Short Notes: Concrete | Short Notes for Civil Engineering - Civil Engineering (CE) PDF Download

 Page 1


CHAPTER-6 
CONCRETE 
Cement concrete is a mixture of cement, sand, pebbles or crushed rock 
and water. When placed in the skeleton of forms and allowed to cure, 
becomes hard like a stone. Cement concrete is important building 
material because of the following reasons. 
1. It can be moulded into any size and shape of durable structural 
member. 
2. It is possible to control the properties of cement concrete. 
3. It is possible to mechanise completely its preparation and placing 
processes. 
4. It possesses adequate plasticity for mechanical working. 
The cement concrete has the following properties 
1. It has high compressive strength 
2. It is free from corrosion 
3. It hardens with age and continues for a long time after concrete 
has attained sufficient strength 
4. It is proved to be economical than steel  
5. It binds rapidly with steel and it is weak in tension, steel 
reinforcement is placed in cement concrete at suitable places to 
take up tensile concrete or simply R.C.C. 
6. It forms a hard surface, capable of resisting abrasion stresses. 
This is called reinforced cement. 
Page 2


CHAPTER-6 
CONCRETE 
Cement concrete is a mixture of cement, sand, pebbles or crushed rock 
and water. When placed in the skeleton of forms and allowed to cure, 
becomes hard like a stone. Cement concrete is important building 
material because of the following reasons. 
1. It can be moulded into any size and shape of durable structural 
member. 
2. It is possible to control the properties of cement concrete. 
3. It is possible to mechanise completely its preparation and placing 
processes. 
4. It possesses adequate plasticity for mechanical working. 
The cement concrete has the following properties 
1. It has high compressive strength 
2. It is free from corrosion 
3. It hardens with age and continues for a long time after concrete 
has attained sufficient strength 
4. It is proved to be economical than steel  
5. It binds rapidly with steel and it is weak in tension, steel 
reinforcement is placed in cement concrete at suitable places to 
take up tensile concrete or simply R.C.C. 
6. It forms a hard surface, capable of resisting abrasion stresses. 
This is called reinforced cement. 
Concrete                                                                             
  
7. It has tendency to be porous to avoid this proper grading & 
consolidation of the aggregates, minimum water-cement ratio 
should be adopted. 
6.1  Constituents - Requirements. 
 The main constituents of concrete are 
a) Cement / Lime: Before introduction of ordinary Portland 
cement, lime was used as cementing material. At present most 
of the cement concrete works in the building construction is 
done with ordinary Portland cement. But other special varieties 
of cement such as rapid hardening cement, high alumina 
cement are used under certain circumstances. The cement 
should comply with all standard specifications 
b) Fine Aggregates: The material, which is passed through 
4.7625mm B.S.test sieve, is termed as fine aggregates. Usually 
natural river sand is used as fine aggregates. But places where 
natural sand is not available economically, finely crushed stone 
may be used as fine aggregates.  
c) Coarse Aggregates: The material retained on 4.7625mm size 
B.S.test sieve is termed as coarse aggregates. Broken stone is 
generally used as coarse aggregates. For thin slabs, and walls, 
the maximum size of coarse aggregates should be limited to 
one third the thickness of the concrete section 
d) Water: Water to be used in the concrete work should have the 
following properties. 
1) It should be free from oils 
Page 3


CHAPTER-6 
CONCRETE 
Cement concrete is a mixture of cement, sand, pebbles or crushed rock 
and water. When placed in the skeleton of forms and allowed to cure, 
becomes hard like a stone. Cement concrete is important building 
material because of the following reasons. 
1. It can be moulded into any size and shape of durable structural 
member. 
2. It is possible to control the properties of cement concrete. 
3. It is possible to mechanise completely its preparation and placing 
processes. 
4. It possesses adequate plasticity for mechanical working. 
The cement concrete has the following properties 
1. It has high compressive strength 
2. It is free from corrosion 
3. It hardens with age and continues for a long time after concrete 
has attained sufficient strength 
4. It is proved to be economical than steel  
5. It binds rapidly with steel and it is weak in tension, steel 
reinforcement is placed in cement concrete at suitable places to 
take up tensile concrete or simply R.C.C. 
6. It forms a hard surface, capable of resisting abrasion stresses. 
This is called reinforced cement. 
Concrete                                                                             
  
