What is Concrete?

What is Concrete?

Concrete is as much a part of the urban landscape
as trees are to a forest. It’s so ubiquitous that we rarely even give
it any regard at all. But, underneath that drab grey exterior is
a hidden world of complexity. Hey I’m Grady and this is Practical Engineering. On today’s episode – it’s concrete 101. This video is sponsored by Brilliant. More on that later. Concrete is one of the most versatile and
widely-used construction materials on earth. It’s strong, durable, low maintenance, fire
resistant, simple to use, and can be made to fit any size or shape – from the unfathomably
massive to the humble stepping stone. However, none of those other advantages would
matter without this: it’s cheap. Compared to other materials, concrete is a
bargain. And, it’s easy to see why if we look at
what it’s made of. Concrete has four primary ingredients: Water,
sand (also called fine aggregate), gravel (aka coarse aggregate), and cement. A recipe that is not quite a paragon of sophistication. One ingredient falls from the sky, and the
rest come essentially straight out of the ground. But, from these humble beginnings are born
essentially the basis of the entire world’s infrastructure. Actually, of the 4, cement is the only ingredient
in concrete with any complexity at all. The most common type used in concrete is known
as Portland cement. It’s made by putting quarried materials
(mainly limestone) into a kiln, then grinding them into a fine powder with a few extra herbs
and spices. Cement is a key constituent in a whole host
of construction materials, including grout, mortar, stucco, and of course, concrete. A lot of people don’t know this, but every
time you say cement when you were actually talking about concrete, a civil engineer’s
calculator runs out of batteries. I’m just kidding of course, and you can
hardly be blamed for not knowing the difference if you’ve never mixed up a batch of concrete
before. Even if you have mixed some concrete, good
chance it was in a ready-mixed bag where all the ingredients were already portioned together. But, each ingredient in concrete has a specific
role to play, and cement’s role is to turn the concrete from a liquid to a solid. Portland cement cures not through drying or
evaporation of the water, but through a chemical reaction called hydration. The water actually becomes a part of cured
concrete. This is why you shouldn’t let concrete dry
out while it’s curing. Lack of water can prematurely stop the hydration
process, preventing the concrete from reaching its full strength. In fact, as long as you avoid washing out
the cement, concrete made with portland cement can be placed and cured completely under water. It will set and harden just as well (and maybe
even better) as if it were placed in the dry. But, you may be wondering, “If water plus
cement equals hard, what’s the need for the aggregate?” To answer that question, let’s take a closer
look by cutting this sample through with a diamond blade. Under a macro lense, it starts to become obvious
how the individual constituents contribute to the concrete. Notice how the cement paste filled the gaps
between the fine and coarse aggregate. It serves as a binder, holding the other ingredients
together. You don’t build structures from pure cement
the same way you don’t build furniture exclusively out of wood glue. Instead we use cheaper filler materials – gravel
and sand – to make up the bulk of concrete’s volume. This saves cost, but the aggregates also improve
the structural properties of the concrete by increasing the strength and reducing the
amount of shrinkage as the concrete cures. The reason that civil engineers and concrete
professionals need to be pedantic about the difference between cement and concrete is
this: even though the fundamental recipe for concrete is fairly simple with its four ingredients,
there is a tremendous amount of complexity involved in selecting the exact quantities
and characteristics of those ingredients. In fact, the process of developing a specific
concrete formula is called mix design. And I love that terminology because it communicates
just how much effort can go into developing a concrete formula that has the traits and
characteristics needed for a specific application. One of the most obvious knobs that you can
