Testing of Cement | Field Tests and Laboratory Tests For Cement14 min read

Testing of Cement done mainly in 2 Categories

  1. Field Test of Cement
  2. Laboratory Test of Cement

1. Field Tests of Cement

  • Colour: Grey color with a light greenish shade.
  • Physical Properties: Cement should feel smooth when rubbed in between the fingers.
  • If hand is inserted in a bag or heap of cement, it should feel cool.
  • If a small quantity of cement is thrown in a bucket of water, it should sink and should not float on
    the surface.
  • Presence of lumps: Cement should be free from lumps.

2. Laboratory Tests for Cement

Tests on cement are performed in accordance with IS: 4032-1985 and IS: 4031 (Parts 1 to 15)- 1988-99 to assess the following:

(i) Chemical composition
(ii) Normal (standard) consistency
(iii) initial and final setting times
(iv) Soundness Test
(v) Strength Test
(vi) Fineness Test
(vii) Heat of hydration Test
(viii) Specific gravity Test

(i) Chemical Composition Test

  • The ratio of the percentage of lime to percentage of silica, alumina, and iron oxide known as Lime Saturation Factor (LSF), when calculated by the formula

shall not be greater than 1.02 and not less than 0.66.

  • The ratio of the percentage of alumina (Al2O3) to that of iron oxide (Fe203) shall not be less than 0.66
  • The weight of insoluble residue shall not be more than 4 per cent.
  • The weight of magnesia shall not be more than 6 per cent.
  • Total loss on ignition shall not be more than 5 per cent.
  • Total sulphur content calculated as sulphuric anhydride shall not be more than 2.5% when CA is 5% or less and shall not be more than 3% when C3A is more than 5%.

(ii) Normal Consistency Test

The normal (standard) consistency of a cement paste is defined as that consistency which will permit a Vicat plunger having 10 mm diameter and 50 mm length to penetrate a depth of 33 to 35 mm from the top (or 5 to 7 mm from the bottom) of the mould.

Vicat Apparatus:

vicat apparatus

Vicat apparatus assembly consists of a plunger 300 gm in weight with a length of 50 mm and diameter of 10 mm and a mould which is 40 mm deep and 80 mm in diameter.

There are two attachments for the plunger viz:
(i) A square needle with a 1 mm2 cross-section which is attached to the plunger for the initial setting time
test.
(ii) A needle with an annular collar of 5 mm diameter is used for the final setting time.

Test Procedure:

  • To prepare the paste, take weighed quantity (300 g) of cement and place it in a crucible.
  • Mix a weighed quantity of water (approximately 24% by weight of cement) for the first trial.
  • The time of mixing or gauging should not be less than 3 minutes nor more than 5 minutes and gauging time should be counted from the time of adding water to the dry cement until commencing to fill the mould.
  • The Vicat mould is filled with the paste, which is levelled off at its top.
  • The mould is placed under the Vicat plunger.
  • The Vicat plunger is brought down to touch the surface of the paste in the mould and quickly released allowing it to sink into the paste by its own weight.
  • Take the reading by noting the depth of penetration of the plunger.
  • Similarly, conduct the trials with increasingly water/cement ratios till such time the plunger penetrates for a depth of 33 to 35 mm from the top (or 5 to 7 mm from the bottom).
  • That particular percentage of water that allows the plunger to penetrate only to a depth of 33 to 35 from the top (or 5 to 7 mm from the bottom) is known as the percentage of water required to produce a cement paste of normal (standard) consistency.
  • This percentage is generally denoted by P.
  • This test should be conducted at a constant temperature of 27° +2°C and a constant humidity of 90%.