7. It has tendency to be porous to avoid this proper grading & 
consolidation of the aggregates, minimum water-cement ratio 
should be adopted. 
6.1  Constituents - Requirements. 
 The main constituents of concrete are 
a) Cement / Lime: Before introduction of ordinary Portland 
cement, lime was used as cementing material. At present most 
of the cement concrete works in the building construction is 
done with ordinary Portland cement. But other special varieties 
of cement such as rapid hardening cement, high alumina 
cement are used under certain circumstances. The cement 
should comply with all standard specifications 
b) Fine Aggregates: The material, which is passed through 
4.7625mm B.S.test sieve, is termed as fine aggregates. Usually 
natural river sand is used as fine aggregates. But places where 
natural sand is not available economically, finely crushed stone 
may be used as fine aggregates.  
c) Coarse Aggregates: The material retained on 4.7625mm size 
B.S.test sieve is termed as coarse aggregates. Broken stone is 
generally used as coarse aggregates. For thin slabs, and walls, 
the maximum size of coarse aggregates should be limited to 
one third the thickness of the concrete section 
d) Water: Water to be used in the concrete work should have the 
following properties. 
1) It should be free from oils 
2) It should be free from acids or alkalies 
3) It should be free from Iron, Vegetables matter or other 
substance, which is likely to have adverse effect on 
concrete. 
4) It should be fit for drinking purpose 
Function of Water 
1. It acts as lubricant for fine and coarse aggregates. 
2. It acts chemically with cement to form binding paste with coarse 
aggregates and reinforcement. 
3. It is necessary to flux the cementing material over the surface of 
the aggregates. 
4. It is employed to damp the concrete in order to prevent them 
absorbing water vitally necessary for chemical action 
5. It enables the concrete mix to blow into moulds. 
 
6.2. Uses and types 
Uses of Concrete: 
1:2:2 - For heavy loaded R.C.C columns and R.C.C arches of long 
spans 
1:2:2 - For small pre cast members of concrete like fencing poles, 
telegraph poles etc. watertight construction.  
1:2:3 - For water tanks, bridges, sewers etc. 
1:2½:3½ - For foot path, concrete roads 
Page 4


CHAPTER-6 
CONCRETE 
Cement concrete is a mixture of cement, sand, pebbles or crushed rock 
and water. When placed in the skeleton of forms and allowed to cure, 
becomes hard like a stone. Cement concrete is important building 
material because of the following reasons. 
1. It can be moulded into any size and shape of durable structural 
member. 
2. It is possible to control the properties of cement concrete. 
3. It is possible to mechanise completely its preparation and placing 
processes. 
4. It possesses adequate plasticity for mechanical working. 
The cement concrete has the following properties 
1. It has high compressive strength 
2. It is free from corrosion 
3. It hardens with age and continues for a long time after concrete 
has attained sufficient strength 
4. It is proved to be economical than steel  
5. It binds rapidly with steel and it is weak in tension, steel 
reinforcement is placed in cement concrete at suitable places to 
take up tensile concrete or simply R.C.C. 
6. It forms a hard surface, capable of resisting abrasion stresses. 
This is called reinforced cement. 
Concrete                                                                             
  
