EP #152: Concrete Mix Design Isn’t Complicated… Here’s the Proof

Seth Tandett (00:00)
And welcome to another episode of the Concrete Logic Podcast. And today I have Dr. Jon Belkowitz back on the show for the, I don't know, we're getting close to a hundred times, something like that. But no, not even close. No, not even close. Anyhow, today, if you've never designed, and I don't want to say designed,

Dr Jon (00:11)
What? I better get a t-shirt.

Seth Tandett (00:23)
If you never came up with your own concrete mix design, we're going to show you how to do that today. So stick with us. But before we get started, I want to remind you how you can support the show. There are a couple of ways. Go to concrete logic podcast.com and up at the top, the top menu, there's a ask Seth button. It's a

up at the top navigation menu. Ask Seth. You're laughing. You click on ask. ⁓ yeah.

Dr Jon (00:52)
I want an Ask Seth t-shirt. I want

a t-shirt that says Ass-Sep. That's a great idea.

Seth Tandett (00:57)
Yeah, that's a great idea.

But anyways, you click on that and that's a way for you to shoot me an email. And what I'm looking for are topic or guest suggestions. So if you want to hear Dr. Jon back on, or you want to hear him talk about something specific, reach out. Or any other topic you want to hear or guest you want to hear from. That's what I'm looking for there. And if you'd rather leave me a voicemail, there's a, at the bottom right hand corner, there's a little microphone there. You can click on that.

and that'll record you right over your computer or your phone if you're on your phone. And you can leave me a voicemail. Same thing. Give me a topic, give me a guest suggestion, because this what the podcast is all about. It's about what you want to hear, what you want to learn about. And the second way is if you get some kind of value out of today's episode or any of the 150 plus episodes we've put out there,

you can donate to the show and how you do that on the same homepage of ConcreteLogicPodcast.com. There's a donate button, big blue button in the upper right hand corner, click on that. And there's no set amount. You just give what you feel was the value you got out of the show. So that's how that works. Another way, Dr. Jon. Yeah.

Dr Jon (02:04)
Set amount, don't be cheap. Advertise

too, get your PDHs here. Seth doesn't know it yet, but some of his PDHs are given away for free. It's such a low cost.

Seth Tandett (02:13)
Hey, easy.

We don't, I wanna go back, because someone actually ⁓ sent in a donation, I wanna thank them. Joseph Swan donated to the show. Thank you, Joseph.

Dr Jon (02:25)
Thank you, Joseph.

Seth Tandett (02:26)
Appreciate

the support So he'll be listed as a producer of the show and the show notes. So check out the show notes So he will always Forever as long as the podcast exists will be attached to this show. How cool is that? All right. Now we'll get to what you're talking about. Are you're a professional engineer, aren't you? Yeah, and you got to take Yeah, you got to take classes to do whatever Yeah, every every year

Dr Jon (02:28)
Appreciate the support.

Me? I hope so. Yeah. I put the letters at the end. PDH is... Yep. Yep. Yep.

yeah. Yeah. And I think it's a bunch of classes and they're not inexpensive and they take a lot of time. the PDH is... So I normally go through PDH engineer, which is really cool. Read about the Hyatt Regency disaster, the Liberty ships.

Seth Tandett (03:01)
Yeah.

Dr Jon (03:10)
you know, concrete stuff, steel stuff, this is a whole bunch, but what I like about your PDHs is they are directly concrete related, although a PDH engineer does have concrete stuff, it's out-frickin' dated. And I mean, shoot, if you took all of Bob Higgins' podcasts and you made quizzes out of those, I would pay big money, more money than you currently have, and I'm not trying to, you know, break the bank for anybody here, but...

Seth Tandett (03:30)
Yeah.

Dr Jon (03:36)
What is it you have nine PDHs?

Seth Tandett (03:38)
No, we have over, we have 25 courses right now. So if like...

Dr Jon (03:43)
What do you

sell them for in it? The bundles.

Seth Tandett (03:44)
Well, you can,

so you can either do a couple of things. You can either go on there and buy them individually, which is like the other websites have out there, like 30 bucks each. So if you think about that, if you bought them individually, it'd be 30 times 25, be $750, which is a lot of money. Or you can get a monthly membership on the Academy for 49 or no, it's $39 a month.

So you just pay by the month, go in there and do as much as you want ⁓ and stay as, and you can get on there and there's other features in there. So just go to ConcreteLogicAcademy.com, check it out. And there's also links on the ConcreteLogicPodcast.com, so check it out. ⁓ But it's the, yeah.

Dr Jon (04:15)
I'd rather do that.

