Promoted from the Ricochet Member Feed by Editors Created with Sketch. Everything You Ever Wanted To Know About Concrete* (But Were Afraid To Ask)

 

In the comments on another post, I mentioned it would be nice if someone talked about concrete — that noble material of the Pax Romana — so I might sound at least slightly knowledgeable on a topic here for once. Sure, it’s not as fun a topic as Same-Sex Marriage or drug legalization, but it may also help me in Dime’s contest this year for worst poster!

A little background: I am one of the owners of a commercial and industrial concrete construction company that does work all across the southeast and as far west as Oklahoma. Yes, it’s exactly as glamorous as it sounds! Concrete is a basically a mixture of cement, aggregate, and water. Yes, cement is an ingredient of concrete, so now you know if someone refers to concrete as “cement” it is appropriate to point and laugh.

Fellow member Captainpower was gracious enough to ask a few questions that I will try to answer adequately here:

Q: Are there different types of concrete?

A: Absolutely! It varies in both compressive and flexural strength, abrasiveness, color, reflectiveness, weight, etc.

Q: What’s the difference between good and bad (or proper and sloppy) concrete mixes and application?

A: I think this question is about the “slump” or “wetness” of concrete when it is first placed. The key measurement in a mix design that many times the “slump” indicates is the water/cement ratio. The concrete is weaker, both chemically and because of material segregation, when that ratio is too high.

Q: Are there any craftsmen left, or is everyone in it for a quick buck?

A: Yes there are some very talented craftsmen out there! It’s actually a pretty tough business to make a quick buck in, though I know residential contracting can attract some unsavory types that will try to take advantage of the unwary homeowner.

Q: Is concrete technology still progressing, or do we pretty much have it mastered since forever?

20141030_165118A: Concrete technology is constantly evolving and advancing, and the Romans would recognize very little about modern concrete, other than that it hardens. There are many chemical admixtures that can make concrete behave in various ways, which means it can be applied in all kinds of different ways. It can have its set time delayed indefinitely, or can be made to set almost immediately. It can be made to flow horizontally like water without losing strength, made waterproof… the list is endless.

Q: What’s better than concrete? What’s worse?

A: It depends on the application. People use concrete in all types of construction. Roadways, precast, structural building elements, kitchen counter tops, even concrete canoes. Does it make good carpet? Not especially, but a polished concrete floor that is colored or stained can look pretty darn good!

Anyone else have questions? The floor is open.

There are 279 comments.

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  1. Arahant Member

    No questions, but some stories. Science has recently found what the Romans used that made their concrete so good that much of it is still out there today: volcanic ash from one of the Italian volcanoes. Keep that in mind the next time a volcano springs up in Oklahoma.

    Another famous concrete story involved Biosphere II in Arizona. They sealed the place up before the concrete was cured. The team simulating being in space found that their oxygen was disappearing. They eventually found that it was going into the concrete as it continued to cure.

    Thanks for the fascinating conversation you have started.

    • #1
    • January 26, 2015, at 7:59 PM PST
    • 1 like
  2. Locke On Member

    What causes a concrete driveway to spall off when it gets hit with salt for melting winter ice and snow?

    • #2
    • January 26, 2015, at 8:21 PM PST
    • 1 like
  3. Larry Koler Inactive

    Man, I have waited so long for something like this:

    1) Is it possible or is it true that the Egyptians used concrete to make their stones for the great pyramid? I read this years ago in an engineering journal and here’s the first link I found just now to have you think about it. There are probably better links but it will get you started. (But maybe you already have an idea about this one.) The Greeks said that all their wisdom came from Egypt. And the Romans built on the Greeks.So… please opine.

    2) So, what is the earliest evidence of concrete that you know of?

    3) The most important question: I have a small 600 sq. ft. house on our property that we use for an AIRBNB and for friends and family. It’s a 1924 house with lathe and plaster, knob and tube wiring (some) and a post and beam foundation. Are there any clever ways to put a concrete foundation under this house? (Please try and save me money here.)

    • #3
    • January 26, 2015, at 8:23 PM PST
    • 1 like
  4. Herbert defender of the Realm,… Inactive

    Is it true that the concrete used to build the Hoover dam is still curing and will be for 100’s of years to come?

    • #4
    • January 26, 2015, at 8:26 PM PST
    • Like
  5. sawatdeeka Member
    sawatdeekaJoined in the first year of Ricochet Ricochet Charter Member

    Like.

