CEMENT TESTING



METHODS OF TESTING OF CEMENT

1. Sampling procedures of cement from bags, bulk storage, wagons, conveyors etc recommended in IS: 3535 are explained below. 

The terms associated with sampling process of cement are given below:
(i) Hydraulic cement: Finely ground material which on addition of water is capable of hardening both under water and in air, by the chemical action of its constituents with water and also capable of binding together appropriate materials.
(ii) Increment: The quantity of cement obtained by the sampling device at a time.
(iii) Lot: The quantity of the cement of the same manufacturer or source not exceeding 2000 tonnes, inspected for testing is called a lot.
(iv) Sub-lot: Before sampling, a lot is divided into a number of sub-lots of equal size.
(v) Gross sample: The unit samples or increments collected from sub-lots constitute gross sample.
(vi) Laboratory sample: The gross sample is reduced by specified procedures to obtain samples for laboratory testing.
(vii) Composite sample: It is the quantity of cement obtained by mixing together equal quantity of cement from the laboratory samples representing the sub-lots.
In drawing, preparing and handling test samples, the following precautions shall be taken:
a) The sampling device shall be clean and dry when used.
b) Contamination of the sample, sampling device or container shall be eliminated.
c) The sample containers shall be selected that it is almost fully filled with the sample.
d) The sample containers shall be sealed air-tight after sampling and particulars of sample, date of sampling etc marked on it.
e) The sample shall be stored at a normal temperature.
f) The location of sampling shall be clean, dry and free from breeze.
g) The interval of drawing the increments shall be uniform in terms of the mass of the lot or sub-lot. If the rate of the quantity handled is uniform, increments may be taken based on time interval.
2. Sampling from conveyors
a) Wherever possible, cement samples shall be obtained when it is in motion, like from conveyor belts or during loading and unloading.
b) For the purpose of sampling, a lot while it is being discharged over a conveyor shall be divided into a number of sub-lots in accordance with table 1.
c) A representative gross sample is collected from each of the sub-lots and kept separately.
d) When the cement is in motion, sample increments shall be taken direct from the point where the material is discharged from the conveyor belt.
Number of sub-lots recommended for different lot sizes:

Sl. No. Weight of tot size in tonnes No of sub-lots
1 Up to 100  2
2 101 to 200  3
3 201 to 300  4
4 301 to 500  5
5 501 to 1000  6
6 1001 to 2000  7