turn on a mix design is how much water is included. Obviously, the more water you add to your
concrete, the easier it flows into the forms. This can make a big difference to the people
who are placing it. But, this added workability comes at a cost
to the concrete’s strength. To demonstrate this balancing act, I’m mixing
up some ready-mix concrete with different amounts of water. For the first sample, I’m using just enough
water to wet the mix. You can see it’s extremely dry. A mix like this is certainly not going to
flow very easily into any forms, but you can compact it into place. In fact, dry concrete mixes like this are
used in roller-compacted concrete which is a common material in the construction of dams. For the next three samples, I used increasing
amounts of water up to what is pretty much concrete soup. After the concrete has had a week to cure,
I cut the samples out of the molds. It’s time to see how strong they are. This is actually more or less how concrete
is tested for compressive strength in construction projects. Obviously I’m not running a testing lab
here in my garage, but I think this will give us good enough results to illustrate how water
content affects concrete strength, plus these cylinders look like they might attack at any
time, and we need to deal with them. I made three cylinders of each mix, and I’ll
break each one, watching how much pressure the cylinder was applying at the moment of
failure. And this experiment was too cool not to invite
my neighbors over to help. We started with the samples that used the
most water. It was no surprise that it took almost no
pressure at all to break them, on average about 700 psi or 5 mPa. You can see how crumbly the concrete is even
after having a week to cure. All that water just diluted the cement paste
too much. The next two samples used the range of water
suggested on the premixed concrete bag. These were much stronger, breaking at an average
of 1600 psi and 2200 psi or 11 mPa and 15 mPa for the high and low end of the water
content range. And you can really see the difference in how
the concrete breaks. Finally we broke the samples with the least
water added to the mix. You can see how rough these samples were,
because there wasn’t enough water for the concrete to flow smoothly into the molds. But, despite looking the worst of the four,
these were the strongest samples of all, breaking at an average of around 3,000 psi or 20 mPa. On this shot you can even see the crack propagating
through the cylinder before it fails. It just goes to show how important mix design
can be to the properties of concrete. Even varying the water content by a small
amount can have a major impact on strength, not to mention the workability, and even the
finished appearance of the concrete. It’s impossible to state how much I am just
scratching the surface here. There is so much complexity to the topic of
concrete partly because it has so many applications: from skyscrapers to canoes and everything
in between. In fact, no matter where you are, you’re
rarely more than a few feet from concrete – a fact that is inexplicably a source of
great comfort to me. But, I took less than 10 minutes to describe
what is literally the foundation of our modern society. So I’m dedicating at least the next few
videos to dive deeper into the topic of concrete. The next video will be about its greatest
weakness. If you’ve got questions about concrete,
put them down below in the comments and maybe I can get them incorporated into the next
videos. Thank you for watching, and let me know what
you think! If you are watching my videos, you probably share my passion for understanding how things work and wanting to apply that knowledge to your everyday life. To do that requires not only learning core concepts, but developing intuition. Brilliant is a problem solving website that teaches you how to think like an engineer. Their courses are designed to help you gain a deep understanding of the topic. I love this one on solar energy that goes into lots of detail on the intricacies of these systems. To get started developing your intuition, go to or just click the link in the description and sign up for free. The first 200 people will get 20% off the annual premium subscription. Again, thank you for watching, and let me know what you think!

Comments (100)

  1. Here's a cool podcast episode on some history of concrete.

    The whole idea is "let's take something 'boring' and make it awesome."

    It talks about (if I remember correctly) how concrete is largely responsible for civilization as we know it!

  2. 5:36 gave me a good giggle

  3. Try your test with super plasticizers.

  4. I want to get a Hysrolic press like yours, maybe Harbor freight> How are you attaching the gauge? What type of guage. Thanks!

  5. These videos are fantastic. Can there be a video for Structural Steel?

  6. Please make sure the same video but this time with metal rebar inside.

  7. "One ingredient falls from the sky"
    Ya referring to people or something?

    oh god what a bad joke

  8. 7:01 to 7:12 Such a cool shot. And I'm glad you're having fund with the neighbours and the kids with the concrete experiments.

  9. 1:50 "a lot of people don't know this but…" 😀

  10. I love googly eyes

  11. What is concrete?

    Baby don't hurt me, don't hurt me—no more.

  12. This video is the first time i have ever heard the word 'pedantic' used in a sentence, that wasn't in response to trolling, or smart-assery.


  14. That's conk creat babey!!

  15. you shouldve cured one of the cylinders per water mix underwater

  16. The romans used blood and volcanic rock/sand. That’s why their building still stand

  17. good video. About a month ago i was just thinking about how revolutionary and world changing concrete is, yet so little is thought about it, i don't even know how or where it was invented on anything about it really.

  18. I wonder if most wet one would have hardened if kept for over a month?

  19. What is the best sealer for concrete art , sculptures?

  20. I learned at work last week, that sugar will really mess up concrete. As little as 1% by weight can completely stop it from setting.

  21. when creating a mix design you are required to increase the amount of cement content relative to the amount of water being added. we call these slump values. this eliminates the problem of weaker concrete with wet mixes.

  22. What is the best stucco mix sir plz

  23. Please do asphalt

  24. At 5:44 I thought I was watching "Hydrooooolic Prasss" Channel

  25. 2:54, cement will set and harden better than in the dry
    6:16 All that Waarler just diluted the cement paste too much
    wtf Wish he make mind up !!!!

  26. How to handle the workability and w/c ratio of concrete?

  27. ‘Portland Cement’ Portland, ENGLAND.

  28. What happens if you fill the gaps in the cylinder created with the least amount of water, with cement?

  29. I think i should have followed those instructions!!!

  30. In some reconstuction of some bridges, after they pour the concrete, they put cloth tarps over and keep them wet to prevent early drying, essentially.

  31. Try adding ash to the mix and see if that makes a difference…

  32. Is it possible to mix cement and water first (i.e. 50 kg cement + 22 L of water) and then add in the sand and rock?

  33. That Hydraulic Press Channel reference had me burst in laughter. Hilarious. I love it.
    This channel is really good. It is educative and easy to understand, yet friendly and with lots of information. Keep doing that!

  34. first u said water gives its resistnace than you said water destory its resitance so im confused.. also why use water at all if it weakens the cement?

  35. Canoes? How? I’m curious

  36. Can you do a video on air crete?

  37. okay and what is cement?

  38. Now im confused. If the concrete with not enough water was stronger, isnt it a better mix then?

  39. What happens if you put the barely wet in the middle, and then a middle amount of water on the outside, to make it look pretty? Would that improve or reduce the strength?

  40. I had a bad experience with a subcontractor who poured a garage floor for me on a job several years ago. The boss sub sent one guy to pour a twenty cubic yard slab. He added too much water and then troweled it to a hard finish while still to wet. Of course it caused problems and had to be ripped out, and there was hydronic radiant heat tubing in it to boot. The surface spalled and the finish layer came loose. Cost ten thousand dollars to rip out, replace radiant, and re-pour. Haven't used that idiot since. Be very careful about the water content.

  41. Can you pour concrete mix into a 4ft deep 12inch wide sono-tube that is filled with water for deck footings without pre-mixing? I'm just outside Toronto, Canada

  42. Thank you for this.

  43. It must be so great to have such a handy man for a husband. My husband is completely incompetent of anything handy or around the house. I blew a fuse upstairs and everyone one knows when that happens and what to do. My husband? I yell down and tell him to check the fuse box but instead he comes upstairs and starts checking and resetting the GRF outlets in the bathroom. He can’t assemble anything right. He will try a house project, make a mess and completely make it worse. Then we have to call a professional.

    It’s very hard to have any respect for him. Until him, I thought those kind of men only existed on comedy shows. So frustrating! 100% of the time epic fail. I wish I could post the picture of what we have to call in a professional right now because he tried to fix something that wasn’t really broken. It’s broken now though. God help me not to kill him….lol

  44. I think your recipe for cement missed out one of the key ingredients: heat. Just grinding the limestone etc to a powder would not do much good. The materials have to be cooked at a very high temperature, which changes their chemistry and makes them ready to combine with water.

  45. Is it possible to make it even stronger?

  46. "obviously I'm not running s testing lab here in my garage"……. no Grady, that is exact;y what you are doing.

  47. Please make videos about aircrete. Thanks.

  48. Some grey stuff.

  49. water/cement ratio. fines modulus for fine aggregates. adding chemicals. air voids ratio. coarse aggregates type. aggregates specific gravity. maximum aggregate size. mixing water temperature. treatment after concrete pouring.

  50. Why are so many old building projects by ancient peoples around the world, like the Romans(not exclusive however), still standing while our concrete fails in 50 years.
    It seems every old civilization knew better recipes than we do today, why?
    P.S. They did not all have Roman volcanic ash.

  51. This was very concrete information.

  52. Why does concrete absorb Oxygen long after it's set and solid?
    When they made the Mars colony test shelter and sealed it off(the world) the oxygen levels kept dropping and in the end they figured out that fresh concrete was using it up…
    Is there anything else besides cement that can make concrete?

  53. I love that Hydraulic Press Channel inset 😉

  54. Awesome videos! Thank you

  55. I love this kind of stuff

  56. can you do a video on rammed earth? very low cement and very low water in this. yet so strong.

  57. States water makes concrete stronger…

    Concrete with least amount of water became the strongest…

  58. Could you use salt instead of sand? because there's a sand shortage and desalination leaves you with an overflow on salt. Two birds with one stone!

  59. This video was so great that I don't even can come up with a concrete question!

  60. Can you please explain why the cement that gets lots of water is very strong but the concrete that gets the least water has the highest break strength?

  61. 7.33 Concrete application … to canoes, say what?

  62. is it true that the dryer concrete get the stronger it becomes? i remeber the when we got into a newly build house there was a special wallpaper on the walls, and we had to leave it on for atleast 2 years, dunno if it has to do anything with making the concrete stronger.

  63. Here is something no one talks about.

    What is concrete resonance vs. granite or quartz? ???

    Since modern cities are flooded with concrete what type of vibations are we introducing into the cities. Ancient cities used marble, specifically for its resonance.

    Modern cities also use glass extensivly, what does glass bring ro the resonance table.

    If you think this is bogus, go into a log cabin and see how you feel in the wood structure.

    Resonance guides what you feel !!!!

  64. Those concrete cylinders you were making towards the end, did you cure them in water as well?

  65. Engineering is very amazing 😎

  66. Thank you so much.

  67. I drive a mini concrete mixer truck and I am looking to learn everything possible that I can about concrete, so I found this video interesting as well as accurate. Nice job!!

  68. And what did the Romans know about concrete that we have seemingly forgotten?

  69. Man, I knew I could use that sooner or later

  70. I love this channel!!

  71. We care about the content of the videos.
    Not the different size gaps between your teeth.
    This has to be the reason for the number of thumbs down.

  72. Dont be the next king of random

    We love your quality not quantity

  73. Thank you — interesting. The last cylinder's surface resembles cinder block. Same recipe?

  74. So what is beton then?

  75. great content my man

  76. I'd like to know the practical engineering aspects of AirCrete. There are many YT videos on AirCrete, but nothing from an engineering perspective.

  77. a few feet, hahaha, my house is entirely made of concrete, even the bricks.

  78. You're awesome man! These videos are helping me a lot for my exams

  79. What is the environmental and psychological impact of the production and application of concrete/cement?

  80. Ahhhh wait so this is how those karate guys break those concrete blocks. They make the weak.

  81. Grady's voice has a calming effect. He should be a hostage negotiator.

  82. i'm actually on the 77th floor of a skyscraper in HK watching this video, and now i just hope that the concrete was well mix

  83. I'm in New England, and they always seem to be pouring concrete even into the freezing temp. Are we being cheated? Good info.

  84. 7:30 hold on a minute… Canoes?

  85. Can you be more concrete?

  86. Cement is stone-glue. It's like proteins (aka gluten) in bread or rubber cement in school projects.

  87. How good is is ready-made cement sold in tubs by Dap and others. Can I add aggregate to it?

  88. Consider me facted.

  89. Nice Hydraulic Press Channel reference XD

  90. Concrete is domesticated rock, fight me

  91. I love your channel

  92. so making concrate is a Engineer form of cake baking…different mixes make different cakes….well concrete in this case

  93. Who is concrete
    I’ll do you one better why is concrete

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