HOW TO PERFORM COMPRESSIVE STRENGTH TEST OF CEMENT(IS:4031-PART 6-1988) ?

Compressive strength of cement is determined by performing the compressive strength test on mortar cubes compacted by vibration machine. For the preparation of cement mortar, Standard sand (IS:650) is used. The specimen is prepared in the form of cubes 70.6 mm x 70.6 mm x 70.6 mm.

OBJECTIVE

To determine the compressive strength of mortar cubes (standard).

APPARATUS

• Cubic Mould : The capacity of cubic mould is 70.6 x 70.6 x 70.6 mm3 (IS : 10080).

• Vibration Machine : The vibration machine should be works as per the IS : 10080.

• Balance : The balance measuring weigh 1000 g with an accuracy of 1 g.

• Measuring Cylinder : The capacity of measuring cylinder s 200 ml with an accuracy of 1 mm.

• Enamel tray, Trowel, Poking rod other apparatus required.

PROCEDURE

• The test specimens are 70.6 mm cubes having face area of about 5000 sq. mm. Large size specimen cubes cannot be made since cement shrinks and cracks may develop. 

• The temperature of water and test room should be 27°± 2°C. 

• A mixture of cement and standard sand in the proportion 1:3 by weight is mixed dry with a trowel for one minute and then with water until the mixture is of uniform colour. 

• Three specimen cubes are prepared. The material for each cube is mixed separately. 

• The quantities of cement, standard sand and water are 185 g, 555 g and (P/4) + 3.5, respectively where P = percentage of water required to produce a paste of standard consistency. 

• The mould is filled completely with the cement paste and is placed on the vibration table. Vibrations are imparted for about 2 minutes at a speed of 12000±400 per minute.

• The cubes are then removed from the moulds and submerged in clean fresh water and are taken out just prior to testing in a compression testing machine.

• Compressive strength is taken to be the average of the results of the three cubes. 

• The load is applied starting from zero at a rate of 35 N/sq mm/minute. The compressive strength is calculated from the crushing load divided by the average area over which the load is applied.The result is expressed in N/mm2.

CALCULATION

P = Maximum load applied to the cube.

A=Cross sectional area (Calculated from the mean dimensions).

Compressive strength is reported to the nearest 0.5 N/mm². when wrong specimen have prepared, or that give strengths differing by more than 10% from the average value of all the test specimen should not be considered.

STANDARD SPECIFICATION

CEMENT TYPE	COMPRESSIVE STRENGTH (Mpa)
	1 Day	3 Days	7 Days	28 Days
OPC(33)	not specified	16	22	33
OPC(43)	not specified	23	33	43
OPC(53)	not specified	27	27	53
SRC	not specified	10	16	33
PPC	not specified	16	22	33
RHPC	16	27	—	—
PSC	not specified	16	22	33
High alumina	30	35	—	—
Super sulphated	not specified	15	22	30
Low heat	not specified	10	16	35

HOW TO CHECK SOUNDNESS OF CEMENT BY LEE-CHATELIERS MATHOD (IS:4031-(PART 3)-1988) ?

In the soundness test a specimen of hardened cement paste is boiled for a fixed time so that any tendency to expand is speeded up and can be detected. Soundness means the ability to resist volume expansion.

OBJECTIVE

To determine the soundness of hardened cement paste by le-Chateliers method.

APPARATUS

• Le-Chateliers Apparatus : The size of apparatus should be made as per IS: 5514.

• Water Bath : The water bath should have a minimum temperature 100 with an accuracy of 1. 

• Caliper : The measuring length of caliper is 30 cm with 0.5 mm accuracy.

• Measuring Cylinder : The volume of measuring cylinder is 100 ml with an accuracy of 1 ml.

• Balance : The should weigh 100 g accurately with an accuracy of 1 g.

• Glass sheets (2 nos), Enamel tray, trowel are the other apparatus required for test.

PROCEDURE

• The mould is placed on a glass sheet and is filled with neat cement paste formed by gauging 100 g cement with 0.78 times the water required to give a paste of standard consistency. 

• The mould is covered with a glass sheet and a small weight is placed on the covering glass sheet. 

• The mould is then submerged in the water at temperature of 27°-32°C. 

• After 24 hours, the mould is taken out and the distance separating the indicator points is measured to the nearest 0.5 mm (L1). 

• The mould is again submerged in water. The water is now boiled for 3 hours. 

• The mould is removed from water and is cooled down. 

• The distance between the indicator points is measured again to the nearest of 0.5 mm (L2). 

