Japanese University Find Rare Mineral for Strengthening Concrete Walls

Nagoya University researchers found aluminous tobermorite inside the walls of a nuclear power plant that formed due to reactions between minerals in the concrete mixture in the presence of water and moderately high temperatures over a prolonged period. Image courtesy of Ippei Maruyama, Nagoya University, and Chubu Electric Power Co.

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 years.

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.