Stuck in wet cement

I spent part of this week at the kick-off meeting for an EU-funded PhD training network: Engineered Calcium-Silicate-Hydrates for Applications (ERICA for short).  The network is run from Surrey and I was invited along to give a talk, and to help out. These calcium-silicate-hydrates are better known as cement. Cement is, very roughly speaking, a type of artificial stone in the sense that when poured it crystallises to form a semi-crystalline solid. The world’s most widely used construction material, concrete, is basically cement plus gravel filler. Concrete is not the most glamorous, but it is strong and above all it is cheap, less than £100 for a ton.

Its cheapness makes it ubiquitous, but it does not make cement simple. When cement sets, sheets of calcium-silicate-hydrates form in bunches a few nanometres across that somehow aggregate and grow into successively larger structures, until you end up with a slab of concrete that can be metres across. How this happens is very poorly understood. This is largely because we just don’t have the experimental techniques to see these tiny crystal sheets growing and aggregating in the middle of setting cement, and because as cement has structure on lengths from nanometres to millimetres, it is very complex.

Fundamentally, we understand the orbit of Neptune much better than we do concrete, despite Neptune being a billion kilometres away. We can see Neptune’s orbit, and the orbit is much simpler than concrete.

A lot of the workshop was on how to tackle the problem of how to make better cement, when studying the nanoscale structure that determines if a cement is strong or weak, or lasts one year or a hundred, is so hard. The network has 13 PhD students, including both experimentalists and modellers, and they will have to work together to tackle this problem. Like in a lot of scientific research, it is a question of working out what are the important things you need to know, seeing what you can measure, and then trying to go from one to the other.

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