Testing methods of pozzolanas
Practical Action
It is also argued that because pozzolanas are used for a variety of different applications, such
as in mortars, concretes, block manufacture, etc., and mixed with a variety of other materials
such as lime, OPC, sand, etc., (which can also radically affect the reaction of the pozzolana),
then perhaps it is better to develop a test to determine the desired properties of the mixture
in
the context for which it is intended. This provides valuable information for specific project
applications and can also help determine the general characteristics of a pozzolana for cases
where the application of the pozzolana is not specified. This approach, along with that of
fineness testing, forms the basis for most field tests.
Tests are required for a number of reasons:
1. to assess the viability of a new potential pozzolanic deposit;
2. to provide quality control on a day-to-day basis as part of a production process;
3. to provide long term quality control of the pozzolanic resource.
Many of the standard tests specified in the relevant literature and in the national Standards
which cover testing of pozzolanas (in India and USA for example), require sophisticated and
expensive laboratory equipment to evaluate the pozzolanicity of a particular material. In
developing countries where such equipment is beyond the reach of small-scale producers and
where such laboratory facilities are often non-existent and many of the consumables hard to
source, determining pozzolanicity can be a major problem. The time required to carry out
such tests is also often very lengthy, often requiring a month or more for curing samples. This
is not such a problem where the aim is to cover points 1 or 3 from the list above, but for
short-term day-to-day analysis of the raw materials, a faster, simpler test is often required.
In this brief the aim is to note the various test methods available for determining the
reactivity of pozzolanas, highlighting those which are particularly suitable for use by small-
scale users of pozzolanas in developing countries. The brief will look quickly at the Standards
available and then describe a simple, practical and rapid field test which has been developed
by practitioners in the field.
Test Methods Designated in the Standards
The following tests are an example of Standards developed by countries to allow accurate
characterisation of pozzolanic materials. Other countries apart from those mentioned below
publish such Standards and these should be referred to where applicable.
There are also even more sophisticated procedures used, such as x-ray diffraction or electron
microscopy to determine whether the structure of a pozzolana is amorphous (more reactive
with lime) or crystalline, but such tests are beyond the scope of this brief.
Indian Standards
The Indian Standard for methods of Test for Pozzolanic Materials (1967) gives a variety of
tests for determining various characteristics of pozzolanas. They are briefly described below.
The address for the Indian Standards Institution is given in the resource section of this brief
for those who wish to study the Standard in more detail (see Reference 2).
1. Chemical analysis
The chemical analysis will determine the following characteristics for pozzolanas:
Loss on ignition. This is the loss of weight due to release of volatiles on
ignition. A sample is ignited in a furnace under controlled conditions and the
weight loss measured. This applies to pozzolanas which have to be calcined
for use. Given as a weight percentage loss.
Silica content
Combined ferric oxide and alumina content
Ferric oxide content
Alumina content
2