What I like about these, hold on, what I

like about these is that I'm listening people that I want to learn from, that I know and I already have like trust and faith in what they're saying. And I'm just, they already have learned from them and now I'm just continuing to educate my education and I get credit for it, 750 bucks you have to spend it anyway or whatever equivalent that is. I would rather.

Seth Tandett (04:37)
Yeah.

Dr Jon (04:52)
do it this way, enjoy my time instead of having to force myself.

Seth Tandett (04:56)
Yeah, and then it's a community. Everyone that joins, they're in there. So you can ask questions or just say hi. It's kind of a little social network for Concrete Logic folks. All right. But yeah, with that, let's get into today's episode. So again, I'm going to learn with everyone else today. We're going to make our own mix design. So I think...

you're going to kind of explain how we come up with a cubic yard of concrete first, What's the pieces and parts of that? Why it's a certain amount? All right. Well, get us started.

Dr Jon (05:27)
Mm-hmm.

You got it, man.

So, concrete mix design, call it, especially when you use the ACI 211 method, I call it a choose your own adventure. Right? And I'm trying to be cute and funny, which of course I am. But I'm also trying to make what could be death through mathematics into fun with mathematics. Right?

Now when it comes to concrete, it's a very easy approach. Concrete, as Seth already stated, is sold here in the United States in one cubic yard. And if you don't know what a cubic yard is, imagine a block.

Sorry about that. Imagine a block that's three foot by three foot by three foot. Seth, why you do the math for me. What is three foot times three foot times three foot? Go ahead, buddy. I checked it for you.

Seth Tandett (06:22)
I believe it's 27 cubic foot.

Dr Jon (06:25)
27 cubic feet in a cubic yard. So when we design for a concrete mix, we have to design within that 27 cubic foot block, that known volume. Hence the reason this is called the absolute volume method. Are you raising your hand or just sticking your thumb?

Seth Tandett (06:47)
No, go ahead.

Dr Jon (06:47)
Okay, sorry. So we call this the absolute volume method because we have to take certain portions of that 27 cubic foot block, certain portion goes to air, certain portion goes to sand, rock, cement, water and admixtures, but we can't design for more than that 27. Now...

When we sell our concrete, we actually use that as a way to measure or verify that the concrete that was ordered is the concrete that was made, is the concrete that was transported, is the concrete that was delivered down the chute into the formwork. And what is that called? Seth? Yield. Good job, Seth. Which is our total weight of materials on the batch ticket.

divided by the unit weight of our concrete measured on the job site. So, for instance, if our total weight of our concrete is 3,930 pounds, which we'll figure out here in a little bit, and we divide that by our unit weight, let's say somebody measured the unit weight, and it's 142 pounds per cubic foot.

We do 3,930 pounds per cubic yard divided by 142 pounds per cubic feet. And what we end up getting, the pounds cancel out, cancel out, cancel out. The cubic feet goes to the numerator, the cubic yards goes to the denominator, and we're left with some number here in our case. is 27.7,

cubic

feet worth of material per cubic yard of concrete. Now what that means is we gave them a little bit too much. We didn't shortchange them which is much better because hey there are contractors that will see a 26.8 and be like whoa I just bought 2 million yards and you shorted me 0.2 cubic feet it adds up I just want my money back.

Seth Tandett (08:24)
Mm-hmm.

Heads up.

Dr Jon (08:43)
So that's where that comes into practice, on the flip side of it. But again, going back full circle, what we're designing is one cubic yard, 27 cubic feet. Now the problem is, if you've never done it before, where the heck do you start? Okay, the concept generally, hey, Jon, that's cool, I get it.

And I, you know, I'm going to imagine that everybody in this conversation understands that concrete generically is made up of what, five materials, right? Cement, water, rock, sand, and, and, come on Seth. Cement, rock, sand, water. What's the last one?

Seth Tandett (09:17)
Cement, water.

You said you already said rock sand air

Dr Jon (09:22)
Cement,

rock, sand, air. No matter what, we don't have to design concrete with admixtures. We don't have to use a single effing admixture. But there will always be air and concrete. So my assumption is that this group at least knows that, and they don't have to go into what the raw materials are, besides what we're going to do in the design. Is that fair?

Seth Tandett (09:43)
Yes.

Dr Jon (09:44)
Cool. Any questions before we move forward with the design?

Seth Tandett (09:47)
⁓ No, I will ask questions as you go. All right.

Dr Jon (09:50)
here we go. ⁓

So there are four design methods you can use.

Portland Cement Association, or I'm sorry, the American Cement Association has one. Darwin and Mendes have one in their textbook. The American Society of Civil Engineers has one. And then my favorite is ACI 211.21, and it's recently been updated, I think in the last few years. Hold on a second. I love it. And I call it Choose Your Own Adventure. And you know, I...

very vocal about the authors behind many of these ACIs. This is one of my favorite ACIs and I absolutely love the authors. mean the authors are just some of like there's some amazing authors in here. Kevin MacDonald, Chellick, Larry Sutter, Tyler Lay, Jay Shilestone, Katie Bordigé.

