Building Materials, Third Edition

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The specimen is weighed initially (usually green) and the length of the specimen is measured
by means of a special screw gauge shown in Fig. 4.8. The specimens are allowed to air-season
and periodically weighed and measured, until a uniform moisture content of nearly 12 per cent
is reached. The specimens are then dried in an oven at 103°  2°C until an approximately
constant weight is attained. Finally, the specimen is weighed and measured.
The radial and tangential shrinkage are calculated from the following formulae:
Shrinkage, s, tangential or radical from green to the required dry condition

= 1r

1

ll

l

× 100 per cent

Moisture content, r, per cent = r^0

0

WW

W

× 100 per cent

where W 1 and l 1 = weight and length in the initial condition (usually green)
Wr and lr= weight and length at r per cent moisture content
W 0 = weight at oven dry condition

p



2R

V e))——/22‚—

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A graph is plotted with r as the ordinate and s as the abscissa. From this graph, the moisture
content at which shrinkage commences appreciably is noted. This is known as Y 0 point. The
average value of the Y 0 point in the radial and tangential cases is taken as fibre saturation point.

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y € v— „X The specimen may be 50 × 50 × 750 mm or 20 × 20 × 300 mm. The test
specimen is supported on the rig as shown in Fig. 4.9. The load is applied continuously at a
constant rate of 2.5 mm per minute in case of 50 × 50 × 750 mm and 1.0 mm per minute in case
of 20 × 20 × 300 mm.

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