concrete questions.pdf

CONSTRUCTION TECHNOLOGY
CLASS QUESTIONS
03 SEPT 2022
SUBMITTED BY
ADITI S. BARANWAL
Enrolment No.- SPA/NS/BEM/2022/864
1

Physical requirements / Properties:
1 Fineness, m2 /kg, Min 225
2 Soundness:
a) By Le Chatelier method, mm, Max 10
b) By autoclave test method, percent, Max 0.8
3 Setting time:
a) Initial, min, Min 30
b) Final, min, Max 600
4 Compressive strength, MPa
a) 72 ± 1 h, Min 16
b) 168 ± 2 h, Min 22
c) 672 ± 4 h, Min 33
Max 48
Q1. VARIOUS TYPES OF CEMENT, THEIR PROPERTY, CHEMICAL COMPOSITION, USES,
LIMITATIONS AS PER IS CODE OR CPWD SPEC.
ANS. Types of cement:
1. ORDINARY PORTLAND CEMENT, 33 GRADE
Ordinary Portland cement is manufactured by intimately mixing together calcareous and
argillaceous and/or other silica, alumina or iron oxide bearing materials, burning them at a
clinkering temperature and grinding the resultant clinker so as to produce a cement
capable of complying with this standard. No material shall be added after burning, other
than gypsum, water, performance improver.
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ORDINARY PORTLAND CEMENT, 33 GRADE
Chemical requirements / composition:
1 Ratio of percentage of lime to percentages of silica,
alumina and iron oxide,
0.66-1.02
2 Ratio of percentage of alumina to that of iron oxide,
Min
0.66
3 Insoluble residue, percent by mass, Max 5.0
4 Magnesia, percent by mass, Max 6.0
5 Total sulphur content calculated as (SO3 ) , percent
by mass, Max
3.5
6 Loss on ignition, percent by mass, Max 5.0
7 Chloride content, percent by mass, Max 0.1
8 Alkali content 0.05
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USES- Masonry work, plaster work, pointing work, laying of floor & roof, construction of
lintels, beams, weather sheds etc.
LIMITATION- Cement remains in good condition if it is not exposed to moisture. However,
after 3 months, it should be tested again to ensure its properties.

2 Soundness:
3 Setting time:
a) 72 ± 1 h, Min 23
b) 168 ± 2 h, Min 33
c) 672 ± 4 h, Min 43
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0.66-1.02
Min
0.66
by mass, Max
3.5
USES- Masonry work, plaster work, pointing work, laying of floor & roof, construction of
lintels, beams, weather sheds etc.
LIMITATION- Cement remains in good condition if it is not exposed to moisture. However,
after 3 months, it should be tested again to ensure its properties.

2 Soundness:
3 Setting time:
a) 72 ± 1 h, Min 27
b) 168 ± 2 h, Min 37
c) 672 ± 4 h, Min 53
Max 58
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0.80-1.02
Min
0.66
by mass, Max
3.5

4. RAPID HARDENING PORTLAND CEMENT
2 Soundness:
3 Setting time:
a) 24 ± 30min, Min 16
b) 72 ± 1 h, Min 27
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RAPID HARDENING PORTLAND CEMENT ADVANTAGES:
1. It requires a short period of curing.
2. It is resistant to sulphate attacks.
3. Shrinkage is reduced during curing and hardening of cement.
4. It is a very durable cement which matches the fast pace of construction.

RAPID HARDENING PORTLAND CEMENT
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0.66-1.02
Min
0.66
by mass, Max
2.5 & 3.0
8 Alkali content, Max 0.06
RAPID HARDENING PORTLAND CEMENT USES:
1. It is used where formwork has to be removed as early as possible in order to reuse it.
2. It is generally used for constructing road pavements, where it is important to open the road
to traffic quickly.
3. It is used in industries which manufacture concrete products like slabs, posts, electric poles,
block fence, etc. because moulds can be released quickly.
4. It is used for cold weather concreting because rapid evolution of heat during hydration
protects the concrete against freezing.

