FINENESS OF CEMENT BY BLAINES AIR PERMEABILITY METHOD (IS-4031-PART-2)

Overview

Blaine’s 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 fineness is expressed as a total surface area in square centimeters per gram.

Apparatus

Measuring instruments

Name	Range	Accuracy
Blaine air permeability apparatus	Refer to IS:5516
Balance	3 g	1 mg
Timer	30 min.	0.2 sec

Environmental condition

Temperature	27 ± 20 C
Humidity	65 % (max.)

Procedure

Procedure consists of 4 steps

(a)Determination of the density of cement

To determine the density or specific gravity of cement click here.

(b)Determination of the bed volume

1. Apply a very thin film of light mineral oil to the cell interior. Place the perforated disc on the ledge in cell. Place two new filter paper discs on the perforated disc.
2. Fill the cell with mercury. Level the mercury to the top of the cell with a glass plate.
3. Remove the mercury from cell and it, M₁.
4. Remove the top filter paper from the permeability cell and compress a trial quantity of 2.80 g of cement into the space above filter paper to the gauge line in the cell. Place the other filter paper above the cement bed.
5. Fill the remaining space in the cell above the filter paper with mercury. Level the mercury to the top of the cell with a glass plate and remove mercury from the cell and weigh it, M₂.
6. Calculate the volume occupied by the cement bed in the cell from the following equation.

V = (M₁-M₂)/D,

Where

D = Density of mercury (13.54 g/cm³)

7. Average at least two volume determinations that agree to within ±0.005cm³ and record this value.

(c)Determination of apparatus constant

1. Take an amount (W) of standard cement so as to give the cement bed of porosity e=0.500.

i.e. W = (1-e)ρV

or W = 0.500ρV

2. Place the perforated disc on the ledge at the bottom of the cell and place on it a new filter paper disc. Place the weighed quantity of standard cement, W, in the cell taking care to avoid loss.
3. Tap the cell to level the cement. Place a second new filter paper disc on the leveled cement.
4. Compress the cement with the plunger until the plunger collar is in contact with the top of the cell. Slowly withdraw the plunger a short distance, rotate 90⁰, repress the cement bed, and then slowly withdraw.
5. Attach the permeability cell to the manometer tube with an air tight connection and slowly evacuate the air in the manometer U-tube until the liquid reaches the top mark, then tightly close the valve.
6. Start the timer when the bottom of the meniscus reaches next to the top mark and stop the timer when the bottom of the meniscus reaches the bottom mark. Record the time t and temp. of test.
7. Repeat the whole procedure on two further samples of the same reference cement. Calculate the average time of the three determinations. Then calculate the apparatus constant using the formula given below.

Where,

K=Apparatus constant

S₀=Specific surface of reference cement

ρ₀=Density of reference cement

t₀=Mean of three measured times

η₀=Air viscosity at the mean of the three temperatures.

(d)Determination of fineness

1. Repeat the steps (1 to 6) as done in determination of apparatus constant, but this time using the cement whose fineness is to be calculated.
2. Calculate fineness of cement using following formula.

 

Where,

S = Specific surface area

K = Apparatus constant

ρ = Density of cement

t = Time

Technical discussion

• Fineness of cement has a great effect on the rate of hydration and hence the rate of gain of strength.
• Fineness of cement increases the rate of evolution of heat.
• Finer cement offers a great surface area for hydration and hence faster the development of strength.
• Increase in fineness of cement also increases the drying shrinkage of concrete and hence creates cracks in structures.
• Excessive fineness requirement increases cost of grinding.
• Excessive fine cement requires more water for hydration, resulting reduced strength and durability.
• Fineness of cement affects properties like gypsum requirement, workability of fresh concrete & long term behavior of structure.
• Coarse cement particles settle down in concrete which causes bleeding.
• Approximately 95% of cement particles are smaller than 45 micrometers, with the average particle around 15 micrometers.
• In the early 1900s, cement fineness was expressed as the mass of cement per fractional size (percent weight retained on specific sieve sizes). Now a day’s fineness is usually measured by the Blaine air-permeability test that indirectly measures the surface area of the cement particles per unit mass.
• Cements with finer particles have more surface area in m² per kg of cement.

Standard specification

Type of cement	Indian Standard Reference	Finenees Value (mm2/g)
OPC (33)	269-1976	225,000
OPC (43)	8112-1989	225,000
OPC (53)	12269-1987	225,000
Rapid hardening	8041-1990	325,000
Low heat cement	12600-1989	320,000
Portland slag cement	455-1989	225,000
PPC	1489-1991 (Part 1)	300,000
High alumina cement	6452-1989	225,000
Super sulphated cement	6909-1990	400,000
IRS-T-40	Railway Standard	370,000

Precautions

• The volume of the compacted cement bed should be calculated accurately.
• The time taken by the manometer liquid to fall from one mark to the other should be measured very accurately.

Test standard reference

IS:4031(Part-2):1996-Method of physical tests for hydraulic cement(Determination of fineness by Blaine air permeability method)