The mineral is known as aluminous tobermorite (Al-tobermorite) and forms fine fibers and plates. It was found in concrete samples retrieved from the wall of the Japanese Hamaoka Nuclear Power Plant which operated from 1976 to 2009.
Al-tobermorite was also found in marine, Roman concrete walls that have presented great performance and durability and survived over 2 millennia. Water has the capability of dissolving the volcanic ash that Romans used in the concrete mixture and, through a chemical process, the mineral was created. The properties that the concrete acquired were impressive and as Marcus Vitruvius Pollio, a Roman author, architect and engineer said, “[Roman concrete] can neither be dissolved in the waves, nor by the power of water”.
The same patterns were found in the concrete samples from the nuclear power plant in Japan. The findings were published in the Materials & Design Journal. "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," Ippei Maruyama, lead author of the study and an environmental engineer at the Nagoya University, stated.
The research team aims at making concrete more sustainable by focusing on alternative mixtures that can provide both significant strength and reduce the material's environmental footprint.
The study suggests that the Al-tobermorite has not been used in concrete infrastructure to increase the material's strength due to practical issues that emerge. In particular, high temperatures (more than 70°C) are required to produce the mineral in the laboratory however, tests have shown that concrete does not perform well in such temperatures. In fact, the limit of its usage is constrained below 65°C. Consequently, it is not feasible to incorporate the mineral into the concrete mixture.
Nevertheless, the research team suggests that over a course of 16.5 years, the mineral was formed within the concrete walls of the power plant at temperatures of 40-55°C (much lower than the literature suggests). Moreover, detailed analyses of the samples showed that the thickness of the walls offered great conditions for moisture preservation, a fact that enabled the formation of Al-tobermorite. The strength of the material increased by a factor of three, a fact that resulted from the mineral's crystallized fabric.
The current study is the first to report the existence of Al-tobermorite in concrete and to derive its mechanical properties after the stabilization that the mineral provides.
The team emphasizes that the knowledge that we have on concrete accounts for its short-term properties, however, there is still much potential for research regarding its long-term capabilities.