Friday, August 30, 2013

Wet process - Cement manufacturing -Flow Diagram

Helllo,

Cement manufacturing is done in the following three major processes:
(a) Mixing
(b) Burning
(c) Grinding

(a) Mixing: Mixing can be done in two ways: (1) dry method and    (2) wet method.
Dry method was used in the early periods in between 1913 to 1982. After 1982 all the cement manufacturing plants in India are equipped with the technologies of Dry process, since this is more energy efficient and environment friendly method of cement manufacturing. In this post I am sharing with you the flow diagram of the wet process of the mixing because it is in the syllabus of the many Diploma courses.
Wet Process - Manufacturing of Cement
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Monday, August 26, 2013

Functions of various Constituents of Cement

Functions of various cement ingredients:

  •      Lime (CaO) :This is the important ingredient of cement and its proportion is to be carefully maintained.  The lime in excess makes the cement unsound and cause the expansion and disintegration of the cement. On the other hand if the lime is deficient it will decrease the strength of the cement and will cause it to set quickly.
  •  Silica (SiO2) :   This is an important ingredient of the cement as it imparts strength to the cement due to formation of di-          calcium silicate and tri-calcium silicate. If silica is present in excess quantity its setting time is prolonged          however strength is increased.
  •  Alumina (Al2O3) :      This ingredient imparts quick setting property  to the cement. It acts as a flux and it lowers the clinkering        temperature. However the high temperature is essential for the formation of a suitable type of cement and       hence in alumina should not be present in excess amount as it weakens cement.
  • Calcium Sulphate (CaSO4) :This ingredient is in the form of gypsum and its function is to increase the initial setting time of cement.
  • Iron Oxide (Fe2O3) :This imparts color, hardness and strength to the cement.
  • Magnesia (MgO) :This ingredient, if present in small amount, imparts hardness and color to the cement. A high content of magnesia makes the cement unsound.
  • Sulphur(S) :A very small amount of sulphur is useful in making sound cement. If it is in excess, it causes cement to become unsound.
  • Alkalies :The most of the alkalies present in raw materials are carried away by the flue gases during heating and the cement contains only a small amount of alkalies. If they are in excess in cement, they cause a number of troubles such as alkali-aggregate reaction, efflorescence and staining when used in concrete, brickwork or masonry mortar.

Harmful Constituents of Cement:
The presence of the following two oxides adversely affects the quality of cement:
        1) Alkali Oxides K2O and Na2O    2)    Magnesium oxide MgO.

    If the amount of alkali oxides exceeds 1 per cent, it leads to the failure of concrete made from that cement.     Similarly, if the content of magnesium oxide exceeds 5 per cent, it causes cracks after mortar or concrete        hardens. It is due to the fact that magnesium oxide, burned at a temperature of about 1500 degree            Celsius, slakes very slowly, when mixed with water.

Reference:


  

Thursday, August 22, 2013

Bricks Classification and Specification (IS-1077:1992)


Hi,

According to Indian standard(IS: 1077: 1992) bricks are classified into the following categories:

Classes of common burnt clay bricks:

       Class Designation             Average compressive strength not less than[ (N/mm^2) (kg/cm2)

  1. 35                                               35            350
  2. 30                                              30                300
  3. 25                                              25             250
  4. 20                                              20                200
  5. 17.5                                           17.5          175
  6. 15                                              15                150
  7. 12.5                                           12.5              125
  8. 10                                               10                100
  9. 7.5                                              7.5               75
  10.  5                                                5                   50
  11.  3.5                                            3.5                35


General Quality



  • Bricks shall be hand moulded or machine moulded and shall be made from suitable soils. They shall be from from cracks and flaws and nodules of free lime. 
  • Bricks with height of 90 mm or 70 mm will be moulded with a frog of  10 mm to 20 mm deep on one of its flat sides. Bricks with height of 40 mm or less, and as well those made by extrusion process  may not be provided with frogs.
  • The bricks shall have smooth rectangular faces with sharp corners and shall be uniform in colour

.For other detailed dimensions and tolerance criteria please visit the IS 1072 : 1992

In some books the classification of the bricks is given as below:

General classification:

(1) First Class Bricks
(2) Second Class Bricks
(3) Third Class Bricks

First class bricks: 

Specifications: 
(1) Plain surface, sharp edges and size with tolerance in dimensions +-3%
(2) Uniform red or brownish colored.
(3) High crushing strength, not less than 10.7 N/mm2
(4) Machine moulded
(5) Efflorescence- NIL
(6) Water absorption less than 15%.
USE: They are used for the exterior wall brick works, short columns and arches.

