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Cement
Chemical Composition
Ordinary cement contains two basic ingredients, namely, 
argillaceous and calcareous. In argillaceous materials, 
clay predominates and in calcareous calcium carbonate 
predominates. 
Broadly, the raw materials used for manufacture of 
cement consist mainly of lime, silica, alumina and iron 
oxide. These oxides interact with one another at high tem-
perature and form more complex compounds. The relative 
proportions of these oxide compounds are responsible for 
influencing the various properties of cement, in addition to 
rate of cooling and fineness of grinding.
Approximate oxide composition ranges for ordinary 
portland cement (OPC) are:
Ingredient Chemical Formula Range (%)
Lime CaO 62–67
Silica SiO
2
17–25
Alumina Al
2
O
3
3–8
Calcium Sulphate CaSO
4
3–4
Iron oxide Fe
2
O
3
3–4
Magnesia MgO 1–3
Sulphur S 1–3
Alkalies – 0.2–1
Functions of Cement Ingredients
 1. Lime (CaO): Excess lime makes the cement unsound 
and causes the cement to expand and disintegrate. 
Deficiency in lime makes loss of strength and makes 
cement to set quickly.
 2. Silica (SiO
2
): SiO
2
 imparts the strength to cement 
by forming the di-calcium and tri-calcium silicates. 
Excess silica makes the strength of cement increases, 
but prolongs the setting time. 
 3. Alumina (Al
2
O
3
): Al
2
O
3
 imparts quick setting 
property to the cement. It acts as a flux and lowers 
the clinkering temperature. Excess alumina makes 
cement weaker. 
 4. Calcium Sulphate (CaSO
4
): It is in the form of 
gypsum and increases the initial setting time of 
cement.
 5. Iron Oxide (Fe
2
O
3
): Fe
2
O
3
 imparts colour, hardness 
and strength to cement.
 6. Magnesia (MgO): MgO imparts hardness and 
colour, if present in small amount. Excess MgO 
makes cement unsound.
 7. Sulphur (S): It is useful in making sound cement.
 8. Alkalis: Most of the alkalis present in raw materials are 
carried away by the flue gases during heating process. 
Presence of alkalis causes problems such as alkali-
aggregate reaction, efflorescence and staining, etc.
Concrete and Its Constituents
Part III_Unit 4_Chapter 01.indd   253 5/20/2017   7:25:32 PM
Page 2


 
 
 
 
Cement
Chemical Composition
Ordinary cement contains two basic ingredients, namely, 
argillaceous and calcareous. In argillaceous materials, 
clay predominates and in calcareous calcium carbonate 
predominates. 
Broadly, the raw materials used for manufacture of 
cement consist mainly of lime, silica, alumina and iron 
oxide. These oxides interact with one another at high tem-
perature and form more complex compounds. The relative 
proportions of these oxide compounds are responsible for 
influencing the various properties of cement, in addition to 
rate of cooling and fineness of grinding.
Approximate oxide composition ranges for ordinary 
portland cement (OPC) are:
Ingredient Chemical Formula Range (%)
Lime CaO 62–67
Silica SiO
2
17–25
Alumina Al
2
O
3
3–8
Calcium Sulphate CaSO
4
3–4
Iron oxide Fe
2
O
3
3–4
Magnesia MgO 1–3
Sulphur S 1–3
Alkalies – 0.2–1
Functions of Cement Ingredients
 1. Lime (CaO): Excess lime makes the cement unsound 
and causes the cement to expand and disintegrate. 
Deficiency in lime makes loss of strength and makes 
cement to set quickly.
 2. Silica (SiO
2
): SiO
2
 imparts the strength to cement 
by forming the di-calcium and tri-calcium silicates. 
Excess silica makes the strength of cement increases, 
but prolongs the setting time. 
 3. Alumina (Al
2
O
3
): Al
2
O
3
 imparts quick setting 
property to the cement. It acts as a flux and lowers 
the clinkering temperature. Excess alumina makes 
cement weaker. 
 4. Calcium Sulphate (CaSO
4
): It is in the form of 
gypsum and increases the initial setting time of 
cement.
 5. Iron Oxide (Fe
2
O
3
): Fe
2
O
3
 imparts colour, hardness 
and strength to cement.
 6. Magnesia (MgO): MgO imparts hardness and 
colour, if present in small amount. Excess MgO 
makes cement unsound.
 7. Sulphur (S): It is useful in making sound cement.
 8. Alkalis: Most of the alkalis present in raw materials are 
carried away by the flue gases during heating process. 
Presence of alkalis causes problems such as alkali-
aggregate reaction, efflorescence and staining, etc.
Concrete and Its Constituents
Part III_Unit 4_Chapter 01.indd   253 5/20/2017   7:25:32 PM
      
