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Ask HN: Does old concrete reveal information about air quality?
88 points by schoen on Oct 10, 2019 | hide | past | favorite | 17 comments
I noticed a worker at a demolition site using power tools to extract cylinders from an old concrete wall. While I'm sure this particular project isn't aimed at scientific research, it made me wonder if there's a demolition-materials equivalent of ice core research.


After all, steel has a different level of radioactivity depending on whether it was manufactured before 1945 (!).


Could there be similar properties in old concrete where one could learn interesting things about the composition of the nearby air at the time the concrete was first poured?

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 (e.g. 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 the concrete.

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:/...

Yup, thanks! I'm sick and on meds, so I'm going to blame that.


Probably depends on what you want to measure.

Concrete is relatively porous to water and gas so things can leech out of it and be deposited into it, confounding your measurements.

Concrete is also chemically reactive, a good example is corrosion caused by salt. Whatever your trying to measure may chemically react with the concrete.

The only way to determine if it could be used is by running a few controls and analyzing the samples.

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

Even if concrete held trapped air ... would we just learn that construction sites for big concrete buildings have a lot of diesel-burning trucks and equipment?

I think OP is thinking of ancient concrete/cement used by ancient cultures such as the Romans.

Very interesting question!

Not directly related, but I found this - https://www.sciencedaily.com/releases/2017/07/170707211420.h...

"Even though producing concrete causes air pollution, concrete buildings in urban areas can serve as a kind of sponge adsorbing sulfur dioxide to a high level,"

Maybe the analysis they did and how they did it, might be interesting?

what formulae for concrete absorbs sulfur dioxide?

calcium silicate

Concrete absorbs carbon from co2 in the air. If you were interested in co2 levels you might be able to deduce something from that.

I seem to recall that the biosphere 2 project had problems with the fresh concrete absorbing too much co2 inside the sealed structure.


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)

Regarding OP's idea, are you saying it's been demonstrated to not be possible, or just that it hasn't been demonstrated to be possible?

Surely humidity and sun exposure have a far larger effect than air pollution.

pH balance of water and oxidization/electronegativity of the air could impact the quality of concrete.

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