e) The sample shall be collected from full width of the stream, without over flowing the sampling pan or any other collecting device.
f) If sampling is not possible at the discharge point, samples may be obtained from the moving belt.
g) Using a scoop, samples are taken from centre and the left and right side of the moving stream along the same width. For this, the conveyor belt may be stopped, if possible.
h) The increments from sub-lots are placed directly in moisture-proof, air-tight containers to avoid moisture absorption and aeration of the sample.
i) One increment is taken from every 10 tonnes or part thereof from the material discharged and the weight of one increment shall not be less than 2 kg.
j) If the increments are placed in cans, the cans are filled completely and sealed immediately.
k) Moisture proof multiple wall paper bags or plastic bags may be used if they are strong enough to avoid breakage.
l) Sealing of paper bags or plastic bags may be done immediately after filling, to eliminate excess air in the bag and avoid moisture absorption and aeration of the sample.
m) The sample containers or bags shall carry suitable identification marks so that they can be related back to the particular sub-lot from where the sample was obtained.
3. Sampling from wagons
This is applied when loose cement is received in wagons. For the purpose of sampling, all the wagons shall be divided into convenient sub-lots of approximately equal number of wagons as given in table.
a) A representative gross sample is collected from each of the sub-lots and kept separately.
b) A slotted tube sampler 60 cm long is used for obtaining sample increments. Samples are to be collected from at least six points in
each selected wagon.
c) From each selected wagon, approximately equal number of increments is taken and the weight of one increment shall not be less than 2 kg.
d) If the increments are placed in cans, the cans are filled completely and sealed immediately.
e) Moisture proof multiple wall paper bags or plastic bags may be used if they are strong enough to avoid breakage.
f) Sealing of paper bags or plastic bags may be done immediately after filling, to eliminate excess air in the bag and avoid moisture absorption and aeration of the sample.
g) The sample containers or bags shall carry suitable identification marks so that they can be related back to the particular sub-lot from where the sample was obtained.
4. Sampling from bulk storage (Silos)
For the purpose of sampling, the quantity of cement in the bulk storage shall be divided into convenient sub-lots depending on the weight of the lot, as given in table.
a) The gross sample from a sub-lot is obtained by taking increments at regular intervals when the cement is being discharged into the bulk storage or discharged from it.
b) One increment is taken from every 10 tonnes or part thereof from the material discharged and the weight of one increment shall not be less than 2 kg.
c) If the increments are placed in cans, the cans are filled completely and sealed immediately.
d) Moisture proof multiple wall paper bags or plastic bags may be used if they are strong enough to avoid breakage.
e) Sealing of paper bags or plastic bags may be done immediately after filling, to eliminate excess air in the bag and avoid moisture absorption and aeration of the sample.
f) The sample containers or bags shall carry suitable identification marks so that they can be related back to the particular sub-lot from where the sample was obtained.
g) It shall be ensured that the cement sample collected is sufficient for all the required tests.
h) A representative gross sample is collected from each of the sub-lots and kept separately.
5. Sampling from bags
For the purpose of sampling, the quantity of cement in the lot shall be divided into a number of sub-lots depending on the weight of the lot, in accordance with table.
a) The sub-lots shall be approximately equal number of bags.
b) For getting a representative gross sample from a sub-lot, at least 2% of the bags subject to a minimum of 5 bags shall be sampled. In case fractional number is obtained, it shall be rounded to the next higher number.
c) The bags are selected at random from the sub-lots. For details of random sampling, IS: 4905 may be referred.
d) A sampling tube is inserted into the bag and sample of cement collected in two or three operations.
e) Equal number of increments is taken from each selected bag and the weight of each increment shall not be less than 2 kg.
f) If the increments are placed in cans, the cans are filled completely and sealed immediately.
g) Moisture proof multiple wall paper bags or plastic bags may be used if they are strong enough to avoid breakage.
h) Sealing of paper bags or plastic bags may be done immediately after filling, to eliminate excess air in the bag and avoid moisture absorption and aeration of the sample.
i) The sample containers or bags shall carry suitable identification marks so that they can be related back to the particular sub-lot from where the sample was obtained.
j) It shall be ensured that the cement sample collected is sufficient for all the required tests.
6. Reduction of gross sample
a) Each gross sample shall be reduced separately.
b) The material of the gross sample is thoroughly mixed, breaking lumps and removing foreign matters.
c) The cement sample is then passed through 850 micron IS sieve. Hardened lumps and foreign matters are discarded.
d) Equal quantities of material from lot samples may be taken and mixed together to form a composite sample representing the whole lot.
e) Reduction by Riffle Divider: The gross sample shall be well mixed and poured into riffle boxes. The process shall be repeated till test sample of suitable size is obtained.
f) Method of quartering: The method of quartering can be adopted for sample reduction. The cement is thoroughly mixed and heaped into a cone shaped pile using a scoop. The cone is then flattened using the smooth surface of the scoop. The flattened cone is cut into 4 quarters by making two deep lines at right angles. The bulk of the sample is reduced by rejecting one set of opposite quarters.
g) The process of reduction of gross sample shall be continued till 11 kg of the material, required to carry out the specified tests, is obtained.
h) The laboratory sample and composite sample are divided into three equal parts, one for the Client, one for the Contractor and one for third party testing in case of disputes.
7. Tests on cement samples
The laboratory samples of cement are subjected to chemical and physical requirement tests given below:
(i) Total sulphur content as sulphuric anhydride.
(ii) Fineness.
(iii) Setting time.
(iv) Strength.
(v) Soundness.
If three or more test results are obtained the compliance to specification is verified statistically by calculating (x±0.5R) which shall be within the limits prescribed.
Where,
x = Average = Sum of all the test results/number of tests.
R = Range = Difference between the maximum and minimum values of the test results.

