Studying Concrete to Improve It

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Studying Concrete to Improve It

The annual worldwide production of more than 20 billion t of concrete contributes 5 –10% of carbon dioxide to the atmosphere, making the industry the third largest source of CO2 emissions in the world (behind transportation and energy).

: “The heart of concrete is C-S-H – that’s calcium, silicate and hydrate (water). There are impurities, but C-S-H is the key binder that holds everything together, so that’s what we focused on. In a nutshell, we tried to decode the phases of C-S-H across different chemistries, thereby improving the mechanical properties of concrete in a material way.”

The study, which was supported by the Concrete Sustainability Hub at MIT, the Portland Cement Association and the National Ready Mixed Concrete Association Research and Education Foundation, involved the analysis of defect attributes for concrete. One was in the ratio of calcium to silicon (the basic elements of concrete) and another looked at the topology of atomic-level structures, particularly the location of defects and the bonds between medium-range calcium and oxygen or silicon and oxygen atoms (atoms that are not directly connected but still influence each other). The combination of these defects gives concrete its properties.

One of the scientists had this to say: “This is the first time we’ve been able to see new degrees of freedom in the formation of concrete based on the molecular topology. We learned that at any given calcium/silicon ratio, there may be 10 to 20 different molecular shapes, and each has a distinct mechanical property. This will open up enormous opportunities for researchers to optimise concrete from the molecular level up for certain applications. There has been a lot of work in metals and semiconductors, but understanding how defects work in cement was far from obvious, and there was pretty much no basic work done at this level. So, I would say, this is perhaps one of the most important discoveries in cement science this century.”