The below mentioned article will guide you about how to determine the fineness of cement.
Determination of Fineness of Cement by Specific Surface by Blaine Air Permeability Method (as per IS 4031-1958):
The determination of specific surface of cement is a recent development. It is a very accurate method of determining the firmness of cement, which affects the hydration and strength development of cement.
Apparatus:
The Blaine air permeability apparatus consists essentially of a means of drawing a definite quantity of air through a prepared bed of cement of definite porosity. The number and size of the pores in a prepared bed of cement of definite porosity is a function of the size of the particles and determines the rate of air flow through the bed.
ADVERTISEMENTS:
The apparatus consists mainly of the following parts:
(a) Permeability Cell:
It consists of a rigid Cylinder 12.7 ± 1 mm inside diameter made of glass or non-corroding metal. The bottom of the cell shall form an air tight connection with the top of the manometer. A ledge of 0.5 to 1.0 mm in width shall be an integral part of the cell for support of the perforated metal disc.
(b) Disc:
ADVERTISEMENTS:
It is made of non-corroding metal 0.9 ± 0.1 mm in thickness having 30 to 40 perforations of 1 mm diameter holes equally distributed over its whole area. This will be fitted in the inside of the cell snugly.
(c) Plunger:
The plunger fits into the cell with a clearance of not more than 0.1 mm. The bottom of the plunger has sharp square edges at right angle to the principal axis. An air vent is provided either in the centre or on one side of the plunger. The top of the plunger is provided with a collar such that when the plunger is placed in the cell and the collar is brought in contact with the top of the cell, the distance between the bottom of the plunger and the top of the perforated disc should remain 15.0 ± 1.0 mm.
(d) Filter Paper:
ADVERTISEMENTS:
It is the medium of retention. This should be equivalent to No. 40 whatman filter paper.
(e) Manometer:
The manometer of standard wall glass tube of outside diameter of 9 mm is made in U shape. The top of one arm of the manometer forms an air tight connection with the permeability cell. On the manometer arm connected with permeability cell a line is engraved around the tube at 125 to 145 mm below the top of the side outlet and also others at distances of 15 ± 1 mm, 70 ± 1 mm and 110 ± 1 mm above that line. A side outlet is provided at 250 mm to 305 mm above the bottom of the manometer.
This outlet is used to evacuate the manometer arm connected to the permeability cell. A positive air tight valve or clamp is provided on the outside out let not more than 50 mm from the arm of the manometer. The manometer is mounted firmly in such a way that its arms are always vertical. It is filled up to the mid-point with a non-volatile and non-hydroscopic liquid of low density and viscosity, such as light grade mineral oil, dibutylphthalate etc.
ADVERTISEMENTS:
Timer:
The stop watch should be capable to read to the nearest 0.5 sec. or less. It should be accurate to 0.5 sec or less for time intervals upto 60 sec and to 1% or less upto 60 to 300 seconds.
Calibration of Apparatus:
Before starting the test, the calibration of the equipment is very essential. The calibration should be made using National Bureau of standards, or Indian Cements having specific surface equivalent to NBS standard. The samples should be at room temperature at the time of test.
ADVERTISEMENTS:
Bulk Volume of Compacted Bed of Powder:
The bulk volume of the compacted bed of powder is determined by the mercury displacement method as follows:
Two filter paper discs are placed in the permeability cell in such a way that the filter discs are flat on the perforated metal disc and then the cell is filled with mercury. Any air bubbles adhering both walls of the cell are removed. The mercury is levelled with the top of the cell with the help of a small glass plate.
Now the mercury is removed from the cell, weighed and its weight recorded. At this stage one of the filter disc is removed and a trial sample quantity of cement of about 2.8 grams is compressed in the cell. At this trial stage use of standard sample is not essential. The prepared bed should be firm. It should not be too loose. In case, the above quantity of cement cannot be compressed to the desired volume, adjust the weight.
After compressing the cement, place the second filter disc over it. The remaining space of the cell is filled with mercury, entrapped air removed, and top of it is levelled off as before. Now the mercury is removed from the cell, weighed and its weight recorded.
The bulk volume of cement is then given by the following relation:
V = (Wa – Wb)/D
where,
V = bulk volume of cement in cm3
Wa = weight of mercury in grams required to fill the cell without cement
Wb = weight of mercury in grams required to fill the top portion of cell not occupied by the prepared bed of cement in the cell.
D = density of mercury at temperature of test in g/cm3. (Table 2.11 shows the relation of temperature, density of mercury, viscosity of air etc.)
At least two determinations of bulk volume of cement should be made using separate compactions for each determination. The bulk volume value to be used for subsequent calculations will be the average of the above two values. The difference acceptable is ± 0.005 cm3. The temperature at the beginning and end of determination should be noted.