DETERMINATION OF FINENESS OF CEMENT

BY DRY SIEVING IS: 4031 - Part 1

1. Introduction
This test method covers the determination of the fineness of cement by sieving it on standard sieve.
2. Apparatus
(i) IS sieve 90 micron with tray fitting beneath the sieve frame and a lid fitting above it shall be provided to avoid loss of material during sieving.
(i) A balance capable of weighing up to 10 gm to the nearest 10 mg.
(ii) A brush for cleaning the sieve.
3. Procedure
a) Shake the sample of cement to be tested for 2 minutes in a closed jar to disperse agglomerates. Wait for 2 minutes.
b) Stir the resulting powder gently using a clean dry rod.
c) Weigh approximately 10 gm of cement and place it on the 90 micron sieve with the tray under the sieve.
d) Break down any air set lumps in the cement sample with fingers. Fit the lid over the sieve.
e) Sieve the sample continuously by swirling, planetary and linear movements until no more fine material passes through it.
f) Weigh the residue and express its mass as a percentage R1 of the quantity first placed on the sieve to the nearest 0.1%.
g) Repeat the whole procedure using a fresh 10 gm sample to obtain R2.
h) Then calculate the residue of the cement R as the mean of R1 and R2 as a percentage, expressed to the nearest 0.1%.
i) If the results differ by more than 1%, then carry out a third sieving and calculate the mean of the three values.
j) In case where correction factor (F) is to be applied, then the residue R shall be corrected by multiplying by F.
4. Checking the sieve
a) The sieve should be checked after every 100 sievings.
b) For this, the above procedure should be repeated and two values of residue of cement should be found.
c) Let this be P1and P2 expressed to the nearest 0.1%. For a satisfactory sieve the two values of P1 and P2 should not differ by more than 0.3%.
d) The mean value is taken as P.
e) Get a reference sample with known residue (M) on the 90 micron sieve.
f) Calculate M/P as the sieve factor, F, expressed to the nearest 0.01.
g) The residue R is multiplied by F which may have a value of 1.0±0.2.
5. Reporting of results
Report the value of R, to the nearest 0.1%, as the residue on the 90 micron sieve for the cement tested.