    • #5
    • January 26, 2015, at 8:30 PM PST
    • Like
  6. Hammer, The Member

    As a concrete specialist, do you shudder every time you see someone buying a bag of quickcrete? What sort of awesome projects might the creative renaissance man come up with for his house this summer with the use of concrete?? Do you give personal lessons?!

    • #6
    • January 26, 2015, at 8:45 PM PST
    • 1 like
  7. Hammer, The Member

    also:

    it looks like some sort of stout or maybe porter that you’re exjoning with in your avatar. Do concrete guys also like good beer? Please tell me it’s not a coke.

    • #7
    • January 26, 2015, at 8:47 PM PST
    • 1 like
  8. Arahant Member

    Ryan M: exjoning

    I didn’t know it had become a verb.

    • #8
    • January 26, 2015, at 8:52 PM PST
    • Like
  9. Jason Rudert Member

    We now and then have to have poured a pit and tunnel underneath our paint booths. The difficulty is that this often gets done in three pours, which all take custom forming, and also no one believes me when I tell them that the weight of the concrete is going to make their forms bow in and then our later parts won’t fit. They just about always end up having to saw cut their new stuff. We’ve done this probably fifty times over the last twenty years and it always seems to exceed the mental abilities of every concrete guy we’ve ever used. Either they screw it up or they lose money.

    I have been kicking around a design for a reusable form, made of foam skinned with fiberglass. Essentially we would have the floor of the pit poured first, about thirty inches down, six inches thick. Let that cure. Then bolt down to that–so it doesn’t float up–a large fiberglass plug, tapered so as to be removable, which establishes the negative space of the pit and tunnel. Pour the sides and cap (final floor grade) in one pour. Cure, remove big fiberglass thingie.

    Questions:

    How smooth is it possible to get the joint where the floor of the pit meets the sides of the plug? I don’t want it all crumbly with aggregate shedding out.

    I have in mind a semi-elliptical cross-section for the tunnel. Which means a large thickness of concrete above the shoulders. Will this cure rapidly enough? Is there some lightweight filler that could be mixed in ? Could permanently embedded styrofoam blocks be anchored in there to act as filler?

    How much would the concrete adhere to the fiberglass? Would it be enough to lube it with some oil to act as a release agent, or should we wrap with polyethylene sheeting? Are there other release agents? I’m leery of using oil because it could contaminate the painting process, and you’re never rely going to get it out of the concrete.

    Thanks!

    • #9
    • January 26, 2015, at 8:53 PM PST
    • Like
  10. Jason Rudert Member

    “I didn’t know it had become a verb.”

    Get with it dude.

    • #10
    • January 26, 2015, at 8:54 PM PST
    • Like
  11. Profile Photo Member

    Concretevol, this post is near and dear to my heart…My dad worked as a troubleshooter/engineer – and later salesman for several cement companies…We kids watched his seminars for the sales staff…Slides and no notes. “Slump tests” were an adventure. Thanks for the memories!

    • #11
    • January 26, 2015, at 8:59 PM PST
    • Like
  12. Arahant Member

    Concretevol: If not….then I am still in the “worst poster” running!

    You’re obviously going to have to do much worse than this.

    • #12
    • January 26, 2015, at 9:04 PM PST
    • 1 like
  13. Larry Koler Inactive

    OK, so Concretevol writes this post and then goes to bed for the night. What’s with that?

    All I know is that I get fist dibs on his answering. I asked the best questions and asked them first.

    • #13
    • January 26, 2015, at 9:04 PM PST
    • 1 like
  14. Boomerang Inactive

    What’s in the cement that makes it harden?

    • #14
    • January 26, 2015, at 9:08 PM PST
    • 1 like
  15. Arahant Member

    Larry Koler: I asked the best questions and asked them first.

    Well, you did get first, but I think Jason’s may be best. That sounds like a fun problem to solve.

    • #15
    • January 26, 2015, at 9:10 PM PST
    • 1 like
  16. Paul Dougherty Member

    This is kind of weird in that I want to spout off and answer a few of these but it is not my thread. I am surely less qualified than Concretevol to give the thorough response but this is kind of what I do. I work for a DOT materials lab which gives me just enough experience to think I know what I am talking about and enough of an authoritative air to really screw up any operation.

    What is better than concrete?

