Concrete Does Not Dry Out

Concrete Does Not Dry Out

In a few hours, this sloppy wet concrete will harden into a solid, which, after a few days will be strong
enough to hold many tons of weight. Pasta also starts in a moist amorphous state,
hardens after a few hours, and it can also hold a lot of weight. But there’s an important difference between
capellini and concrete – noodles dry out (which you can tell because when you add water,
they re-absorb it and become soft again), while concrete sets (you can pour as much
water on it as you want, and it won’t become soggy – which is good because you don’t
want buildings and bridges to get soggy when it rains). The distinction is that when pasta is made,
water simply evaporates out of the dough, leaving behind a desiccated, starchy scaffolding
with plenty of holes & gaps ready to re-absorb water in the future and re-soften the dough. When concrete sets, on the other hand, calcium
oxide, silicon dioxide and other molecules in the cement chemically combine with water
molecules to create new compounds like calcium silicate hydrate. These molecules grow into
crystalline fibers that bond with each other and literally cement together rock, sand,
metal or whatever else you put into the mix. So when concrete hardens, it’s not drying
out, because water isn’t leaving it – water is reacting with and becoming PART of the
cement. In fact, concrete continues to set for months and even years after it’s poured,
increasing in strength over time and enabling the construction of miraculously strong and
durable structures, like the 2000 foot tall CN Tower in Toronto or the 2000 year old Pantheon in Rome.

Comments (100)

  1. So really concrete bridges get stronger over time? Amazing ..

  2. i knew it set but didn't know what that meant, ty!

  3. Why didn't you bring up the Hoover Dam instead? It's ALWAYS settling!

  4. Concrete is NOTHING against the over 2000 year old Opus Caementitium!!

  5. So what happens if you put concrete in a microwave oven?

  6. I love Slow Regard For Silent Things. In fact I really recommend that you read Patrick Rothfuss's books 😉

  7. Since it becomes part of the cement, is the water permanently gone? That is, does it reduce the world's water supply?

  8. TIL everything I thought I knew about concrete was wrong. And now I understand why we do things like cover concrete with a wet cloth, to help avoid evaporation of water from the concrete.

  9. the problem with the bit at the end is that roman concrete was actuall fundamentally different from what we use today.  a 10 year old bit of roman concrete would still be much stronger than a ten year old bit of modern concrete, since it has a different recipe.  why don't we use the roman recipie?  two reasons: 1) The Roman recipie had been lost to history until very recently when we found a document describing it, which it turns out 2) calls for volcanic ash.

  10. minutephysics is the second level of smatereveryday

  11. The book he recommends is quite good. However I would much more strongly recommend the Kingkiller Chronicles, starting with Name of the Wind, of which the novella that Henry recommends is a small side-story. If memory serves, reddit recently voted them the 3rd best fantasy series behind Song of Ice and Fire and Stormlight Archives. I know he's trying to advertise for audible so I'll also add that the audiobooks for that series are great imo, although I don't think they're read by the author as in the case of Slow Regard.

  12. It's neat how the Roman Empire crumbled, but their concrete structures are still getting stronger. When the U.S.A. eventually crumbles, what will we leave behind?

  13. 0:30 I literally grew up about 30 minutes from that bridge 😀

  14. Modern day concrete gets harder for the first fifty years, then it starts getting softer for the next fifty or so. Roman concrete is a different story, it's been around for over 2,000 years and has a long time to go. And we don't know how it was made. As far as I know, we can't make it today. And I have checked.

  15. the first Bonito concrete floor

  16. the first Bonito concrete floor

  17. the first Bonito concrete floor

  18. Ugh, don't show your face

  19. While the chemistry is correct, you forgot to mention that most of the water used to mix concrete does evaporate (or dry out) during the first few days. Only about 30% combines with cement to form what you listed. The reason the excess water is needed is to make the mix workable.

  20. I also have read Patrick Rothfuss. I cannot wait for book 3, Beyond The Doors of Stone. Fantastic author.

  21. I helped my neighbor pour his concrete driveway today. Now we're out in the backyard drinking beer. We're worn out tired.

  22. Omg the Patrick Ruthfuss is great love is books great recommendation

  23. The CN Tower is actually 1815 feet 5 inches. Source: CN Tower website. Thanks for another excellent video.

  24. Everybody knows concrete does not dry, It Sets.

  25. I highly recommend watching at 0.5 speed.

  26. he does not sound his age XD

  27. You should a sequel video and talk about how "thirsty cement" or "water absorbing cement" works

  28. It may not dry ‘out’, but it is drying in the chemical reaction.

  29. Hi Henry, I really enjoy your videos. I just came across them and intend to watch many more. I have long been interested in making videos about biological principles and other great things about life science. I notices u said that ur videos are sponsored by Would you mind explaining the concept to me and how it works so maybe I can find something similar. If you want to speak privately about it I will gladly give you the info so we can discuss it comfortably. Thanks again. You are awesome.

  30. what a comparison, pasta with concrete 😀

  31. excellent video!!!! You could have mentioned that reinforced concrete has metal. And that the metal can deal with strain. And that concrete is best with compression.

  32. I think, in construction the pour water on fresh cast concrete to fasten the process. There is an excess of heat in the reaction too.