(iii) (A) Initial Setting Time Test

  • It is the time elapsed between the moment that the water is added to the cement, to the time that the paste starts losing its plasticity.
  • The test procedure is as follows:
    (i) Take 300 gm of cement and make a cement paste of consistency of 0.85 P
    (ii) Attach the square needle to the Vicat plunger and lower it gently to make contact with the
    the surface of the test block and quickly release it.
    (ii) When the needle penetrates only to a depth of 33 to 35 mm from the top (or 5 to 7 mm from the
    bottom), the test is completed.
  • The initial setting time should not be less than 30 minutes for OPC and 60 minutes for low heat cement.

(iii) (B) Final Setting Time Test

  • The final setting time is the time elapsed between the moment the water is added to the cement and the time when the paste has completely lost its plasticity and has attained sufficient firmness to resist certain definite pressure.
  • The test procedure is as follows:
    (i) Take 300 gm of cement and make a cement paste of consistency of 0.85 P.
    (ii) Replace the square needle by a needle with an annular collar.
    (iii) Lower the attachment to gently cover the surface of the test block.
    (IV) If the needle makes an impression, while the annular collar of the attachment fails to do so, the cement is considered to be finally set. Thus, the paste has attained such hardness that the needle does not pierce through the paste more than 0.5 mm.
  • The final setting time should not be more than 10 hours.

NOTE:
Significance of initial and final setting time:

(a) Concrete, once place should not be disturbed till the final setting, has taken place.
(b) The transportation of concrete from the place where concrete is prepared to the placing of concrete required some finite time that should be within the initial setting time.
(c) Final setting time test is done because the concrete should achieve the desired strength as early as possible so that the shuttering can be removed and reused.

(iv) Soundness Test

  • The soundness of cement indicates that the cement paste, once it has been set, does not undergo an appreciable change in volume causing the concrete to crack.
  • The cement having some quantity of free lime, magnesia and excess sulphates undergoes large changes in volume as the time elapses tending to cause cracks.
  • The soundness of cement is determined either by ‘Le Chatelier’s method’ or by means of ‘Autoclave test.
  • No satisfactory test is available for the assessment of soundness due to excess calcium sulphate, but its content can be easily determined by chemical analysis.

(a) Le-Chatelier’s Method:

Le-Chatelier Apparatus

  • The Le-Chatelier’s apparatus consists of a small split cylinder of spring brass. It is 30 mm in diameter and 30 mm high. On either side of the split are attached two indicator arms 165 mm long with pointed ends.
  • Take 100 gm of cement and make a cement paste of consistency of 0.78 P.
  • Fill the cement paste in the mould and keep it on a glass plate.
  • Cover the mould on the top with another glass plate.
  • The whole assembly is immersed in water at a temperature of 270-32°C and kept there for 24 hours.
  • The assembly is taken out after 24 hours and the distance between the indicator points is measured.
  • The mould is then immersed in a water bath.
  • The water of the bath is brought to boiling point with the mould submerged in 25 to 30 minutes and kept boiling for 3 hours.
  • The mould is taken out from the water and allowed to cool.
  • Distance between the points is then measured.
  • The difference between the two measurements represents the expansion of cement.
  • Le-Chatelier’s method detects unsoundness due to free lime only.
  • This method of testing does not indicate the presence and after effect of the excess magnesia and calcium sulphate.
  • The expansion of cement must not exceed 10 mm for OPC, rapid hardening and low heat Portland cement by this method.
  • OPC, Rapid Hardening Cement, Low Heat Cement, and PPC can have a maximum expansion of less than 10 mm whereas high alumina cement and super sulphated cement can have a maximum expansion of less than 5 mm.

(b) Autoclave Test:

  • Indian Standard specification recommends that a cement having a magnesia content of more than 3 per cent shall be tested for soundness by autoclave test which is sensitive to both free magnesia and free lime.
  • In this test, a cement paste of 25 mm x 25 mm x 250 mm is placed in a standard autoclave.
  • Now, the steam pressure inside the autoclave is raised at such a rate so as to bring the gauge pressure of the steam to 21 kg/cm2 in 1 hour to 1 hour 15 minutes from the time the heat is turned on.
  • This pressure is maintained for three hours.
  • The autoclave is cooled and the length of the specimen is measured again.
  • The expansion should not exceed 0.8%.
    – For OPC (33, 43, 53); SRC; PPC, RHC, LHC, Slag cement
    – 1% for masonry cement.