The above mentioned constituents in chemical reactions 
form the following compounds, called ‘bogue’ s compounds’.
Tri-calcium silicate (Alite) C
3
S 45%
Di-calcium silicate (Belite) C
2
S 25%
Tri-calcium Aluminate (celite) C
3
A 11%
Tetra-calcium Alumino Ferrite (Felite) C
4
AF 9%
The functions of each of these compounds are as follows:
 1. C
3
S
 • Hydrates quickly and contributes more to the early 
strength. 
 • High heat of hydration.
 2. C
2
S
 • Strengthen the concrete from 7days – 1 year. 
 • Less heat of hydration.
 • Initial setting of cement.
 3. C
3
A
 • Small contribution to the strength within first 24 hours.
 • Very high heat of hydration.
 4. C
4
AF
 • Comparatively inactive.
Types of Cements
 1. Ordinary portland cement (OPC):
 • OPC is used in general concrete construction 
where there is no exposure to sulphates in soil or 
in groundwater.
 • Initial and final setting times are 30 minutes and 
10 hours.
Different Grades of Ordinary Portland Cement (OPC)
Grade of 
Cement
Details
33 grade 
ordinary 
portland 
cement 
(IS:269-
1998)
•	 The compressive strength after 28 days 
is 33 N/mm
2
.
•	 Used for general construction works in 
normal environmental conditions.
•	 Cannot be used where higher grade 
concrete above M20 is required.
43 grade 
ordinary 
portland 
cement 
(IS:8112-
2000)
•	 Minimum 28 days compressive strength 
43 N/mm
2
.
•	 Used for construction of residential, 
commercial and industrial building, roads, 
bridges, flyovers, irrigation projects and 
other general civil construction works.
•	 Suitable for all types of applications 
RCC, plastering, masonry, etc.
53 grade 
ordinary 
portland 
cement 
(IS:12269-
1999)
•	 Minimum 28 days compressive strength 
53 N/mm
2
.
•	 Gives 10–15% saving in cement 
consumption and 5–8% saving in steel 
consumption provided higher grades of 
concrete, say M30 and above.
•	 Useful for high-rise buildings, bridges, flyo-
ver, chimneys and pre-stressed structures 
where high-grade concrete is required.
•	 Gives better durability characteristics to 
concrete.
 2. Rapid hardening cement:
 • Contains high percentage of C
3
S to the extent 
about 56%.
 • 3 days strength is equivalent to 7 days strength of 
OPC.
 • Initial and final setting times are as same as OPC.
  Advantages:
 • Sets rapidly and requires a short period of curing.
 • Early removal of formwork.
 3. Extra rapid hardening cement:
 • Imparts strength about 25% higher than that of 
rapid hardening cement.
 • It is obtained by inter-grinding calcium chloride 
(CaCl
2
) with rapid hardening of portland cement.
 4. Low heat cement:
 • Contains lower % of C
3
A of about 5% and higher % 
of C
2
S about 46%.
 • Initial setting time is about an hour and final setting 
time is about 10 hours.
 • Mainly used for mass concrete works.
 5. Hydrophobic cement:
 • Contains admixtures which decrease the wetting 
ability of cement grains.
 • Frost resistance and water resistance of concrete 
can be increased by using this type of cement.
 • Examples for hydrophobic admixtures includes oleic 
acid, oxidized petroleum, naphthalene, soap, etc.
 6. Quick setting cement:
 • Produced by adding small percentage of alumin-
ium sulphate and by finely grinding the cement.
 • Setting action starts within 5 minutes after addition 
of water and within 30 minutes it hardens.
 • Used to lay concrete under water.
 7. Expanding cement:
 • Produced by adding an expanding medium like 
sulpho-aluminate and a stabilizing agent to OPC.
 • Used for repairing damaged concrete surfaces and 
for construction of water retaining structures.
 8. High alumina cement:
 • Produced by grinding clinkers formed by calcined 
bauxite and lime.
 • Initial setting time is more than 3
1
2
 hours and final 
setting time is about 5 hours.
 • Acid resistant, but high heat of hydration.
 9. Pozzolana cement:
 • Pozzolana is a silicacious material which has no 
cementitious properties when it is used alone, but 
in the presence of cement it posses cementitious 
properties.
 • Pozzolana materials should be between 10–30%.
 • Fly ash, blast furanace slag, silica fume are exam-
ples for artificial pozzolans and burnt clay, pumic-
ite are examples for natural pozzolana materials.
Part III_Unit 4_Chapter 01.indd   254 5/20/2017   7:25:32 PM
Page 3


 
 
 
 
Cement
Chemical Composition
Ordinary cement contains two basic ingredients, namely, 
argillaceous and calcareous. In argillaceous materials, 
clay predominates and in calcareous calcium carbonate 
predominates. 
Broadly, the raw materials used for manufacture of 
cement consist mainly of lime, silica, alumina and iron 
oxide. These oxides interact with one another at high tem-
perature and form more complex compounds. The relative 
proportions of these oxide compounds are responsible for 
influencing the various properties of cement, in addition to 
rate of cooling and fineness of grinding.
Approximate oxide composition ranges for ordinary 
portland cement (OPC) are:
Ingredient Chemical Formula Range (%)
Lime CaO 62–67
Silica SiO
2
17–25
Alumina Al
2
O
3
3–8
Calcium Sulphate CaSO
4
3–4
Iron oxide Fe
2
O
3
3–4
Magnesia MgO 1–3
Sulphur S 1–3
Alkalies – 0.2–1
Functions of Cement Ingredients
 1. Lime (CaO): Excess lime makes the cement unsound 
and causes the cement to expand and disintegrate. 
Deficiency in lime makes loss of strength and makes 
cement to set quickly.
 2. Silica (SiO
2
): SiO
2
 imparts the strength to cement 
by forming the di-calcium and tri-calcium silicates. 
Excess silica makes the strength of cement increases, 
but prolongs the setting time. 
 3. Alumina (Al
2
O
3
): Al
2
O
3
 imparts quick setting 
property to the cement. It acts as a flux and lowers 
the clinkering temperature. Excess alumina makes 
cement weaker. 
 4. Calcium Sulphate (CaSO
4
): It is in the form of 
gypsum and increases the initial setting time of 
cement.
 5. Iron Oxide (Fe
2
O
3
): Fe
2
O
3
 imparts colour, hardness 
and strength to cement.
 6. Magnesia (MgO): MgO imparts hardness and 
colour, if present in small amount. Excess MgO 
makes cement unsound.
 7. Sulphur (S): It is useful in making sound cement.
 8. Alkalis: Most of the alkalis present in raw materials are 
carried away by the flue gases during heating process. 
Presence of alkalis causes problems such as alkali-
aggregate reaction, efflorescence and staining, etc.
Concrete and Its Constituents
Part III_Unit 4_Chapter 01.indd   253 5/20/2017   7:25:32 PM
      