  33. So why is it in rainy parts of the world the concrete has "raindrop holes" on them over time?

  34. One of my old high school teachers AND later in life my co-workers told me more or less the same thing. Takes about (more or less?) 25 years for concrete to fully harden. Someone else once told me that it never fully hardens and is always curing. So idk what one to believe 😐

  35. I didn't think Minute Physics was actually literal!

  36. Some cemets are really strong, even give out blue or green hues depending on the ocidation compounds.

  37. Over-articulating.

  38. Great explanation, couldn't find one on the web for a long time…

  39. Little known fact: Concrete can harden under water.

  40. Getting concrete in your hair must be hell

  41. His editor is hitfilm 4

  42. The concrete strength curve is way off… The curve tops at around 28 days

  43. 1:25 Pantheon's dome is an optical illusion xD

  44. So that's why when I made a fire on the sidewalk it popped open!

  45. FYI. The majority of water in the mix does evaporate and dry out. The voids left over where water was causes weaknesses and that's why the strength of concrete is related to the water cement ratio, generally speaking. It also is why the concrete shrinks when setting.

  46. I always wondered how the water could get out of the concrete so quickly! Tanks for teaching stuff!

  47. Just a quick fact: CaO, SiO2, Al2O3 and Fe2O3 aren't molecules, since they form ionic lattices.

  48. It actually takes 13 years for concrete to cure and at that point be 99% full strength. But even after that concrete will continue getting stronger.

  49. Bread doesn't dry out either when it gets hard. It absorbs the moisture from the air and reacts with the H2O. So there is actually more water in what we call dry bread. That's why heating the bread in a toaster, makes the bread soft again. It drives out some of the moisture.

  50. So, in infinite time, will concrete become infinitely strong?

  51. How I never noticed that?… thanks!

  52. God bless you my brothers.

  53. I think you will find the Parthenon is in Athens 😊

  54. I'm civil engineering student and so surprised that this video was made by minutephysics.

  55. This is not true. Ever see the potholes here in Pennsylvania?

  56. Uhhhh…. was not expecting the Nicholson Bridge to show up in a minutephysics video.

  57. This video got me harder than Trumpo win

  58. Man, I hate those short titles that are almost misleading.
    If you had excess water at mixing concrete then it will come out and then the concrete will actually "dry out".

  59. love your narration mr henry

  60. hey! first time I've seen the narrator. you don't look like I imagined hearing your voice. completely irrelevant just saying

  61. pasta should not dry out. at least from what Alton brown says. the water should be trapped inside. a microwave should prove my theory. same with hard cookies.

  62. I keep reading about concrete and I have discovered something a little bit disturbing. Apparently it keeps absorbing CO2 from the air and this changes the acidity of it. If the concrete is not reinforced this is not a problem but if it is reinforced it means the concrete will eat away at the reinforcement metal bars. This happens in about 100 years. So here's my question: does this mean that all the reinforced concrete structures we've built in the 20th century are doomed? Will they all start failing towards the end of the 21st century? None of the materials that talk about the carbonification of concrete dare to approach this issue. What do you think?

  63. Minute chemistry?

  64. Fun fact: they have found wet concrete in castle ruins from the middle ages

  65. Concrete will set under water.

  66. That why it give off heat as it sets.

  67. people are saying you cant do chemistry, do they not get physics is literally everything.

  68. The pantheon blew my mind. Incredible!

  69. Quite true, of course. But not entirely. Only 30-40% of the water mixed into concrete actually gets used in forming the crystals. The rest evaporates slowly.

  70. 30% of this video is an ad. Fuck you.

  71. lol minecraft 1.12 doesnt dry out. it came out

  72. Actually, pasta also reacts with water. It's just a bidirectional chemical reaction.

  73. Does it mean that pouring concrete on a very hot and dry day is not optimum?

  74. wow so concrete is stronger over time I had no idea

  75. lol the things on the bridge are sogging too!

  76. ok, i understand the univers now but about that book at the end…

  77. Good to know.
    However, if concrete is so damn strong how come concrete streets break up on a few years after they were poured?

  78. I cant believe it has taken me this long to learn this!

    Ive always wondered where the water goes. And why thick concrete doesnt stay soggy in the middle. Its so simple; the water never leaves!

  79. Hmmmmm mmmmmoooiiiiiiisssssssssssssttttttttttttt

  80. Somebody toucha my concrete!

  81. That is not completely true. Concrete actually does dry out. The shrinkage of concrete is mainly because water evaporates.There are two types of shrinkage: the drying shrinkage, which is because water evaporates and the autogenous shrinkage, which is due to hydration of the cement. The drying shrinkage is approximately 3-4 times larger than the autogenous shrinkage. Therefore, concrete dries out more than it sets.

  82. Concrete can dry out if not cured properly and protected from excessive heat/wind. The water within a fresh mix causes the hardening of concrete through a process called hydration. If the freshly placed concrete is not properly protected, the water within the concrete could escape and potentially lead to shrinkage cracking due to change in volume and overall weakness.

  83. Love how this MinutePhysics video is 2 minutes long and about chemistry😂

  84. chemistry is just physics in fancy dress

  85. concrete can dry out, put a concrete brick on a kiln and itll turn into dust , it just holds on to those water molecules a lot stronger, but this is also true for rocks, which will also turn into dust if left in a high temperature environment. It also does dissolve in water, but itll take extremely long for that to happen (also depending on the quality of the concrete)

  86. This makes so much sense to me I don't know why lol

  87. Having been told for decades that the Hoover Dam is "still drying" has always confused me because obviously the water vapor isn't getting out if the water behind the dam isn't getting in. Glad to finally have that cleared up.

  88. just a civil engenner passing by…

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