Like, you've got people, like, did you know there's something called the Shilestone method? Like, these are, yeah, I mean, well, it's a way to design concrete, know, specifically for a certain type of concrete, but still a way to design concrete. So there are people who helped, um...

Seth Tandett (10:43)
⁓ no, until today.

Dr Jon (10:58)
know, clean this up, which it had been worked on since 1991, but the method behind this is really up to date, especially with admixtures. So, really, really love this method, and it's a really good read. Like, like, for our readers at home, what I'm showing Seth now is I pulled my version of the 211 out, and it's beat up, because I read this thing all the time. Now, you compare that to...

ACI 323. I mean, the cover is still shiny. Because I can't stand reading it. I read it when I have to. This thing? I freaking love it. Anyway, okay, so I recommend readers get this. It's a great freaking manuscript. All right, so do you mind if I get into what we're doing today?

Seth Tandett (11:43)
Yeah, you're going to walk us through that, right? The absolute volume method.

Dr Jon (11:46)
Well, specific to a customer. imagine, if you will, you were just hired. ⁓ You got fired from your job at Baker, Seth. And now you're working for Mark McCoy's Ready Mix. Or Jon Belkowitz's concrete pre-cast plan, architectural cast stone. And I say, hey, man. No, Ready Mix plan. I said, I need you to design a mix for me.

It's gonna be a section thick, interior concrete slab. I've got the worst finishers in the world, so I need you to design the maximum slump allowable within this guide here for ACI 211. My compressive strength is 4000 PSI. I don't need you to remember this, because I've got it all written down here. 4000 PSI at 28 days, not an air and train mix. I got a 57 aggregate.

And that's crushed, right? Crushed aggregate, so it's a bit angular, and I can give you all the aggregate properties. But I need you to design me a book-create mix that I can take to my lab, do a couple run-throughs, dial it in, and then we can dial it into the plant. Cool? Where the hell do you start?

Seth Tandett (12:53)
Yeah.

Dr Jon (12:54)
So in this presentation, what I do is I'm going through the different tables that take you through the decision making process through ACI 211, and then we're going to go through some of the math. So what Seth has got is paper, pencil. He's got his TI-30X2S calculator. Right, Seth?

Seth Tandett (13:16)
Yep, sounds good.

Dr Jon (13:17)
Doesn't sound like he does. And we're going ahead and we're going to actually do the math together and see if we come up with the same answer. Fair?

Seth Tandett (13:24)
Alright, I'll try to stay up with you.

Dr Jon (13:26)
Cool. Well, you don't have to try. We're going to do this together. So the great thing about ACI 211, the first thing that it starts out with is the first thing that our customer really made important, which was the slump. And that's table 5.3.1. And it's called typical slump rages for concrete without water-reducing admixtures.

Seth Tandett (13:45)
So the water.

Dr Jon (13:46)
Just water alone. Now the reason why we do that is no two chemical admixtures work the same. Even when it comes to water reducing and the water that we're gonna talk about now that's associated with slump and then you'll see some other things goes directly back to our strength and hence our durability. Or in this case our durability too. Questions?

So in our table, and Seth, can't see this right now because he doesn't allow me to share my screen. Isn't that nice guy? It gives you different options for them to be specific. And those options are based, there are slump ranges, one to four, two to four, two to five, three to five, and they're based on the type of construction.

Slip formed is construction one, then mass concrete, and then we have this huge selections of pavements and slabs, plain footings, caissons, substructure walls, reinforced concrete, foundation walls, and footings, and then we have beams, reinforced walls, building columns.

Now those two, the first selection has a 2 to 5 inch slump range and then the one below that has a 3 to 5 inch. So, I mean the maximum on both of them, whatever we wanted to call this, whether it's a slab or some reinforced structure, the maximum allowable here is a 5 inch slump. Cool? So when it asks us what our slump is, the answer is 5 inch.

Seth Tandett (15:05)
Okay.

Dr Jon (15:10)
We're going to underline it once. Have we done any true mathematics yet?

Seth Tandett (15:14)
No, we're just picking slump.

Dr Jon (15:16)
No, we're choosing a portion of our adventure. Isn't that nice? Isn't that nice? I'm okay with that. It's gonna get nerdier. Hold on. The second part of this is where we choose our water and our air content based on two things. Excuse me, three things, I apologize. Whether or not we have air, non-air entrained concrete.

Seth Tandett (15:19)
all right. You're really nerding out today.