The above mentioned constituents in chemical reactions 
form the following compounds, called ‘bogue’ s compounds’.
Tri-calcium silicate (Alite) C
3
S 45%
Di-calcium silicate (Belite) C
2
S 25%
Tri-calcium Aluminate (celite) C
3
A 11%
Tetra-calcium Alumino Ferrite (Felite) C
4
AF 9%
The functions of each of these compounds are as follows:
 1. C
3
S
 • Hydrates quickly and contributes more to the early 
strength. 
 • High heat of hydration.
 2. C
2
S
 • Strengthen the concrete from 7days – 1 year. 
 • Less heat of hydration.
 • Initial setting of cement.
 3. C
3
A
 • Small contribution to the strength within first 24 hours.
 • Very high heat of hydration.
 4. C
4
AF
 • Comparatively inactive.
Types of Cements
 1. Ordinary portland cement (OPC):
 • OPC is used in general concrete construction 
where there is no exposure to sulphates in soil or 
in groundwater.
 • Initial and final setting times are 30 minutes and 
10 hours.
Different Grades of Ordinary Portland Cement (OPC)
Grade of 
Cement
Details
33 grade 
ordinary 
portland 
cement 
(IS:269-
1998)
•	 The compressive strength after 28 days 
is 33 N/mm
2
.
•	 Used for general construction works in 
normal environmental conditions.
•	 Cannot be used where higher grade 
concrete above M20 is required.
43 grade 
ordinary 
portland 
cement 
(IS:8112-
2000)
•	 Minimum 28 days compressive strength 
43 N/mm
2
.
•	 Used for construction of residential, 
commercial and industrial building, roads, 
bridges, flyovers, irrigation projects and 
other general civil construction works.
•	 Suitable for all types of applications 
RCC, plastering, masonry, etc.
53 grade 
ordinary 
portland 
cement 
(IS:12269-
1999)
•	 Minimum 28 days compressive strength 
53 N/mm
2
.
•	 Gives 10–15% saving in cement 
consumption and 5–8% saving in steel 
consumption provided higher grades of 
concrete, say M30 and above.
•	 Useful for high-rise buildings, bridges, flyo-
ver, chimneys and pre-stressed structures 
where high-grade concrete is required.
•	 Gives better durability characteristics to 
concrete.
 2. Rapid hardening cement:
 • Contains high percentage of C
3
S to the extent 
about 56%.
 • 3 days strength is equivalent to 7 days strength of 
OPC.
 • Initial and final setting times are as same as OPC.
  Advantages:
 • Sets rapidly and requires a short period of curing.
 • Early removal of formwork.
 3. Extra rapid hardening cement:
 • Imparts strength about 25% higher than that of 
rapid hardening cement.
 • It is obtained by inter-grinding calcium chloride 
(CaCl
2
) with rapid hardening of portland cement.
 4. Low heat cement:
 • Contains lower % of C
3
A of about 5% and higher % 
of C
2
S about 46%.
 • Initial setting time is about an hour and final setting 
time is about 10 hours.
 • Mainly used for mass concrete works.
 5. Hydrophobic cement:
 • Contains admixtures which decrease the wetting 
ability of cement grains.
 • Frost resistance and water resistance of concrete 
can be increased by using this type of cement.
 • Examples for hydrophobic admixtures includes oleic 
acid, oxidized petroleum, naphthalene, soap, etc.
 6. Quick setting cement:
 • Produced by adding small percentage of alumin-
ium sulphate and by finely grinding the cement.
 • Setting action starts within 5 minutes after addition 
of water and within 30 minutes it hardens.
 • Used to lay concrete under water.
 7. Expanding cement:
 • Produced by adding an expanding medium like 
sulpho-aluminate and a stabilizing agent to OPC.
 • Used for repairing damaged concrete surfaces and 
for construction of water retaining structures.
 8. High alumina cement:
 • Produced by grinding clinkers formed by calcined 
bauxite and lime.
 • Initial setting time is more than 3
1
2
 hours and final 
setting time is about 5 hours.
 • Acid resistant, but high heat of hydration.
 9. Pozzolana cement:
 • Pozzolana is a silicacious material which has no 
cementitious properties when it is used alone, but 
in the presence of cement it posses cementitious 
properties.
 • Pozzolana materials should be between 10–30%.
 • Fly ash, blast furanace slag, silica fume are exam-
ples for artificial pozzolans and burnt clay, pumic-
ite are examples for natural pozzolana materials.
Part III_Unit 4_Chapter 01.indd   254 5/20/2017   7:25:32 PM
    
 • Used to prepare mass concrete of lean mix and for 
marine works sewage works and for laying con-
crete under water.
 10. White cement and coloured cement:
 • Used for finishing, plastering and architectural, 
and ornamental works.
 • Colouring agents, such as iron oxide, cobalt, man-
ganese dioxide, etc., are added to white cement 
to obtain red and yellow, blue and black colour 
cements.
Tests on Cement
Field Tests
Carried out to roughly ascertain the quality of cement.
 1. Colour:
 • Should be uniform and in grey colour with light 
greenish shade.
 • Gives an indication of excess lime or clay and the 
degree of burning.
 2. Physical properties:
 • Should feel smooth when rubbed between fingers.
 • It should sink, but not float when small quantity of 
cement thrown in a bucket.
 • Should feel cool and not warm when hand is 
inserted in a bag/heap of cement.
 3. Presence of lumps:
 • Should be free from any hard lumps.
Laboratory Tests
 1. Fineness:
 • Carried out to check proper grinding of cement. 
 • Determined either by sieve test or by permeability 
apparatus test.
 • In permeability test, ‘specific surface area’ is cal-
culated as a measure of frequency of the average 
size of particles, expressed in cm
2
/g.
 • It should not be less than 2250 cm
2
/g for OPC, 
3250 cm
2
/gm for rapid hardening and 3200 cm
2
/
gm for low heat cements.
 2. Consistency:
 • To determine the % of water required for making 
workable cement paste.
 • Apparatus used: Vicat’ s apparatus with Vicat plunger 
of 1 cm diameter.
 • As per Vicat’s test, percentage of water added 
to cement at which the needle penetration is in 
between 5–7 mm (from the bottom of the mould) 
is called ‘consistency’.
 • For OPC, consistency is around 30%.
 3. Setting times:
  Initial setting time: Determined by Vicat’ s apparatus 
using Vicat’ s needle of 1 mm squared needle.
 • Water added to cement is about 0.85 times the 
water required for standard consistency. Weight of 
the cement taken is 300 g to carry out this test.
 • Period elapsing between the time when water is 
added to the cement and the time at which the nee-
dle fails to pierce the test block by 5 ± 0.5 mm is 
taken as the initial setting time.
 • For OPC, it should not be less than 30 minutes. 
For low heat cements, it should not be less than 60 
minutes.
  Final setting time: Determined by Vicat’s apparatus 
using Vicat’s needle with annual collar of 5 mm 
diameter.
 • Time lapsed since addition of water to time at 
which needle with annual collar can only make a 
mark on hard concrete surface, but not piercing is 
taken as final setting time.
 • It should not be more than 10 hours for OPC.
 4. Soundness:
 • Soundness refer to the ability of cement to main-
tain constant volume.
 • Carried out to detect the presence of un-combined 
lime in cement.
 • Determined by Le Chatelier apparatus, or Autoclave 
test.
 • Le Chatelier’s method measures expansion due to 
lime, and Autoclave method measures expansion 
due to magnesia.
 • Expansion more than 10 mm indicates unsound-
ness of cement.
 5. Heat of hydration:
 • Hydration is the process of adding water to cement.
 • Determined by adiabatic calorimeter test or vac-
uum flask test.
 • For OPC, heat of hydration at 7 days should not 
be more than 65 cal/g, and at 28 days should not 
more than  75 cal/g.
 6. Specific gravity:
 • Determined through test conducted—using kero-
sene and specific gravity bottle at 27° temperature.
 • Specific gravity for OPC is about 3.1.
Some Important Specifications—OPC
Fineness (cm
2
/gm) 2250 minimum
Setting times
Initial 30 hours duration
Final 10 hours maximum
Specific gravity 3.1
Compressive strength (kg/cm
2
)
3 days 230 minimum
7 days 330 minimum
28 days 430 minimum
Part III_Unit 4_Chapter 01.indd   255 5/20/2017   7:25:32 PM
Page 4


