Standard Consistency of Cement (Paste)

Experiment:- To determine standard consistency of cement paste.

Purpose- The purpose of this test is to find out the percentage by weight of water to be added to cement to make a paste of standard consistency.

Consistency: -  A certain minimum quantity of water is required to mixed with cement so as to complete chemical reaction between water and cement, less water than this quantity would not complete chemical reaction thus resulting in reduction of strength and more water would increase water cement ratio and so would reduce its strength. So, correct proportion of water to cement is required to be known to achieve proper strength while using cement in structure. This can be found out knowing standard consistency of cement paste.

Standard consistency:  (Normal consistency)

Standard consistency of cement paste is defined as that consistency which permits the Vicat plunger to penetrate to a point 5 to 7 mm from the bottom of the Vicat mould in this test. It is expressed as amount of water as a percentage (by weight) of dry cement.

Necessity and uses of standard consistency

• Generally the water percentage for standard consistency is about 30%. However cement produced by different factories may not have same properties and so it is necessary to standardize the consistency using standard equipment.
• The knowledge of standard consistency is required while performing other important test such as setting time, soundness etc. as these tests are performed on cement paste using a certain percentage of water required for standard consistency.

Gauging time

It is period observed from the time when water is added to cement for making cement paste till commencing the filling of mounld of Vicat Apparatus, in this test.

Apparatus :-

• A Vicat apparatus with plunger 10mm dia
•  Weighing balance
• Trowel weighing 210g ± 10g
•  Measuring glass 200ml
• Clean platform to make cement paste

Materials: -

• Cement 3 to 4 kg
• Water

Procedure: -

• Take a sample off cement 300g. Weigh it correctly.
• Add water 25% by weight i.e., 75g (75ml) to the cement and mix it thoroughly, to make a cement a cement paste.
• Place the Vicat mould on a non-porous plate, fill the mould with cement paste, smooth off the surface of the paste making it level with the top of the mould. To expel air shake the mould slightly. The care that the gauging time is between 3 to 5 minutes. While filling the mould use of operator’s hand and blade of trowel only should be used.
• Place the test block in the mould together with the non-porous plate, under the rod bearing the 10mm dia plunger gently to touch the surface of the test block and quickly release, allowing it to sink into the cement paste. Carry this operation immediately after filling the mould. Note the penetration of the needle from the bottom of mould indicated on the scale.
• Prepare trial pastes with varying percentages of water, increasing water percentage by 1 % each time, until the amount of water necessary for making standard consistency (which permits plunger to penetrate to a point 5 to 7 mm from the bottom of the mould) is determined. 

Observations:

S. No.	Wt. of water, W1 g	Wt of cement, W2 g	(W2/W1) X10	Positon of Vicat needle point after penetration from bottom
1. 2. 3. 4. 5. 6.

Result: - The percentage by weight of water with respect to cement to produce standard consistency is ______%.

Requirement: - As per IS 4031-1968 the standard consistency is obtained when the Vicat plunger penetrates to a point 5 to 7 mm from bottom of Vicat mould.(This is generally 30%)

Conclusion:- For the given sample of cement, the standard consistency is achieved with water percentage equal to _______%. 

Fineness of Cement by Dry Sieving (Very Simple Procedure)

To find fineness of cement by dry sieving method. In this method the cement sample is sieved dry on IS sieve no. 9. The residue left is expressed as percent of weight of sample, and in an indirect measure of fineness of cement.

Apparatus:

1. 90 micron IS sieve

2. Weighing balance (2kg) accurate to 0.1g, with weights

3. Bristle brush 25mm size.

Material: Cement sample weighing about 100g.

Procedure:

1. Weigh cement sample accurately and record weight W1. Place the sample on IS sieve no.9 (It is preferable to take W1= 100g for simplifying calculations).

2. Break air set humps in the sample with fingers.

3. Hold the sieve in both hands and sieve with a gentle wrist motion without spilling the cement and keeping cement well spread on the screen. Carry out continuous circular motion of the sieve for a period of 15 minutes.

4. Collect the residue left on the sieve, using brush if necessary, and weigh and residue. Let the weight of residue be W2.

Observations and Calculations:

1. Weight of the cement sample = W1 gms.

2. Weight of residue = W2 gms.

    Hence,  Percentage residue = P = (W2/W1) x 100 %

Results: Percent of residue of cement sample by dry sieving = P %. It is less than/ more than 10%

Requirement: As per IS 269-1976, the residue by weight on 90 micron IS sieve by dry sieving should not exceed 10% by weight in case of Ordinary Portland Cement. Coarser material more than 10% signifies less fine cement and vice versa.

Conclusion:

The given sample of cement contains less than/ more than 10% by weight of materials coarser than 90 micron sieve. Therefore it satisfies/ does not satisfy the criteria as specified by IS.

Fineness of Cement

Experiment: To determine the fineness of cement.

