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Unformatted text preview: ed on the second and third readings differ by more
than 5 percent, the loading cycle shall be repeated until the difference in
strain between consecutive readings at ( C + 1.5 ) kg/sq cm does not
exceed 5 percent.
9.9 Calculation — The strains at the various loads in the last two
cycles shall be calculated separately for each extensometer and the
results shall be plotted graphically against the stress. Straight lines
shall be drawn through the points for each extensometer; the slopes of
these two lines shall be determined and from them the average value
shall be found. If the difference between the individual values is less
than 15 percent of the average value, this average value, expressed in
kg/sq cm to the nearest 1 000 kg/sq cm shall be recorded as the modulus
of elasticity of the concrete. If the difference is greater than 15 percent,
the specimen shall be re-centred in the testing machine and the test
repeated. If the difference after re-centring and testing is still greater
than 15 percent of the average value, the results of the test shall be
9.10 Report — The following information shall be included in the
a) identification mark;
b) date of test;
c) age of specimen;
d) shape and nominal dimensions of specimen;
e) modulus of elasticity; and
f) remarks, such as number of loading cycles.
10. DETERMINATION OF THE MODULUS OF ELASTICITY BY
10.1 This clause specifies the procedure for determining the modulus of
elasticity of concrete by an electrodynamic method, namely by
measuring the natural frequency of the fundamental mode of
longitudinal vibration of concrete prisms. This is a non-destructive test 19 IS : 516 - 1959
and therefore the same specimens may subsequently be used for the
flexural strength test specified in 8.
10.2 Specimens — The specimens shall in all respects comply with the
requirements of 9.2.
10.3 Apparatus — The apparatus shall consist of the following.
10.3.1 A variable frequency oscillator with a working range up to 10 000
cycles per second, reading to an accuracy of ± 0.5 percent. A means of
varying the output power shall be incorporated, and the output power
shall be not less than 2 watts.
10.3.2 An electro-magnetic exciter unit of the moving-coil or variable
air-gap type. If the moving-coil type is used, the former and coil should
have as low an inertia as possible, the mass being not more than 0.2
percent of the mass of the specimen (the former should be of light card or
paper). A suitable type of instrument is shown in Fig. 4. If a variable
air-gap exciter unit is used, this shall be of a similar type to the pick-up
10.3.3 An electro-magnetic pick-up unit of the ordinary telephone type.
Alternatively, a piezo-electric gauge may be used, provided that its mass
is not more than 0.2 percent of the mass of the specimen.
10.3.4 An audio-frequency amplifier.
10.3.5 An amplitude indicator consisting of a voltmeter, milliammeter or
cathode ray oscilioscope.
10.3.6 A fixed clamp or...
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This document was uploaded on 10/01/2013.
- Fall '13