Dr Jon (15:38)
Our maximum size of our aggregate, which in this case we have non-air and train mix, they told us. The second thing is our aggregate size, which we know is one inch. And the third thing is what? Our slump. So what we've got right now is that value. We have a table here that has a non-air and train version up top.

has an air entrained version on the bottom, has slump on the left, maximum sized aggregate, and through that matrix, you line it up and it tells you how much water per cubic yard. And here, we've got 330 pounds per cubic yard for our five to six inch slump with a one inch aggregate.

Now consequently, this table also gives you your entrapped air content.

And here we could just call it air content. You go to the bottom of that top section, and for a one inch aggregate, our entrapped air content is 1.5%.

Again, have we done any math?

Seth Tandett (16:38)
No, you just picked off the off of the table based on what you needed. So based off of the slump you wanted and if you're doing air or non-air, right? There was a third thing.

Dr Jon (16:50)
Yup.

Non-air, air, and then your aggregate size. Right. Now you might have to do a little homework. They'll tell you it's a 57 or 67, blah, blah. That's homework. That's easy. But outside of that, I mean, again, we haven't done any major math, and we're one sixth the way through this design. This is fucking awesome stuff. All right, so the next thing.

Seth Tandett (16:54)
Aggregate size, max ag size, right?

There you go.

Dr Jon (17:13)
Our next table, table 5.3.1 is adjustments to estimated water content for various conditions including rounded aggregate, air content over the entrapped air, water reducer, high range water reducer, blah blah blah blah. Temperature decreases.

even if we want to increase the slump by an inch or so, or for every inch we want to increase it. So there really is like a lot of, you know, what do I want to take with me on this adventure type choices that you can make in this table. And that's what I love about this new version of the 211. I mean, now it's taking it from the guest creed into the closer creed within our book creed.

So when we were designing it without consideration of admixtures, we were doing a lot of guesswork on what we have to do with the water content based on our admixtures. This new table, whether it's admixtures, raw content, air content, I need to bump up the slump, there was really no direction. Now this gives you a direction. Does that make sense? Gets you closer to the finish line or...

Seth Tandett (18:23)
Yeah, following you.

Dr Jon (18:26)
gets you more efficiently closer to the efficient line. So here, we've got a mid-range water reducer. Now with the mid-range, we're going to subtract our water content by 5%. So it says in the table. Okay, so we write down minus 5%. We have crushed aggregate.

So we don't have to worry about rounded aggregate shit, which is in the table. We're not playing with the slump. We're not playing with the air. We're not playing with temperature. So the only thing we have to take into account on our estimated water to refine it is minus subtracting 5 % because we are going to use a water reducer. Cool? The next step is based on strength. What does the water cement ratio need to be?

Seth Tandett (19:02)
All right.

Dr Jon (19:12)
to yield our 28 day strength. And bear in mind, we're not gonna take the stance of, we're the ready mix provider and according to ASTMC 94, we need to have a certain standard DV8, uh-uh, we're not playing that game. We're just gonna say they want, they asked for 4,000, we'll let the ready mix provider do that, okay? It happens to be that you're the ready mix provider, but we're just going with the standard 4,000 PSI mix, for now.

Okay, so we needed a 4000 PSI and in this image it gives you a table that goes through 2000, 3000, 4000, 5000, 6000, 7000 PSI increments and it gives you water cement ratios whether you're using non-air entrained concrete or air entrained concrete. And for us we're using air entrained concrete and you remember what our strength was, Seth? So in this case when we use the...

Seth Tandett (19:56)
four thousand

Dr Jon (20:00)
It tells us we need a water cementitious ratio of 0.57. Okay, so again, we're just writing that down. Now, there's another table that says, hey, if you've got structures that are continuously wet or exposed to sulfates or seawater or, you know, has a concrete cover less than one inch, there are certain checks that you've got to have.

You can't have a water cementitious ratio lower than either a 0.4, 0.45, or 0.5 for certain structures in these freezing and thawing and sea environments. Do we need to worry about those?

Seth Tandett (20:36)
Are you slab? No.

Dr Jon (20:37)
No, it's an interior slab, doesn't really matter. Okay, can you hear me right now? Yeah. All right, my headset just died. So we're gonna stick with our water cementitious ratio of 0.57. And I believe this is the last table we've got to run through. Now this table is the ugliest one. This table makes you want to stay in bed in the morning or just jump into jacuzzi.

The name of the table is the bulk volume of coarse aggregate per unit volume of concrete. Who the heck? You you just need a better title. It's a very confusing title. And then when you look at the table itself, what you're doing is you're taking the finest modulus of your sand, comparing it to your maximum sized aggregate,

Seth Tandett (21:08)
Yeah.