    Asphalt. (but that is another thread)

    • #16
    • January 26, 2015, at 10:15 PM PST
    • 1 like
  17. Paul Dougherty Member

    As for spalling driveway slabs, I don’t know the particulars of the mix being used or the craftsman placing the slab but a few thoughts:

    It is rare to encounter a finisher who is not convinced of their skill and expertise in finishing concrete. Failures in finish rarely display in the first few weeks after placement (the period in which they come back to admire the work). Therefore they are convinced that “blessing” the fresh slab with water just prior to floating or finishing the surface does no damage to the surface. Rest assured, water added to cement whether in the truck, at the plant, or just prior to initial set, will eventually weaken the concrete. Salts can inflict tremendous pressure in the pores of concrete when they dry just as water does when freezing. The best defense is a tight pore structure in the concrete at a low water/cement ratio. A low water cement ratio helps reduce shrinkage in the greater concrete mass which induces counterproductive internal forces resulting in cracks. A sealer can help reduce permeation of salts and water if sealer is regularly maintained.

    • #17
    • January 26, 2015, at 10:44 PM PST
    • Like
  18. Concretevol Thatcher
    Concretevol

    Arahant:No questions, but some stories. Science has recently found what the Romans used that made their concrete so good that much of it is still out there today: volcanic ash from one of the Italian volcanoes. Keep that in mind the next time a volcano springs up in Oklahoma.

    Another famous concrete story involved Biosphere II in Arizona. They sealed the place up before the concrete was cured. The team simulating being in space found that their oxygen was disappearing. They eventually found that it was going into the concrete as it continued to cure.

    Thanks for the fascinating conversation you have started.

    That’s a cool story, I hadn’t heard that about the Biosphere project! Unintended consequences and all that. Lots of nasty things can happen when you cover or seal up concrete too soon.

    • #18
    • January 26, 2015, at 10:46 PM PST
    • 1 like
  19. Concretevol Thatcher
    Concretevol

    Larry Koler:OK, so Concretevol writes this post and then goes to bed for the night. What’s with that?

    All I know is that I get fist dibs on his answering. I asked the best

    Larry Koler:OK, so Concretevol writes this post and then goes to bed for the night. What’s with that?

    All I know is that I get fist dibs on his answering. I asked the best questions and asked them first.

    I found this to be in pour taste too Larry so I have returned! (may have dozed off watching Conan.)
    questions and asked them first

    • #19
    • January 26, 2015, at 10:47 PM PST
    • Like
  20. Concretevol Thatcher
    Concretevol

    Locke On:What causes a concrete driveway to spall off when it gets hit with salt for melting winter ice and snow?

    The reason varies depending on what type of chemical is used to melt the ice and snow. The thing to remember is that concrete is porous and water will seep down into its surface. The most common problem is salt does for example. It can increase the number of freeze thaw cycles the concrete goes through. You have a layer of ice and snow and when salt is sprinkled on it basically lowers the freezing point of the water to around 20 degrees. The ice melts and seeps down just under the surface of the concrete…..temp drops below 20 or salt gets diluted down over time, water freezes and expands below the surface. If this happens on relatively new concrete or multiple times it causes spallation. (top pops off) There are also some chemical deicers that actually react with the concrete itself and weaken the surface with makes the spallation worse and also increases wear later.

    • #20
    • January 26, 2015, at 11:04 PM PST
    • 1 like
  21. Concretevol Thatcher
    Concretevol

    Larry Koler:Man, I have waited so long for something like this:

    1) Is it possible or is it true that the Egyptians used concrete to make their stones for the great pyramid? I read this years ago in an engineering journal and here’s the first link I found just now to have you think about it. There are probably better links but it will get you started. (But maybe you already have an idea about this one.) The Greeks said that all their wisdom came from Egypt. And the Romans built on the Greeks.So… please opine.

    2) So, what is the earliest evidence of concrete that you know of?

    3) The most important question: I have a small 600 sq. ft. house on our property that we use for an AIRBNB and for friends and family. It’s a 1924 house with lathe and plaster, knob and tube wiring (some) and a post and beam foundation. Are there any clever ways to put a concrete foundation under this house? (Please try and save me money here.)

