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Introduction to Concrete Mix Design

Introduction to Concrete Mix Design


welcome concrete superfreaks today we’re gonna talk about the introduction to concrete mix design concrete mix design it’s pretty challenging actually it’s pretty complicated it’s kind of like trying to make soup but you have no idea what the ingredients are you know kind of how you want it to taste you kind of know what you don’t want it to do but you have no idea how you’re gonna get all these different bits and pieces put it together to make something great that people are gonna be happy with at the end yeah that’s what it’s like let’s get started when you design a concrete mixture you have to decide exactly what specific properties that you want to achieve what are some of these properties what are some things that you might want for example you may be interested in making very very high strength concrete that may be something that that you need done maybe you want something like that’s very low strength concrete say what why would I ever want low strength concrete that just doesn’t sound right why would I want something not to be very strong well sometimes you want to make concrete and you want to be able to excavate it you wanna be able to get to it later like for example if you’re embedding pipes in the ground that’s a you might wanna have to repair those areas that’s something called a controlled low strength material and it’s typically made yep you guessed it with a wild concrete mix maybe you want it to set very fast gain strength fast maybe you want it to set slow maybe you want to ship it a very long way like for 24 hours you want to not get hard and then all of a sudden you want to get hard Wow yeah you might want to have to do that you might want to control some other property like the creep what’s creep creep is how much a material deforms under a constant load so if you have a very very very high building tall building you don’t want it to creep that means it might change dead formations over time that means after 30 years you might cause the windows to pop out oh yeah that’d be awful maybe you want to change modulus what’s modulus well modulus is usually usually using something called Hookes law which is modulus is equal to stress over strain okay that’s kind of how squishy something is that’s what modulus means how squishy how much does it give for a certain amount of load okay it’s kind of like it’s something to do with stiffness what else well maybe you want it to have a very low shrinkage that’s we talked about drying shrinkage before and test methods for that maybe you want that to be extremely low maybe you want it to be low cracking what hat sounds great wouldn’t that be great if we could make low cracking concrete we’ll talk about that coming up maybe you want to make it pumpable maybe that’s important maybe you want to make it easy to finish or maybe pay verbal able to be make a slip form paver be able to place the concrete now I’ve just shown a few examples and there’s more out there of things that you might want your concrete to be able to do and you can you can make it do any of these things but be careful be really careful to only choose the properties that you really want only choose the properties that you really need so like I said here well while controlling all these properties are possible it’s not possible to control all of them at once for example it’s pretty challenging to make a lightweight high strength low crack pumpable mix with a great modulus that’s asking for too much gotta be careful just ask for what you really really need and don’t worry about the others as engineers we love to ask for everything we say will we can maximize we can optimize we can make it happen and maybe we might be able to but your life is gonna be a lot easier if you just pick out the things you really want to have happen things you really have to have focus on those make sure those work the more things you require in a concrete mixture to do the more costly and the lower probability that you’re going to succeed and when you don’t succeed that’s not good because concrete’s gonna get hard usually and when it gets hard and it’s not right you have to remove it that’s not good typically though typically though all concrete mixtures have some certain criteria we always shoot for we always want them to be workable and that’s kind of a way to think about construct ability and that depends on what you’re building so you may want your concrete to be different if it’s going to be pumped on top of the building or if you’re making a wall or if you’re making a slab or a bridge or a pavement all of those require a different way to build the concrete a different construct ability or workability and you have to understand that and tailor your concrete for that everything needs strength but it needs enough strength so we got to ask that question doesn’t have enough too much strength doesn’t help you additional strength isn’t better concrete get that in your head right now you need enough strength for what’s asked for it durability is he gonna perform over the service life of the concrete in my opinion durability is much more important than strength you need enough of it the durability got to have that we need it to last we needed to be here so our children’s children can use it economy is it cost-effective if we design and try to make things that are not cost-effective they won’t be used no one will use them or do anything with them that’s a big challenge what controls all of these critical requirements let’s first start out with workability workability is controlled by the amount and the viscosity of the pace what’s viscosity viscosity is resistance to flow something like honey is pretty resistant to flow it has a high viscosity so the more paste you have the easier it’ll be for the aggregates to move within the mixture and the viscosity of the paste is also something that’s another lever that we can use to control to get exactly what we want and the viscosity is usually controlled by two different things one the water content and this controls a very very important parameter probably one of the most important parameters in mixture design the water to cement ratio or the water to cement ish as’ ratio because as we get more and more exotic and different cements and binders we use change the word to cement ishes this is just the mass of the water divided by the mass of the cement this is very important very very helpful and as this number goes up it makes our concrete flow better it makes the viscosity go down add mixtures are another useful lever very very powerful lever that can help us modify the viscosity of the concrete without changing the water spin tricks as we’ve seen the water cement ratio is important for lots of stuff that’s important for strength it’s important for durability we don’t want to move to be changing it just for fun gotta be careful another thing that’s important for workability is the aggregate the gradation that’s the size distribution the shape and the texture of the aggregates are also all really am Orton will talk more about that strength strength is typically controlled by the water to cement ratio as water to cement ratio goes down strength goes up to a point to a point more on that coming up your aggregates are also important as we’re gonna find the aggregates are a huge volume of your concrete mixture so if they’re kind of weak the concrete’s isn’t gonna be strong either also dragnets are pointy they’re elongated okay then within the concrete they’ll actually cause stress concentrations and they’ll cause premature cracking of the concrete and they’ll make your strength go down so again these are another reason why aggregates are important for the strength of our concrete also the bond how the paste hydrated paste bonds or sticks to the concrete or stick to the aggregate that’s actually really important durability oh man oh really important one as far as I’m concerned water cement ratio big player the air void system also important the chemical resistance of the paste another really really important thing something called secondary cementitious materials these are fly ash slag SIL of silica fume and natural pozzolans these are things that are typically waste products from other industries or things we dig out of the ground and cook that we add to concrete to try to make it better try to make better reactions with Portland cement bunch more on those coming up but they’re really important for durability cracking and the resistance to the penetration of outside chemicals are all things that help control durability and again we want we want these things we want at least enough of them economy the most expensive thing in your concrete is the cement okay I’ll show you some numbers coming up if you can typically reduce the amount of Portland cement in your concrete you can typically save money it’s not always the case depending on how expensive some of your other ingredients are okay but typically that has been a great way to reduce the cost of your concrete I reduce the amount of cement if you maximize SCMS this is these waste products if you can use a lot of them you use less cement typically that’s been a way to save money if you can reduce construction labor how much effort does it take to place and finish the concrete how many times do they have to mess with the concrete before they get it right if you can make these things minimal you’re going to save money you can minimize the usage of special equipment do they have to have a special place or for this concrete they have to have a special pump to pump it that’s only available in like one in the in the outside hundred miles that’s not good you want to develop your concrete for generic for the everyday use of tools and equipment also Hall distances if you have to use a special aggregate to make it happen it’s only available in several states away you’re not gonna save anybody any money and they’re not gonna make or use your concrete because it’s not gonna be economical but what we’re gonna find is concrete mixture design is a balancing act if we try to push any one of these topics too much in one direction will cause a problem and another one we have to understand how all this comes together to make great concrete it’s really challenging but when it’s right it’s pretty awesome now let’s talk about typical concrete mixture proportions don’t worry we’re gonna learn some very very sophisticated ways to calculate the proportions of a concrete mixture but the results that you get are gonna typically fall in these ranges this is like a big secret and if they don’t fall in these ranges then you need to think about why do you have some special aggregate or do you have some special property or you do are you trying to do something crazy or different because if you’re not if you’re May typical concrete there usually following this criteria I’m about to show you so have it I have a table shown here with the typical volumes now I’m talking in volumes not weights volumes of a concrete mixture and if we have we have the ingredients over here we have coarse aggregate fine aggregate paste that’s the water in the cement the air that’s the bubbles you stabilize inside the concrete and that’s the total 100% and if you want it’s a low workable mix that’s something with like a slump of maybe like three inches so why would you need that well maybe for a pavement maybe for a wall maybe for something that you don’t want a lot of flow ability in about a three inch slump or so three to four inch slump usually you find about you get about forty two percent volume of course at twenty eight percent volume of fine aggregate twenty four percent by pace and six percent air now that doesn’t mean that these numbers are exact by the way these are kind of ballpark numbers and they could vary by maybe one to three percent either way now if you want high workable concrete now this is something with a slump of maybe six inches to eight inches something in that range okay this is more the volumes that you would typically be using in your in your mixture now let’s look at the differences between these two notice that the coarse aggregate has gone down a little bit and the fine aggregate has gone down a little bit and the paste has gone up it’s like I said earlier if you want more flowable concrete typically need more paste okay and the change here is about six percent and you noticed I’ve taken out exactly here I’ve I’ve removed three percent course and three percent fine now there’s lots of arguments on the best way to do that and we’ll talk more about that coming up in the end sometimes they’re not that important sometimes they are it just depends but notice I’ve taken out some amount of aggregate and I’ve put in so much some amount of paste that’s typically the way you change the workability now another thing that’s kind of cool is that if you look at the total here that about seventy percent of your mixture about about 70 percent of your mixture volume is aggregate yeah that’s a lot that’s why it’s so important to understand how your aggregates impact your concrete mixture that’s a future video now just to give you a kind of a better scale of these things I have actually stacked them up here in a bar chart and showing you the amount of coarse aggregate – the amount of fine aggregate – the amount of pace – the amount of air and this is all drawn to scale okay and you can see the paste and the fine aggregate are pretty similar okay and the coarse aggregate is the most and here’s these same bars stacked up or you can easily compare them again the pace and fine aggregate are pretty similar to one another this coarse aggregate is is the most and then there’s the amount of air at the bottom now another thing that’s kind of cool about air is that most people think about adding air for just durability but adding air is good for lots of stuff air will actually make your concrete more workable and if you add air to the concrete you’re selling your customer more air ha air is free right we breathe it all the time it’s all around us wow that’s pretty cool so like I said before these are typical numbers but you’re gonna be surprised how close these typical numbers are to the practical numbers that you calculate or use in day-to-day concrete production when to aggregates are used then a typical proportion typical it’s 60% of the volume of aggregates is coarse and about 40% of the volume of the aggregates are fine and many many modern concrete mixtures will use to coarse aggregates as in most concrete mixtures today most of the real groundbreaking work will actually use at least two sometimes more coarse aggregates to better the size distribution talk about that in just a second for example instead of just using one coarse aggregate at 60% they may use two different coarse aggregates and these are just numbers this is about 40% of one and about 20% of another and that’s going to change based on the gradation of the aggregates but again still the fine aggregates about 40% well that’s it for the introduction next I’m going to talk about aggregates and how they impact concrete mixtures even more thanks

