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TECHNICAL PAPER COLLECTOR’S EDITION

on either an economic or environmental basis in
general use. The need to support consumers in
their use of cements that behave differently to the
Portland reference, in addition to the higher raw
materials cost, will mean that the commercially
viable cost will be very much more than that of
Portland cement. Nevertheless such developments
may be interesting in more specialist applications,
for example for precast concrete.

• Third, the durability and long term
Clinker free binders
performance of these materials is not well
At present many researchers (and funding known.
agencies) are attracted by the idea of “clinker
free binders, such as alkali activated materials, • Finally, and perhaps most importantly, the
also known as “geopolymers,” claiming their materials used in these alkali activated
advantages as low CO cements. Despite the hype, materials are the same SCMs discussed
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it is highly unlikely that such materials will have a above – slag, fly ash, etc., which are only
major impact on the sustainability of cementitious available in relatively low amounts compared
materials for many reasons: to cement clinker. The materials that perform
best in these systems are the same as those
that perform best in cement blends.
• First, the environmental advantages of
these materials are questionable. The So from a practical point of view, one is faced with a
environmental assessment made by Habert choice of how to use slag: either (a) as a component
et al [8] indicates that while the production of a Portland based blend in a well-known and
of geopolymer concrete can have a slightly tested technology with proven durability that can
lower impact on global warming than be used in existing mix designs with conventional
standard Ordinary Portland Cement (OPC) equipment, or (b) in a clinker free system with the
concrete, it has a higher environmental attendant problems of sensitivity, strongly alkali
impact regarding other impact categories materials, risks of contamination, and unknown
long-term performance. Again the cost of providing
related to the production of concentrated
technical support to users also means that a price
sodium silicate solution and the dangers of
handling highly alkaline solutions. significantly higher than that of Portland cement
will have to be charged for such materials to be a
• Second, the performance of these materials commercially viable.
is very sensitive to small variations in the
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starting materials, such as slag or fly ash. ALTERNATIVE SCMS: LC – LIMESTONE,
The setting time and rheology are difficult CALCINED CLAY, CLINKER CEMENTS
to control and may vary widely on a batch- Faced with the limited supply of traditional SCMs,
to-batch basis. They are also very sensitive the key question becomes: what alternative
to contamination by conventional Portland SCMs are available in the very large quantities
cements. This makes use on-site by typical needed? Materials such as plant ashes, notably
construction workers challenging.

The Indian Concrete Journal | November 2018 137