• The difference between the two measurements represents the unsoundness of cement.

CALCULATION

The difference between the two  measurements to the nearest of 0.5 mm represents the unsoundness of cement.

Soundness Of Cement = L₁-L₂

PRECAUTIONS

• All the measurements should be done accurately.

• Extra pressure should not apply while filling the moulds.

• During boiling water level should not fall below the height of the mould.

STANDARD SPECIFICATIONS

Type/Name of cement	Reference Indian standard	Expansion (max.)
OPC (33)	IS:269-1989	10 mm
OPC (43)	IS:8112-1989	10 mm
OPC (53)	IS:12269-1987	10 mm
Rapid hardening	IS:8041-1990	10 mm
Low heat cement	IS:12600-1989	10 mm
Super sulphated	IS:6909-1990	5 mm
Portland pozzolana	IS:1489-1991(part 1)	10 mm
PSC	IS:455-1976	10 mm
High alumina cement	IS:6452-1989	5 mm
SRC	IS:12330-1988	10 mm
Masonry cement	IS:3466-1988	10 mm
IRS-T-40	Railway standards	5 mm

INITIAL AND FINAL SETTING TIME OF CEMENT TEST (IS: 4031-(PART-5)-1988)

INITIAL AND FINAL SETTING TIME  CEMENT TEST

The initial setting time may be defined as the time taken by the paste to stiffen or solidify to such an extent that the Vicat’s needle is not permitted to move down through the paste to within 5 to 7 mm measured from the bottom of the mould. 

The final setting time is the time after which the paste becomes so hard that the angular attachment to the needle, under standard weight, fails to leave any mark on the hardened concrete.

Factors Affecting Initial And Final Setting Time Of Cement :

The factors influencing the setting properties of cement are : 

• Its composition, The effect of gypsum is to increase the setting time of freshly ground cement. 

• The percentage of retardant. 

• Degree of calcination. 

• Fineness of grinding.

• Aeration subsequent to grinding clinker. 

• Percentage of water used to make cement paste. 

• The temperature of the mixing water. 

• Cement and the atmosphere where the cement paste is placed.

OBJECTIVE 

To determine the initial and final setting time of cement paste of normal consistency.

APPARATUS

• Vicat’s Apparatus :

SAMPLE/SPECIMEN 

300 gm of cement is taken and then mix it with the required water percentage mentioned  in the consistency test of cement.

PROCEDURE FOR INITIAL SETTING TIME

• The prepared cement paste is filled in the vicat mould.
• The square needle of cross-section 1 mm x 1 mm is attached to the movable rod of the Vicat apparatus.

• Then the needle is allowed to quickly release to penetrate in the cement paste. during initial stage, the needle penetrates completely. It is then taken out and dropped at a fresh place. The test procedure is repeated at regular intervals till the needle does not penetrate completely. The needle should penetrate upto about 5 mm measured from bottom.

• The initial setting time is found out by taking  the interval between the addition of water to cement and the stage when needle stops to penetrate completely. The time should be less than 30 minutes for ordinary cement.

PROCEDURE FOR FINAL SETTING TIME :

• 300 gm of cement is taken and then mix it with the required water percentage mentioned  in the consistency test of cement.

• The prepared cement paste is then fill in the vicat mould.

• Instead of square needle, annular collar is used. The annular collar is attached to the movable rod of vicat apparatus.

• The annular rod is gently released. The time at which the annular rod makes an impression on test block and the collar fails to do so is noted.

• The final setting time is found out by taking the difference between the time at which water is added to cement and time as recorded in.

• The final setting time for ordinary cement should be 10 hours.

Initial And Final Setting Time Of Various Types Of Cement :

• Ordinary Portland Cement : The initial setting time of OPC should not be less than 30 minutes and the final setting time of this type of cement should not be greater than 10 hours or 600 minutes.

• Rapid Hardening Cement : for this type of cement, initial and final setting time is same as OPC cement.

• Portland Pozzolana Cement :  For this type of cement, initial and final setting time is same as OPC cement.

• Low Heat Portland Cement : For this type of cement, initial and final setting time is not less than 30 min and not greater than 600 minutes.

• Portland Blast Furnace Slag Cement : For this type of cement, initial and final setting time is same as OPC cement.

FINENESS TEST OF CEMENT (IS:4031-1996)

Test for fineness of cement is carried out for proper grinding of cement and to measure the mean size of the grains in it. 