    Ok Larry, here goes. Gonna do this off the top of my head so I may not be 100% on this on. May come back to it after doing some reading…

    1) This seems to be an extension of the argument over how did the Egyptians move those giant stones around. I don’t see why they couldn’t have used some type of non-hydraulic lime mortar with primarily sand to cast some of their pieces. (haven’t read your link yet so I may be way off) It does seem however that this would be fairly obvious to the experts that have tried to duplicate their building methods. I would be more inclined to think they just used a type of mortar to fasten cut stone together as lime type mortars adhere really well to softer stone like sandstone and limestone.

    2) Ok this one goes back to your statement about the Romans using and improving on Greek tech. My understanding is the Greeks were some of the first to use a form of concrete in large scale projects although I’m not sure that timeframe vs the Great Wall in China. Romans revolutionized the practice though by using “hydraulic” mortars that set under water and new pozzolan materials such as volcanic sands etc. This is where actual flowable concrete that was cast and hardened in forms was used extensively. There methods were obviously affective as you can still see them standing today!

    3) Not a ton of options here but it’s not that expensive on a house that small to merely jack it up, remove the old foundation material, and dig and pour concrete footings under it. Labor intensive yes….difficult not really. Pour some simple footings under the perimeter (may be able to space out square pier foundations instead of trying to dig a continuous footing) and lay a block up to the house frame. As old as the house is you may need to use some type of new beam to span the piers then sit the house back down and you’re done! Feel free to message me if I’m not being clear on this.

    • #21
    • January 26, 2015, at 11:40 PM PST
    • Like
  22. Concretevol Thatcher
    Concretevol

    Herbert Woodbery:Is it true that the concrete used to build the Hoover dam is still curing and will be for 100′s of years to come?

    Absolutely true! It will pretty much cure indefinitely and concrete gets stronger not weaker over time without outside variables that can cause deterioration. (see above freeze/thaw comments) It can however become more brittle also which anyone who has removed very old concrete can attest to. It tends to be very difficult to break and when it does it shatters rather than break into large chunks.

    • #22
    • January 26, 2015, at 11:44 PM PST
    • Like
  23. Concretevol Thatcher
    Concretevol

    Ryan M:As a concrete specialist, do you shudder every time you see someone buying a bag of quickcrete? What sort of awesome projects might the creative renaissance man come up with for his house this summer with the use of concrete?? Do you give personal lessons?!

    Haha, nope not when the need is a small amount to put posts in the ground or other home improvement type projects. Yes when they have a truckload of the stuff to mix with a mortar mixer to pour a patio….wrong application and probably costs more.

    I don’t recommend the do-it yourselfer to pour larger projects and a word to the wise, most DYI shows show incorrect concrete finishing techniques. Besides, a lot of it is a matter of timing. However, not to be a wet blanket there are good small projects out there. I love the concrete counter tops people are doing now. You can also do some cool acid etching and stains on existing basement or garage slabs or cast your own concrete pavers/stepping stones to make a decorative walkway.

    Not exactly lessons but I can try for helpful advice!

    • #23
    • January 26, 2015, at 11:55 PM PST
    • 1 like
  24. Concretevol Thatcher
    Concretevol

    Ryan M:also:

    it looks like some sort of stout or maybe porter that you’re exjoning with in your avatar. Do concrete guys also like good beer? Please tell me it’s not a coke.

    This concrete guy is very much into craft beer. I wish I could tell you exactly what that one was but winter time means porters and/or stouts so it was one or the other. If you happen to use the fantastic beer app “Untappd” it is possible I am on there under the same name.

    • #24
    • January 26, 2015, at 11:59 PM PST
    • 1 like
  25. Concretevol Thatcher
    Concretevol

    Arahant:

    Ryan M: exjoning

    I didn’t know it had become a verb.

    It totally is a verb. lol

    • #25
    • January 26, 2015, at 11:59 PM PST
    • Like
  26. Concretevol Thatcher
    Concretevol

    Jason Rudert:We now and then have to have poured a pit and tunnel underneath our paint booths. The difficulty is that this often gets done in three pours, which all take custom forming, and also no one believes me when I tell them that the weight of the concrete is going to make their forms bow in and then our later parts won’t fit. They just about always end up having to saw cut their new stuff. We’ve done this probably fifty times over the last twenty years and it always seems to exceed the mental abilities of every concrete guy we’ve ever used. Either they screw it up or they lose money.

