Building Materials, Third Edition

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To determine the fineness, a cement sample of 20 mm height is placed on a perforated plate
(40 micron perforations) 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 (h 2 ) of 30-50 cm. The reading (h 1 ) in the manometer is
recorded. The process is repeated till the ratio h 1 /h 2 is constant. The specific surface is given by
the expression

S =

`

`

2

1

2

14 A h

d(1 ) KL h

where L = thickness of cement layer

A = area of cement layer

d = density of cement

‰ = porosity of cement (0.475)

h 2 = flowmeter reading

h 1 = manometer reading

K is the flowmeter constant and is obtained by

Q =

€

Kh d 2 1

where = viscosity of air

d 1 = density of kerosene

Q = quantity of air passed per second

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