Concrete, a Centuries-Old Material, Gets a New Recipe

[cpzilliacus]

New York Times: Concrete, a Centuries-Old Material, Gets a New Recipe

On any given day, Central Concrete, in San Jose, Calif., does what concrete companies have been doing for centuries: combining sand, gravel, water and cement to create the slurry that is used in construction.

But Central – one of a handful of companies at the forefront of a movement to make a greener concrete – is increasingly experimenting with some decidedly new mixtures.

In one part of the plant, carbon dioxide from a chemical gas company is injected into the concrete, locking in that greenhouse gas and keeping it out of the atmosphere, where it would contribute to global warming. Elsewhere, engineers tinker with the recipe for concrete, trying out substitutes for some of the cement, which makes up about 15 percent of the mix and functions as the glue that holds it all together. Cement, however, is also responsible for most of concrete's carbon emissions – emissions so high that some have abandoned concrete for alternative building materials like mass timber and bamboo.

[kphoger]

carbon dioxide from a chemical gas company is injected into the concrete, locking in that greenhouse gas and keeping it out of the atmosphere,

What, forever?

[GaryV]

carbon dioxide from a chemical gas company is injected into the concrete, locking in that greenhouse gas and keeping it out of the atmosphere,

What, forever?

Maybe until the concrete is ripped up and pulverized, then the CO2 bubbles could leak out.  I suppose a small amount could leak any time the concrete cracks.

[kphoger]

To me, it's like throwing your trash into a lake:  Look, I got rid of it!

[skluth]

To me, it's like throwing your trash into a lake:  Look, I got rid of it!

That or a shell game. Look, it's not here. Not here either!

[kalvado]

with primary components of cement being C2S and C3S - alite and belite - I cannot see how one can add CO2 early on without compromising structural properties. Heck, cement firing releases bound CO2 to begin with.... Until they are using excess of C in the mixture - but how would that affect things?  Of course, both alite and belite release CH which eventually absorbs CO2, but that happens during hardening and aging.
Expedite aging of concrete, maybe that is the main purpose?   

[kalvado]

As a side note:
First pass of Biosphere 2 experiment failed because structural concrete absorbed CO2 from the atmosphere.
https://en.wikipedia.org/wiki/Biosphere_2
So concrete aging may do interesting things...