Second class bricks:


Specifications:
(1) Slightly uneven faces and edges with tolerance in dimensions +-8%
(2) Uniform colored but may be slightly over burnt.
(3) High crushing strength, not less than 7 N/mm2
(4) Hand moulded
(5) Efflorescence- Little
(6) Water absorption less than 20%.
USE: They are used for internal walls and compound walls.

Third class bricks:


Specifications:
(1) May be distorted with blunt edges.
(2) Over burnt or under burnt and non uniform color.
(3) High crushing strength, not less than 3.5N/mm2
(4) Hand moulded
(5) Efflorescence- Large
(6) Water absorption less than 25%.
USES: They are used for flooring, paving, small brick foundations and brick bat lime concrete(B.B.L.C.).

Relevant books:   



  

Drying, Burning of Bricks- Bull's Trench Kiln, Hoffman's kiln

Hello!






The Manufacturing of bricks is consists of  following processes:


  1.  Preparation of brick clay
  2.  Moulding of Bricks
  3.  Drying
  4. Burning of bricks
First two operations are already discussed in the previous two parts of the article in the same blog. In this blog I am going to discuss with you the Drying and the Burning of the bricks:

  • Drying Of Bricks: 

Drying of the bricks at lower temperature is done to strengthen the bricks to have sufficient strength so that they do not crack or crumble while holding and carrying them in hand.
Finally bricks are to be stacked in the kiln, but they must possess the sufficient strength to maintain their shape while the transportation and loading operations, so drying of the bricks is important process. Drying of the bricks can be done in two ways:


(a) Natural Drying: Natural drying is done by putting the bricks in the under the air circulation, generally avoided to direct Sun-light.


(b) Artificial Drying: In artificial burning bricks are put under a temperature of about 120 degrees Celsius in a tunnel like structure where arrangements are there to maintain the temperature.


 These tunnel kilns can be period or continuous. In periodic kilns the bricks are dried periodically but in the continuous they are put continuously at one end and dried bricks are taken out at the other end.


  • Burning of Bricks: 

Bricks are burned at high temperature to gain the strength, durability, density and red color appearance.
All the water is removed at the temperature of 650 degrees but they are burnt at an temperature of about 1100 degrees because the fusing of sand and lime takes place at this temperature and chemical bonding takes between these materials after the temperature is cooled down resulting in the hard and dense mass.

 Bricks are not burnt above this temperature because it will result in the melting of the bricks and will result in a distorted shape and a very hard mass when cooled which will not be workable while brickwork. Bricks can be burnt using the following methods:
(a) Clamp Burning
(b) Kiln Burning

  •   Clamp Burning: 

Clamp is a temporary structure generally constructed over the ground with a height of about 4 to 6 m. It is employed when the demand of the bricks is lower scale and when it is not a monsoon season.

 This is generally trapezoidal in plan whose shorter edge among the parallel sides is below the ground and then the surface raising constantly at about 15 degrees to reach the other parallel edge over the ground.

 A vertical brick and mud wall is constructed at the lower edge to support the stack of the brick. First layer of fuel is laid as the bottom most layer with the coal, wood and other locally available material like cow dung and husk.

Another layer of about 4 to 5 rows of bricks is laid and then again a fuel layer is laid over it. The thickness of the fuel layer goes on with the height of the clamp.

After these alternate layers of the bricks and fuel the top surface is covered with the mud so as to preserve the heat.
Fire is ignited at the bottom, once fire is started it is kept under fire by itself for one or two months and same time period is needed for the cooling of the bricks. 