Purpose: The purpose of this test is to find out the quantity of coarse material present in cement. It is an indirect test of fineness of cement.

What is fineness?

Cement is in the form of powder, which is obtained by grinding the various raw materials after calcimining. The grinding produces finer particles of cement. The degree to which the cement is ground to smaller and  smaller particles is called fineness of cement

Effect of fineness on properties if cement: 

During use of cement in structure water is mixed with cement. A chemical reaction takes place between water and cement, and it is called hydration. The strength of cement concrete or mortar develops with hydration. More the rate of hydration faster is the development of strength. This is because finer cement offers greater surface area of particles for hydration. At the same time the rate of development of heat due to hydration also increases.

Advantage of using finer cement:

The cement develops strength earlier and so formwork can be removed earlier thus reducing the cost of construction.

Disadvantage of using finer cement:

The finely ground cement is likely to deteriorate earlier due to setting because of moisture in air. Also the drying shrinkage is higher in case of finer cements.  
Methods of finding fineness of cement:
Fineness of cement is found by two methods
A) By method of dry sieving
B) By specific surface method- finding fineness of cement using Blanine's air permeability apparatus.
Though method B is more accurate it is rarely used for specific purpose.Method A is quite good for field work.

DETERMINATION OF FINENESS BY DRY SIEVING (IS 4031 Part 1 : 1996)

SIEVING METHOD

Principle: The fineness of cement is measured by sieving it on standard sieve. The proportion of cement of which the grain sizes are larger than the specified mesh size is thus determined. A reference sample having a known proportion of

material coarser than the specified mesh size is used for checking the specified sieve.

Apparatus:

a) Test Sieve: It comprises a firm, durable, non-corrodible, cylindrical frame of 150 mm to 200 mm nominal diameter and 40 mm to 100 mm depth, fitted with 90 pm mesh sieve cloth of woven stainless steel, or other abrasion-resisting and non-corrodible metal wire. The sieve cloth shall comply with the requirements of IS 460 ( Part 1) : 1985 and IS 460 ( Part 3 ) : 1985

and shall be free of visible irregularities in mesh size when inspected optically by the methods of IS 460 ( Part 3 ) : 1985. A tray fitting beneath the sieve frame and a lid fitting above it shall be provided to avoid loss of material during sieving.

b) Balance: Capable of weighing up to 10 g to the nearest 10 mg.

c) Brush: A nylone or pure bristle brush, preferably with 25 to 40 mm bristle, for cleaning the sieve.

Material for Checking the Sieve:

A Standard reference material of known sieve residue shall be used for checking the sieve. The material shall be stored in sealed, airtight containers to avoid changes in its characteristics due to absorption or deposition from the atmosphere. The containers shall be marked with the sieve residue of the reference material.

Procedure: 

a) Determination of the Cement Residue

Agitate the sample of cement to be tested by shaking for 2 min in a stoppered jar to disperse agglomerates. Wait 2 min. Stir the resulting powder gently using a clean dry rod in order to distribute the fines throughout the cement.

Fit the tray under the sieve, weigh approximately 10 g of cement to the nearest 0.01 g and place it on the sieve, being careful to avoid loss. Disperse any agglomerates. Fit the lid over the sieve. Agitate the sieve by swirling, planetary and linear movement until no more fine material passes through it. Remove and weigh the residue. Express its mass as a percentage, R1, of the quantity first placed in the sieve to the nearest 0.1 percent. Gently brush all the fine material off the base of the sieve into the tray. 

Repeat the whole procedure using a fresh 10 g sample to obtain 5. Then calculate the residue of the cement R2 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. The sieving process is carried out manually by a skilled and experienced operator.

NOTE - Alternatively a sieving machine may be used provided that it can be shown to give the same results as the manual operation.

b) Checking the Sieve

Agitate the sample of cement to be tested by shaking for 2 min in a stoppered jar to disperse agglomerates. Wait 2 min. Stir the resulting powder gently using a clean dry rod in order to distribute the fines throughout the cement.

Fit the tray under the sieve. Weigh approximately 10g of the reference material to the nearest 0.01 g and place it in the sieve, being careful to avoid loss. Carry out the sieving procedure as above including the repeat determination of residue to yield two values p1 and P2 expressed to the nearest 0.1 percent. The two values of P1 and P2 for a satisfactory sieve should differ by not more than 0.3 percent. Their mean P characterizes the state of the sieve.

Given the known residue on the 90 m mesh of the reference material, R0 calculate R0/P as the sieve factor, F, expressed to the nearest 0.0 1. The residue, R determined as in 1 step shall be corrected by multiplying by F, which may have a value of 1.00+-0.20. 

EXPRESSION OF RESULTS

Report the value of R, to the nearest 0. I percent, as the residue on the 90 pm sieve for the cement tested. The standard deviation of the repeatability is about 0.2 percent and of the reproducibility is about 0.3 percent.