Page 134 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

1. Improvement of energy efficiency (red part); efficiency are limited as they are reaching a plateau
of optimization. Gains from alternative fuels are
2. Use of biofuels and other alternative fuels
(blue part), and projected to increase, but remain a fairly modest
proportion of the total. The projected impact of the
3. Replacement of clinker by substitute third option, substituting clinker by SCMs, is limited
materials or supplementary cementitious by the forecast supply of commonly used SCMs,
materials (SCMs). Materials used include fly notably slag and fly ash. For example, although
ash, various slags, and natural pozzolans slag can substitute up to 90% and typically 70%
(green part). of clinker in blends, the worldwide amount of
slag available is only around 5% of the amount of
Beyond these approaches the CSI study imagines
the remaining reduction in CO to come from clinker produced. Fly ash, although available in
2
Carbon Capture and Storage (CCS) (grey area), larger amounts (around 30% of clinker worldwide,
which is now widely thought to be, at best, very but absent in many countries), is of variable quality
expensive (increasing cement prices 2-4 times). As and much is unsuitable for cement production. So
seen in the Figure 4, the further gains from energy the strategy of clinker substitution could go much
further if new sources of SCMs were available.
However very few materials are available in the
large quantities needed for cement production.

RADICALLY DIFFERENT TECHNOLOGIES

Before discussing in detail alternative
supplementary cementitious materials it is
important to say something about radically
different technologies such as alternative clinkers
or clinker free materials.

Alternative clinkers
Figure 5 shows the “chemical” CO emissions of
2
the hydraulic minerals in the CaO – SiO – Al O –
3
2
2
(SO ) system from two perspectives: first per g of
3

The Indian Concrete Journal | November 2018 135