Procedure & Apparatus of A Fitness Test for Cement
Particles of cement are not the same in size. The average size of particles in cement should not be too fine and not too coarse. The particle size in cement is decided by fitness test for cement according to the Indian Standard.
The standard sieve size is 90 µm which shows that residue of grain size more than 90 Micron of cement is not kept about more than 10% on the sieve. The value of fineness for different cement is should be less than 10% percentage of the residue by weight. The fineness of cement should be between 5% to 10%.
Importance of Fineness of Cement
- The fineness of cement is able to decrease bleeding, increase in finance of cement and also increase the cohesiveness of the concrete mix.
- It can increase the final setting time of cement.
- Fineness and workability are complimenting.
- The fineness test also measures the surface area of a particle of cement per unit mass.
- The fineness of cement increases the strength development in the cement during its first 7 days.
- If the cement is of good quality then it increases the rate of hydration.
Fitness Test according to Sieve Method
Sieve Test Procedure
AIM - According to Indian Standard 4031 90 µm IS sieve is used to examine the fitness of cement. IS code for finance test of cement is Indian Standard: 4031.
Apparatus used for fineness test of cement is:
1. 90µm IS Sieve,
2. Weight Balance having capacity 10mg to 100g,
3. Nylon or pure bristle brush and
4. sieve shaking machine.
- At first, users have to collect a sample of cement and rub it with their hands. The sample should be free of any kind of lamp.
- Then users have to take 100 gm. Of cement sample and notes the weight.
- After that, they have to drop 100 gm of cement into a 90 µm sieve and close it with the lid.
- Next users have to shake the sieve with their hands and linear movements for 15 minutes in all directions or by Sieve shaking machine.
- After that, users should check the weight of the cement left on the 90 µm sieve as W2.
- The fineness test for cement formula is (W2/W1)×100
Fineness test for cement formula = (W2/W1)×100, where,
W2 = Cement residue on a sieve,
W1 = Weight of given sample of cement.
- Now users have to calculate the percentage of Weight of cement-retained on Sieve.
- Test Result 1 for sample: Let W1 = 100g, W2= 4.68,
then fineness = (W2/W1)×100 = (4.68/100)×100 = 4.48%
- Test Result 2 for sample: Let W1 = 100g, W2= 6.28,
then fineness = (W2/W1)×100 = (6.28/100)×100 = 6.28%
- Test Result 3 for sample: Let W1 = 100g, W2= 7.64,
then fineness = (W2/W1)×100 = (7.64/100)×100 = 7.64%
- Now average = (4.48%+6.28%+7.64%)/3= 6.14%, so Fineness value for given sample of cement is 6.14%.
According to the Indian Standard, the standard cement should have fineness less than 10 %.
Air Permeability Test
An apparatus test the fitness of cement which is developed by Lea and Nurse. In the apparatus test cell is consisted, where cement is placed and air pressure is applied. flow–metre examine the quantity of air passing per second per unit through its capillary tube.
Users have to place the cement sample of 20 mm height on the perforated plate of 40-micron perforations and then apply the air pressure and connect the manometer to the top of the permeability cell and the air is turned on.
1. Here the lower end of the permeability cell is less than slowly connected to the other end of the manometer.
2. Rate of flow is so adjusted that the flow meter shows a pressure difference of 30- 50cm and reading in the manometer is recorded.
3. The process is repeated till the ratio h1/h2 is constant and a specific surface is given by the expression.
S = 14/d(1_Ψ) (√AΨ^2/KL. √h1/h2)
S = specific surface
L = thickness of cement layer
A= area of cement layer
d = density of cement
Ψ = porosity of cement (0.475)
h1 = manometer reading
h2 = Flowmeter reading
K = is the flow metre constant and it is obtained by Q = Kh2d1/μ
μ = viscosity of air
d1 = density
Q = quantity of air passed per second
Q = (V/t) × (P_p)/P
P = atmospheric pressure
p = vapor pressure of water at room temperature.
The minimum specific surface of cement are:
- 2250 cm2/g for ordinary Portland cement
- 3250 cm2/g for Rapid hardening cement
- 3250 cm2/g for low heat cement
- 3000 cm2/g for Portland pozzolana cement
- 2250 cm2/g for high alumina cement
- 4000 cm2/g for super sulfate cement