Preparation of Sample:
The sample of cement is enclosed in a 125 gram jar and shaken vigorously for two minutes to make it soft (stuff) and break lumps if any.
Weight of Sample:
The weight of standard sample should be sufficient to produce a bed of cement having a porosity of 0.500 ± 0.005 and is calculated as-
w = V . ρ (1 – e)
where,
w = weight of sample required in grams
ρ = specific gravity of cement usually taken as 3.15 for Portland cement
v = bulk volume of bed of cement in cm3 as determined above
e = desired porosity of bed of cement (0.500 ± 0.005).
Preparation of Bed:
The perforated disc is seated on the ledge in the permeability cell and a filter paper disc is placed in the metallic cell and the edges pressed down with a rod slightly smaller than the cell diameter. The quantity of cement determined as above is placed in the cell. The weight of the cement should be correct upto 0.001 gram. To level the cement upto the bed, the side of the cell is tapped slightly.
A filter paper disc is placed on the top of the cement and the cement is compressed with the plunger till the plunger collar is in contact with the top of the cell. The plunger is then removed slowly. For each determination fresh filter paper disc should be used.
Permeability Test:
The permeability cell is attached to the manometer. Care should be taken that the prepared bed is not disturbed and air tight connection is obtained. The air in the one arm of the U tube manometer is slowly evacuated until the liquid in the manometer reaches the top mark. At this stage the valve is closed tightly.
The stop watch or timer is started as soon as the meniscus of the manometer liquid reaches the second (i.e., next to the top) mark and stopped as soon as the bottom of the meniscus of liquid reaches the third next to the bottom mark. The time interval is measured in seconds and noted. The temperature of test also is noted and recorded in degree centigrade.
Procedure of Test Sample:
Before starting the test, the calibration of the equipment is very essential. The calibration should be made using National Bureau of standards, or Indian Cements having specific surface equivalent to NBS standard. The samples should be at room temperature at the time of test.
Calculation:
Calculations of specific surfaces are made by the following equations-
where,
S = specific surface in sq. cm per gram of the test sample.
Ss = specific surface in sq. cm per gram of the standard sample used in calibration of the apparatus.
T = measured true interval in seconds of manometer drop for test sample.
Ts = measured true interval in seconds of manometer drop for standard sample used in calibration of the apparatus.
ns = viscosity of air in poise at the temperature of test of the standard sample used in calibration of the apparatus
n = viscosity of air in poise at the temperature of the test sample
es = porosity of prepared bed of standard sample used in calibration of apparatus.
e = porosity of prepared bed of test sample.
ρs = specific gravity of standard sample used in calibration of apparatus (assumed as 3.15).
ρ = specific gravity of test sample (3.15).
Note:
1. Equations (5) and (6) are used for materials other than Portland cement. Equation 5 is used when the temperature of the test of the sample is with in ± 3°C of the temperature of calibration test of the standard fineness sample and equation 6 is used if the temperature of test is outside of this range.
2. Equations (1) and (2) are used in calculation if fineness of Portland cements compacted to the same porosity as the standard fineness sample. Equation (1) is used if the temp, of test sample is within ± 3°C of the temperature of calibration test of the standard fineness and equation 2 is used if the temperature range is outside this range.
3. Equations (3) and (4) are used if the Portland cement is compacted to other porosity than that of the standard fineness sample used in the calibration test.
Table 2.11 Showing density of mercury, viscosity of air etc., at a given temperature.
Fineness of Cement by Lea & Nurse Method:
The specific surface is expressed as total surface area in square cm per gram or square metre per kg of cement. The principle of the method is based on the relation between the flow of air through the cement bed and the surface area of the particles consisting of the cement bed.
From this, the surface area per unit weight of the body material can be related to the permeability of a bed of a given porosity. The cement bed in the permeability cell is 2.5 cm in diameter and 1 cm depth knowing the density of cement the weight required to make a cement bed of porosity of 0.475 can be calculated. This quantity of cement is placed in the permeability cell.
Now the air is passed through the cement bed at a constant velocity. The rate of flow of air is adjusted till the flow meter shows a difference in level of 30 to 50 cm. The difference in level of manometer say h2 is read carefully and noted. Similarly the difference hi of flow meter is noted. To ensure the steady conditions, the observations are repeated. The steady condition is ensured by taking h1/h2 ratio which should be constant.
Then specific surface area Sw is calculated from the following relation-
where,
n = porosity of cement taken as 0.475
A = area of cement bed in cm2
L = length of cement bed in cm
d = density of cement
C = flow meter constant.
Cements should comply with the following requirements:
