Making a greener concrete

Concrete: as integral to the modern world as electricity or the internet. But did you know that making it causes 8% of global co2 emissions? Once concrete sets and cures after 28 days, it does capture co2 from the air for up to 100 years, but, as well as taking ages, this process has the additional downside of degrading the strength of the material. Admir Masic and his team at MIT have come up with a way to make more CO2 lock itself into the concrete earlier in its lifetime, reducing emissions and avoiding the degradation from carbon capture. It has to do with the cement hydration process, as Chris Smith heard…

Admir - You can create the atmosphere of CO2 around your hydrating cement block, you can pump CO2 into your track that is mixing your fresh concrete, or do it as we did it in this paper where we added sodium bicarbonate that allows you, once you add water into this additive and the water into the mix, saturates the solution, hydrating solution with the carbonates and eventually react with our hydrating cement.

Chris - The problem is obviously if you're using sodium bicarbonate, you've gotta make that in the first place, haven't you?

Admir - Any sort of carbonates that are soluble in the hydrating solution eventually will work. And we are trying different types of these. So there is a lot of work to do in that space. Nevertheless, what we show in our work here is that we can push significant amounts of CO2 into the structure of cement, which was kind of unknown. So we were talking about 15% of the entire emissions associated with the cement production. That can be remineralized in the very early stages, making cement and concrete a carbon sink.

Chris - That flips the equation round completely, doesn't it? Because if making it has a carbon footprint of about 8% of all emissions and you are saying you make it and we can actually remove 15% of the emissions, that sounds extremely attractive. Is the concrete you make any good? Have you structurally tested this stuff to make sure that what we end up with is something which is gonna hold up a building?

Admir - We did test the mechanical performance after carbonation, using carbonates in different concentrations, and we set this 15% limit exactly based on our mechanical testing results. We statistically show that we do not compromise mechanical performance after adding up to 15% of bicarbonates.