires to be turned inside (should not touch formwork). G.I. wires to be used in
aggressive environment.
7) Proper cover with dense concrete / mortar is must.
8) Provision of drip course for projections should be made.
9) Proper cement to be used to prevent sulphate and chloride attack.
10) Cement not more than 3 months old should be used.
3. Protection of reinforcement bars:
Protection to reinforcement bars against corrosion can also be provided by:
(i) Using corrosion resistant steel
Constituents of steel alloy are adjusted to resist corrosion.
(ii) Fusion bonded epoxy coating
This process has good results in protecting reinforcement bars from corrosion. Powder epoxy is
fusion bonded to bar at about 2500C temperature.
This is being used in coastal areas particularly in Mumbai in prestigious projects like Bridges,
Flyovers, Shipyards and Jetties. Loss of bond is about 20%. IS:13620 – 1993 provides the specification
for “Fusion Bonded Epoxy Coated Reinforcement Bars”.
(iii) Passive coating with polymer based cement slurry:
In this process, reinforcement bars are cleaned for rust and freshly prepared polymer cement slurry
is applied by brushes.
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Concrete Technology
By SHAH SIR (7888280720)
B.E. (Civil Engineering) Third Semester (C.B.S.)
(iv) Protective epoxy coating:
Certain epoxy coating are also available in the market. Firstly rust is removed by wire brush or sand
blasting. Thereafter, epoxy as per manufacturer’s specifications are applied by spray / brush. Loss of
bond may be upto 30%.
*****
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Mob- +91 7888280720
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