Dr Jon (21:23)
And then from there you're picking this ratio that goes back to how much coarse aggregate do you want in your concrete. So the number it gives you, whether it's what I think the highest number is 70 or 82 and the lowest number is 0.44.

So it's either you have, it tells you to put 82 % of your concrete is gonna be rock, your coarse aggregate, or as low as 44 % of your coarse aggregate, of your concrete is your coarse aggregate.

Now what do you think Seth changes the amount of coarse aggregate? And by the way, the column is sizes of aggregate. So it starts at 3 eighths of an inch and it goes up to three inch. Right? And then in your rows up top, it goes from sand with less fines in it to sand with more fines in it.

Seth Tandett (22:16)
So size of each.

Dr Jon (22:18)
Right, yes. Damn, see folks, this is why he's the guy who hosts these freaking podcasts. Because his brain works that freaking quickly. You're so smart.

Seth Tandett (22:28)
Good teacher. Keep going.

Dr Jon (22:29)
So yeah, so if I have a really coarse sand with no fines in it, and my aggregate is really, really flippin' small, I'm gonna use 50 % of my concrete is gonna be my coarse aggregate.

Now, if I make that sand really, really fine, like just put a whole bunch of fines in it, then 44 % of that concrete is gonna be my 3 1⁄8 inch aggregate. Right, get a whole bunch of fricking fines in there.

We want to reduce the amount of fines. That's one thing we know in concrete. Reduce the amount of fines as much as we can, because fines, or get us to balance the amount of fines, that's where you have the Shilestone method, the Tarantula curve, the Lisa model, you know, the gradation envelope theory, all of those refine what we're doing here. This is a very basic concept of those different methods.

Now if we have a three inch aggregate, so really coarse coarse aggregate or big big aggregate and we have a very clean sand with almost no fines in it, we need a bunch of our coarse aggregate.

82 % that's the biggest number now if we start making a dirtier sand we can drop that to 76 Does that make sense? that combination so for us our our Finest modulus was somewhere around 2.6 now the thing is I say somewhere around the finest modulus in these tables goes from 2.4 to 2.6 2.8 and 3.0

Seth Tandett (23:47)
Yeah, makes sense.

Dr Jon (24:03)
So if you're closer to 2.6, traditionally, just use the 2.6. You could do linear extrapolation to find out the exact value, but going from 2.6 to 2.8, you're going up 2 % in your total volume. And you'll find out that's not much.

But using our maximum size aggregate, which was one inch, and our finest modules for sand, which is 2.6, it gives us a value of 0.69, which means that our concrete mix, 69 % of it, will be our coarse aggregate.

We have not made a single decision or excuse me, have not done a single calculation yet, have we? All right. So I just wanted to go through our numbers. Our slump, we said five inches. Yeah? Our water, we figured out was 330 pounds per cubic yard. Our entrapped air content is 1.5%.

Seth Tandett (24:47)
Not yet.

Dr Jon (25:02)
Did you get that too or did you miss that? No, no, Just, did you remember where that was in the table though?

Seth Tandett (25:04)
missed that one, so I'm writing it down.

yeah, that was near the beginning.

Dr Jon (25:11)
Yeah, yeah, yeah, okay, good. I was just making sure of that. So it's 1.5 % our water adjustment because we're using a mid-range, we're doing a minus 5 % on the designed water.

Cool. Our water cement ratio was 0.57. We didn't have to worry about any checks. And our percent, of course, aggregate was 69%, but we're gonna write that as 0.69.

questions before we get into gymnastics with math.

Seth Tandett (25:39)
Yeah, the 330 pounds of water does not reflect the reduction of 5 % for the midrange, right?

Dr Jon (25:46)
That'll be one of our calculations.

Seth Tandett (25:48)
Okay.

Dr Jon (25:48)
Are you ready to do gymnastics with mathematics? Or would I like to call mathematics?

Seth Tandett (25:54)
boy. Here we go.

Dr Jon (25:56)
Okay, so the first, what's it called, calculation we're gonna do is that water reduction. Okay, so we start out with, we're gonna call this our new water.

going to equal our old water which is 330 pounds are you writing this down and doing the math 330 pounds per cubic yard he's not doing the math folks if you're listening in your car 330 pounds per cubic yard times the quantity 1 minus 0.05

Seth Tandett (26:14)
huh.

Dr Jon (26:28)
Now if you don't know what that means, can, in lieu of writing that, I'm erasing and I'm rewriting, you can write 100 % minus 5 % all over 100%. Same difference. Now when we do that, Seth has got his TI-30X2S.

We're doing 330 times, as it turns out, 0.95. So our new water is 314 pounds per cubic yard. Seth, did you get that?