METHOD OF TESTING FINENESS OF CEMENT  : 

Sieve Analysis Method

Weighing a 100 g of cement with accuracy of 0.1 g as a sample and if any air-set lumps present in the sample are broken with finger. The sample is placed on a 90 micron sieve and continuously sieved for 15 minutes. 

The residue should not exceed the following limits :

• For Ordinary Portland Cement : The residue present in OPC cement should not exceed 10% by the dry weight of cement. The specific surface of this type of cement should not be less than 225 m2/kg.
• For Rapid Hardening Cement : The residue present in this rapid hardening cement should not exceed 5% by the dry weight of cement. The specific surface of this type of cement should not be less than 325 m2/kg.
• For Portland Puzzolana Cement : The residue present in PPC cement should not exceed 5% by the dry weight of cement. The specific surface of this type of cement should not be less than 300 m2/kg.

Test Procedure

Objective

To determine the fineness of cement by dry sieve method.

Apparatus

• Standard BIS Sieve No. 9 : With capacity of retaining particle size over 90 micron.

• Weighing Balance : Measures 10 g of cement with accuracy 0.01 mg.
• Glass rod, Stoppered Jar Pen, Lid other apparatus used.

Sample/Specimen

100 g of cement sample is taken and broken air-set lumps in the sample with fingers.

Procedure 

• Weigh approximately 10 g of cement to the nearest 0.01 g and place it on the sieve.
• Agitate the sieve by swirling, planetary and linear movements, until no more fine material passes through it.
• Weigh the residue and express its mass as a percentage R1,of the quantity first placed on the sieve to the nearest 0.1 percent
• Gently brush all the fine material off the base of the sieve.
• Repeat the whole procedure using a fresh 10g sample to obtain R2. Then calculate R as the mean of R1 and R2 as a percentage, expressed to the nearest 0.1 percent. When the results differ by more than 1 percent absolute, carry out a third sieving and calculate the mean of the three values.

Result

Read and report the value of R, to the nearest of 0.1 percent, as the residue on the 90 micron sieve.

OTHER METHODS

Air Permeability Method

In air permeability test, The fineness of cement is represented or calculated by specific surface, i.e. total surface area in cm2 per gram or m2 per kilogram of cement and is measured by permeability apparatus. 

This permeability apparatus essentially consists of :

• Permeability Test Cell : Place where cement is stored and air pressure is applied. 
• Flowmeter : Flowmeter help to determine the quantity of air passing per second through its capillary tube per unit difference of pressure.
• Manometer : Manometer help to measure the air pressure.

To determine the fineness, a cement sample of 2 cm height is placed on a perforated plate and air pressure is applied. The manometer is connected to the top of the permeability cell and the air is turned on. The lower end of the permeability cell is then slowly connected to the other end of the manometer. The rate of flow is so adjusted that the flowmeter shows a pressure difference (h2) of 30-50 cm. The reading (h1) in the manometer is recorded. The process is repeated till the ratio h1/h2 is constant.

The specific surface should not be less then following limits :

• For Ordinary Portland Cement : The specific surface of this type of cement should not be less than 225 m2/kg.
• For Rapid Hardening Cement : The specific surface of this type of cement should not be less than 325 m2/kg.
• For Portland Puzzolana Cement : The specific surface of this type of cement should not be less than 300 m2/kg.

The Sedimentation Method

The turbidometer is a apparatus used  to estimate the surface area of one gram of cement. The cement is  uniformly in a rectangular glass tank filled with kerosene. Then, parallel light rays are passed through the solution which strike the sensitivity plate of a photoelectric cell. The turbidity of the solution at a given instant is measured by taking readings of the current generated by the cell. By recording the readings at regular intervals while the particles are falling in the solution, it is possible to secure information regarding the grading in surface area and in size of particle. Readings are expressed in cm2/g.

HOW TO PERFORM CONSISTENCY TEST OF CEMENT ?

Consistency test is used to estimate the quantity of mixing water to form a paste of normal consistency. The normal consistency defined as that percentage water requirement of the cement paste, the viscosity of which will be such that the Vicat’s plunger penetrates up to a point 5 to 7 mm from the bottom of the Vicat’s mould.

FACTOR AFFECTING FINENESS OF CEMENT 

1. The chemical composition and the degree of calcination influence the hardness of the clinker and consequently the fineness to which the cement is ground. 

2. Clinker, high in iron or silica, is apt to be hard and difficult to grind. The same is true with a hard burned clinker. 

