A relatively novel supplementary
cementitious material (SCM) could offer
special advantages for concrete used
in marine environments, according to
researchers at the University of Dundee.
They are exploring the possibilities of
calcined clay: clay that has been heated to
about 850°C and then ground to a mixable
powder. “Our earlier research shows that
it can work well as an SCM, and we’re
currently investigating how it performs in
different situations, including the marine
environment,” says Dr Michael McCarthy,
reader in civil engineering.
This MPA/Energy Technology Partnershipfunded
project has focused on physically
and chemically characterising calcined
clay materials, as well as examining their
reactivity, in order to understand how they
behave in cementitious systems. Now, it is
looking into the implications for concrete
construction and performance, including
properties such as workability, flow and
heat development, and long-term strength
and durability.
“Some of our early tests suggest calcined
clay-cement combinations can achieve
good chloride migration resistance, which is
important for protecting steel reinforcement
in marine exposures,” says McCarthy.
Longer-term tests covering this and other
aspects of durability, including resistance to
sulfate attack, alkali-aggregate reaction and
reinforcement corrosion, are planned or in
progress. The team hope that this research
will feed into guidance for how calcined
clay could be used in marine and other
environments.
Calcined clay can also reduce the embodied
carbon of concrete by replacing a proportion
of Portland cement. SCMs that can
produce marine-grade concrete will
be particularly valuable, says Dr Moray
Newlands, McCarthy’s co-researcher. “Marine
structures, such as sea defences and wind
turbine bases are often quite substantial,
and require large amounts of concrete, so
low-carbon options are vital and can make
a big difference in terms of a project’s total
carbon footprint.”
The UK’s strategy to expand offshore
wind power will involve the creation of
hundreds of huge floating turbine platforms,
he points out, which could be made either
from steel or from concrete. “The steel
would be largely imported, involving longdistance
transport,” he says. But with the
capacity to provide large amounts of locally
sourced, low-carbon and chloride-resistant
concrete, this strengthens the case for local
construction. “I think calcined clay mixes
have the potential to play a major role in that
supply chain.”