Le-Chatelier's Apparatus- Soundness Test of Cement

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• Aim: To find out the Soundness of Cement.
• Apparatus: Le- Ch-atelier's Apparatus, Weighing balance, measuring cylinder, trowel, mixing pans heater, thermometer.
• Standard Reference:  Test is performed as per IS: 4031 (Part - 1) - 1988,

• Theory: 

Cement of good quality does not contain the impurities like free lime, magnesia and sulphates, so this should be checked before use.

When it contains the impurities named above, it can expand after reacted with the water, which will result in the unwanted results like, cracking, unwanted expansion of the dimensions and lower strength. 

Le-Ch-atelier's Apparatus is the standard apparatus prescribed as per IS:5514 -1969 to check the presence of the impurities in cement.  Cement is said to be sound when the expansion is below 10 mm.

• Procedure: 

Prepare a cement paste of 78% of standard consistency of the cement, and fill it into the split brass cylinder.

Cover the top and bottom of the cylinder and put it in water at 27 degrees Celsius for 24 hours.

After 24 hours, measure the separation between the two indicators at their pointed ends.

Then heat the whole water and immersed cylinder with paste up to a boiling temperature in 30-35 minutes and then boiling  for 3 hours.

After cooling it down, again measure the separation between the two pointers.

• Calculations: 

Let the reading before putting the cement paste into the boiling temperature  = L1

                         After three hours of hot water immersion = L2

                  Expansion = L2-L1

• Result: As the value of expansion is (Less/More)..... than 10 mm so the cement is .........(Sound/Unsound).

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Tensile strength of Cement - Briquette Mould Test

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• Briquette's mould machine is an apparatus which is used to form the briquettes of the cement mortar which are used to find out the tensile strength of the cement. 

These briquettes are of standard dimensions are constructed by pouring in the fresh cement mortar into the briquette mould and then followed by required curing.

• After the curing, these mortar briquettes are tested for the amount of tensile load they can bear before getting failed. This load is the tensile strength of the cement. You have to test more than 3 briquettes, some suggest 6 nos. of them to get the desired results. Average of these results is taken as the final value.

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Relevant Books:

  

BIS: 712 -1984 Classification of Lime

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Introduction- Lime as a cementing material:

Lime has been used as a cementing material since the ancient times  in India and abroad. Ancient Egyptians and Romans used this material for various constructional processes. Even in India, various engineering structures like palaces, bridges, temples etc were constructed with lime mortar and still are in shape.

After the invention of cement in 1824 lime has been replaced by the cement to a large extent, however it is still used at certain places, like for the repairing of the structures which were originally built with the lime mortar and at the places where lime is freely available and cement has its acute shortage.

• Classification of Lime:

Broadly lime is classified into three categories:

(1) Fat Lime   (2) Hydraulic lime  (3) Poor Lime

(1) Fat Lime/Pure Lime:-  Fat lime is also known as pure lime, white lime or rich lime, this is manufactured using the purest form of the limestone. It is popular with its name as fat lime since its volume is increased to about 2 to 2.5 times its originally volume after getting slaked. It slakes vigorously.

(2) Hydraulic Lime: This lime has the hydraulic property, means it can set under the water also. It contains clay and some amount of ferrous oxide also. This is also known as water lime.Depending upon the amount of clay hydraulic lime is classified into further three categories:

(a) Feebly hydraulic lime

(b) Moderately hydraulic lime

(c) Eminently hydraulic lime

Increase in the percentage of clay makes the slaking difficult and thus increases the hydraulic property of lime. With about 30 per cent of clay lime resembles the color of cement.

The color of fat lime is not white therefore fat lime looks more sanitary than the hydraulic lime.

(3) Poor Lime: Poor lime contains more than 30 percent of clay therefore it is also known as impure lime. It slakes very slowly and also does not dissolve into water. It has poor binding property and its color is muddy white.