DETERMINATION OF FINENESS OF CEMENT

USING BLAINE’S AIR PERMEABILITY APPARATUS IS: 4031 - Part 2

1. Introduction
This test method covers the determination of the fineness of hydraulic cement using the Blaine air permeability apparatus. The variable flow type air permeability apparatus (Blaine type) and the accessories shall conform to IS: 5516. The fineness of cement is indicated in terms of specific surface and is expressed as the total surface area in square centimeters per gram or square meter per kilogram of cement.
2. Apparatus
(i) The Blaine air permeability apparatus consists essentially of an arrangement to draw a definite quantity of air through a prepared bed of cement of definite porosity. The rate of air flow through the bed depends on the number and size of the pores in the cement bed which is a function of the particle size of the cement tested.
(ii) The permeability cell shall consist of a rigid cylinder 12.7±0.1 mm inside diameter, constructed with austenitic stainless steel with interior finish of 0.81 μm. The bottom of the cell must be able to form an air tight fit with the upper end of the manometer. A ledge 0.5 to 1.0 mm shall be fitted at 55 ± 10 mm from top of the cell to support the perforated metal disc.
(iii) The disc shall be constructed of noncorrodible metal 0.9±0.1 mm thick, perforated 30 to 40 holes 1 mm diameter equally distributed over its area. Inscribe a suitable mark on one side of the disc to ensure that this face is always on the down side.
(iv) The plunger shall be made with austenitic stainless steel and shall fit inside the cell with clearance not more than 0.1 mm. The bottom of the plunger shall sharply meet the lateral surfaces. An air vent 3.0±0.3 mm wide shall be provided on one side of the
plunger. The plunger is provided with a collar at the top which will rest on the top of the cell such that the gap between the bottom of the plunger and top of the perforated plate shall be mm 15 ± 1 mm.
(v) Circular discs of filter paper of medium porosity (Mean pore dia 7 mic) having a smooth circumference adapted to the dimensions of the cell.
(vi) The standard glass-wall U-tube manometer shall have a nominal outside diameter of 9 mm. The top of one arm should form an air tight connection with the permeability cell. A side out let for evacuation shall be provided at 250 to 305 mm above the bottom of the
manometer. The manometer shall be etched with a line 125 to 140 mm below the outlet and three other lines at 15±1 mm, 70±1 mm and 110±1 mm above this line. A positive air tight valve shall be connected to the side out let not more than 50 mm away from the
arm of the manometer. The manometer shall be mounted firmly such that the arms are vertical.
(vii) Non-volatile, non-hygroscopic liquid of low viscosity and density like Dibutyl phthalate or light grade mineral oil as manometer liquid.
(viii) Mercury of reagent grade or better.
(ix) Light grease for ensuring an airtight joint between cell and manometer and in the stopcock.
(x) Pyknometer or other convenient means of determining the density of cement.
(xi) Time with starting and stopping mechanisms and to read to the nearest 0.2 seconds.
(xii) Standard weights.
3. Preparation of compacted bed of cement
a) Samples of cement for testing shall be taken in accordance with the requirements of IS: 3535 and the relevant standard specification for the type of cement tested.
b) Agitate the sample for 2 minutes in a stoppered jar to disperse agglomerates. Stir the powder with a clean dry rod to distribute the fines uniformly.
c) Determine the density of cement sample using Pyknometer or Le-chatelier flask. Use a non-reactive liquid such as kerosene for the test. Calculate the density of cement ρ to the accuracy of 0.01 gm/cm3 from the mean of two determinations.
d) The weight of cement m1 required to produce a porosity e = 0.500 is calculated from the formula: m1 = 0.500 ρ V where V= volume of the cement bed for testing.
e) Place the perforated disc on the ledge at the bottom of the cell. Place a new filter paper disc flat on it. Weigh the calculated quantity of cement and place it in the cell without any loss. Gently tap the cell to level the cement. Place a new filter paper on the top of the cement.
f) Insert the plunger to make contact with the disc. Press gently until the lower face of the cap is in contact with the cell. Slowly lift the plunger for about 5 mm, rotate for 90° and press the cement bed firmly until the plunger cap is in contact with the cell. Avoid exerting too much pressure on the sample bed. The bed is now ready for permeability test. Slowly withdraw the plunger.
4. Calibration of the apparatus
The testing and calibration of the apparatus shall be made at a laboratory temperature of 27±2°C and relative humidity not exceeding 65%.
4.1 Bulk volume of compacted bed of powder by mercury displacement
a) Apply a thin film of light mineral oil to the cell interior.
b) Place the perforated disc on the ledge in the cell. Place two filter paper disks on the perforated disc. Push them with a rod until they are placed flat on the perforated metal disk.
c) Fill the cell with mercury without any air bubbles. Use tong when handling the cell.
d) Press the top of mercury with a glass plate and flush the surface with the top edge of the cell. Ensure that no air bubbles or voids exist between the mercury and the glass plate.
e) Remove the mercury from the cell and record its mass m2 to the nearest 0.01 gm. Record the temperature also.
f) Remove one filter disc from the cell and form a compacted bed of cement as described earlier. Place a new paper disc and compress the cement.
g) Pour mercury over the filter disc till the space left in the cell is filled up. Remove the entrapped air and level off the mercury as before.
h) Remove the mercury and record its mass m3 to the nearest 0.01 gm, noting the temperature also.

i) Calculate the volume V of cement bed as follows:

V = (m2 – m3)/D cm3) where,
m2 = Mass of mercury required to fill the cell without cement bed, in gm.
m3 = Mass of mercury in gm required to fill above the cement bed in the cell in
gm and
D = Density of mercury at the time of test in gm/cm3.
j) The density of mercury at the test temperature may be taken from table given below

Table : Temperature Vs Density of mercury D, Air viscosity (μ) and √0.1μ:

Tempe

-rature

Density of
mercury gm/cm3

Viscosity of  air, μ
Pa.S

√0.1μ
16 13.56 0.00001788 0.001337
18 13.55 0.00001798 0.001341
20 13.55 0.00001808 0.001345
22 13.54 0.00001818 0.001348
24 13.54 0.00001828 0.001352
26 13.53 0.00001837 0.001355
28 13.53 0.00001847 0.001359
30 13.52 0.00001857 0.001363
32 13.52 0.00001867 0.001366
34 13.51 0.00001876 0.00137

NOTE: Intermediate value shall be obtained by linear interpolation

k) Take average of at least two determinations of bulk volume of cement bed agreeing within ±0.005 cm3 and record this as V.
l) Note the temperature in the vicinity of the cell at the beginning and end of determination.
m) Adjust the volume of cement to get the required porosity.
NOTE: Care should be taken to avoid splashing or spilling of mercury and contact with the skin of the technician.

4.2 Air permeability test

a) Attach the permeability cell to the socket at the top of manometer tube ensuring an airtight connection without disturbing the cement bed.
b) Apply a little grease if required.
c) Open the stopcock and slowly evacuate the air in one arm of the manometer tube until the liquid reaches the top mark. Close the stopcock.
d) If the level of liquid falls, improve the sealing till the level is maintained steady.
e) Remove the top plug. The manometer liquid will begin to fall.
f) Start the timer when the bottom meniscus of the manometer liquid reaches the second mark and stop when it reaches the third mark (next to the bottom).
g) Note the time interval t to the nearest 0.2 seconds and test temperature to the nearest °C.
h) Repeat the procedure with the same bed to get additional values of time and temperature.
i) Carry out the permeability test on a second cement bed, two times.
NOTE: The calibration and fineness shall be determined.
The specific surface S is given by the equation S = (K /ρ) x √e3 /(1-e) x [√t /√0.1μ].

5. Procedure

a) The cement sample shall be at room temperature when used.
b) The mass of sample shall be the same as that used in the calibration test on the standard sample.
c) However for cements other than Ordinary Portland cement, the test bed may be prepared for a porosity of 0.530±0.005.
d) The preparation of bed is done as described in 3 above.
e) Carry out the permeability tests in accordance with the method described in 4.2 above. Only one time of flow determination is made on each bed.
6. Calculation
Calculate the specific surface values with the following equation:
S = (K /ρ) x √e3 /(1-e) x [√t /√0.1μ] where
K = Apparatus constant
ρ = Density of cement in gm/cm3
e = Porosity of cement
t = Time in seconds
μ = Viscosity of air at the test temperature (From table 1)
When porosity is specified as 0.500, the equation simplifies to
S = [521.08 K√ t ]/ ρ cm2/gm at temperature 27±2°C and
S = [524.2 K√ t ]/ ρ cm2/gm at temperature 20±2°C.
The specific surface values of cm2/gm are rounded to the nearest 10 units and values in m2/kg to the nearest unit.

DETERMINATION OF CONSISTENCY OF STANDARD CEMENT PASTE IS: 4031 - Part 4

1. Introduction
This test method covers the determination of quantity of water required to produce a cement paste of standard consistency. The standard consistency of a cement paste is defined as that consistency which will permit the Vicat plunger having 10 mm diameter and 50 mm length to penetrate up to a depth of 5 to 7 mm from the bottom of the Vicat mould.
2. Apparatus

(i) The Vicat apparatus, conforming to IS: 5513-1976, consisting of a frame having movable rod with a platform at one end with the following that can be attached at the other end:
? Needle for determining the initial setting time.
? Needle for determining the final setting time.
? Plunger with a diameter of 10±0.05 mm and a length of 50±1mm, for determining the standard consistency.
(ii) A balance with permissible variation at a load of 1000 gm shall be ±1.0 gm.
(iii) Standard weights for weighing cement.
(iv) Gauging trowel.

3. Procedure
a) Prepare a paste of weighted quantity of cement with a weighed quantity of potable or distilled water taking care that the time of gauging is 3-5 minutes, and the gauging shall be completed before any sign of setting occurs.
b) The time counted from the time of adding water to the dry cement until commencing to fill the mould is called gauging time.
c) Fill the Vicat mould with this paste, the mould resting upon a non-porous plate.
d) After completely filling the mould, smoothen the surface of the paste, making it level with the top of the mould.
e) Shake the mould to expel the air.
f) Place the test block in the mould along with the non-porous resting plate, under the rod bearing the plunger.
g) Lower the plunger gently to touch the surface of the test block, and quickly release, allowing it to shrink into the paste by its own weight.
h) This operation shall be carried out immediately after filling the mould.
i) Take the reading from the indicator of the un-penetrated depth by the plunger.
j) Similarly conduct trials with varying percentages of water as described above until the amount of water necessary for making up the standard consistency is obtained.

4. Result

Express the amount of water as a percentage by mass of the dry cement to the first place of decimal.

DETERMINATION OF INITIAL AND FINAL SETTING TIME OF CEMENT IS: 4031 - Part 5

1. Introduction

This test method determine the time of setting of cement by means of the Vicat?s needle. The initial setting time is the interval between the addition of water to cement and the stage at which needle stops to penetrate at 5+0.05mm from the bottom. The final setting time is the period elapsing between the time when water is added to the cement and time at which the circular cutting edge fails to make an impression on the surface of the test block.

2. Apparatus

(i) The Vicat apparatus (conforming to IS: 5513-1976) shall consist of a frame having a movable rod with a platform
at one end and the following which can be attached at the other end:
(a) Needle C for determining the initial setting time.
(b) Needle for determining the final setting time.
(c) Plunger G with a dia of 10+0.05 mm and a length of 50+1 mm, for determining the standard consistency.
(ii) A balance with permissible variation at a load of 1000 gm shall be +1.0 gm.
(iii) Standard weights for weighing cement.
(iv) Gauging trowel.

3. Temperature and humidity

a) The temperature of moulding room, dry materials and water shall be maintained at 27+2°C.
b) The relative humidity of the laboratory shall be 65%.
c) The moist room shall be maintained at 27±2°C and at a relative humidity of not less than 90%.

4. Standard Consistency

The Standard Consistency of a cement paste is defined as that consistency which will permit a Vicat Plunger 10 mm dia and 50 mm long will penetrate to a depth of 33-35 mm from top of the mould. The equipment used to determine the Standard Consistency (Usually denoted as „P) is called Vicat?s Apparatus. Standard Consistency is sometimes referred as normal consistency.

5. Preparation of sample

a) Prepare a paste of 500 gm of cement with 0.85 times the water required for to make a cement paste of Standard Consistency.
b) The gauging time counted from the time of adding water to the dry cement until commencing to fill the mould is 3-5 minutes.
c) Potable or distilled water shall be used in preparing the paste.
d) Fill the Vicat mould with a cement paste gauged as above with the mould resting on a non-porous plate.
e) Fill the mould completely and smooth off the surface of the paste making it level with the top of the mould. The cement block thus prepared in the mould is the test block.
f) Immediately after moulding, place the test block in the moist closet or moist room and allow it to remain there except when determinations of time of setting are being made.
g) Keep all apparatus free from vibrations during the test and keep the Vicat needle clean and straight.
6. Procedure for determining initial setting time
a) Place the test block, under the rod bearing the needle.
b) Lower the needle gently until it comes in contact with the surface of the test block and quickly release, allowing it to penetrate into the test block.
c) In the beginning, the needle will completely pierce the test block. Repeat this procedure until the needle, fails to pierce the block beyond 5.0±0.5 mm measured from the bottom of the mould.
d) The elapsed time when water is added to the cement and the time at which the needle fails to pierce the test block to a point 5.0±0.5 mm shall be the initial setting time.

7. Procedure for determining final setting time

a) Replace the rod bearing needle of the Vicat apparatus by the needle with circular attachment.
b) Lower the needle gently to the surface of the test block.
c) The cement shall be considered as finally set, when the needle makes an impression, while the attachment fails to do so.
d) The elapsed time when water is added to the cement and the time at which the needle makes an impression on the surface of test block while the attachment fails to do so shall be the final setting time.
e) In the event of a scum forming on the surface of the test block, use the underside of the block for the determination.

8. Reporting the result

The results of initial and final setting time shall be reported to the nearest five minutes.

DETERMINATION OF SOUNDNESS BY LE-CHATELIER METHOD IS: 4031 - Part 3

1. Introduction

Cement should not exhibit large change in volume after setting. Soundness of cement is determined to ensure that the cement does not show any appreciable subsequent expansion after setting. This test method covers the determination of the soundness of hydraulic cement by Le-Chatelier method. The apparatus for conducting the Le-Chatelier test shall conform to IS: 5514-1969.

2. Apparatus

(i) Le-Chatelier apparatus with a pair of glass base plate and cover plates for each mould.
(ii) A balance or scale of capacity not less than 1000 gm, readable and accurate to 1 gm.
(iii) Standard weights with permissible variations in weight as stipulated in table 1 of IS: 4031 Part 3-1988.
(iv) A water bath capable of immersing the Le- Chatelier moulds with specimens and of raising their temperature from 27±2°C to boiling in 27±3 minutes.