  • Disadvantages of Clamp burning: 

  1. Bricks at the bottom are over-burnt while at the top are under-burnt. 
  2. Bricks loose their shape, and reason may be their descending downward once the fuel layer is burnt.
  3. This method can not employed for the manufacturing of large number of bricks and it is costly in terms of fuel because large amount of heat is wasted.
  4.  It can not be employed in monsoon season.


  • Kiln Burning: 

Kiln is a large oven used for the burning of bricks. Generally coal and other locally available materials like wood, cow dung etc can be used as fuel. They are of two types:
(a) Intermittent  Kilns.
(b) Continuous Kilns.


  • Intermittent Kilns 

are also the periodic kind of kilns, because in such kilns only one process can take place at one time. Various major processes which takes place in the kilns are:

Loading, unloading, Cooling, and Burning of bricks.

There are two kind of intermittent kilns:
(i) Up-draught Intermittent Kilns
(ii) Down draught Intermittent Kilns

Down draught kilns are more efficient because the heat is utilized more by moving the hot gases in the larger area of the kiln. In up draught kilns the hot gases are released after they rise up to chimney entrance.

  • Continuous Kilns: 

These kilns are called continuous because all the processes of loading, unloading, cooling,  Heating, pre-heating take place simultaneously. They are used when the bricks are demanded in larger scale and in short time. Bricks burning is completed in one day, so it is a fast method of burning.
There are two well known continuous kilns:

  • Bull's Trench Kiln: 

Bull's trench kiln consist of a rectangular, circular or oval plan shape. They are constructed below the ground level by excavating a trench of the required width for the given capacity of brick manufacturing.

This Trench is divided generally in 12 chambers so that 2 numbers of cycles of brick burning can take place at the same time for the larger production of the bricks. Or it may happen that one cycle is carried out at one time in all the 12 chambers by using a single process in the 2-3 chambers at the same time.

The structure is under-ground so the heat is conserved to a large extent so it is more efficient.  Once fire is started it constantly travels from one chamber to the other chamber, while other operations like loading, unloading, cooling, burning and preheating taking place simultaneously.

Such kilns are generally constructed to have a manufacturing capacity of about 20,000 bricks per day. The drawback of this kiln is that there is not a permanent roof, so it is not easy to manufacture the bricks in the monsoon seasons.

  • Hoffman's Kiln:

The main difference between the Bull's trench kiln and the Hoffman kilns are:

  1.  Hoffman's kiln is an over the ground structure while Bull's Trench Kiln is an underground structure.
  2. Hoffman's kiln have a permanent roof while Bull's trench Kiln do not have so it former can be used in 12 months a year to manufacture bricks but later is stopped in the monsoon season.

Hoffman's kiln is generally circular in plan, and is constructed over the ground. The whole structure is divided into the 12 chambers and all the processes takes place simultaneously like in Bull's trench Kiln.

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Wednesday, August 21, 2013

Manufacturing of Bricks -part II (Moulding and Drying)

Hi,

Preparation of the brick clay is already discussed in the earlier post, is this post I am going to discuss the second operation of brick manufacturing i.e. Moulding

Moulding: Moulding of the bricks into the proper shape and size can be done manually with the hands or it can be done with the help of machines. Hand moulding can take more time as compare to the machine moulding. Hand moulding is employed when the cheap labor available to us and less numbers of bricks are required to be manufactured and machine moulding can be employed when the labor is costly and the large numbers of bricks are required. Machine moulding is more accurate than the hand moulding.

Hand Moulding: It is again can be done in the following two manners:
(a) Moulding on the ground.
(b) Moulding on the table

In hand moulding on the ground following instruments are used:
       (a) Mould
       (b) Pallet
       (c) Strike
       (d) Clay
Mould of the size about 10 to 12% greater dimensions than the standard brick size for the allowance of the shrinkage of the brick, is used which can be made either of the seasoned wood or with the steel plates and the angle. Pallet is used to in-script the frog in the bricks. Frog is necessary for the proper bonding of the bricks and for the advertisement of the manufacturer.
Strike is used to strike off the excess clay from the top of the mould after it is filled with the brick. Following procedure is followed to carry the moulding of the bricks on the ground:
 First of all a dried plane ground is chosen on which dry sand is sprinkled to check the adherence of the brick clay to the ground. mould with the pallet is put on the ground. Clay is taken in lumps in hands and it is slashed on the mould with force so that every corner of the mould is filled with the clay. Excess of clay is struck off with the strike which can be wooden or wired. Mould is turned upside down and it is removed leaving the moulded brick in its place. It is kept at a near place and whole procedure is followed again.

Hand moulding on the table: Here the moulding is done on the table which is generally of the size 2 m * 1m. It may take somewhat longer time than the ground moulding.

Machine Moulding : As the name suggests, machine moulding is carried out with the help of a machine. It produces them in faster rate and in a better shape than that in the hand moulding.

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Relevant Books:


  

        

Sunday, August 18, 2013

Manufacturing of Bricks - Part I (Preparation of brick clay)

Hello there,
how you doing? Please read on:

Manufacturing of bricks
Selection of the brick field:
Selection of the brick field where you have to establish your small scale  industry is done correctly when you check the following things:


  1.  Site should be well connected with the road transportation facilities so as to transport your product.
  2. There should be plenty of the clay available which is to be used for the manufacturing of the bricks.
  3. All the necessary facilities for the workers should be checked and made available before starting the work.
  4. Site should be of plane topography.
  
After the site selection and establishing the plant you can carry the manufacturing process in the following four processes:

  •  Preparation of the brick earth
  •  Moulding
  • Drying
  • Burning


  • Preparation of the brick clay:  
Preparation of the brick clay can be done by completing the following processes:
(1) Un-soiling
(2) Digging
(3) Cleaning
(4) Weathering
(5) Blending
(6) Tempering

(Ref: Civil Engineering materials by Rangawala)
To be continued.....     

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Relevant Books:


  

Wednesday, August 14, 2013

Composition of a Good Brick Earth

Hello There,
How you doing? Well, here is what you searched for:


Composition of a good brick earth:

Following are the constituents of a good brick earth:

(1)    Alumina (Al2O3):

 It is the chief constituent of a good brick earth. A content of about 20% to 30% is necessary to form the brick earth of a good quality. It imparts plasticity to the earth so it helps in the moulding of the brick earth. 
If alumina is present in excess with inadequate quantity of sand then the raw bricks shrink and warp during drying, on burning they become too hard. So it is important to have an optimum content of alumina.

(2)    Silica (SiO2):  

It exists in the brick earth either free or combined. As free sand it is mechanically mixed with clay and in combined form it exists in chemical composition with alumina. A good brick earth should contain about 50% to 60% of silica. 


The presence of this constituent prevents the shrinkage, cracking and warping of raw bricks. It thus imparts uniform shape to the bricks. The durability of bricks depends upon proper composition of silica in brick earth. The excess of silica destroys the cohesion b/w particles and brick become brittle.

(3)    Lime(CaCO3):

A small quantity of lime not more than 5% is desirable in good brick earth. It should be present in very fine state, because even small particles of size of a pin-head can result in the flaking of the brick. 
The lime prevents shrinkage of the raw bricks, sand alone is infusible, but it slightly fuses at kiln temperature in presence of lime. Fused sand acts as a hard cementing material for brick particles. 


The excess of lime causes brick to melt and therefore its shape is lost.  The lumps of lime turns into quick lime (CaO) after burning and this free lime can later react with water  to form slaked lime. This process is called slaking it may result in splitting of the brick into pieces.

(4)    Oxide of Iron (Fe2O3):

Iron oxide performs two functions, first it helps in fusing of the sand like lime and second it provides the red color to the bricks. It is kept below 5 to 6% because excess of it may result in the dark blue or black color of brick.

(5)    Magnesia:

It is used to provide a yellow tint to the bricks. Its content is only about 1% or less.



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I hope the article was helpful please, contribute to make this article more useful!

Relevant Books:


  

Tuesday, August 13, 2013

Introduction of Bricks - Brickwork superior or inferior to stonework??

Bricks:
General: The bricks are manufactured by moulding the clay in the rectangular blocks of uniform size and then by drying and burning these blocks. Bricks are easy to work with because of their uniform size and light weight. They do not require the dressing and the brickwork can be done by the non-skilled workers. Stones are not easily available so if clay is available bricks can be manufactured and utilized.
The bricks are very old Civil engineering material which were utilized in many historical buildings of the Roman Empire and also in the Chinese Civilization burnt bricks and Sun dried bricks were utilized to construct the Great Wall of China (210 B.C.). Wood was used earlier but due to its fire catching risks it was replaced with the bricks. The great fire of the London in 1666, converted the city from the wooden city to the brick city.
According to the data provided in a book titled “Engineering Materials” by India has more than about 45000 local kilns and has a capacity of about 10,000 crores of brick production. Further it says that this sector is un-organized so there are not many improvements in the methods of manufacturing and technology utilized for the manufacturing of bricks. The fuel cost is high so one cannot care much about the quality of the bricks.
Is brickwork better than stonework?
It is superior to stone work in the following ways:
  • Bricks are easily available at many places but building stones are not easily available everywhere.
  • The brickwork can be can out by the less skilled workers so the cost of construction can be reduced due to the lower wages to be paid.
  • Light weight bricks can be easily lifted but other materials requires mechanical ways.
  • Bricks can be manufactured to resist higher temperatures as compared to the stones.
  • Similarly higher durability bricks can be manufactured which can prove to be more durable than the stones.
  • Bricks need thin mortar joint so the structure becomes more durable.
  • Connections and openings can be constructed easily in case of the brickwork than stonework.
Brickwork is inferior to the stone work in the following ways:

  • Bricks absorb more moisture as compared to the stone, so it may result in the dampness of the building.
  • For monumental structures the stone create a solid appearance which bricks cannot create, in those cases the stones are useful than the brickwork.
  • The stonework has more strength.
  • The stone work is cheaper at places when the stones are easily available.

Monday, August 12, 2013

Uses of Stones

Uses of Stones:
The stones are used in the construction of buildings from the ancient times and most of the ancient temples, forts and mosques of India were built with stones as the major material. The Taj Mahal, Red Fort, Jama Masjid, Parliament house and Rashtrapati Bhawan at Delhi and various other prominent structures spread throughout the length and breadth of our country furnish us the awesome examples of uses of the stone as building material. At present, they are largely used as the basic material for the manufacturing of the other construction materials like concrete, bricks etc.
Following are the various uses to which stones are employed:-
  1. Structural elements: The stones are used for foundations, walls, columns, lintels, roofs, floor, damp proof courses etc.
  2. Facing: The stones are adopted to give massive appearance to the structure. The walls are of bricks and facing is done in stones of desired shades. This is known as the composite masonry.
  3. Paving: The stones are used to cover floor of buildings of various types such as residential, commercial, industrial etc. They are also adopted to form paving of roads, footpaths etc.
  4. Basic Material: The stones are disintegrated and converted to form a basic material for cement concrete, murum of roads, calcareous cements, artificial stones, hollow blocks etc.
    Miscellaneous uses : In addition to the above uses the stones are also used as:
  1. Ballast for railways,
  2. Blocks in construction of bridges, piers, abutments, retaining walls, light houses, dams etc.
  3. Flux in blast furnaces.
Stones are losing their popularity as the building material because of the following reasons:

  1. The dressing of stones proves to be tough, laborious and time consuming.
  2. The stones of desired strength and quality are not easily available at reasonable rates, especially in plain areas.
  3. The alternatives to stones namely, R.C.C. and steel have proved to be stronger, less bulky, more durable and more suitable for present day construction of multistory and important buildings.
  4. The structures constructed of stones cannot be rationally designed as in case of R.C.C. or steel structures.   

Friday, August 9, 2013

General characteristics of marble, Kota stone, granite, basalt etc

You can/may find here the following stone's characteristics discussed below:
(1) Marble (2) Limestone (3) Sandstone (4) Granite (5) Basalt (6) Slate  (7) Kota Stone

(1) Marble: 

A view of Taj Mahal(built with Marble)from the bank of the Yamuna river.
(a)Marble is a metamorphic rock formed    after after the metamorphism of the limestone. Under high temperature and pressure, re-crystallization of  calcite and dolomite takes place to a compact structure.
(b) It is largely used for the ornamental, carvings and molding works.
(c) It is available in many color from white to black including, red, green, yellow, blue and gray.
(d) It is porous to some degree and more after getting the polish.
(e) It has lustrous and glossy appearance.
(f) It is used as flooring, wall linings, table roofs, bath tubs, and sculpture making etc.
(g) Limestone(CaCO3) being the main compound it is liable to acid attacks, if MgCO3 is the major constituent then it is more acid resistant.
(h) Its specific gravity is 2.72
(i) Its crushing strength varies from 50 to 60 MN/m2

(2) Limestone:

(a)Limestone is a sedimentary and calcareous variety of rock. With CaCO3 it may contain MgCO3, and if both are present in equal proportion then it is known as dolomite.
(b) Generally it has  a stratified structure.
(c) It is available in few colors.
(d) It is used in the blast furnaces of many manufacturing industries like cement and bricks.
(e) It is used to get the pure lime.
(f) It is not suitable for use near industrial areas for building construction due to its chemically reactive property.
(g) Its specific gravity is 2.6.
(h) Its crushing strength is 52 MN/m2.

(3) Sandstone: 

(a) It is a type of rock which has the quartz or the sand bound together with the cementing minerals like mica, feldspar etc.
(b) It is a sedimentary rock
(c) Its color depends upon that of the feldspar.
(d) It can be used as a road metal if the higher quality stones like basalt and granite is not available.
(e) It is fire resistant.
(f) Its specific gravity is 2.25
(g) Its crushing strength varies 35 to 40 MN/m2.


(4) Granite: 


(a)It is a igneous rock of the plutonic variety.
(b)It contains the feldspar in abundance.
(c)It has a coarse grained crystalline structure.
(d)It is very hard, tough, durable and has a high specific gravity,
(e) It is used as a road metal, fine grained granite can be used for the masonry work.
(f) It has less fire resistance, so it cracks at high temperatures.
(g) It is best suited for industrial towns.
(h) The life of granite is over 300 years.
(i) Its specific gravity is  2.64.
(j) Its crushing strength varies 110 to 140 MN/m2.

(5) Basalt:

(a)It is a kind of igneous rock of the volcanic variety
(b) It possess a very fine grained and almost non crystalline structure.
(c) It is tougher and has more specific gravity than the granite.
(d) It is non water absorbent.
(e) Crushed basalt is highly used as road metal.
(f) Its specif gravity is 2.96.
(g) Its crushing varies from 70 to 80 MN/m2

(6) Slate:  

(a)Slate is a metamorphic rock obtained after the metamorphism of the shale which is a sedimentary             rock of the argillaceous variety.
(b) It is a foliated rock and can be split  into thin sheets.
(c)  It is available in grey or dark blue color.
(d)  It is widely used as the roofing material in the hilly areas, cisterns and urinal separations.
(e) It is non water absorbent and smooth surfaced.
(f) Its specific gravity is 2.8.
(g) Its crushing strength varies from 60 to 70 MN/m2.

(7) Kota Stone:

(a) Kota stone is a kind of the limestone which is available in the Kota district of the Rajasthan.
 (b) It has fine grained structure, so it can be polished and is famous as the flooring, wall lining, paving material.