Seth Tandett (26:54)
Five.

Is it 313.5 and you round up? Okay.

Dr Jon (27:06)
Yeah.

Batch computer can definitely hold a decimal point for pounds per cubic yard. But let's be realistic. We can't measure that. And with a true level of uncertainty, that 0.1 pounds. All right. So that's item number one. Let's do item number two, which is determining our cement content.

Now we know that our weight of water over weight of cementitious, here we're just going to use cement, equals 0.57. We can erase our weight of water because we know it and we can fill it in. That's 314 pounds per cubic yard.

Now we want to measure or determine the amount of cement. The problem is cement's in the denominator. So we go back to seventh grade. We multiply both sides by cement. The word cement. On the left hand side where we have 314 pounds divided by cubic or per cubic yard divided by cements. The cements cancel out.

Seth Tandett (27:54)
Yeah.

Dr Jon (28:08)
and that equals 0.57 times cement. Again, we want cement on its own. So next, we divide both sides by 0.57, and what we're left with on the left is 314 pounds per cubic yard divided by 0.57 equals weight of cement.

Seth Tandett (28:31)
Yeah,

551.

Dr Jon (28:34)
⁓ come on, give me a second. Is that what you got? Good job. I'm just double checking them, folks. You can't trust these project managers to do math. What did you say? 551?

Seth Tandett (28:44)
551 pounds of cement.

Dr Jon (28:47)
Okay, so our cement equals, our weight of equals 551 pounds per cubic yard. Okay, don't forget the units, pounds per cubic yard. Seth, we've gotten into the majority of the math, or excuse me, a minority of the math. How bad is it?

Seth Tandett (29:05)
It's not bad so far.

Dr Jon (29:06)
Okay, come on, let's keep going before we get tired. It's kind of like a marathon. So we know the amount of cement, or excuse me, we know the amount of water, we know the amount of cement. Now we're gonna figure out the amount of rock. Okay?

weight of rock per cubic yard. Now the way we do this, we're going to call it weight of rock. take, what was our percent that they gave us or that we determined? What was it? Six, seven, six, nine. So 69 % of our rock or of our concrete is our coarse aggregate.

Seth Tandett (29:33)
6.69, 6.7, yep.

Dr Jon (29:39)
Now that's based on a very specific type of rock and that's our dry rotted unit density. Now they gave that to us early on. Remember I said that, we have a list of all of our material properties and our dry rotted unit weight is 98.2 pounds per cubic foot.

So we got 69 % times 98.2 pounds per cubic foot. We need one more thing, and that's to convert this weight from cubic feet to a cubic yard. And we do that by multiplying the entire thing by 27 cubic feet per cubic yard. Now that should make sense, because 69 % of that is our rock.

So we take 69 % times our dry rotted unit weight times our volume of concrete. Which gives us what?

room room.

Go ahead Seth, I'm listening.

Seth Tandett (30:38)
I'll let you get this one.

Dr Jon (30:39)
Why are you embarrassed to be wrong? Lean into being wrong. Nothing wrong with being wrong. That's why there's erasers on pencils. Look.

Seth Tandett (30:42)
No, no.

I gotcha. So you're multiplying what now?

Dr Jon (30:51)
69%, that .69 times something called our dry, rotted unit weight of our aggregate, our coarse aggregate. That's the, yes sir, and then 27 cubic feet per cubic yard.

Seth Tandett (30:51)
Yep.

Yep, that's 98.2.

Got it.

Dr Jon (31:07)
What's that magic number, sir?

Seth Tandett (31:09)
day.

Dr Jon (31:10)
me have this one. Tell me.

Seth Tandett (31:12)
Got your teacher now, times 98.

1829.4647

Is that what you got?

Dr Jon (31:21)
Yes.

So what are you rounding that up to?

Seth Tandett (31:24)
I guess you would round it up to make it easy. 1830.

Dr Jon (31:27)
1830.

Seems like we got all of our weights. What weight are we missing?

Seth Tandett (31:31)
did we do sand?

Dr Jon (31:32)
Nope. Didn't do sand. Now it's funny you should ask that because now we get into the scary math.

Now remember how I said this was called the absolute volume method? Seth, we haven't determined any volumes yet.

Seth Tandett (31:43)
Yeah.

Uh-huh.

Dr Jon (31:46)
Guess what we have to do.

Seth Tandett (31:48)
before you figure out the sand.

Dr Jon (31:49)
We've used up almost all of our materials. What we have to do now is determine how much room is left for the sand. The admixtures don't take up any room. Our cement, I mean, there's 550 pounds of it. Water is 314 pounds. There's 1830 on the rock. And we have 1.5 % air.

