Researchers from Nagoya
University (Nagoya, Japan) have discovered the formation of aluminous
tobermorite in the thick concrete walls of the Hamaoka Nuclear Power Plant in
Japan. According to the university, aluminous tobermorite is a rare mineral
used in Roman concrete barriers that helped those structures to survive for
more than 2,000 years.
Nagoya University researchers
reported their finding in the journal Materials and Design.
In terms of long-term applications, researchers hope this discovery will aid in
the development of stronger, more eco-friendly concrete that still meet
standardized requirements for strong concrete structures.
“We found that cement hydrates
and rock-forming minerals reacted in a way similar to what happens in Roman
concrete, significantly increasing the strength of the nuclear plant walls,”
says Ippei Maruyama, an environmental engineer at Nagoya University.
The Roman concrete used in the
construction of marine barriers has managed to survive for more than two
millennia due to the chemical reaction caused when seawater dissolves volcanic
ash in the mixture, leading to the formation of aluminous tobermorite. Because
it is a crystal, aluminous tobermorite can strengthen and stabilize concrete.
However, not only is aluminous tobermorite difficult to incorporate into modern
forms of concrete, it also requires higher temperatures to manufacture that can
prove detrimental to concrete strength.
Such issues are what make the
discovery of aluminous tobermorite inside the concrete walls of Hamaoka—a
now-decommissioned nuclear power plant that operated from 1976 to 2009—so
significant to Maruyama and his colleagues. Taking samples from this plant,
they found that aluminous tobermorite formed in a nuclear reactor's concrete
walls when temperatures of 40-55 °C (104-131 °F) were maintained for 16.5
Further analysis revealed that
the reactor's thick walls were able to retain moisture, which aided in the
reaction process between minerals and water. In turn, this resulted in
increased availability of silicon and aluminum ions and the alkali content of the
wall, and ultimately led to the formation of aluminous tobermorite.
“Our understanding of concrete
is based on short-term experiments conducted at lab time scales,” Maruyama
says. “But real concrete structures give us more insights for long-term use.”
Source: Nagoya University, http://en.nagoya-u.ac.jp.