The old saying “step on a crack, break your mother’s back” may not apply to sidewalks for much longer now that MIT researchers have figured out why concrete breaks down. As a result of the discovery, structures like buildings, bridges, and yes, sidewalks, could last for hundreds of years longer than they currently do. A nuclear waste container built to last 100 years could, for example, last 16,000 years.
According to MIT professor Franz-Josef Ulm, creep (the process that create cracks) is created when calcium-silicate-hydrates (CSH) rearrange at the nano scale. When mixed with water, CSH particles change in density from 64% to 74%. By adding silica fumes–a waste product from aluminum production–to concrete, overall density can increase to 87%. That’s a change that could eventually lead to longer-lasting, lighter structures.
If Ulm’s theories are put it into practice, the concrete industry and the planet could benefit immensely. 5 to 8% of all manmade CO2 comes from manmade concrete construction, so any reduction in the need to produce more of the stuff would slow global warming. And with twenty billion tons of concrete churned out annually, there’s plenty of room to cut down on production.
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