 
 
 
 
Cement
Chemical Composition
Ordinary cement contains two basic ingredients, namely, 
argillaceous and calcareous. In argillaceous materials, 
clay predominates and in calcareous calcium carbonate 
predominates. 
Broadly, the raw materials used for manufacture of 
cement consist mainly of lime, silica, alumina and iron 
oxide. These oxides interact with one another at high tem-
perature and form more complex compounds. The relative 
proportions of these oxide compounds are responsible for 
influencing the various properties of cement, in addition to 
rate of cooling and fineness of grinding.
Approximate oxide composition ranges for ordinary 
portland cement (OPC) are:
Ingredient Chemical Formula Range (%)
Lime CaO 62–67
Silica SiO
2
17–25
Alumina Al
2
O
3
3–8
Calcium Sulphate CaSO
4
3–4
Iron oxide Fe
2
O
3
3–4
Magnesia MgO 1–3
Sulphur S 1–3
Alkalies – 0.2–1
Functions of Cement Ingredients
 1. Lime (CaO): Excess lime makes the cement unsound 
and causes the cement to expand and disintegrate. 
Deficiency in lime makes loss of strength and makes 
cement to set quickly.
 2. Silica (SiO
2
): SiO
2
 imparts the strength to cement 
by forming the di-calcium and tri-calcium silicates. 
Excess silica makes the strength of cement increases, 
but prolongs the setting time. 
 3. Alumina (Al
2
O
3
): Al
2
O
3
 imparts quick setting 
property to the cement. It acts as a flux and lowers 
the clinkering temperature. Excess alumina makes 
cement weaker. 
 4. Calcium Sulphate (CaSO
4
): It is in the form of 
gypsum and increases the initial setting time of 
cement.
 5. Iron Oxide (Fe
2
O
3
): Fe
2
O
3
 imparts colour, hardness 
and strength to cement.
 6. Magnesia (MgO): MgO imparts hardness and 
colour, if present in small amount. Excess MgO 
makes cement unsound.
 7. Sulphur (S): It is useful in making sound cement.
 8. Alkalis: Most of the alkalis present in raw materials are 
carried away by the flue gases during heating process. 
Presence of alkalis causes problems such as alkali-
aggregate reaction, efflorescence and staining, etc.
Concrete and Its Constituents
Part III_Unit 4_Chapter 01.indd   253 5/20/2017   7:25:32 PM
      
The above mentioned constituents in chemical reactions 
form the following compounds, called ‘bogue’ s compounds’.
Tri-calcium silicate (Alite) C
3
S 45%
Di-calcium silicate (Belite) C
2
S 25%
Tri-calcium Aluminate (celite) C
3
A 11%
Tetra-calcium Alumino Ferrite (Felite) C
4
AF 9%
The functions of each of these compounds are as follows:
 1. C
3
S
 • Hydrates quickly and contributes more to the early 
strength. 
 • High heat of hydration.
 2. C
2
S
 • Strengthen the concrete from 7days – 1 year. 
 • Less heat of hydration.
 • Initial setting of cement.
 3. C
3
A
 • Small contribution to the strength within first 24 hours.
 • Very high heat of hydration.
 4. C
4
AF
 • Comparatively inactive.
Types of Cements
 1. Ordinary portland cement (OPC):
 • OPC is used in general concrete construction 
where there is no exposure to sulphates in soil or 
in groundwater.
 • Initial and final setting times are 30 minutes and 
10 hours.
Different Grades of Ordinary Portland Cement (OPC)
Grade of 
Cement
Details
33 grade 
ordinary 
portland 
cement 
(IS:269-
1998)
•	 The compressive strength after 28 days 
is 33 N/mm
2
.
•	 Used for general construction works in 
normal environmental conditions.
•	 Cannot be used where higher grade 
concrete above M20 is required.
43 grade 
ordinary 
portland 
cement 
(IS:8112-
2000)
•	 Minimum 28 days compressive strength 
43 N/mm
2
.
•	 Used for construction of residential, 
commercial and industrial building, roads, 
bridges, flyovers, irrigation projects and 
other general civil construction works.
•	 Suitable for all types of applications 
RCC, plastering, masonry, etc.
53 grade 
ordinary 
portland 
cement 
(IS:12269-
1999)
•	 Minimum 28 days compressive strength 
53 N/mm
2
.
•	 Gives 10–15% saving in cement 
consumption and 5–8% saving in steel 
consumption provided higher grades of 
concrete, say M30 and above.
•	 Useful for high-rise buildings, bridges, flyo-
ver, chimneys and pre-stressed structures 
where high-grade concrete is required.
•	 Gives better durability characteristics to 
concrete.
 2. Rapid hardening cement:
 • Contains high percentage of C
3
S to the extent 
about 56%.
 • 3 days strength is equivalent to 7 days strength of 
OPC.
 • Initial and final setting times are as same as OPC.
  Advantages:
 • Sets rapidly and requires a short period of curing.
 • Early removal of formwork.
 3. Extra rapid hardening cement:
 • Imparts strength about 25% higher than that of 
rapid hardening cement.
 • It is obtained by inter-grinding calcium chloride 
(CaCl
2
) with rapid hardening of portland cement.
 4. Low heat cement:
 • Contains lower % of C
3
A of about 5% and higher % 
of C
2
S about 46%.
 • Initial setting time is about an hour and final setting 
time is about 10 hours.
 • Mainly used for mass concrete works.
 5. Hydrophobic cement:
 • Contains admixtures which decrease the wetting 
ability of cement grains.
 • Frost resistance and water resistance of concrete 
can be increased by using this type of cement.
 • Examples for hydrophobic admixtures includes oleic 
acid, oxidized petroleum, naphthalene, soap, etc.
 6. Quick setting cement:
 • Produced by adding small percentage of alumin-
ium sulphate and by finely grinding the cement.
 • Setting action starts within 5 minutes after addition 
of water and within 30 minutes it hardens.
 • Used to lay concrete under water.
 7. Expanding cement:
 • Produced by adding an expanding medium like 
sulpho-aluminate and a stabilizing agent to OPC.
 • Used for repairing damaged concrete surfaces and 
for construction of water retaining structures.
 8. High alumina cement:
 • Produced by grinding clinkers formed by calcined 
bauxite and lime.
 • Initial setting time is more than 3
1
2
 hours and final 
setting time is about 5 hours.
 • Acid resistant, but high heat of hydration.
 9. Pozzolana cement:
 • Pozzolana is a silicacious material which has no 
cementitious properties when it is used alone, but 
in the presence of cement it posses cementitious 
properties.
 • Pozzolana materials should be between 10–30%.
 • Fly ash, blast furanace slag, silica fume are exam-
ples for artificial pozzolans and burnt clay, pumic-
ite are examples for natural pozzolana materials.
Part III_Unit 4_Chapter 01.indd   254 5/20/2017   7:25:32 PM
    