This lime forms very poor mortar and so such lime can be used for inferior types of work or at places where good lime is not available.

BIS: 712 - 1984 classifies lime under six categories, namely Class A, Class B, Class C, Class D, Class E and Class F.

Class A lime is used for structural purposes because it is eminently hydraulic lime and has the property of setting even in the absence of air. It has to be supplies in the hydraulic form only. Its minimum strength with lime sand mortar of proportion(1:3) by weight at the end of 14 days and 28 days should be respectively 1.75 N/mm2  and 2.80 N/mm2.

Class B lime is the semi-hydraulic lime which is used for mortars for masonry and it can be supplied either as quick lime or as hydrated lime. Its minimum compressive strength with lime sand mortar of proportion(1:3) by weight at the end of 14 days and 28 days should be respectively 1.25 N/mm2 and 1.75 N/mm2.

Class C lime is the fat lime which is used mainly for finishing coat in plastering, whitewashing and with suitable admixture such as surkhi or any other pozzolanic material to produce artificial hydraulic mortars. It is to be supplied in hydraulic or quick form.

Class D lime is the magnesium or dolomitic lime which is used for finishing coat in plastering, whitewashing, etc. It is to be supplied in the hydrated or quick form.

Class E lime is the kankar lime and is used for the masonry works, it is to be supplied in the hydraulic form only.

Class F  lime is also known as Siliceous dolomitic lime which is used for undercoat and finishing coat of plaster. It is to be supplied in the hydrated or quick form.

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Vicat's Apparatus - Consistency and Setting Time of Cement

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• Vicat's Apparatus 

is used to find out the consistency, initial setting time and final setting time of the cement. In the normal consistency test we have to find out the amount of water to be added to the cement to form a cement paste of normal consistency.

 Vicat's apparatus consists of an arrangement to hold the plunger of 10 mm diameter and two other needles which are made to freely fall into a mould filled with the cement paste and the amount of penetration of the needles of plunder can can be noted using the vertical graduations from 0 mm to 50 mm.

•   Consistency Test: 

To find out the consistency test you have to take a sample of dried cement of about 400 g weight which must pass through the 90 micron IS Sieve. Then mix in it about 25% of  water by weight a form a uniform paste withing 2 minutes of time.

 Fill the Vicat's mould with this paste and make the 10 mm plunger fixed to the arrangement to just touch the top surface of the cement paste. Make it freely fall and note the amount of penetration.

When the penetration is of about 42 to 45 mm or when the reading on the vertical graduation is about 5mm to 7mm that means cement is of normal consistency. Generally the water required to form a paste of normal consistency is 30%.

Vicat's Apparatus with all the accessories

• Initial Setting Time: 

Initial time of Cement is the time required by the cement for its early setting. Cement must be applied to the place of its use before its initial setting so it is necessary to find out the initial setting time that is available with us.

Vicat's apparatus is the standard apparatus used to find out this initial setting time. Look in the figure above, there is a needle of diameter 1 mm. This needle is fixed to the movable rod weight.

The cement paste of normal consistency is formed and is filled in the mould. Now the needle is made just touch the top surface of the cement paste and made freely fall in it. Initial setting time is the time from the mixing of the cement and the water to the time when the penetration of the needle is just above 5 mm from the bottom of the base plate or mold.

Generally the initial setting time of the ordinary Portland cement is 30 minutes. For Slow setting cement this time may be increased by adding the admixtures or Gypsum up to 60 minutes.

Similarly, for the final setting time we have to use the third needle which has a enlarged  5mm hollow cylindrical base. The final setting time is the time from the mixing of the water to the time when this needle just makes the impression on the surface of the cement but do not penetrate into it. Generally the final setting time of cement (OPC) is 10 hrs to 12 hrs.

 

Photograph of the Vicat's Apparatus

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Wet process - Cement manufacturing -Flow Diagram

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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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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:


  

Bricks Classification and Specification (IS-1077:1992)

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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: