Testing methods of pozzolanas
Practical Action
water measured. The resulting coefficient of permeability is given in cm/second/unit
gradient.
10. Reduction in alkalinity and silica release
Only applicable to certain pozzolanas, this test helps to ascertain the effectiveness of
some pozzolanas in reducing the harmful effects of alkali-aggregate reaction in
concrete. It is a chemical test using reagents to determine the reduction in alkalinity,
given in millimoles/litre.
11. Specific gravity
A simple measurement of the specific gravity of the raw pozzolana uses a piece of
apparatus known as the ‘Le Chatelier’ flask. Given in g/ml.
The above test procedure will give a comprehensive characterisation of any pozzolana.
The equipment required to perform such testing is, however, very costly and sophisticated. It
is simply not possible in some regions of the world to carry out such tests, and where the
application of the pozzolana is such that knowledge of the characteristics on such a level is
not critical, then tests of this complexity are not suitable or necessary.
The Indian Standard ‘Specification for Lime-Pozzolana Mixture’ (IS 4098 - 1967) stipulates
specific characteristics of different grades of such a mixture in terms of maximum free
moisture content, loss on ignition and proportion retained on a 150 micron sieve; initial and
final setting times; compressive strength and moisture retention. The minimum 28 day
compressive strength, for example, is specified at between 7 and 40 kg/cm2 , depending on
grade of material.
Characteristic
Requirements
Type
LP40*
Type Type
LP20* LP7*
1. Free moisture percent, maximum
5
2. Loss on ignition percent, maximum
20
3. Fineness, percent retained on 150 micron IS sieve 10
4. Setting time
a/ initial, minimum
b/ final, maximum
2h
24 h
5. Compressive strength (kg/cm2)
a/ 7 days, minimum
b/ 28 days, minimum
20
40
6. Water retention (percent of original flow,
minimum)**
70
*Type LP40 for masonry mortars up to GradeMM5
Type LP20 for Masonry mortars up to Grade MM2 and for foundation concrete
Type LP7 for masonry mortars up to Grade MM0.5 and for foundation concrete
**No test is specified for this characteristic, however, in the Standard above.
55
20 20
10 -
2h
36 h
2h
48 h
10 3
20 7
70 70
American Society for Testing and Materials (ASTM) Standard
The ASTM Standard (ASTM C311 - 77) varies slightly in content from the Indian Standard.
Below is given a brief summary of the test methods of the ASTM standard.
Chemical analysis
1. Moisture content
4