 • Used to prepare mass concrete of lean mix and for 
marine works sewage works and for laying con-
crete under water.
 10. White cement and coloured cement:
 • Used for finishing, plastering and architectural, 
and ornamental works.
 • Colouring agents, such as iron oxide, cobalt, man-
ganese dioxide, etc., are added to white cement 
to obtain red and yellow, blue and black colour 
cements.
Tests on Cement
Field Tests
Carried out to roughly ascertain the quality of cement.
 1. Colour:
 • Should be uniform and in grey colour with light 
greenish shade.
 • Gives an indication of excess lime or clay and the 
degree of burning.
 2. Physical properties:
 • Should feel smooth when rubbed between fingers.
 • It should sink, but not float when small quantity of 
cement thrown in a bucket.
 • Should feel cool and not warm when hand is 
inserted in a bag/heap of cement.
 3. Presence of lumps:
 • Should be free from any hard lumps.
Laboratory Tests
 1. Fineness:
 • Carried out to check proper grinding of cement. 
 • Determined either by sieve test or by permeability 
apparatus test.
 • In permeability test, ‘specific surface area’ is cal-
culated as a measure of frequency of the average 
size of particles, expressed in cm
2
/g.
 • It should not be less than 2250 cm
2
/g for OPC, 
3250 cm
2
/gm for rapid hardening and 3200 cm
2
/
gm for low heat cements.
 2. Consistency:
 • To determine the % of water required for making 
workable cement paste.
 • Apparatus used: Vicat’ s apparatus with Vicat plunger 
of 1 cm diameter.
 • As per Vicat’s test, percentage of water added 
to cement at which the needle penetration is in 
between 5–7 mm (from the bottom of the mould) 
is called ‘consistency’.
 • For OPC, consistency is around 30%.
 3. Setting times:
  Initial setting time: Determined by Vicat’ s apparatus 
using Vicat’ s needle of 1 mm squared needle.
 • Water added to cement is about 0.85 times the 
water required for standard consistency. Weight of 
the cement taken is 300 g to carry out this test.
 • Period elapsing between the time when water is 
added to the cement and the time at which the nee-
dle fails to pierce the test block by 5 ± 0.5 mm is 
taken as the initial setting time.
 • For OPC, it should not be less than 30 minutes. 
For low heat cements, it should not be less than 60 
minutes.
  Final setting time: Determined by Vicat’s apparatus 
using Vicat’s needle with annual collar of 5 mm 
diameter.
 • Time lapsed since addition of water to time at 
which needle with annual collar can only make a 
mark on hard concrete surface, but not piercing is 
taken as final setting time.
 • It should not be more than 10 hours for OPC.
 4. Soundness:
 • Soundness refer to the ability of cement to main-
tain constant volume.
 • Carried out to detect the presence of un-combined 
lime in cement.
 • Determined by Le Chatelier apparatus, or Autoclave 
test.
 • Le Chatelier’s method measures expansion due to 
lime, and Autoclave method measures expansion 
due to magnesia.
 • Expansion more than 10 mm indicates unsound-
ness of cement.
 5. Heat of hydration:
 • Hydration is the process of adding water to cement.
 • Determined by adiabatic calorimeter test or vac-
uum flask test.
 • For OPC, heat of hydration at 7 days should not 
be more than 65 cal/g, and at 28 days should not 
more than  75 cal/g.
 6. Specific gravity:
 • Determined through test conducted—using kero-
sene and specific gravity bottle at 27° temperature.
 • Specific gravity for OPC is about 3.1.
Some Important Specifications—OPC
Fineness (cm
2
/gm) 2250 minimum
Setting times
Initial 30 hours duration
Final 10 hours maximum
Specific gravity 3.1
Compressive strength (kg/cm
2
)
3 days 230 minimum
7 days 330 minimum
28 days 430 minimum
Part III_Unit 4_Chapter 01.indd   255 5/20/2017   7:25:32 PM
      
Aggregates
 • Aggregates are the inert or chemically inactive materials, 
which are considered to be as important constituents in 
concrete.
 • The aggregates may be classified as natural and artificial 
aggregates based on source of the aggregates.
 • Examples for natural aggregates include sand, gravel, 
crushed-rock such as granite, quartz, basalt, sand stone, 
etc. Similarly, examples for artificial aggregates include 
broken-brick, slag, bloated clay, sintered fly ash, etc.
Properties of Aggregates
 1. Size: On the basis of size, these are classified into two 
categories. These are: 
 (a) Fine aggregates
 (b) Coarse aggregates
  The size of aggregate bigger than 4.75 mm is 
considered as coarse aggregate. The size of aggregate 
whose size is 4.75 mm and less is considered as fine 
aggregate. The maximum size of aggregate should 
be as large as possible within the specified limits, 
but in any case not greater than 
1
4
 of the minimum 
thickness of the member.
 2. Shape: Since shape of aggregate affects the 
workability of concrete, it is considered to be an 
important characteristic of aggregate.
 • Rounded aggregates are preferable to angular 
aggregates for a given water cement ratio.
 • In contrast, angular aggregates exhibits bet-
ter interlocking effect, higher bond strength than 
rounded aggregates which makes this suitable for 
roads and pavements construction.
 3. Texture: Rough textured aggregate develops higher 
bond strength in tension than smooth textured 
aggregate.
Tests on Aggregates
Aggregate Crushing Value
 • Aggregate crushing value gives a relative measure of 
‘resistance of an aggregate to crushing under gradually 
applied compressive load.’
 • The crushing value of aggregate is restricted to 30% for 
concrete used for roads and pavements and 45% may be 
permitted for other structures.
Aggregate Impact Value
 • Measures toughness of aggregate.
 • Toughness is usually considered as the ‘resistance of the 
material to failure by impact.’
 • Aggregate impact value shall not exceed 45% by weight 
for aggregate used for concrete other than wearing surface 
and 30% by weight for concrete for wearing surfaces, 
such as runways, roads and pavements.
Aggregate Abrasion Test
 • Measures hardness or ‘resistance against wear’, which is 
important for aggregates to be used for road and pave-
ment construction.
 • Common tests to measure abrasion resistance are: 
 (a) Deval attrition test
 (b) Dorry abrasion test
 (c) Los Angels test
Bulking of Aggregates
 • Free moisture content in fine aggregate results in bulking 
of volume.
 • Free moisture forms a film around each particle, and this 
film exerts surface tension which causes the bulking of 
sand.
Flakiness Index
 • It is the % by weight of particles in it whose least dimen-
sion (thickness) is less than three-fifths of their mean 
dimension. 
 • This test is not applicable to sizes smaller than 6.3 mm.
Elongation Index
 • It is the % by weight of particles whose greatest dimension 
(length) is greater than 1.8 times their mean dimension.
 • This test is also not applicable to sizes smaller than 
6.3 mm.
Specific Gravity and Water Absorption
 • Test methods for determining these properties are based 
on ‘archimedes principle’.
 • Specific gravity =
-
C
BA
 
