Comment by Fyrezerk | Hacker News Reader

Comment by Fyrezerk | Hacker News Reader

This article isn't very clear on the fact that CO2 can be re-injected back into the cement later in the production stage. I work with a startup using direct air capture tech to capture ambient CO2, store it, and inject it back into cement production. This has a massive offset in the CO2 produced during the calcination stage.

https://www.carbon-direct.com/insights/direct-air-capture-to...

There is also lots of work already underway on electrified calcination. Plenty of industries, such as carbon fiber production, already take advantage of electrified kilns in their production process. This tech just needs to be scaled up. As the article mentioned, cement manufacturing isn't exactly on the cutting edge of technology.

> This article isn't very clear on the fact that CO2 can be re-injected back into the cement later in the production stage.

How can that work? The calcium oxide (or hydroxide) reacts with silica to make silicates, which bind things together. That CaO which reacted is not available to soak up CO2.

In this particular case the CO2 mineralization is taking place in a wastewater slurry that comes from washing out cement trucks. The carbonated slurry is then re-used as an additive by cement manufacturers.

Won't cement slowly reabsorb half of the CO2 it released when making it (excluding the heating part)? What is the big advantage to making it reabsorb it early in its lifetime?

1. That’s a big half 2. The heating part releases an incredible amount of carbon

(If I can dig up some solid links after dinner I’ll edit the post. But Chris Magwood at The Endeavor Center has some fantastic reference material for lifecycle carbon intensiveness)

How much compressive stress is lost when you aerate concrete? Would consolidation with a concrete vibrator release the CO2 like shaking a soda?

How is the carbon bound in the concrete? I doubt CO2 bubbles would last very long, so is it just forming carbonates?

Last time this was mentioned someone claimed this drastically reduces the strength and lifetime of the concrete, effectively pre-aging it and is probably a wash in terms of carbon savings.

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