    I have been kicking around a design for a reusable form, made of foam skinned with fiberglass. Essentially we would have the floor of the pit poured first, about thirty inches down, six inches thick. Let that cure. Then bolt down to that–so it doesn’t float up–a large fiberglass plug, tapered so as to be removable, which establishes the negative space of the pit and tunnel. Pour the sides and cap (final floor grade) in one pour. Cure, remove big fiberglass thingie.

    Questions:

    How smooth is it possible to get the joint where the floor of the pit meets the sides of the plug? I don’t want it all crumbly with aggregate shedding out.

    I have in mind a semi-elliptical cross-section for the tunnel. Which means a large thickness of concrete above the shoulders. Will this cure rapidly enough? Is there some lightweight filler that could be mixed in ? Could permanently embedded styrofoam blocks be anchored in there to act as filler?

    How much would the concrete adhere to the fiberglass? Would it be enough to lube it with some oil to act as a release agent, or should we wrap with polyethylene sheeting? Are there other release agents? I’m leery of using oil because it could contaminate the painting process, and you’re never rely going to get it out of the concrete.

    Thanks!

    This is awesome, you have some good ideas. Of course my first reaction is you haven’t hired us so there is your first problem! lol It sounds like a forming system problem and from what you describe a lack of knowledge. An elevated structural slab we just poured on a hotel in downtown Charleston was 3′ thick in places, was only around 7,000 sqft, took 550 cuyds of concrete and there weren’t any dimensional issues. Your solution is a creative one however and sounds like it would work to me. Fiberglass forms are used in certain instances where custom shapes or dimensions are needed. Compound curves for instance are difficult to accomplish with traditional forming methods. Using a high density foam is also a good method of filling voids under a slab.

    Your question about the joint smoothness I think is referring to the form intersecting the initial floor pour? That should be a fairly tight joint if the concrete floor section is finished under the wall line. More critical than that is the consolidation of the concrete in the walls at the time of placement. Concrete vibrators need to be used so you don’t have issues with the exposed aggregate you discussed.

    If you used a form like this you could definitely use foam to fill voids, reduce weight and lower material cost.

    I would use a chemical release agent as long as the fiberglass is relatively smooth. A concrete supply company (not a readymix company) could easily recommend the right product to use with fiberglass. You are on the right track tapering the plug for removal also.

    • #26
    • January 27, 2015, at 12:20 AM PST
    • 1 like
  27. Profile Photo Member

    Concretevol,

    I hate this post. I wonder if I can get a refund from Ricochet. I will ask but the last guy who did this found themselves in Lake Squish with cement, aggregate, and water around their ankles. Someone said it was a professional job and came under contract so it couldn’t have been a Democrat. That someone was last seen near Rico Bay. Funny there was a concrete conference (When concrete guys want to mix they MIX.) at the Rudert Lake Rico Hideaway Motel and Convention Center.

    Sincerely yours,

    Larry Koler

    PS I live in Seattle. Elliot Bay, Lake Washington, and Lake Union are nearby.

    • #27
    • January 27, 2015, at 12:29 AM PST
    • Like
  28. Concretevol Thatcher
    Concretevol

    Boomerang:What’s in the cement that makes it harden?

    Concrete is a basic mixture of portland cement, water and various aggregates. When the cement and water mix it starts a process called hydration. The basic compounds in the cement each undergo hydration and form a paste that is the binder material in the concrete. The sand and stone (aggregate component of concrete) form the filler material that the paste binds together. As the hydration process slows over time the paste hardens and adheres the aggregate together making hardened concrete.

    • #28
    • January 27, 2015, at 12:31 AM PST
    • 1 like
  29. Concretevol Thatcher
    Concretevol

    Paul Dougherty:This is kind of weird in that I want to spout off and answer a few of these but it is not my thread. I am surely less qualified than Concretevol to give the thorough response but this is kind of what I do. I work for a DOT materials lab which gives me just enough experience to think I know what I am talking about and enough of an authoritative air to really screw up any operation.

    What is better than concrete?

    Asphalt. (but that is another thread)

    After that last comment you are dead to me. lol

    Going to sleep, I am happy to hear what you think about any of these items Paul. You come from a different perspective I’m sure. I will check back in the morning!

    • #29
    • January 27, 2015, at 12:33 AM PST
    • 1 like
  30. Profile Photo Member

    The Concretevol Drink-o-matic Martini Mixer

    Operation_of_a_truck_mixer

    • #30
    • January 27, 2015, at 12:35 AM PST
    • 1 like

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