 • Apparent specific gravity =
-
C
CA
 • Water absorption =
- 100( ) BC
C
 
Where
A = Weight (in g) of saturated aggregate in water
B = Weight (in g) of saturated surface dry aggregate in air
C = Weight (in g) of oven-dried aggregate in air
 • Specific gravity for aggregates commonly used in con-
struction varies between 2.5–3.
 • Water absorption is generally regarded as measure of 
‘porosity’ and it varies from 0.1–2 per cent.
Stripping Value Test
 • Also known as ‘bitumen affinity’ test and is carried out to 
know the behaviour of aggregates towards bitumen.
Part III_Unit 4_Chapter 01.indd   256 5/20/2017   7:25:33 PM
Page 5


 
 
 
 
Cement
Chemical Composition
Ordinary cement contains two basic ingredients, namely, 
argillaceous and calcareous. In argillaceous materials, 
clay predominates and in calcareous calcium carbonate 
predominates. 
Broadly, the raw materials used for manufacture of 
cement consist mainly of lime, silica, alumina and iron 
oxide. These oxides interact with one another at high tem-
perature and form more complex compounds. The relative 
proportions of these oxide compounds are responsible for 
influencing the various properties of cement, in addition to 
rate of cooling and fineness of grinding.
Approximate oxide composition ranges for ordinary 
portland cement (OPC) are:
Ingredient Chemical Formula Range (%)
Lime CaO 62–67
Silica SiO
2
17–25
Alumina Al
2
O
3
3–8
Calcium Sulphate CaSO
4
3–4
Iron oxide Fe
2
O
3
3–4
Magnesia MgO 1–3
Sulphur S 1–3
Alkalies – 0.2–1
Functions of Cement Ingredients
 1. Lime (CaO): Excess lime makes the cement unsound 
and causes the cement to expand and disintegrate. 
Deficiency in lime makes loss of strength and makes 
cement to set quickly.
 2. Silica (SiO
2
): SiO
2
 imparts the strength to cement 
by forming the di-calcium and tri-calcium silicates. 
Excess silica makes the strength of cement increases, 
but prolongs the setting time. 
 3. Alumina (Al
2
O
3
): Al
2
O
3
 imparts quick setting 
property to the cement. It acts as a flux and lowers 
the clinkering temperature. Excess alumina makes 
cement weaker. 
 4. Calcium Sulphate (CaSO
4
): It is in the form of 
gypsum and increases the initial setting time of 
cement.
 5. Iron Oxide (Fe
2
O
3
): Fe
2
O
3
 imparts colour, hardness 
and strength to cement.
 6. Magnesia (MgO): MgO imparts hardness and 
colour, if present in small amount. Excess MgO 
makes cement unsound.
 7. Sulphur (S): It is useful in making sound cement.
 8. Alkalis: Most of the alkalis present in raw materials are 
carried away by the flue gases during heating process. 
Presence of alkalis causes problems such as alkali-
aggregate reaction, efflorescence and staining, etc.
Concrete and Its Constituents
Part III_Unit 4_Chapter 01.indd   253 5/20/2017   7:25:32 PM
      
The above mentioned constituents in chemical reactions 
form the following compounds, called ‘bogue’ s compounds’.
Tri-calcium silicate (Alite) C
3
S 45%
Di-calcium silicate (Belite) C
2
S 25%
Tri-calcium Aluminate (celite) C
3
A 11%
Tetra-calcium Alumino Ferrite (Felite) C
4
AF 9%
The functions of each of these compounds are as follows:
 1. C
3
S
 • Hydrates quickly and contributes more to the early 
strength. 
 • High heat of hydration.
 2. C
2
S
 • Strengthen the concrete from 7days – 1 year. 
 • Less heat of hydration.
 • Initial setting of cement.
 3. C
3
A
 • Small contribution to the strength within first 24 hours.
 • Very high heat of hydration.
 4. C
4
AF
 • Comparatively inactive.
Types of Cements
 1. Ordinary portland cement (OPC):
 • OPC is used in general concrete construction 
where there is no exposure to sulphates in soil or 
in groundwater.
 • Initial and final setting times are 30 minutes and 
10 hours.
Different Grades of Ordinary Portland Cement (OPC)
Grade of 
Cement
Details
33 grade 
ordinary 
portland 
cement 
(IS:269-
1998)
•	 The compressive strength after 28 days 
is 33 N/mm
2
.
•	 Used for general construction works in 
normal environmental conditions.
•	 Cannot be used where higher grade 
concrete above M20 is required.
43 grade 
ordinary 
portland 
cement 
(IS:8112-
2000)
•	 Minimum 28 days compressive strength 
43 N/mm
2
.
•	 Used for construction of residential, 
commercial and industrial building, roads, 
bridges, flyovers, irrigation projects and 
other general civil construction works.
•	 Suitable for all types of applications 
RCC, plastering, masonry, etc.
53 grade 
ordinary 
portland 
cement 
(IS:12269-
1999)
•	 Minimum 28 days compressive strength 
53 N/mm
2
.
•	 Gives 10–15% saving in cement 
consumption and 5–8% saving in steel 
consumption provided higher grades of 
concrete, say M30 and above.
•	 Useful for high-rise buildings, bridges, flyo-
ver, chimneys and pre-stressed structures 
where high-grade concrete is required.
•	 Gives better durability characteristics to 
concrete.
 2. Rapid hardening cement:
 • Contains high percentage of C
3
S to the extent 
about 56%.
 • 3 days strength is equivalent to 7 days strength of 
OPC.
 • Initial and final setting times are as same as OPC.
  Advantages:
 • Sets rapidly and requires a short period of curing.
 • Early removal of formwork.
 3. Extra rapid hardening cement:
 • Imparts strength about 25% higher than that of 
rapid hardening cement.
 • It is obtained by inter-grinding calcium chloride 
(CaCl
2
) with rapid hardening of portland cement.
 4. Low heat cement:
 • Contains lower % of C
3
A of about 5% and higher % 
of C
2
S about 46%.
 • Initial setting time is about an hour and final setting 
time is about 10 hours.
 • Mainly used for mass concrete works.
 5. Hydrophobic cement:
 • Contains admixtures which decrease the wetting 
ability of cement grains.
 • Frost resistance and water resistance of concrete 
can be increased by using this type of cement.
 • Examples for hydrophobic admixtures includes oleic 
acid, oxidized petroleum, naphthalene, soap, etc.
 6. Quick setting cement:
 • Produced by adding small percentage of alumin-
ium sulphate and by finely grinding the cement.
 • Setting action starts within 5 minutes after addition 
of water and within 30 minutes it hardens.
 • Used to lay concrete under water.
 7. Expanding cement:
 • Produced by adding an expanding medium like 
sulpho-aluminate and a stabilizing agent to OPC.
 • Used for repairing damaged concrete surfaces and 
for construction of water retaining structures.
 8. High alumina cement:
 • Produced by grinding clinkers formed by calcined 
bauxite and lime.
 • Initial setting time is more than 3
1
2
 hours and final 
setting time is about 5 hours.
 • Acid resistant, but high heat of hydration.
 9. Pozzolana cement:
 • Pozzolana is a silicacious material which has no 
cementitious properties when it is used alone, but 
in the presence of cement it posses cementitious 
properties.
 • Pozzolana materials should be between 10–30%.
 • Fly ash, blast furanace slag, silica fume are exam-
ples for artificial pozzolans and burnt clay, pumic-
ite are examples for natural pozzolana materials.
Part III_Unit 4_Chapter 01.indd   254 5/20/2017   7:25:32 PM
    