3. Procedure

a) Samples of cement for testing shall be taken in accordance with the requirements of IS: 3535 and the relevant standard specification for the type of cement tested.
b) The temperature of the moulding room, dry materials and water shall be maintained at 27±2°C. The-relative humidity of the laboratory shall be 65±5%.
c) The moist closet or moist room shall be maintained at 27±2°C and at a relative humidity of not less than 90%.
d) Place the lightly oiled mould on a lightly oiled glass sheet and fill it with cement paste formed by gauging cement with 0.78 times the water required to give a paste of standard consistency [See IS: 4031 (Part 4 ) -1988].
e) The paste shall be gauged in the manner and under the conditions prescribed in IS: 4031 (Part 4) - 1988, taking care to keep the edges of the mould gently together while this operation is being performed.
f) Cover the mould with another piece of lightly oiled glass sheet and place a small weight on this covering glass sheet.
g) Immediately submerge the whole assembly in water maintained at a temperature of 27±2°C and keep there for 24 hours.
h) Measure the distance separating the indicator points to the nearest 0.5 mm.
i) Submerge the mould again in water at the temperature prescribed above. Bring the water to boiling, with the mould kept submerged in 25 to 30 minutes, and keep it boiling, for three hours.
j) Remove the mould from the water, allow it to cool and measure the distance between the indicator points.
k) The difference between the two measurements indicates the expansion of the cement.4. Calculation
Calculate the mean of two values to the nearest 0.5 mm to represent the expansion of cement. In the event of cement failing to meet the test for soundness, a retest may be made after aeration as given below:
a) Spread out the cement in a layer of 75 mm thickness.
b) Store it for 7 days in an atmosphere maintained at 27±2°C and relative humidity of 50 to 80 percent.
c) Retest this cement.

DETERMINATION OF COMPRESSIVE STRENGTH OF CEMENT IS: 4031 - Part 6

1. Introduction

This part explains the procedure to find the strength of cement as represented by the compressive strength of standard cement mortar cubes compacted by standard vibration machine.

2. Apparatus

(i) Compression testing machine.
(ii) 7.06 cm cube moulds conforming to IS: 10080-1982.
(iii) Vibration machine conforming to IS: 10080-1982.
(iv) Poking rod conforming to IS: 10080-1982.
(v) Gauging trowel with steel blade with straight edges 100 to 150 mm long, weighing 210±10 gm.
(vi) Balance with a permissible variation of ±10 gm for 1000 gm.
(vii) Standard weights.
(viii) Graduated glass cylinders of 150 to 200 ml capacity.
(ix) Standard sand conforming to IS: 650-1991.
The standard sand shall be of quartz of light, gray or whitish variety and shall be free from silt. The sand grains shall be angular, the shape of grains approximating to the spherical form, elongated and flattened grains being present only in very small quantities. Standard sand shall pass through 2 mm IS sieve and shall be retained on 90 microns IS sieve with the following particle size distribution.
Particle size Requirement %
Greater than 1 mm and less than 2 mm 33.33
Smaller than 1 mm and less than 500 micron 33.33
Less than 500 micron 33.33

3. Sample preparation

a) Maintain the temperature of room and water at 27±1°C throughout the test period.
b) Use only potable/distilled water for making test cubes.
c) Take 200 gm of cement and 600 gm of standard sand in a clean dry pan. Mix the cement and sand in dry condition with a trowel for 1 minutes and then select water to be added. The quantity of water shall be [(P/4) +3] % of combined weight of cement and sand where, P is the % of water required to produce a paste of standard consistency determined earlier as per IS: 4031 Part 4.
d) Add water and mix it until the mixture is of uniform colour. The time of mixing shall not be less than 3 minutes and not greater than 4 minutes.
e) Immediately after mixing the mortar, place the mortar in the cube mould and prod with the help of the rod.
f) The mortar shall be prodded 20 times in about 8 seconds to ensure elimination of entrained air and honey combing. If vibrator is used, the period of vibration shall be 2 minutes at the specified speed of 12000±400 vibrations /minute.
g) Keep the compacted cube mould at a temperature of 27±2°C and 90% relative humidity for 24 hours. After 24 hours, remove the cubes from the mould and immediately submerge in clean water till testing.
h) Take out the cubes from water just before testing. Testing should be done on their sides without any packing.
i) The rate of loading should be 350 kg/cm2/minute and uniform. Test should be conducted for 3 cubes and report the average value as the test result for both 7day and 28 day compressive strength.

4. Calculation

Calculate the compressive strength of the cube tested by dividing the maximum test load by the cross sectional area.
Compressive Strength = Maximum load applied kg/cm2
Mean cross-sectional area of the specimen
Defective specimens and strength values differing by more than 10% shall be discarded from the average value of compressive strength. After discarding specimens or test values a minimum of two values shall be available for calculating the average strength. If two values are not available for a particular age, the test shall be repeated.
5. Reporting of results
The compressive strength values are reported to the nearest kg/cm2 or to the nearest 0.5 units of N/mm2.

*****