3. Fineness is also influenced by the time of grinding and the character of the pulverizing machinery. It has been found that cement becomes finer with age provided it does not absorb too much moisture. This is probably due to the decrepitation of the coarser grains resulting from the hydration of the embedded lime particles.

TEST IMPORTANCE

Finer the cement, more is the strength since surface area for hydration will be large. With increase in fineness, the early development of strength is enhanced but the ultimate strength is not affected. An increase in the fineness of the cement increases the cohesiveness of the concrete mix and thus reduces the amount of water which separates to the top of a lift (bleeding), particularly while compacting with vibrators. However, if the cement is ground beyond a certain limit, its cementative properties are affected due to the prehydration by atmospheric moisture. Finer cement reacts more strongly in alkali reactive aggregate. Also, the water requirement and workability will be more leading to higher drying shrinkage and cracking.

TEST PROCEDURE

Objective

To determine the water requirement of the cement paste with normal consistency.

Apparatus

• Vicat’s Apparatus

Sample/Specimen

To makes a viscous paste as a sample, 300 g of cement is mixed with 25 per cent water.

Procedure

• The paste is filled in the mould of Vicat’s apparatus and the surface of the filled paste is smoothened and leveled.

• A square needle 10 mm x 10 mm attached to the plunger is then lowered gently over the cement paste surface and is released quickly. The plunger pierces the cement paste. 
• The reading on the attached scale is recorded. 

• When the reading is 5-7 mm from the bottom of the mould, the amount of water added is considered to be the correct percentage of water for normal consistency.

Result

The normal consistency of cement paste is achieved as a result.

MANUFACTURING OF ORDINARY PORTLAND CEMENT

RAW MATERIALS

• Calcareous (material having content of lime)
• Argillaceous (material having content of silica and alumina)
• Gypsum

Composition Of Raw Materials :

Lime (CaO)	60 to 67%
Silica (SiO2)	17 to 25%
Alumina (Al2O3)	3 to 8%
Iron oxide (Fe2O3)	0.5 to 6%
Magnesia (MgO)	0.1 to 4%
Sulphur trioxide (SO3)	1 to 3%
Soda and/or Potash (Na2O+K2O)	0.5 to 1.3%

MANUFACTURING PROCESSES OF CEMENT (OPC)

Cement is manufactured by the following two processes :

• Dry Process 

• Wet Process

These two processes differ in operation but fundamentals of both these processes are same.

• Crushing and grinding
• Mixing the material in proportion
• Heating the prepared mixture in rotary kiln
• Grinding the heated product known as clinker
• Mixing and grinding of cement clinker with gypsum

DRY PROCESS

The dry process is adopted when the raw materials are quite hard. The process is slow and the product is costly. 

Steps involve in manufacturing of portland cement by dry method :

            

• Limestone and clay are ground to fine powder separately and are mixed. Water is added to make a thick paste. 

• The cakes of this paste, which contain about 14 per cent of moisture, are dried and are charged into rotary kiln. 

                              Rotary Kiln

• The product obtained after calcination in rotary kiln is called clinker. The clinker is obtained as a result of incipient fusion and sintering at a temperature of about 1400°- 1500°C. 
• Because ferric oxide has lower melting point than the other oxides, it acts as a flux. Aeration of cement clinker, which is commonly practised to slake free lime, also causes an absorption of some moisture and carbon dioxide. Absorption of moisture tends to decrease the setting whereas that of carbon dioxide accelerates setting. 
• The clinker is cooled rapidly to preserve the meta stable compounds and their solid solutions dispersion of one solid in another which are made as the clinker is heated. Clinker is then cooled and ground in tube mills.
• where 2-3% of gypsum is added. Generally, cement is stored in bags of 50 kg. The purpose of adding gypsum is to coat the cement particles by interfering with the process of hydration of the cement particles. This retards the setting of cement.

WET PROCESS

The operations in the wet process of cement manufacture are mixing, burning and grinding. 

Step involve in the manufacturing of portland cement by wet process are :

• The crushed raw materials are fed into ball mill and a little water is added. On operating the ball mill, the steel balls in it pulverize the raw materials which form a slurry with water. 

• This slurry is passed to storage tanks where the proportioning of the compounds is adjusted to ensure desired chemical composition. The corrected slurry having about 40 per cent moisture content, is then fed into rotary kiln where it loses moisture and forms into lumps. 

• These are finally burned at 1500-1600°C. The lumps change to clinker at this temperature. Clinker is cooled and then ground in tube mills. While grinding the clinker, about 3 per cent gypsum is added. The cement is then stored in storage tanks from where it is supplied.