Saturday, August 3, 2013

Types of Cement

Cement is a Civil Engineering Material which is worldwide used to form concrete and mortar and other soil stabilization works. It is  possible after the invention of the cement to get the structures with high strength and of various attractive architectural shapes at the same time. The strength of cement depends on its constituents and their relative proportions.
1.Ordinary Portland Cement:
Ordinary Portland Cement(OPC) is used for the normal concrete works. It has cohesive and adhesive properties when mixed with water. After the evaporation of water it forms a solid mass. OPC manufactured by burning the following materials in a definite proportion:
(a) Siliceous Materials 
(b) Argillaceous Material (containing clay)
(c) Calcareous material (Containing Lime) 
The mixture of the above constituents is burnt to a temperature of about 1400 degrees celcius in the Rotary kiln which results in the formation of the clinker.  The clinkers so obtained are cooled and crushed to form the powder form which is known as cement. Cements of different kinds are obtained by mixing the above constituents in different proportions.
Constituents of OPC : 
(i) Lime : 60% to 67%
(ii) Silica: 17% to 25%
(iii) Alumina: 3% to 8%
(iv) Iron Oxide: 0.5% to 6%
(v) Magnesia: 0.1% to 4%
(vi) Soda and Potash : 0.2% to 1%
(vii) Sulphur tri-oxide: 1% to 2.75%
(viii)  Free lime: 1% to 1%
Cement constitutes chemical compounds formed after the burning of the above mentioned ingredients. The main constituents found in cement are as follows:
(1) Tri-Calcium Silicate (C3S)
(2) Di-Calcium Silicate(C2S)
(3) Tri-Calcium Aluminate (C3A)
(4) Tetra calcium Aluminoferrate (C4AF)
About 70% to 80% of cement is contributed by the C3S and C2S which are responsible for the strength of the concrete. C3S or Tri-calcium Silicate has the property to hydrate rapidly so mainly it is responsible for the early strength of the cement and also responsible for the ultimate strength of cement.
Di-Calcium Silicate has the property to hydrate slowly and provides strength after a period of seven days. Tri-calcium Aluminate also helps in gaining early strength due to early hydration but it is said to retard the ultimate strength, and is susceptible to the alkali and salts attacks.
Tetra-calcium alumino ferrate do not provide any strength to the cement and is said to be an unwanted compound in the cement.
2.Rapid Hardening Cement (IS:804)

This is manufactured in the similar manner as we do OPC, however it differs in its constituents, it contains more lime and is burned under a better controlled temperature over a longer time. The clinkers are ground to much finer extent. The quick rate of gain of the early strength is due to the higher content of tri-calcium silicate.  It gains the same strength in 3 days which OPC gains in 7 days for the same water cement ratio, and it gains the strength in 7 days what the OPC gains in 28 days. Advantages of using this type of cement is when the shuttering is to be removed early on to save the time, it is best.
Second it is best for the cold regions, where the frosting conditions occur. In case of roads it can be used to open the road to traffic at lower time period.
3.Low Heat Portland Cement(IS: 269)
In the mass concrete structures like Dams, retaining walls and abutments, if we use the normal cement which generates a large amount of heat(about 80 cal/gm at the end of 3 days), will result in the shrinking of the concrete and may affect the water tightness of the structure. Low heat Portland cement is specifically made for such uses because it generates a heat of about 75 cal/gm at the end of 28 days. Its setting rate is slower than the OPC. It is due to the fact that it contains low percentage of C3S and C3A, which are responsible for the early strength strength of concrete. So its strength is less than OPC in the early days but with the time it gains the same strength as that of the OPC. To ensure the rate of strength code recommends a specific surface requirement of 3200 cm^2/gm.
                                                 4. Portland Blast Furnace Slag Cement(IS: 455)
This cement is manufactured by mixing the blast furnace slag with the OPC clinkers. The properties of the cement are not affected by the blending of the blast furnace cement however it enhances its properties, but the content of the blast furnace slag cement is kept less than 65%. Blast furnace slag has latent hydraulic property which is highly activated when mixed with the cement clinkers. This cement can be used almost everywhere where the OPC is used and in addition to that it can be used in the huge mass concrete structures like dams, retaining walls, foundations and abutments of bridges. This cement has a good sulphate resistance and is very suitable for use in constructions in sea water.
                  5. Portland Pozzolana Cement (IS: 1489)
This cement is made either by blending and grinding the OPC cement clinkers and Pozzolana or by intermixing the OPC and fine pozzolana. Intergrinding must be preferred because it forms a uniform composition while blending forms non uniform composition. The blending should be preferred only when the uniform blending is assured by some mechanical process.  Content of Pozzolana varies from 10 % to 25% by weight of cement. Pozzolana in itself do not have the cementing properties but it forms the cementing material with the lime. When mixed with OPC it reduces the amount of free lime in cement and therefore it reduces the chances of the chemical attacks. It also lowers the heat of hydration and resists the sulphate attacks and was popularly used in the construction of the Bhakra Dam.

Garsa Stone -A Construction Material found in Kullu

Hi, Garsa is a place near to Bajaura, Bhunter at a distance of about 8 km from Bajaura. Recently I was nearby to this place and was told a...