 • Used to prepare mass concrete of lean mix and for 
marine works sewage works and for laying con-
crete under water.
 10. White cement and coloured cement:
 • Used for finishing, plastering and architectural, 
and ornamental works.
 • Colouring agents, such as iron oxide, cobalt, man-
ganese dioxide, etc., are added to white cement 
to obtain red and yellow, blue and black colour 
cements.
Tests on Cement
Field Tests
Carried out to roughly ascertain the quality of cement.
 1. Colour:
 • Should be uniform and in grey colour with light 
greenish shade.
 • Gives an indication of excess lime or clay and the 
degree of burning.
 2. Physical properties:
 • Should feel smooth when rubbed between fingers.
 • It should sink, but not float when small quantity of 
cement thrown in a bucket.
 • Should feel cool and not warm when hand is 
inserted in a bag/heap of cement.
 3. Presence of lumps:
 • Should be free from any hard lumps.
Laboratory Tests
 1. Fineness:
 • Carried out to check proper grinding of cement. 
 • Determined either by sieve test or by permeability 
apparatus test.
 • In permeability test, ‘specific surface area’ is cal-
culated as a measure of frequency of the average 
size of particles, expressed in cm
2
/g.
 • It should not be less than 2250 cm
2
/g for OPC, 
3250 cm
2
/gm for rapid hardening and 3200 cm
2
/
gm for low heat cements.
 2. Consistency:
 • To determine the % of water required for making 
workable cement paste.
 • Apparatus used: Vicat’ s apparatus with Vicat plunger 
of 1 cm diameter.
 • As per Vicat’s test, percentage of water added 
to cement at which the needle penetration is in 
between 5–7 mm (from the bottom of the mould) 
is called ‘consistency’.
 • For OPC, consistency is around 30%.
 3. Setting times:
  Initial setting time: Determined by Vicat’ s apparatus 
using Vicat’ s needle of 1 mm squared needle.
 • Water added to cement is about 0.85 times the 
water required for standard consistency. Weight of 
the cement taken is 300 g to carry out this test.
 • Period elapsing between the time when water is 
added to the cement and the time at which the nee-
dle fails to pierce the test block by 5 ± 0.5 mm is 
taken as the initial setting time.
 • For OPC, it should not be less than 30 minutes. 
For low heat cements, it should not be less than 60 
minutes.
  Final setting time: Determined by Vicat’s apparatus 
using Vicat’s needle with annual collar of 5 mm 
diameter.
 • Time lapsed since addition of water to time at 
which needle with annual collar can only make a 
mark on hard concrete surface, but not piercing is 
taken as final setting time.
 • It should not be more than 10 hours for OPC.
 4. Soundness:
 • Soundness refer to the ability of cement to main-
tain constant volume.
 • Carried out to detect the presence of un-combined 
lime in cement.
 • Determined by Le Chatelier apparatus, or Autoclave 
test.
 • Le Chatelier’s method measures expansion due to 
lime, and Autoclave method measures expansion 
due to magnesia.
 • Expansion more than 10 mm indicates unsound-
ness of cement.
 5. Heat of hydration:
 • Hydration is the process of adding water to cement.
 • Determined by adiabatic calorimeter test or vac-
uum flask test.
 • For OPC, heat of hydration at 7 days should not 
be more than 65 cal/g, and at 28 days should not 
more than  75 cal/g.
 6. Specific gravity:
 • Determined through test conducted—using kero-
sene and specific gravity bottle at 27° temperature.
 • Specific gravity for OPC is about 3.1.
Some Important Specifications—OPC
Fineness (cm
2
/gm) 2250 minimum
Setting times
Initial 30 hours duration
Final 10 hours maximum
Specific gravity 3.1
Compressive strength (kg/cm
2
)
3 days 230 minimum
7 days 330 minimum
28 days 430 minimum
Part III_Unit 4_Chapter 01.indd   255 5/20/2017   7:25:32 PM
      
