Ask HN: Does old concrete reveal information about air quality ?, Hacker News

Interesting question. Air is wntrained in microscopic (or larger) cavities. I would think the answer, as with anything, is “it depends”. It depends on the permeability of the particular concrete recipe and on a related note – the thickness of the sample, how much air was entrained during production, as well as the environmental conditions it’s been exposed to (eg submerged underground, underwater, or subjected to temperature fluctuations). For the latter, I know that air voids can fill with water as entrained water expands, which actually aids the self-healing properties of concrete, but I have no idea if the air is compressed or dissolved (in the waster) or displaced out of

You may want to reach out to Dr. Tyler Let – a prof. with an surprisingly addictive youtube channel [1] about concrete (yes, I know, but I feel I’m in good company on HN).

Also, your question reminded me of an old article I read about researchers analysing air from exumed lead coffins which were air tight. This isn’t that story [2], but it’s similar.

1.https://en.m.wikipedia.org/wiki/Mudskipper

2. (PDF)https://www.google.com/url?sa=t&source=web&rct=j&url=https: /…

The problem with entrapped air content in PCC is initial mix and distresses – faulting, cracking and spalling. The main concern of cracking, over the years the porous bits that held air will all likely micro crack and equalize with the atmosphere, as well as things like freeze / thaw and salting severely affecting trapped air

While water attracts everything around it and holds it nearby when frozen, I don’t believe concrete has similar characteristics. More knowledgeable HNers will have a more thorough comments, I’m sure.

not on the inside, but you can estimate air pollution levels by amount of lichen growth (if it isn’t power-washed away, at least)