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Concrete is the key ingredient to building housing, roads, and all kinds of infrastructure. Curing of concrete makes sure that the infra is rock solid and reliably durable and safe. But, it also consumes humongous amounts of water irreversibly, and this water is not returning to the ecosystem of water cycle.

Till how many years can we carry this on until the situation becomes grave?

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  • $\begingroup$ Probably not a bad idea but my answer below is from an earth science perspective. $\endgroup$
    – Mehmet
    Mar 31 at 15:23
  • $\begingroup$ What exactly do you mean by "the situation becomes grave"? Water is far from equally distributed, and the boundary for a grave situation in Sudan is very different from the boundary for a grave situation in Norway. $\endgroup$
    – gerrit
    Apr 1 at 7:42
  • $\begingroup$ @gerrit exactly. Usable water is a basic resource, and even if we use oceanic desalination for fulfilling the needs, I think that the process is neither net water positive or energy positive. $\endgroup$
    – lousycoder
    Apr 1 at 9:45
  • $\begingroup$ @lousycoder If considering the local situation, the question is too broad. Depending on location, the answer varies from 0 (concrete production infeasible already today due to lack of water) to forever (lack of water will never become an issue). $\endgroup$
    – gerrit
    Apr 1 at 9:51
  • $\begingroup$ I'm wondering how much water is released in the concrete-making process (e.g. as vapour) in proportion to the liquid water consumed. Some of the input minerals hold a fair bit of water before being heated. $\endgroup$
    – Chris H
    Apr 1 at 9:55

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The top twelve cement producing countries in 2020 produced 3191 Mt of cement. Increase this to 4000 Mt to include the rest of the world.

Depending on the application, the water to cement ratio of concrete is between 0.4 and 0.6.

Assuming the worst case scenario of 0.6, then 2400 Mt of water was locked in concrete in 2020.

Now, 1 t of water occupies 1 m3, which is the same a 1000 L (1 kL). This means 2400 million cubic meters of water (2.4(10)12 L, or 2.4 TL, or 2400 GL) was locked in concrete in 2020.

Another way of looking at it is, 2400 million cubic meters is 2.4 km3, which is a minuscule fraction of the total volume of the worlds oceans, which is 1,335,000,000 km3.

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    $\begingroup$ Just one final point missing to answer the question: at current rates, around 556 million years to empty the oceans (and a fraction of that until the situation "becomes grave"). However, locally the situation may of course be grave even if in total the planet has more than enough (salt) water (can concrete plants work with salt water?) $\endgroup$
    – gerrit
    Apr 1 at 7:41
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    $\begingroup$ @lousycoder Does not all fresh water come from evaporation mostly from the ocean? I've never heard of an area with its own water cycle isolated from everything else. Concerns about running out of fresh water are usually about using it faster than it arrives, not about using it all up so there won't be any more left. $\endgroup$
    – user253751
    Apr 1 at 10:26
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    $\begingroup$ I'm not doing the maths, but I bet we make more water through combustion with all the stuff we burn $\endgroup$ Apr 1 at 12:59
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    $\begingroup$ Ocean water is transported to metropolises via rain. Ocean water evaporates to form clouds & wind transports the clouds everywhere. Fresh water sources on land are replenished by rain. It's an integral part of the water cycle. Also, any additional water used in the manufacturing of concrete is still going to be a minuscule amount of the total water on the surface of the planet. $\endgroup$
    – Fred
    Apr 1 at 16:18
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    $\begingroup$ @Persistence It looks like for every 2 molecules of octane (I'll just assume gasoline is all octane) combusted, 18 molecules of water are produced. There are ~6.15 moles of octane in a liter, so one liter of gasoline burnt produces almost exactly one liter of water. 562 billion liters of gasoline are consumed in a year, so about 23% of the water lost to concrete production is made up for just by combustion of gasoline (not gonna bother doing the calculations for natural gas, coal, wood, etc.,) $\endgroup$ Apr 1 at 19:47
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Concrete loses some minute water over time. It's undergoing curing....however for most part, Concrete does not harden by evaporation, it hardens by a chemical process called hydration. The water added to concrete mix becomes a part of the concrete and never leaves concrete or evaporates,in essence becoming a new substance.
As a whole average water use is 82.8 liters per ton, with 365 billion liters used yearly... According to researchers, Global concrete production and totals since 1900, Humanity has produced 549 Gigatons (billion) of Concrete, using 12 TRILLION gallons of water. Oceans water mass is 1.4 × 10^21 kg or 1.4 Quintillion tonnes. Human concrete use in a Century used 1/2,500,000th of the Earths water. Comparison: If you have a 1 gallon jug of water representing ALL water on Earth, You've used ONE drop.

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Global sea level rise is an increasing problem that governments are struggling to find a solution to. Sea level rise is mostly caused by ice sheets, and other permanent snow/ice, melting and a little by expansion of the sea due to higher temperatures. If sea level rise could be mitigated by use of concrete I assume this would have been mentioned in the IPCC reports. Overall I cannot imagine that what you suggest is a serious problem or likely to become one.

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Not to worry, the gas burned in the kiln to produce the cement produces an offsetting amount of water.

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    $\begingroup$ You make a very good point... the balanced combustion reaction for octane shows a bit more H2O is released than CO2. And en.wikipedia.org/wiki/Cement_kiln suggests cement kiln's are responsible for 2.5% of anthropogenic CO2 emissions :-o Even if cement were created with different fuel sources, it seems we're releasing much more stored up H2O globally than we're storing back up in concrete. $\endgroup$ May 31 at 15:51
  • $\begingroup$ (to be clear to my comment: more H2O than CO2 by quantity measures, like volume [for gases]/moles/ppm, not by mass) $\endgroup$ Jun 1 at 9:24
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    $\begingroup$ I was only saying it is a substantial source for water If you want more water ,figure how much water is produced by burning diesel and gasoline to quarry, crush, and process gravel and sand for the concrete. $\endgroup$ Jun 1 at 23:59

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