Comments (24)

  1. Hi there
    I want to mak a diy concete kitchen coutertop in a melamine mold about 2 inch thick reinforced with rebar.
    Quickcete 5000 is a wery popular mix for this aplication.
    Unfortunatily where i live (in Romania) these kind o concrete mixes are not avalable.
    I did find two kinds of potland cement, one with intitial high strenght the other with high final strenght.
    Also i found a liquide aditive for concrete. The label sais it is used to encrease workability. reduce amount of water and make it water resistent, along with dosage.
    I found some proportions for the kind of concrete for a slab, pawement and structural beams or pillars.
    I need some help figuring out the corect recipe for my aplication.
    Thanx

  2. I enjoy your presentation and methods of teaching.

  3. Thanks for your videos Sir.
    I am a visual learner and your videos make everything on paper make sense. I just started a new position as Concrete Technician and this is so helpful. Thanks again

  4. It is so good how you presented it. It makes all the difference when someone with practical experience is teaching! Thanks a lot.

  5. wow amazing explanation.

  6. A Doc, your a concrete lover… as am I… An idea for a video for you, fiber vs metal fiber and the disadvantages of metal fibers as points of rust and expansion in those metals… as they cause ''failure"…
    Especially, in salt and freeze thaw cycle areas… I am just sharing, as I know we need ideas as Youtube creators.
    (As I am stuck on stupid with the FIU Bridge collapse — it is owning me right now… )

  7. This is how Engineering is learnt!!👍

  8. Nice and Informative!!! Please make a Video on Life Cycle Analysis of Concrete and Durability of Concrete.

  9. Fantastic explanation on concrete. What can I use with a superplasticizer that will make pencil thick cement rod not break if dropped? Maybe something that gives it more flex?

  10. I do not speak English very well, but with the subtitles I can understand everything, I have not found in Spanish a video like that, fantastic.

    I would like to ask you a question, I am interested in looking for more information the method of fineness module of the combination of aggregates or optimal fineness module, through tests this method gives more workable concrete. Will not you have some biographies in English that you can recommend me about this?

  11. Ok.. if I am using a general build type, such as 1:2:4 and want to add fibers and water reducer, for use in forms for walls, how much fibers, how much reducer, and how much can I reduce the water yet get flow? Area is using hand mix or small mixers, sand, and 94 lb bags of cement… so need to figure it out..lol…

  12. Creep is my neighbor

  13. 1/2 aggregate for line pump truck through some old plasticizer left over from a previous pour helps.
    I poured straight simple plasticizer in the pump truck before pumping and added in my mix to help push through 3/4 inch aggregate.
    Line pump trucks hate larger than 1/2 inch aggregate.
    Doesn't pump well.
    I have had many inexperienced pump truck operators who ran lines up hill then to reducer line to make their job easier.
    But clueless about how hard the pump truck has to work to flow that mix through.
    Trust me, living in Metro Vancouver, I have seen this many times.
    Pumping up a steep driveway, then pump truck operator put on a reduced hose line for last 40 to 50 feet.
    To get it through, it would have to be a 6 inch slump, concrete would fail a test.
    I have had many arguments with contractors and pump truck operators.
    No problem if they sign a waiver.
    Leaves my company guilt free
    Funny how nobody wants to do that.
    Customer always right, hardly in the concrete business.

  14. Your the best for sure always rescuing me

  15. I've just discovered that you can not only add colour to concrete (oxides) but glitter too, just before you seal it, both available from a company called 'Hemway'. I loved concrete before, but now it sparkles, I'm obsessed.

  16. This video is so clear and educative

  17. I am not an engineer but just curious are you guys still memorizing these things? Who does that in the era of automatic calculators that work together with databases and cloud services? I am guessing many engineers don't even bother to memorize these things and maybe simply use a specific software that easily calculates everything for you by taking all the inputs you provide and in return gives you a list of all the material and even the steps and procedures to be followed by even connecting to global services to find the lowest cost products in the current markets that helps you to prepare the best and most cost effective concrete you need. If that software doesn't exist yet what a pity for humanity and what a shame for all the brains wasting their energy in silicon valley. Please someone tell me that this kind of software exists..

  18. Dr. Tyler, is there away to get in touch with you for advice on making a formula that suits a very special need?

  19. You had me at "Welcome concrete superfreaks" 🙂

  20. 1:51 It looked like you said it, realized what you said, and kept on trucking like it never occurred to you that you may be talking about penis… lmao

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