Seth Tandett (31:58)
Okay.

Dr Jon (32:10)
Like there's only so much left somewhere like somewhere between seven and nine cubic feet that's left over for sand. So we got to figure those other ones out. And then what's left over? Does that make sense?

Seth Tandett (32:22)
Yeah.

Dr Jon (32:23)
Alright, so we have a new sheet and we call it volume. See, I told you, this is an adventure! An adventure! Let's start out with the first one, it's the easiest one. Let's start out with air. Air, we're gonna go from simple to really freaking annoying. Air, they told us was 1.5%.

So you take 1.5 % and you multiply it by a cubic yard, which is 27 cubic feet per cubic yard. How much air do we have in cubic feet per cubic yard?

Seth Tandett (32:48)
okay.

So 0.015 times 27.

Dr Jon (32:53)
We got it, sir.

Seth Tandett (32:54)
point four one.

Dr Jon (32:56)
You got it, .41 what, chickens? Twinkies?

Seth Tandett (33:00)
cubic feet.

Dr Jon (33:01)
her.

Seth Tandett (33:01)
Yard.

Dr Jon (33:02)
cubic yard.

because a yard is a linear measurement, a square yard is an area.

Seth Tandett (33:07)
You're right. Yep. 0.41 cubic feet per cubic yard. That's how much air we got.

Dr Jon (33:12)
Okay, from there we go to water. Now we have 314 pounds per cubic yard of water. Now we need to convert this to cubic feet per cubic yard. And the way that we do that is we divide 314 pounds per cubic yard of water by the density of water, which is 62.4 pounds per cubic foot.

Now what happens is the pounds up top and the pounds on the bottom, cancel each other out. The cubic feet in the denominator goes to the top of the cubic yards and the nominator and the numerator go on the bottom. And we're left with 314 divided by 62.4. 5.03 cubic feet per cubic yard of water.

Seth Tandett (34:03)
Okay. And that's just a known number, right, for water?

Dr Jon (34:04)
Now that was 62

at standard temperature and pressure. The unit weight of water is 62.4 pounds per cubic foot. The pounds per gallon is 8.345 pounds per gallon. And then what you, this is the next step. Now the question is, how do you go from the unit weight of water to the unit weight of cement?

because we need to the same thing. We have 550 pounds per cubic yard of cement and we need to go to cubic feet per cubic yard of cement. Now you ready for the trick?

You take the unit weight of water, 62.4 pounds per cubic foot, and you multiply it by the specific gravity of cement. Which the specific gravity of cement is 3.15.

Seth Tandett (34:51)
Okay.

Dr Jon (34:51)
And when you multiply 62.4 pounds per cubic foot by 3.15, the product is 196.6 pounds per cubic foot. Now that's for cement.

We're going to do the same thing for our ⁓ rock and eventually we'll use the same concept for our sand.

Okay? So 550 divided by 196.6, excuse me, 550 pounds per cubic yard divided by 196.6 pounds per cubic foot. My pounds cancel out. My cubic feet goes to the top, my cubic yard goes to the bottom.

What did you get?

Seth Tandett (35:30)
2.8.

Dr Jon (35:31)
That's what I got.

Alright, let's do rock.

many pounds of rock did we have?

Seth Tandett (35:36)
1,830.

Dr Jon (35:41)
1830 pounds per cubic yard divided by 62.4 pounds per cubic foot times the specific gravity of our rock which was 2.7.

Oh shit. Wrong decimal place. 1830, fuck off. Divided by 62.4 times 2.7. We got a big old number there.

10.86.

Is that what you got?

Seth Tandett (36:10)
I'm getting there.

What'd get?

Dr Jon (36:12)
10.86.

Seth Tandett (36:14)
I did

something wrong. Are you multiplying 62.4 times 2.7 first?

Dr Jon (36:22)
Yeah, that was...

168.5

Seth Tandett (36:26)
Okay, that's what I did wrong.

10.86. Is that what you said? Yeah.

Dr Jon (36:28)
You got it.

second to last part we're almost there man you're almost done designing your first concrete mix so you remember what I said about the sand the sand is what's left over so you got to add everything up point the the air the water the cement what's up oh hi babies

Seth Tandett (36:41)
Yeah.

Dr Jon (36:54)
Hey Jamie!

Nobody ever says hi to me. You notice that? So when you add all those up...

What do you get?

Seth Tandett (37:07)
So we're adding up 0.41 plus 62.4. No? Or, sorry.

Dr Jon (37:12)
No, no, 0.41

plus 5.03, right? Plus 2.80.

Seth Tandett (37:16)
Plus 0.03. Yeah.

Dr Jon (37:20)
plus 10.86.

And that gives us a certain amount of cubic feet per cubic yard.

