Testing methods of pozzolanas
Practical Action
Calcium oxide content
Magnesia content
Sulphuric anhydride content
Determination of soluble salts
These chemical tests are performed using specified reagents. Results of chemical
content are given as a weight percentage.
2. Fineness
To determine the specific surface of the pozzolana - given in cm2/g
To determine the fineness by sieving
3. Soundness
Soundness of a sample (see below) is a measurement of its tendency to crack,
distort, pit or disintegrate. Either of the two following tests can be used to establish
soundness:
‘Le Chatelier’ method uses a simple expandable ring to indicate the
expansion of a sample over a set period of time
The autoclave method. This method tests for expansion after a certain period
of time at elevated temperature in an autoclave.
The sample is prepared in accordance with the Indian Standard for testing cement,
but in place of cement a mixture of pozzolana and cement in the ratio 0.2N: 0.8 by
weight is used, where,
N = Specific gravity of pozzolana
Specific gravity of cement
4. Initial and final setting time
Simple tests are carried out to determine the setting times for a lime-pozzolana and
lime-cement sample. Apparatus used is called the Vicat set
5. Lime reactivity
The test for lime reactivity as given in these standards is very similar to the test for
compressive strength. A series of 50mm cubes are prepared using a lime : pozzolana
: sand mixture. They are allowed to cure for 8 days in an incubator and the
compressive strength of the cubes is measured. Results are given in kg/cm2.
6. Compressive strength
A similar test is carried out as for the lime reactivity given above, but the mix
contains cement in place of lime. Compressive strength tests are carried out on
specimens which have been incubated for 7, 28 and 90 days. A control test is also
carried out using a pozzolana-free mixture. Three 50mm cubes are tested and the
average figure used. Again the result is given in kg/cm2.
7. Transverse strength
The transverse strength test is again similar to the compression strength test but in
place of cubes, rectangular blocks (160 x 40 x 40mm) are prepared and tested using
specially designed equipment. The ratio of the pozzolana: cement: standard sand mix
is 0.2N : 0.8 : 3 by weight (N is given above in section 3).
8. Drying shrinkage
A simple test on a 250 x 10 x 10mm block to deduce the shrinkage over a 7 and 35
day period.
9. Permeability
A specially designed ‘permeability unit’ is used to test a series of specimens for
porosity. Water is forced under pressure through cured specimens and the passage of
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