5. PORTLAND SLAG CEMENT/ SUPER SULPHATED CEMENT
An intimately interground mixture of Portland cement clinker and granulated slag With
addition of gypsum and permitted additives or an Intimate and uniform blend of Portland
cement and finely ground granulated slag. Granulated slag is, essentially, a non-metallic
product comprising more than 90% glass content with silicates and alumino-silicates of lime.
2 Soundness:
3 Setting time:
4 Compressive strength, Mpa
a) 72 ± 1 h Not less than 16 MPa
b) 168 ±2 h Not less than 22 MPa
c) 672 ±4 h Not less than 33 MPa
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PORTLAND SLAG CEMENT
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Chemical requirements / composition: Percentage
Max
1 Magnesium Oxide ( MgO) 8·0
2 Sulphur trioxide ( SO3 ) 3.0
3 Sulphide sulphur ( S ) 1.5
4 Loss on ignition 5.0
5 Insoluble residue 4.0
PORTLAND SLAG CEMENT ADVANTAGES:
1. Higher level of compressive strengths in concrete when compared to OPC.
2. Higher flexural strength to concrete, which enhances its structural stiffness and minimizes load
deflections.
3. Reduces the ingression of harmful substances such as chlorides and sulphates due to low
permeability.
4. Environment-friendly due to reduced GHG emissions.
5. The manufacture of Portland slag cement has been developed primarily to utilize blast
furnace slag, a waste product from blast furnaces.
6. It stops sulphate action, as it is already saturated with sulphate. Used in dam construction too.

6. PORTLAND POZZOLANA CEMENT (FLY ASH BASED)
An mixture of Portland clinker and pozzolana with the possible addition of gypsum ( natural
or chemical ) or an intimate and uniform blending of Portland cement and fine pozzolana.
Pozzolana is an silicious material which in itself has little or no cementitious properties. But in
finely divided form and in the presence of water, react with calcium hydroxide at ambient
temperature to form compounds possessing cementitious properties.
2 Soundness:
3 Setting time:
a) 72 ± 1 h 4 MPa
b) 168 ±2 h Not less than 22 MPa
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PORTLAND POZZOLANA CEMENT (FLY ASH BASED)
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Max
1 Fly ash constituent 10-25%
2 LOSS on ignition, percent by mass, Max 5.0
3 Magnesia ( MgO ), percent by mass, Max 6.0
4 Sulpburic anhydride ( SOS ), percent by mass, Max 3.0
5 Insoluble material percent by mass, Max. (Here x is
% of fly ash in the cement)
PPC FLY ASH BASED CEMENT ADVANTAGES:
1. PPC is an eco-friendly product as it is manufactured using fly-ash, a by-product from the
thermal power plants.
2. It provides better resistance to alkali-silica reaction.
3. PPC is preferred in mass construction because of its low heat of hydration.
4. PPC has a good compatibility with all kinds of admixtures.
5. when it comes to durability, PPC is referred to as one of the most preferred cement for
concrete constructions.

7. PORTLAND POZZOLANA CEMENT (CALCINED CLAY BASED)
Portland-pozzolana cement shall be manufactured either by intimately intergrinding
Portland cement clinker and pozzolana or by intimately and uniformly blending Portland
cement and fine pozzolana. The pozzolana constituent shall be 10-25% by mass of PPC.
2 Soundness:
3 Setting time:
a) 72 ± 1 h 16 Mpa min
b) 168 ±2 h 22 Mpa min
c) 672 ±4 h 33 Mpa min
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PORTLAND POZZOLANA CEMENT (CALCINED CLAY BASED) ADVANTAGE:
1. It produces less heat of hydration and offers greater resistance to the attack of
aggressive waters than normal Portland cement.
2. It reduces the leaching of calcium hydroxide liberated during the setting and
hydration of cement.
3. It is particularly useful in marine and hydraulic construction and other mass
concrete structures.
4. PPC can generally be used wherever 33 grade OPC is usable under normal
conditions.
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Max
1 Pozzolana constituent 10-25%
2 LOSS on ignition, percent by mass, Max 5.0
3 Magnesia ( MgO ), percent by mass, Max 6.0
4 Sulpburic anhydride ( SOS ), percent by mass, Max 3.0
5 Insoluble material percent by mass, Max. (Here x is
% of fly ash in the cement)

a) 72 ± 1 h, Min 15.69
b) 168 ± 2 h, Min 21.57
c) 672 ± 4 h, Min 30.40
8. HYDROPHOBIC CEMENT
Cement obtained by grinding 33 grade OPC clinker with an that decrease the wetting
ability of cement grains by forming thin water repellant film around it. This film is torn when
water is added to the cement such as In concrete mixer. and in no way hinders the normal
hydration of cement. The hydrophobic quality of cement would facilitate Its storage for
longer periods in extremely wet climatic conditions.
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HYDROPHOBIC CEMENT ADVANTAGES:
1. It is useful in places having poor transportation system,
high humidity and need for storage of cement for
longer period of time.
2. It can also be used in drainage pipes and manholes.
3. Water retention structures such as dams and spillways.
4. Underground structures such as tunnels, basements.
5. It has good water impermeability.
DISADVANTAGES:
1. The cost of this cement is
nominally higher than OPC.
2. Initial strength gain is less as the
hydrophobic film on cement grain
prevent interaction with water.
However it is equal to OPC after 28
days.

9. LOW HEAT PORTLAND CEMENT
Low heat cement is particularly suited for making, concrete for dams and many other types
of water retaining structures, bridge abutments, massive retaining walls, piers and slabs, etc.
In mass concreting, there is often considerable rise in temperature because of the heat
evolved as the cement sets and hardens, and the slow rate at which it is dissipated from the
surface. The shrinkage which occurs on subsequent cooling sets up tensile stresses in the
concrete which may result in cracking. The use of low heat cement is advantageous since it
evolves less heat than ordinary Portland cement.
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1 Ratio of percentage of alumina to that of iron oxide > 0.66
2 Insoluble residue, % by mass < 4 %
3 Magnesia, % by mass < 6 %
4 Total sulphur content calculated as Sulphuric
anhydride ( SO3 ), % by mass
Not more than 2.5 and 3.0
5 Total loss on ignition < 5 %

LOW HEAT PORTLAND CEMENT
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LOW HEAT PORTLAND CEMENT ADVANTAGES:
1. In huge scale concreting, more heat can damage a no. of things. So low heat cement is rqd.
2. Final strength is unaffected.
3. Only initial/ early strength is delayed.
4. Lower value of C3S and C3A.
2 Soundness:
3 Setting time:
a) 72 ± 1 h Not less than 10 Mpa
b) 168 ±2 h Not less than 16 Mpa
5 Heat of hydration 7 days, < 272 kJ/kg,
28 days, < 314 kJ/kg,

10. SULPHATE RESISTING PORTLAND CEMENT
Sulphate resisting Portland cement is a type of Portland cement in which the amount of
tricalcium aluminate “C3A” is restricted to an acceptably low value. Sulphate resisting
Portland cement can be used for structural concrete wherever ordinary Portland cement or
Portland pozzolana cement or Portland slag cement are useable under normal conditions.
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2 Soundness:
3 Setting time:
a) 72 ± 1 h > 10 MPa
b) 168 ±2 h > 16 MPa
c) 672 ±4 h > 33 MPa
5 Sulphate expansion < 0.045 % at 14 days

SULPHATE RESISTING PORTLAND CEMENT USES:
1. Use of super sulphated cement is generally restricted where the prevailing
temperature is below 40°C.
2. It is beneficial in such conditions where the concrete is exposed to the risk of
deterioration due to sulphate attack.
3. For example, in contact with soils and ground waters containing excessive
amounts of sulphates as well as for concrete in sea water or exposed directly to
sea coast.
4. In sea shore area where sulphar content is more, so calcium silicate is formed, this
is undesirable. So less C3A is used for sulphate resistant.
5. Continuous wetting and drying increases sulphate attack, so this cement is used.
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0.66-1.02
2 Insoluble residue, % by mass < 4.0
3 Magnesia, % by mass < 6.0
4 Total sulphur content calculated as sulphuric
anhydride (SO3), % by mass
< 2.5
5 Tricalcium aluminate ( C3A ). % by mass < 5.0
6 ( C4AF + 2C3A ), % by mass < 25
7 Total loss on ignition, % by mass < 5.0

Q2. WHAT IS CONCRETE? PROPERTIES, REQUIREMENT AND VARIOUS COMPONENTS,
SPECIFICATION AS PER IS CODE.
ANS. Concrete is a composite material composed of fine (sand) and coarse aggregate
bonded together with cement paste that hardens over time. Concrete is the most widely used
building material. It is a mixture of cement, water, fine aggregate, coarse aggregate and
admixtures.
Properties of concrete:
1. Increase of strength with age.
There is normally gain of compressive strength beyond 28 days.
2. Tensile strength of concrete.
We can estimate the tensile strength from the compressive strength by the formula-
3. Elastic deformation.
The modulus of elasticity is influenced by the elastic properties of the aggregate, by the
conditions of curing, and age of the concrete, the mix proportions and the type of cement.
It is measured by-
4. Shrinkage.
The total shrinkage of concrete depends upon the ingredients of concrete, size of
member, environmental conditions. In a given environment, shrinkage of concrete is mostly
influenced by the amount of water present in the concrete at the time of mixing and a bit
affected by the cement content. In absence of test data, total shrinkage strain for design can
be assumed as 0.0003.
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Q3. CONCRETE TESTING, SAMPLING AND ACCEPTANCE CRITERIA AS PER IS CODE.
ANS. Testing plays an important role in controlling the quality of cement concrete work.
Systematic testing of the raw materials, the fresh concrete and the hardened concrete is very
important part of quality control of concrete. It helps to achieve higher efficiency of the
materials and greater performance of the concrete in terms of strength and durability.
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Testing of concrete:
List of Mandatory test-slump test, cube test.
Tests for workability of concrete-
1. Slump cone test- The conical mould is placed on smooth
surface. The container is filled in 3 layers. Each layer is tamped
25 times with a steel rod. Immediately after filling, the cone is
slowly lifted. The concrete will then slump. The decrease in the
height of centre of slumped concrete is called slump. This test
is most commonly done at site, other tests are done at factory
setting.

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2. Compacting factor test- The upper hopper is filled
with concrete, then its bottom door is released. Now the
concrete falls in middle hopper. Bottom door of 2nd
hopper is released to let concrete fall into the cylinder.
The density of concrete in the cylinder is now
calculated. The ratio of concrete density in cylinder to
the density of fully compacted concrete is defined as
the compacting factor.
Test for Consistency of concrete-
3. Vebe test- Initial reading is taken in the
graduated scale before remoulding (a)in mm.
Final reading in graduated scale after remoulding
(b) in mm. Slump= (a-b). Consistency of concrete
is measured in Vee-bee seconds. Basically one
switch on the vibrator and stopwatch till concrete
surface is equal plane. This time is Vee-bee
seconds.

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4. Flow table test- the table top has concrete in cone
which is lifted slowly. Then dia of flow is measured. A
value of 400mm indicates medium workability and
500mm a high workability. Concrete at this stage should
appear uniform and cohesive or else the test is
considered inappropriate for the given mix.
5. Ball penetration test- also known as Kelly ball test. Used to determine workability of concrete.
Reading or depth of penetration is taken in 3 samples. Average value= slump value. It has
greater precision than slump test but concrete wastage is higher.

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Concrete sampling as per IS code-
• Making and curing compression test specimens. Test specimens cubical in shape shall be
15x15x15cm. The moulds can be metal/steel/cast iron to prevent distortion.
• Samples from fresh concrete shall be taken and cubes shall be made, cured and tested at
28days.
• In order to get a relatively quicker idea of quality of concrete, compressive strength test at
7 days may be carried out in addition of 28 days compressive strength test.
• A random sampling procedure shall be adopted to ensure that each concrete batch shall
have a reasonable chance of being tested.
• Test results of the sample shall be average of strength of 3 samples. The individual variation
should not differ by more than +_15% of the average. If it is not in the range, the test results
of the samples are invalid.
Concrete sampling acceptance criteria-
1. Compressive strength: the mean strength determined from any group of 4 consecutive test
results complies with appropriate limits in col2 of table below. Any individual test result
complies with the limits in col3 of table below.
2. Flexural strength: the mean strength determined from group of 4 test results exceeds the
specified characteristic strength by at least 0.3N/mm2. The strength obtained from any
test result is not less than the specified characteristic strength less than 0.3 N/mm2.

Q4. DESIGN MIX, VOLUMETRIC MIX, NOMINAL MIX, WEIGH BATCHING AS PER IS 456.
ANS.
Design Mix:
As the guarantor of quality of concrete used in the construction, the constructor shall carry out
the mix design and the mix so designed shall be approved by the employer within the
limitations of parameters and other stipulations laid down by this standard.
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Designing the concrete mix within the limitation of parameters and other stipulation laid down
by the Indian standard code IS 456:2000 shall be called design mix concrete. The Constructor
shall carry out the mix design and the mix so designed (not the method of design) shall be
approved by the employer.
The target mean strength of concrete mix should be equal to the characteristic strength plus
1.65 times the standard deviation. And design mix to produce the grade of concrete having
the required workability and a characteristic strength not less than appropriate values given in
Table2.

Nominal Mix:
it is used for concrete of M20 or lower. The proportion shall be according to table 9.
For any nominal mix if the proportion of water has been increased then for the proper water-
cement ratio, specified cement content should also be increased proportionately.
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Batching:
In batching concrete. The quantity of both cement and aggregate shall be determined by mass;
admixture. if solid. by mass; liquid admixture may however be measured in volume or mass; water shall be
weighed OJ' measured by volume in a calibrated tank. (As per IS 4925)
• The material should be stock-piled for several hours preferably a day before use. The grading of coarse
and fine aggregate should be checked as frequently as possible. the frequency for a given job being
determined by the engineer-in charge to ensure that the specified grading is maintained.
• The accuracy of the measuring equipment shall be within±2 percent of the quantity of cement being
measured and within ± 3 present of the quantity of aggregate. Admixture sand water being measured.
• All ingredients of the concrete should be used by mass only.
• Volume batching may be allowed only where weigh-batching is not practical and provided accurate
bulk densities of materials to be actually used in concrete have earlier been established. the given job
being determined by engineer-in-charge 10ensure that the specified grading is maintained.
• As it is important to maintain the water-cement ratio constant at its correct value. To this end
determination of moisture contents in both fine and coarse aggregates shall be made as frequently as
possible. In the absence of exact data. only in the case of nominal mixes.

Q5. REINFORCEMENT STEEL TYPES, PROPERTIES, APPLICATION, SPECIFICATION, LIMITATION AS
PER IS 1786.
ANS. IS 1786 covers the requirements of deformed steel and wires for use as reinforcement in
concrete. Following are the strength grades:
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The nominal sizes of bars/ wires shall be- 4mm, 5mm, 6mm, 8mm, 10mm, 12mm, 16mm, 20mm,
25mm, 28mm, 32mm, 36mm, 40mm.
Properties:
• The bars/ wires shall withstand the bend test and rebend test.
The reinforcement shall be any of
the following:
a) Mild steel and medium tensile
steel bars
b) High strength deformed steel bars
c) Hard-drawn steel wire fabric
d) Structural steel

Q6. CONCRETE MIX DESIGN AS PER IS STD.
ANS.
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Q7. TENSILE STRENGTH, SHEER STRENGTH AND COMPRESSIVE STRENGTH TESTING OF CONCRETE.
ANS.
Compressive strength testing of concrete
• Its determined using 150x300mm cylinders and 150mm cubes.
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Tensile strength testing of concrete
• Its determined by methods- the flexure test and the splitting test. These methods yield
strength values higher than the true tensile strength under uniaxial loading.

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Shear strength testing of concrete
Shear strength of concrete was determined by applying direct shear force on push-off
specimen. The test for determining shear transfer strength for concrete employs a specimen of
230 mm × 150 mm × 150 mm size, which is subjected to uniaxial compression in a compression-
testing machine. Shear strength of concrete is the ratio of ultimate shear force at which the
specimen fails to the shear area of push-off specimen.
Shear strength (τ) = Ultimate shear force/ Shear area