7. It has tendency to be porous to avoid this proper grading & 
consolidation of the aggregates, minimum water-cement ratio 
should be adopted. 
6.1  Constituents - Requirements. 
 The main constituents of concrete are 
a) Cement / Lime: Before introduction of ordinary Portland 
cement, lime was used as cementing material. At present most 
of the cement concrete works in the building construction is 
done with ordinary Portland cement. But other special varieties 
of cement such as rapid hardening cement, high alumina 
cement are used under certain circumstances. The cement 
should comply with all standard specifications 
b) Fine Aggregates: The material, which is passed through 
4.7625mm B.S.test sieve, is termed as fine aggregates. Usually 
natural river sand is used as fine aggregates. But places where 
natural sand is not available economically, finely crushed stone 
may be used as fine aggregates.  
c) Coarse Aggregates: The material retained on 4.7625mm size 
B.S.test sieve is termed as coarse aggregates. Broken stone is 
generally used as coarse aggregates. For thin slabs, and walls, 
the maximum size of coarse aggregates should be limited to 
one third the thickness of the concrete section 
d) Water: Water to be used in the concrete work should have the 
following properties. 
1) It should be free from oils 
2) It should be free from acids or alkalies 
3) It should be free from Iron, Vegetables matter or other 
substance, which is likely to have adverse effect on 
concrete. 
4) It should be fit for drinking purpose 
Function of Water 
1. It acts as lubricant for fine and coarse aggregates. 
2. It acts chemically with cement to form binding paste with coarse 
aggregates and reinforcement. 
3. It is necessary to flux the cementing material over the surface of 
the aggregates. 
4. It is employed to damp the concrete in order to prevent them 
absorbing water vitally necessary for chemical action 
5. It enables the concrete mix to blow into moulds. 
 
6.2. Uses and types 
Uses of Concrete: 
1:2:2 - For heavy loaded R.C.C columns and R.C.C arches of long 
spans 
1:2:2 - For small pre cast members of concrete like fencing poles, 
telegraph poles etc. watertight construction.  
1:2:3 - For water tanks, bridges, sewers etc. 
1:2½:3½ - For foot path, concrete roads 
Concrete                                                                                    
  
1:2:4     - For general work of RCC such as stairs, beams, columns, 
slabs, etc 
1:4:8 /     
1:5:10   For mass concrete for heavy walls, foundation footings 
etc.  
 
6.3  Preparation of concrete mix: 
There are two types of concrete mixing 
(i) Hand mixing 
(ii) Machine mixing 
1. Hand Mixing: This method of mixing concrete is resorted to when 
the quantity if concrete to be used in a work is insufficient to warrant the 
necessity of machine. This is used with advantage in places where 
machinery cannot be used on account of their non-availability or in 
works near a hospital where the noise of machine is not desirable. Hand 
mixing is done on a clean, hard and impermeable surface. Cement and 
sand are first mixed dry with the help of shovels until the mixture attains 
a uniform colour. Aggregative are then added to this mixture and the 
whole mixture is then turned by shovels until the stone pieces uniformly 
spread throughout. After this, desired are quantity of water is poured into 
the heap from a can fitted with a rose. The mass is then turned until a 
workable mixture is obtained. It is advised to add 10% extra cement to 
guard against the possibility of inadequate mixing by this method. 
Page 5


CHAPTER-6 
CONCRETE 
Cement concrete is a mixture of cement, sand, pebbles or crushed rock 
and water. When placed in the skeleton of forms and allowed to cure, 
becomes hard like a stone. Cement concrete is important building 
material because of the following reasons. 
1. It can be moulded into any size and shape of durable structural 
member. 
2. It is possible to control the properties of cement concrete. 
3. It is possible to mechanise completely its preparation and placing 
processes. 
4. It possesses adequate plasticity for mechanical working. 
The cement concrete has the following properties 
1. It has high compressive strength 
2. It is free from corrosion 
3. It hardens with age and continues for a long time after concrete 
has attained sufficient strength 
4. It is proved to be economical than steel  
5. It binds rapidly with steel and it is weak in tension, steel 
reinforcement is placed in cement concrete at suitable places to 
take up tensile concrete or simply R.C.C. 
6. It forms a hard surface, capable of resisting abrasion stresses. 
This is called reinforced cement. 
Concrete                                                                             
  