(v) Strength Test

(a) Compressive Strength Test:

  • The compressive strength of the hardened cement is the most important of all the properties.
  • Take 185 gm of standard sand (Ennore sand), and 55 gm of cement (i.e. the ratio of cement to sand is 1:3) and mix them with a trowel for one minute.
  • Add water of quantity (P/4+30)% of the combined weight of cement and sand where P is the percentage of water required to produce a cement paste of normal consistency.
  • This time of mixing should not be less than 3 minutes and not more than 4 minutes.
  • Immediately, after mixing, the mortar is filled in a cube mould of size 7.06 cm. The area of the face of the cube should be 50 cm2.
  • Compact the mortar either by hand compaction in a standard specified manner or on the vibrating
    equipment for 2 minutes. (vibrations = 1200 + 400 vibrations/minute)
  • Keep the compacted cube in the mould at a temperature of 27° +2°C and at least 90% relative humidity for 24 hours.
  • After 24 hours, the cubes are removed from the mould and immersed in clean fresh water until taken out for testing.
  • Three cubes are tested for compressive strength at 1 day, 3 days, 7 days and 28 days where the period of testing is reckoned from the completion of vibration.
  • The compressive strength shall be the average of the strengths of the three cubes for each period respectively.
  • The compressive strength of 33 grade OPC at 3 days, 7 days and 28 days is 16 MPa, 22 MPa and 33 MPa respectively.
  • A load was applied gradually as 0 to 35 N/mm/min on cubes by using a compressive testing machine (UTM machine).

(b) Tensile Strength Test:

  • The tensile strength of cement may be obtained by the Briquette test.
  • A mixture of cement and sand is gauged in the proportion of 1:3 by weight
  • The percentage of water to be used is calculated by the formula (P/5+2.5)% where P is the percentage of water required to produce a paste of standard consistency.
  • The mix is filled in the briquette moulds and the surface of the mould is finished with the blade of a trowel.
  • Briquette mould is then kept for 24 hours at a temperature of 27° +2°C and in an atmosphere having 90% humidity.
  • The briquettes (6.45 cm?) are then kept in clean water and are taken out before testing.
  • Six briquettes are tested and average tensile strength is calculated.
  • Load is applied steadily and uniformly, starting from zero and increasing at the rate of 0.7 N/mm2 in 12 seconds.
  • OPC should have a tensile strength of not less than 2 MPa and 2.5 MPa after 3 and 7 days respectively.
  • Generally, tensile strength is 10-15% of compressive strength.
  • The load was applied steadily or uniformly from 0 to 0.7 N/mm2 in 12 seconds.

(vi) Fineness Test

  • Fineness is the measure of the size of the cement particles in terms of specific surface (.e. surface area per unit mass).
  • The rate of hydration and hydrolysis and the subsequent setting of cement depends upon the fineness of the particles.
  • The rate of gain of strength is rapid for finer cement, though the final strength is not affected by fineness.
  • The fineness of cement is measured in terms of its specific surface.
  • There are three methods for testing fineness viz.
    (i) Sieve method or particle size distribution method
    (ii) Air permeability method (Nurse and Blaine’s method)
    (iii) Sedimentation method or Wagner’s turbidimeter method

(a) Sieve Method:

  • 100 gm of cement sample is taken and air set lumps, if any, in the sample are broken with fingers.
  • The sample is placed on a 90-micron sieve and continuously sieved for 15 minutes.
  • The residue should not exceed the limits specified below:
S. No. Types of cement  % Residue by weight
(i) Ordinary Portland cement 10
(ii) Rapid Hardening cement 5
(iii) Portland pozzolana cement 5

