Materials

Cement-free concrete recipe bonds sand using alcohol

Cement-free concrete recipe bo...
A sample of the new cement-free concrete, made by bonding sand directly through alcohol and a catalyst
A sample of the new cement-free concrete, made by bonding sand directly through alcohol and a catalyst
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A sample of the new cement-free concrete, made by bonding sand directly through alcohol and a catalyst
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A sample of the new cement-free concrete, made by bonding sand directly through alcohol and a catalyst

Concrete is the most commonly used building material in the world, but unfortunately the cement used to make it carries quite a carbon footprint. Now, scientists at the University of Tokyo have created a cement-free alternative that directly bonds sand particles together using a reaction between alcohol and a catalyst.

Concrete is made up of an aggregate material, usually sand and gravel, and cement, which acts like glue to hold it all together. Portland cement is the most common type, but making it is a pretty environmentally unfriendly affair – between the high heating temperatures and the limestone outgassing, about 1 kg (2.2 lb) of carbon dioxide is produced for every kilogram of cement. Considering just how much of the material is made every year, cement production accounts for around eight percent of global CO2 emissions.

With that in mind, scientists are working on greener alternatives, most commonly substituting the cement for waste materials like fly ash or steel slag. But for the new study, the researchers developed a new recipe that directly bonds the sand particles together.

"Researchers can produce tetraalkoxysilane from sand through a reaction with alcohol and a catalyst by removing water, which is a byproduct of the reaction,” says Yuya Sakai, lead author of the study. “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 team experimented with mixtures of silica sand, ethanol, potassium hydroxide, and 2,2-dimethoxypropane, heated in a copper vessel. They ran dozens of different variations on the setup, changing the volumes and ratios of the ingredients, the temperature at which it was fired, and for how long – 24, 36, 48 or 72 hours.

The sand bonded together to different degrees depending on the variation, with several tests yielding a concrete material that was stable and relatively strong. That said, its compressive strength doesn’t yet match up to what you’d expect of traditional concrete. The team has so far only tested it by squeezing it between their fingers – future experiments will put it through more vigorous tests, and look for ways to potentially make it stronger.

There are other advantages to the new method, though. The researchers say that this new type of concrete could be more durable than the normal stuff against common foes like chemicals, temperature and humidity. It can also be used with a wider variety of aggregates, including sand of different particle sizes, and other materials that could expand where it might be used.

"We obtained sufficiently strong products with, for example, silica sand, glass beads, desert sand, and simulated moon sand," says Ahmad Farahani, second author of the study. "These findings can promote a move toward 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."

The research is due to be published in the journal Seisan Kenkyu.

Source: University of Tokyo

13 comments
SpieroFantasio
The gaining of sand causes vast environmental impacts. In India the depletion through illegal sand exploitation from strands caused protests . Many protesters and a journalist were murdered by the sand mafia. It is not feasible yet to use the sand of deserts like Sahara to make concrete, because the grains are not suitable. Even the arab countries import sand, biggest consumer is China.

Would this new procedure be appropriate to use desert sand? That would be extremly advantagous beyond evoiding carbon-emissions.
guzmanchinky
Spiero makes a very good point! This is interesting progress to be sure, hopefully it works well...
paul314
If this has to be fired, it's not going to be useful for many, many of the applications of regular concrete. (I have visions of controlled torching of entire buildings...)
madsci
I like the concept but.... Needed to heat for up to 72 hours? At what temperature? Is that practical for building construction?
nehopsa
I was only waiting before "space" pops up. There it is, the second last word. It felt kind of spacey technology from the get go.

I wonder about how practical, how costly, how affordable this green new way of building is expected to be on day in the spacey foggy after-corona world.
niio
"Squeezing it between their fingers" level of strength and they call it concrete?
SWB
To quote: "... its compressive strength doesn’t yet match up to what you’d expect of traditional concrete. The team has so far only tested it by squeezing it between their fingers ..."

Uhh? Why is this even newsworthy? It sounds like kitty litter could give this stuff a run for its money! This reminds me of a scam I heard about around 25 years ago where a guy took loads of investors to the cleaners with a product that he said could be sprayed on the sand flattened out and when it dried you had an instant road. It never got manufactured, but apparently, the dream is still alive.
Worzel
Cement is made from calcium carbonate, or limestone. Lime stone was made by sea creatures, using CO2. That CO2 came from the atmosphere!
Present amount of atmospheric CO2 is too low! So the more CO2 the better.
If you heat sand, you get glass. Glass blocks are used in building work. Maybe if this process was used to directly bond glass blocks, it might be useful.
As a substitute for cement, doesn't seem likely.
Spud Murphy
I see the climate change denier worzel is here again, you really need to educate yourself mate, not keep parroting right-wing garbage you hear on fox news or wherever.

But anyway, this material doesn't sound like a goer, the need to fire it in-situ is a show-stopper, and compared to materials like hempcrete and magnesium-based concretes, which are actually easy to mix and lay, and which actually absorb CO2 as they harden, this will never have the practicality required of a concrete alternative. This sounds like another group of scientists trying to justify their research and maintain their funding by sending out press releases.
Brian M
@Spud Murphy
Of course it comes down what you think is the right level of CO2 in the atmosphere, 100 million odd years ago its was many times higher than today. Changes in CO2 is not going to kill the planet, yes it will make changes to the climate that might not be so good for us and the biological diversity will change to meet the new levels.

Selfishly, I would prefer the levels not to rise further!