Aggregates
 • Aggregates are the inert or chemically inactive materials, 
which are considered to be as important constituents in 
concrete.
 • The aggregates may be classified as natural and artificial 
aggregates based on source of the aggregates.
 • Examples for natural aggregates include sand, gravel, 
crushed-rock such as granite, quartz, basalt, sand stone, 
etc. Similarly, examples for artificial aggregates include 
broken-brick, slag, bloated clay, sintered fly ash, etc.
Properties of Aggregates
 1. Size: On the basis of size, these are classified into two 
categories. These are: 
 (a) Fine aggregates
 (b) Coarse aggregates
  The size of aggregate bigger than 4.75 mm is 
considered as coarse aggregate. The size of aggregate 
whose size is 4.75 mm and less is considered as fine 
aggregate. The maximum size of aggregate should 
be as large as possible within the specified limits, 
but in any case not greater than 
1
4
 of the minimum 
thickness of the member.
 2. Shape: Since shape of aggregate affects the 
workability of concrete, it is considered to be an 
important characteristic of aggregate.
 • Rounded aggregates are preferable to angular 
aggregates for a given water cement ratio.
 • In contrast, angular aggregates exhibits bet-
ter interlocking effect, higher bond strength than 
rounded aggregates which makes this suitable for 
roads and pavements construction.
 3. Texture: Rough textured aggregate develops higher 
bond strength in tension than smooth textured 
aggregate.
Tests on Aggregates
Aggregate Crushing Value
 • Aggregate crushing value gives a relative measure of 
‘resistance of an aggregate to crushing under gradually 
applied compressive load.’
 • The crushing value of aggregate is restricted to 30% for 
concrete used for roads and pavements and 45% may be 
permitted for other structures.
Aggregate Impact Value
 • Measures toughness of aggregate.
 • Toughness is usually considered as the ‘resistance of the 
material to failure by impact.’
 • Aggregate impact value shall not exceed 45% by weight 
for aggregate used for concrete other than wearing surface 
and 30% by weight for concrete for wearing surfaces, 
such as runways, roads and pavements.
Aggregate Abrasion Test
 • Measures hardness or ‘resistance against wear’, which is 
important for aggregates to be used for road and pave-
ment construction.
 • Common tests to measure abrasion resistance are: 
 (a) Deval attrition test
 (b) Dorry abrasion test
 (c) Los Angels test
Bulking of Aggregates
 • Free moisture content in fine aggregate results in bulking 
of volume.
 • Free moisture forms a film around each particle, and this 
film exerts surface tension which causes the bulking of 
sand.
Flakiness Index
 • It is the % by weight of particles in it whose least dimen-
sion (thickness) is less than three-fifths of their mean 
dimension. 
 • This test is not applicable to sizes smaller than 6.3 mm.
Elongation Index
 • It is the % by weight of particles whose greatest dimension 
(length) is greater than 1.8 times their mean dimension.
 • This test is also not applicable to sizes smaller than 
6.3 mm.
Specific Gravity and Water Absorption
 • Test methods for determining these properties are based 
on ‘archimedes principle’.
 • Specific gravity =
-
C
BA
 
 • Apparent specific gravity =
-
C
CA
 • Water absorption =
- 100( ) BC
C
 
Where
A = Weight (in g) of saturated aggregate in water
B = Weight (in g) of saturated surface dry aggregate in air
C = Weight (in g) of oven-dried aggregate in air
 • Specific gravity for aggregates commonly used in con-
struction varies between 2.5–3.
 • Water absorption is generally regarded as measure of 
‘porosity’ and it varies from 0.1–2 per cent.
Stripping Value Test
 • Also known as ‘bitumen affinity’ test and is carried out to 
know the behaviour of aggregates towards bitumen.
Part III_Unit 4_Chapter 01.indd   256 5/20/2017   7:25:33 PM
    
 • Aggregates can be classified into 2 categories:
 (a) Hydrophilic
 (b) Hydrophobic
 • Hydrophilic are water liking and they lose their bitumi-
nous coating in presence of water. On the other hand, 
hydrophobic retains bituminous coating even in presence 
of water.
Angularity Number
 • It indicates the amount by which the percentage voids 
exceeds 33% after being compacted in prescribed manner.
 • Angularity number = 67% solid volume
 • The angularity number is expressed to the nearest whole 
number, and it ranges for aggregates used in construction 
is from 0 to 11.
Admixtures
Admixture is defined as a material other than cement, water 
and aggregates, that is used an ingredient of concrete and is 
added to batch immediately before or during mixing.
Types of Admixtures
Mineral Admixtures
 1. Fly ash
 2. Silica fume
 3. Ground granulated blast furnace slag (GGBS)
 4. Stone powder, etc.
Chemical Admixtures
 1. Accelerators:
 • Increases the rate of strength development or 
reduces the setting time.
 • Calcium chloride (CaCl
2
) is widely used 
accelerator.
 • Other examples include tri-ethenoalamine, fluosili-
cates, etc.
 2. Retarders:
 • Delays the setting time of cement paste. 
Examples: Gypsum (calcium sulphate), mucic 
acid, calcium acetate, sugar, etc.
 3. Plasticizers (water reducers):
 • Increases the workability of concrete without alter-
ing the water/cement ratio.
Examples: Ligno sulphuric acids in form of cal-
cium or sodium salts, oleate, etc.
 4. Super plasticizers (high range water reducers):
 • Imparts very high workability with large decrease 
in water content (at least 20%) for a given 
workability.
Examples: Hydroxylated carboxylic acids, for-
maldehyde derivates, such as melamine formalde-
hyde, naphalene sulphonate formaldehyde, etc.
Uses of Admixtures
Admixtures are used to:
 1. Accelerate or retard setting times.
 2. Decrease heat of evolution, rate of bleeding, 
segregation.
 3. Increase the rate of hydration and strength 
development.
 4. Increase water tightness and reduce capillary flow, 
etc.
Concrete
Fresh concrete: Fresh concrete or plastic concrete is a 
freshly mixed material which can be moulded into any 
shape.
Workability
Workability is defined as the property of concrete which 
determines the amount of useful internal work necessary to 
produce full compaction. 
In another words, it is defined as the ‘ease with which 
concrete can fully compacted having regard to the mode of 
compaction and place of deposition. 
The following factors affect the workability of concrete.
Water Content
 • Higher the water content, higher will be the fluidity of 
concrete. 
 • It is important to maintain the water and cement ratio 
constant while adding water to the concrete, for the pur-
pose of achieving high workability.
Water and cement ratio, more than 0.38, will results in 
capillary cavities. A ratio which is less than this will result 
in incomplete hydration.
NOTE
Mix Proportions
 • Higher the aggregate and cement ratio, leaner the 
concrete. 
 • In lean concrete, less quantity of paste is available for 
lubrication per unit surface area of aggregate; hence 
mobility of aggregate is restrained. 
 • On the other hand, lesser the aggregate and cement ratio, 
higher the work-ability.
Size and Shape of Aggregate
 • Bigger the size of aggregates, higher the workability. 
 • Angular, elongated, or flaky aggregate makes the con-
crete very harsh when compared to rounded aggregates 
or cube-shaped aggregates.
Part III_Unit 4_Chapter 01.indd   257 5/20/2017   7:25:33 PM
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