(b) Air Permeability Method:

air permeability apparatus

  • The fineness of cement is represented by a specific surface i.e. the total surface area in cm2 per gram of
    cement.
  • Fineness can be estimated either by using Lea and Nurse’s air permeability apparatus or by using Blaine’s air permeability apparatus.
  • To determine the fineness, a cement sample of 2 cm height is placed on a perforated plate (size of perforations is 40 u) 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 in the manometer (h1) is recorded.
  • The process is repeated till the ratio h1/h2 attains a constant value.
  • The specific surface is given by the expression


where L is the thickness of the cement layer
A is an area of the cement layer
d is the density of cement
V is the porosity of cement (i.e. 0.475)
h2 is a flowmeter reading
h1 is a manometer reading
K is flow meter constant

(c) Wagner Turbidimeter Test:

  • The cement is dispersed uniformly in a rectangular glass tank filled with kerosene.
  • Parallel light rays are passed through the solution which strikes the sensitive 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 particles are falling in the solution, it is possible to secure information regarding the grading in surface area and in size of particles.
  • Readings are expressed in cm²/gm.

(vii) Heat of Hydration Test

  • Heat is evolved during the hydration of cement, the amount being dependent on the relative quantities of clinker compounds.
  • The apparatus used to determine the heat of hydration of cement is known as a calorimeter.
  • 60 gm of cement and 24 ml of distilled water are mixed for 4 minutes at a temperature between 150-25°C
  • Three specimen glass vials 100 mm x 20 mm are filled with this mixture, corked and sealed with wax
  • The vials are then stored with the mixture in a vertical position at 27°+2°C.
  • The heat of hydration is obtained by subtracting the respective heat of the solution of hydrated cement from the heat of the solution of unhydrated cement calculated nearest to 0.1 calories.
  • The heat of the solution of hydrated cement is calculated by using a calorimeter.
  • The heat of hydration for low heat Portland cement should not be more than 66 and 75 cal/gm for 7 and 28 days respectively.

(viii) Specific Gravity Test

  • The specific gravity of cement is obtained by using Le Chatelier’s flask.
  • Long seasoning is the chief cause for low specific gravity in unadulterated cement.
  • The flask is filled either with kerosene free of water or naphtha having a specific gravity not less than 0.7313 to a point on the stem between zero and 1 ml mark.
  • The flask is then immersed in a constant temperature water bath and the reading is recorded.
  • A weighed quantity of cement is then introduced in small amounts at the same temperature as that of the liquid
  • After introducing all the cement, the stopper is placed in the flask and the flask is rolled in an inclined position, or gently whirled in a horizontal circle so as to free the cement from the air until no further air bubbles rise to the surface of the liquid.
  • The flask is again immersed in a water bath and the final reading is recorded.
  • The difference between the first and the final reading represents the volume of liquid displaced by the weight of cement used in the test.
    Specific gravity = Weight of cement (in gms)/Weight of displaced volume of liquid (in ml)
  • The specific gravity of Portland cement is generally about 3.15.
  • Specific gravity is not an indication of the quality of cement. It is used in the calculation of mixed proportions.

 

FAQS
Que. Match the apparatus for the conduct of the test in List 1 with the property of
cement in List 2.

List 1

Vicat’s apparatus test

Le-Chateller’s apparatus

Briquette test method

Air permeability method

List 2

Soundness testFineness

Setting time

Tensile strength

(a) A-3, B-1, C-4, D-2  (b) A-4, B-1, C-3, D-2

(c) A-4, B-3, C-1, D-2  (d) A-3, B-4, C-2, D-1

Solution: (a)
Soundness test:
(a) Le-chatalier apparatus
(b) Autoclave method

Fineness test:
(a) Sieve method
(b) Air permeability method
(c) Wanger turbidity method

Setting time:
Vicat’s apparatus

Tensile strength test:
(a) Briquette test
(b) Split tensile strength test

 

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