Scientists replaced 40 percent of cement with rice husk cinder, limestone crushing waste, and silica sand, giving concrete a rubber-like quality, six to nine times more crack-resistant than regular concrete. It self-seals, replaces cement with plentiful waste products, and should be cheaper to use.

[u/mvea]

https://newatlas.com/materials/rubbery-crack-resistant-cement/

[u/danielravennest]

For those not familiar with concrete, it typically is made from gravel, sand, cement, and water. The water turns the cement powder into interlocking crystals that bind the other ingredients together.

There are a lot of recipes for concete, but the typical "ordinary Portland Cement" concrete is made with a cement that starts with about 5 parts limestone to 1 part shale. These are burned in a high temperature kiln, which converts them chemically to a product that reacts with water.

Lots of other materials will do this too. The ancient Romans dug up rock that had been burned by a volcano near Pozzolana, Italy. The general category is thus called "Pozzolans". Coal furnace ash and blast furnace slag are also rocks that have been burned. They have long been used as partial replacements for Portland Cement. Rich husk ash and brick dust are other, less common, alternative cements.

Note: Natural coal isn't pure carbon. It has varying amounts of rock mixed in with it. That's partly because the coal seams formed that way, and partly because the mining process sometimes gets some of the surrounding bedrock by accident.

Portland Cement got its name because the concrete it makes resembled the natural stone quarried in Portland, England at the time.

[u/Vanderdecken → u/danielravennest]

Worth noting that the process of burning the limestone and shale to make clinker is a bigger contributor to carbon dioxide emissions than any single country in the world except China or the US (source). The construction industry, via the creation of cement, is killing the planet. more

[u/danielravennest → u/Vanderdecken]

Correct. Concrete is the single most used solid product on Earth, and about 1/6 of the mass is cement. Burning rock to make cement is done at very high temperatures, and usually by burning fossil fuels.

In theory, a solar furnace could be used, but nobody has developed an economical way to do it yet. Tests have been run with small amounts in solar furnaces, so we know it works, but not on an industrial scale.

[u/ProjectSnowman → u/danielravennest]

I think we'll have an easier time getting off fossils fuels than replacing cement. Rock in liquid form is just too useful.

[u/coffeemonkeypants → u/ProjectSnowman]

The bigger problem for us getting off cement/concrete is that we're running out of sand. Even though we have deserts full of the stuff, the properties of wind blown sand (it has no rough edges), make it unsuitable for concrete.

[u/Hybrazil → u/coffeemonkeypants]

Perhaps one day we could sequester carbon into some sort of rough sand and use that for concrete. A more economical carbon sequestration.