Testing methods of pozzolanas
Practical Action
sample.
Simple field tests
Over the years many field workers have developed simple tests, often based on the tests set
out above in the national Standards (and vice versa), to allow rapid evaluation of pozzolanas
in the field. Such tests need to be carried out in basic conditions, without sophisticated
equipment, in field laboratories, and allow for a reasonably accurate determination of the
working characteristics of a pozzolana or cement/lime - pozzolana mixture. The tests are
almost universally based on the cube compressive strength and are accelerated to allow rapid
testing to be carried out. The fineness test is also useful to meet day-to-day quality control
needs as the fineness for a given pozzolana is one of the determinants of strength
development. Allen (4) proposes the following criteria for a suitable compressive strength
test for pozzolanic mixes:
Equipment must be simple and test methods should be easy to use in all
environments
Reproducibility should be within acceptable limits
The relationship between accelerated strength and 28 day strength should hold good
for a variety of mixes and a variety of materials
The results should be suitable in their own right for compliance with specifications
and quality control
Results should be available soon after mixing the test cubes
Robin Spence and J.W. Allen (see reference 7) have suggested a performance related test for
pozzolanic materials based on their compressive strength when mixed with lime or Portland
cement. The tests were developed in response to the need for testing of pozzolanic materials
at a site near Arusha in Tanzania in an area where a large deposit of volcanic pozzolana is
found. The test is meant mainly for comparison and quality control purposes. It is suggested
that these tests could be used not as legally binding, rigid commitments, but as a guide to
the manufacturer where there is no means of carrying out full tests. It is not recommended
that this test be adopted in place of the standards which legally apply. It is also
recommended, based on the experience of some practitioners, that the 28 day strength test
should be carried out on a regular basis even where the 7 day test has been carried out after
curing at normal temperatures, as the 7 day test might not give a particularly accurate
indication of eventual compressive strength with some types of materials.
The test procedure
The rapid field test for pozzolana based mixtures is based on the cube compressive strength
test, since it is fairly easy to perform. The first step is the standardisation of the variables
involved in each of the steps of the test. These are:
Size of specimen
Curing regime
Type of lime and lime-pozzolana ratio
Type of aggregate and aggregate cement ratio
Water content and mixing procedure
Casting and compaction procedure
Method of performing compression test
Each of these is considered and a standard procedure adopted.
1. Size of specimen
This test uses 25mm cubes which are cast in 9 compartment gang moulds. The cube
size is small to allow for compact transportable equipment.
2. Curing regime
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