7. It has tendency to be porous to avoid this proper grading & 
consolidation of the aggregates, minimum water-cement ratio 
should be adopted. 
6.1  Constituents - Requirements. 
 The main constituents of concrete are 
a) Cement / Lime: Before introduction of ordinary Portland 
cement, lime was used as cementing material. At present most 
of the cement concrete works in the building construction is 
done with ordinary Portland cement. But other special varieties 
of cement such as rapid hardening cement, high alumina 
cement are used under certain circumstances. The cement 
should comply with all standard specifications 
b) Fine Aggregates: The material, which is passed through 
4.7625mm B.S.test sieve, is termed as fine aggregates. Usually 
natural river sand is used as fine aggregates. But places where 
natural sand is not available economically, finely crushed stone 
may be used as fine aggregates.  
c) Coarse Aggregates: The material retained on 4.7625mm size 
B.S.test sieve is termed as coarse aggregates. Broken stone is 
generally used as coarse aggregates. For thin slabs, and walls, 
the maximum size of coarse aggregates should be limited to 
one third the thickness of the concrete section 
d) Water: Water to be used in the concrete work should have the 
following properties. 
1) It should be free from oils 
2) It should be free from acids or alkalies 
3) It should be free from Iron, Vegetables matter or other 
substance, which is likely to have adverse effect on 
concrete. 
4) It should be fit for drinking purpose 
Function of Water 
1. It acts as lubricant for fine and coarse aggregates. 
2. It acts chemically with cement to form binding paste with coarse 
aggregates and reinforcement. 
3. It is necessary to flux the cementing material over the surface of 
the aggregates. 
4. It is employed to damp the concrete in order to prevent them 
absorbing water vitally necessary for chemical action 
5. It enables the concrete mix to blow into moulds. 
 
6.2. Uses and types 
Uses of Concrete: 
1:2:2 - For heavy loaded R.C.C columns and R.C.C arches of long 
spans 
1:2:2 - For small pre cast members of concrete like fencing poles, 
telegraph poles etc. watertight construction.  
1:2:3 - For water tanks, bridges, sewers etc. 
1:2½:3½ - For foot path, concrete roads 
Concrete                                                                                    
  
1:2:4     - For general work of RCC such as stairs, beams, columns, 
slabs, etc 
1:4:8 /     
1:5:10   For mass concrete for heavy walls, foundation footings 
etc.  
 
6.3  Preparation of concrete mix: 
There are two types of concrete mixing 
(i) Hand mixing 
(ii) Machine mixing 
1. Hand Mixing: This method of mixing concrete is resorted to when 
the quantity if concrete to be used in a work is insufficient to warrant the 
necessity of machine. This is used with advantage in places where 
machinery cannot be used on account of their non-availability or in 
works near a hospital where the noise of machine is not desirable. Hand 
mixing is done on a clean, hard and impermeable surface. Cement and 
sand are first mixed dry with the help of shovels until the mixture attains 
a uniform colour. Aggregative are then added to this mixture and the 
whole mixture is then turned by shovels until the stone pieces uniformly 
spread throughout. After this, desired are quantity of water is poured into 
the heap from a can fitted with a rose. The mass is then turned until a 
workable mixture is obtained. It is advised to add 10% extra cement to 
guard against the possibility of inadequate mixing by this method. 
2. Machine Mixing: - The machine used for mixing concrete is termed 
as concrete mixer. Two types of concrete mixers are in common are 
1. Continuous mixers 
2. Batch mixers 
Continuous mixers are employed in massive construction 
where large and continuous flow of concrete is desired. The 
process of feeding the mixing is more or less automatic. The 
machine requires careful supervision so as to obtain the concrete 
mix of desired consistency. 
In batch type of concrete mixer. The desired proportion of 
materials are fed into the hopper of a drum in which the materials 
get mixed by the series of blades or baffles inside the mixer. 
Batch mixers are further two types  1. Tilting drum type   2. 
closed drump type. In the first type, components are fed in the 
revolving drum in a tilted position and after sometime the 
concrete mix is discharged by tilting the drums in the opposite 
direction. In the latter type the drum remains rotating in one 
direction and emptied by means of hopper which tilts to receive 
the discharge. 
While using the mixer, coarse aggregates should be fed 
first, sand and cement should be put afterwards. In this revolving 
state, the components get mixed while water is poured with the 
help of can. The concrete should be for atleast 2 minutes, the time 
being measured after all the ingredients including water have 
been fed into the drum. The batch type concrete mixer is as 
shown in the fig 6.1.