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No-cement concrete holds potential for decarbonisation and Moon buildings

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Researchers from the University of Tokyo have developed a new method of producing concrete without cement. Their technique offers a means for the construction industry to reduce its carbon emissions, as well as offering potential for building on the Moon and Mars.

Concrete consists of two parts: an aggregate (typically made of sand and gravel) and cement. Cement has been estimated to be associated with 8 per cent of global carbon emissions, making it difficult for the construction industry to reduce its climate impact. Another issue facing the industry is the limited availability of suitable sand for concrete production, which must have a specific size distribution to provide the correct properties.

“In concrete, cement is used to bond sand and gravel,” said lead author of the study, Yuya Sakai. “Some researchers are investigating how more cement can be replaced with other materials, such as fly ash and blast furnace slag, to reduce CO2 emissions, but this approach is unsustainable because the supply of these materials is decreasing owing to reduced use of thermal power systems and increased use of electrical furnace steel.”

A new approach will be required to produce concrete from more abundant materials with less environmental impact. “Researchers can produce tetraalkoxysilane from sand through a reaction with alcohol and a catalyst by removing water, which is a by-product of the reaction," said Sakai. "Our idea was to leave the water to shift the reaction back and forth from sand to tetraalkoxysilane, to bond the sand particles with each other.”

The researchers placed a copper foil cup in a reaction vessel with sand and other materials. They varied the reaction conditions (such as amount of each material, heating temperature, and reaction time) to find the right conditions to obtain a strong enough product.

The product is likely to have greater durability than conventional concrete due to the absence of cement paste, which is relatively weak against chemical attack and which undergoes growing and shrinking with changes in temperature and humidity.

Ahmad Farahani, second author of the study, said: “We obtained sufficiently strong products with, for example, silica sand, glass beads, desert sand, and simulated Moon sand. These findings can promote a move towards a greener and more economical construction industry everywhere on Earth. Our technique does not require specific sand particles used in conventional construction; this will also help address the issues of climate change and space development.”

It is hoped that – as it does not require the specific type of sand required in conventional construction – this technique could help address climate issues as well as provide a potential way to construct buildings in desert regions and even on the Moon and Mars.

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