Materials

Ancient Roman concrete mineral found strengthening nuclear reactor walls

Ancient Roman concrete mineral...
Concrete walls at the Hamaoka Nuclear Power Plant were found to have become stronger over their lifetime
Concrete walls at the Hamaoka Nuclear Power Plant were found to have become stronger over their lifetime
View 2 Images
Concrete walls at the Hamaoka Nuclear Power Plant were found to have become stronger over their lifetime
1/2
Concrete walls at the Hamaoka Nuclear Power Plant were found to have become stronger over their lifetime
A microscope image of aluminous tobermorite crystals that formed inside the concrete walls of a power plant, strengthening the concrete over the years
2/2
A microscope image of aluminous tobermorite crystals that formed inside the concrete walls of a power plant, strengthening the concrete over the years

In a list of walls that you’d want to stay strong, those in a nuclear reactor would be near the top. Now, researchers have found that the walls in a decommissioned power plant in Japan have not only kept their strength but have actually gotten stronger with use, thanks to a rare mineral also found in ancient Roman concrete.

We tend to think of our modern materials as superior to the primitive ones of old, but that’s not always the case. A concrete structure made from regular Portland cement, standing in seawater, will need repairs and may succumb to the elements within a few decades. Yet there are marine barriers in Italy still standing strong after more than 2,000 years.

Recent studies uncovered the mechanism behind that feat. The original mixture contains volcanic ash, and when salt water gets inside it dissolves that ash, creating a mineral called aluminous tobermorite. These crystals actually make the concrete stronger than it was when it was first made.

It may sound like aluminous tobermorite would be a perfect addition to cement to make it stronger, but it’s not that easy. Making the crystals in the lab requires temperatures of over 70 °C (158 °F), which can weaken the concrete itself.

Out in the field though, it seems other chemical processes are producing the mineral at lower temperatures and reinforcing concrete structures. It happened with the ancient Roman sea walls – and now, scientists have discovered the process at work in the walls of a nuclear reactor.

The researchers on the new study took samples from thick concrete walls and a slab from Unit 1 of the Hamaoka Nuclear Power Plant in the city of Omaezaki in Japan. This unit operated between 1976 and 2009, and for 16.5 years during that period it ran at full power, constantly exposing the walls to temperatures of between 40 and 55 °C (104 and 131 °F).

Sure enough, aluminous tobermorite was detected in the samples. The team calculated that the mineral had made these walls more than three times stronger than they had been when first built.

"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, corresponding author of the study.

On closer examination, the team found that the walls had retained moisture, which reacted with minerals like portlandite in the concrete. This boosted the alkali content of the wall, and made silicon and aluminum ions more available, which eventually helped form the aluminous tobermorite.

The team hopes that the find could improve cement recipes to make stronger, longer lasting and more environmentally friendly concrete.

"Our understanding of concrete is based on short-term experiments conducted at lab time scales," says Maruyama. "But real concrete structures give us more insights for long-term use.”

The research was published in the journal Materials & Design.

Source: Nagoya University

15 comments
15 comments
tony
Pro Roma
Chris Coles
The headline should have read; Strengthening by Orders of Magnitude" Three times stronger is a very significant result. If the follow up research can bring such results within a more reasonable timescale, then we can reduce the amount of concrete we use, again significantly reducing the carbon footprint of that otherwise crucial industry.
Geoff NH
The Roman concrete mixture had Pozzolans' as part of the Mixture and this is the secret to its corrosion resistance and strength. Also reduction of Portland type cement.
Pozzolans are found in Fly Ash from coal combustion.
Aross
So why do our concrete roads and bridges in Canada deteriorate after being exposed to salt water from road salt used here in the winter?
jerryd
All concrete gets stronger with age.
And we have been using the same materials for decades though from fly ash.
AbsolutJohn
This is absolutely true - and is the only reason why the city of Naples, Italy itself hasn’t been blasted into oblivion as it is sitting on a massive magma chamber, but the previous ancient eruptions have mixed with seawater and mineral deposits, creating a massive mile-thick pozzolano cement shield. Incredible.
Douglas Bennett Rogers
In my master's thesis I discovered that gypsum has a dihydrate to hemihydrate phase transition at 59 C.
bytheway
CO2 is not a pollutant.........it is a main building block of life on earth....and comprises less than 2% of the worlds atmosphere.....without it there is no life, period. Ice core samples taken in the arctic show up to 4 times current CO2 levels from the time when the arctic was tropical.....the vilification of carbon is part of the coordinated attack on civilization and the excuse to tax us out of existance.
Kpar
Three times stronger is not "an order of magnitude". That is 10x.

Yes, concrete gets harder over time (I'm not sure that that equates with "stronger"?). Concrete, I have been told, continues to harden for at least one hundred years. That is because concrete does not "dry", it forms a crystalline structure bridging the materials within as it sets.
McDesign
Hmm - seems generally, nuke plant concrete is a minimum of 6500 psi. Don't think that the jump to 20Kpsi is realistic.