Q8. TRANSPORTATION, PLACING, COMPACTING AND CURING OF CONCRETE.
ANS.
Transportation and handling:
• Concrete after mixing should be transported to the formwork as rapidly as possible.
• Transportation by methods to prevent segregation or interference of any foreign matter or
water.
• In extreme hot or cold climate, it should be transported in deep containers. It should avoid
loss of water by evaporation in hot weather and heat loss in cold weather.
Placing:
• Concrete should be deposited to the nearest possible final position to avoid rehandling.
• Concrete should be placed and compacted before initial setting of concrete starts.
• Methods of placing should avoid segregation of items.
• Care should be taken to avoid movement of formwork or reinforcement.
• Maximum allowed free fall of concrete is 1.5m.
• Concrete should be placed in uniform layers.
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Compaction:
• Concrete should be properly compacted and fully worked around the reinforcement,
around corners of formwork and embedded fixtures.
• Shall be com[acted by mechanical vibrators.
• Over vibration & under- vibration of concrete should be avoided.
• Each layer to be compacted before placing the next layer.
• Each next layer to be placed while the underlying layer is still plastic so that monolithic
construction is achieved.
• Various types of vibrators are used depending upon the specific condition- internal vibrator,
needle vibrator, external vibrator, surface vibrator, vibrating tables etc.
Curing of concrete:
• Curing is procedure used for promoting hydration of cement, and so the development of
strength of concrete.
• Moist curing- exposed surfaces of concrete to be kept continuously in wet condition by
ponding, or covering with a layer of sacking etc. It should be wet constantly for minimum 7
days from the date of placing of concrete, in case of OPC. And 10 days where mineral
admixtures are used. In dry & hot weather sites, the curing should be minimum 10 days.
• Membrane curing- approved curing compounds may be used and applied to all exposed
surfaces of the concrete. It is done as soon as possible the concrete is set. Impermeable
membranes like polyethylene sheeting covering closely the concrete surface may be used
to avoid evaporation.
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Q9. READY MIX CONCRETE.
ANS. If concrete is delivered for placing from a plant, instead of being mixed at site, it is called
as ready- mix concrete (pre-mix). Advantages of RMC:
1. Quality control of concrete batching which reduces variation of hardend concrete
properties.
2. Used for sites with space constraints for mixing plant and aggregate stockpiles.
3. Use of agitator trucks for transportation hence preventing segregation and maintaining
workability.
4. It is convenient when small quantities of concrete or intermittent placing is needed.
5. RMC is costlier than regular site mixed concrete, but it saves other resources
Types of ready-mix concrete:
a) Central mixed RMC
Mixing is done at a central plant and then concrete is transported in agitator truck.
b) Transit – mixed or truck-mixed RMC
The materials are batched in a central plant but its mixed in transit or immediately before
discharging the concrete at site. It is less time consuming but truck is smaller in size.
c) Shrink Mixed concrete
Concrete is partially mixed at the central plant and mixing is completed in the transit.
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Q10. CHEMICAL REACTION OF CONCRETE AND ROLE OF EACH INGREDIENT.
ANS. Cement and water form a paste that coats each particle of stone and sand—the
aggregates. Through a chemical reaction called hydration, the cement paste hardens and
gains strength. The quality of the paste determines the character of the concrete.
The 2 calcium silicates C3S & C2S are the main cementitious compounds in cement. C3S
hydrates more rapidly than C2S.
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The product of hydration of C3S is microcrystalline hydrate C3S2H3 with some lime separating
out as crystalline Ca(OH)2.
The C2S behaves same as C3S but contain less lime.
The amount of C3A in most cements is comparatively small. The reaction of C3A with water is
very rapid and would lead to a Flash set. This flash setting is prevented by gypsum. The reaction
of C3A is quicker than calcium silicates C3S & C2S.
*Note- The numbers in square
brackets are the
corresponding masses.

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Major products of hydration:
• Calcium silicate hydrate or C-S-H or Tobermorite gel. This is the most important of all the
products and is responsible for all the good properties of concrete i.e. strength, durability, etc.
• Calcium Hydroxide or Ca(OH)2. It helps in maintaining a pH value of 13 around the
reinforcement, which acts as a passive protective layer preventing the corrosion of
reinforcement.
• Calcium Aluminate Hydrate or C3AH6. These hydration products do not impart any strength or
unique property to concrete; instead, their presence is harmful to the concrete, particularly in
cases where concrete is prone to sulfate attack.

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