Seth Tandett (37:25)
19.08.

Dr Jon (37:26)
Yep.

So from there it's 27 minus 19.08.

That is the amount of volume we have left for our sand. Drum roll please.

Seth Tandett (37:40)
7.92.

Dr Jon (37:41)
Good looking,

Seth Tandett (37:42)
pounds per cubic feet foot.

Dr Jon (37:44)
No,

no, no. That's cubic feet per cubic yard.

Seth Tandett (37:48)
okay,

cubic feet per cubic yard, all right.

Dr Jon (37:50)
Okay, so then the next question begs, how do we determine sand?

the weight of sand from this and as easy we've already done our weight of sand is going to equal 7.9 cubic feet per cubic yard times that unit weight of water 62.4 pounds per cubic foot times our specific gravity of sand which in this case is 2.59

or cubic feet and cubic feet cancel out.

7.29 x 62.4 x 2.59 and I'll do this one. We got 1178 pounds per cubic yard. I'm gonna call it 1180 pounds per cubic yard.

Seth Tandett (38:42)
7.92.

Dr Jon (38:44)
times

Seth Tandett (38:45)
times 62.4

times 2.59.

Dr Jon (38:51)
Yep, because that's our specific gravity.

Seth Tandett (38:53)
I get 12... 1280.

Dr Jon (38:55)
Then we do it again.

No, was 7.29. Is that what you said?

Seth Tandett (38:59)
⁓

no, I said nine, too. Is it two, nine?

Dr Jon (39:02)
Did I do, wait, wait, I might have done the wrong math. Dyslexia at its finest. Yeah, it's 1280. Did you get 1280? Okay, look at that, see? That's where they put erasers on pencils.

Seth Tandett (39:07)
Yeah, it's nine two.

1280.

Dr Jon (39:14)
okay to be wrong so that's 12 so 1280 so what's our final mix and this is a pound per cubic yard we have cement

water.

and sand.

What do we got good sir?

Seth Tandett (39:25)
So, cement.

551.

Dr Jon (39:28)
We said 550.

Seth Tandett (39:30)
or five,

yeah, whatever, pounds per cubic yard.

water.

We did with the water reducer, we reduced 5 % with the mid range. So we came up with 314 pounds.

Dr Jon (39:40)
Mm-hmm.

Mm-hmm.

Seth Tandett (39:45)
And then Rock came up with 1,830 pounds.

And then sand, just did 1,280 pounds per cubic yard.

Dr Jon (40:00)
Okay. Congratulations.

Seth Tandett (40:01)
Wow, we did that under an hour.

Dr Jon (40:03)
Okay, now here's the thing. What we did is a design mix. We do not have the batch mix. In the batch mix, we change up our rock weight and our sand weight based on the moisture content. And then we change up our water weight.

Seth Tandett (40:08)
Uh-huh.

Dr Jon (40:20)
based on how much rock and sand or how much water is being brought by the rock and sand. We're not gonna do that today. That's episode two. Level two, well, it's the second part of it, but yeah. So far though, this wasn't that bad, was it?

Seth Tandett (40:29)
Uh-huh. That's level two.

Okay.

No, it's not terrible.

Dr Jon (40:39)
And you could even imagine a way to create some type of Excel file or...

I mean, quite honestly, a calculator and pencil and paper, this is not hard. And then when you start knowing a material, like when you start doing enough mixes, you'll recognize that, okay, interior slab, you're at 550, exterior slab, because you got air and train, you're probably gonna have to bump it up like to 580 pounds from 550 pounds, because you got air in it and you have to compensate for that strength because of the air with a little more cement. And because of that, you got to drop your

rock and sand down because you just pulled that yield from somewhere. So once you start learning your materials you don't need ACI 211.

Seth Tandett (41:20)
Right.

Dr Jon (41:21)
And once you really learn the concept behind it, again, you stop needing this. This is for, I've never designed concrete before. I want to learn how, or I've never used these materials, and I need a good starting place, or somewhere in between.

Seth Tandett (41:35)
Cool.

Dr Jon (41:35)
Okay.

Seth Tandett (41:36)
I appreciate it.

Dr Jon (41:37)
Yep. Next time. I wrote it down.

Seth Tandett (41:39)
Yeah,

time we'll do the... So there's adjustments you got to make for the batch mix. That's basically what we're going to talk

Dr Jon (41:46)
and then we'll do the mid-range water reducer calculation. Sweet.

Seth Tandett (41:50)
Okay.

All right. Well, thanks for coming on the show today. Appreciate it.

Dr Jon (41:54)
Sir, thank you for having me.

Seth Tandett (41:56)
Yes, sir. And folks, until next time, let's keep it concrete.