Cement-Free Concrete Recipe Bonds Sand Using Alcohol

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."