EP #153: Your Concrete Mix Design Still Isn’t Ready… Until You Do This

Seth Tandett (00:00)
And welcome to another episode of the Concrete Logic Podcast. And today, as promised, I brought Dr. Jon Belkowitz back to continue our last episode on Ready Mix Design. So if you listened to the last episode, you probably, if you haven't, you probably should, so you know why we're continuing. So we came up with...

a mix design. did all the calculations and all the choosing through ACI 211. Is that right? ACI 211. And the way we left it was that although we came up with the mix design, that mix design is not necessarily the batch design. So today we're going to go over what adjustments you need to make to make a batch design. Are you with me so far?

Dr Jon (00:47)
Yes, sir.

Seth Tandett (00:48)
All right. But before we get started, as always, I'd to remind everyone how you can support the show. First, go to ConcreteLogicPodcast.com. And there's a couple ways you can get a hold of me. At the menu at the top of the page, there's a Ask Seth.

option on the menu and you click on that and you can email me topic or guest suggestions, which folks must have been listening because I've already got a couple of those. So I appreciate that. Thank you.

And also, if you don't like to write the emails, there's another way. You can get a hold of me by leaving me a voicemail, and you can do that by clicking on there's a little microphone icon in the bottom right-hand side of the home page on ConcreteLogicPodcast.com.

So that's the first way you can support. Second way is on the same home page, there is a donation button. So if you get value out of this episode or any other Dr. Jon episodes or other 150-something episodes that we put out there, we can do it.

Dr Jon (01:56)
My favorite are the

Bob Higgins ones. We were just talking about one yesterday. The one he did on degree of hydration and relative humidity within the concrete and different admixture interactions. It should be one of your courses. That is textbook awesome chemistry information. Sorry, go ahead.

Seth Tandett (02:15)
Yeah.

Yeah. And then I had someone reach out to me today and say they use one of the episodes as a introduction to the industry for their new employees. So people are listening. People are using the podcast. So.

You know, donate. Anyhow. And then the next way can support the show is you could join the ConcreteLogicAcademy.com.

check that out. It's the same kind of format as the podcast, except for we give you quizzes and additional resources to use that kind of reinforce your learning of the topic that we're talking about in that particular episode. So check it out, ConcreteLogicAcademy.com. All right. Yep.

Dr Jon (03:03)
Wait a second, and if you're doing

PDHs as an engineer, because that's coming up, you think you need 16 a year, Concrete Logic Academy has what is a nine credit, nine PDH system there. Was it nine or six? And it's 299 bucks, and it's concrete related. I'm a huge fan of the Academy, and I totally recommend you joining it.

Seth Tandett (03:30)
I appreciate that. We actually have 25 courses on there now. So yep, you got plenty of choices there. All right. So today, let's continue on with the ready mix design. And we're going to make adjustments for a batch design. So what you actually use in production. Is that what we're doing today, Dr. Jon? You look like you're staring off in space.

Dr Jon (03:56)
Yeah, yeah, yeah,

yeah. there's no, no, no, no, I'm, you're breaking up a little bit. ⁓ but I'm staring off into space. That's just my face. So what we did is we did the, the book Crete. So I think you'd mentioned it. took ACI, ACI two 11, you know, guide for design of normal weight concrete, whatever the heck it's called.

Seth Tandett (04:02)
Okay.

Dr Jon (04:22)
Great publication. We went through that last time. We came up with a mix that didn't take into account the moistures of the material and the admixtures. And that's really the last step that we have to take to go from design to, or paper to, what we can use in the batch computer. Now, technically the batch computer takes care of the sand and rock.

water content, but I tell you it's a good idea to know how it works, especially when it comes to our dosages. And, you know, we're just dealing with a lawsuit right now where the intended amount of chemical was quadrupled in the back of the truck and nobody had noticed it until after the fact. And they noticed it because of the change in the mix design. Okay. You look confused already and we haven't even started.

Seth Tandett (05:10)
Now

I'm going back and writing down the pounds per cubic yard from our last discussion. Because that's what we're adjusting, right? No, I have them.

Dr Jon (05:18)
You looking for those? Yeah, so

we're adjusting three things today. Okay, we're adjusting three things. The sand, the rock, and then the water. Okay?

So let's start off with the sand and for our viewers at home, am I allowed to share the presentation window that just gives you the raw materials?

Seth Tandett (05:43)
Yeah, real quick.

Dr Jon (05:44)
So remember again, we're designing for a six inch thick interior slab. It's gonna be used for a floor, so it's a slab on grade. We need a compressive strength of 4,000 PSI. And because it's interior, it's a non-air entrained mix, so we're not gonna be using any chemical for that. But they did ask us for the maximum slump allowed, which according to our paperwork was five inches. But we're gonna design it for six to seven inch with a mid-range water user as part of our design here. Now from this,

The lower portion gives us the aggregate information. What we need from this right now is our moisture content and absorption. For the rock, our moisture is 1.3%.

Seth Tandett (06:28)
Where do you get that from?

Dr Jon (06:30)
right here where it says course aggregate. Man, I did that math wrong. I knew I was going to do that. When it says course aggregate.

Seth Tandett (06:34)
huh.

I ask you before we get

started, are the numbers right?

Dr Jon (06:41)
Yeah, the numbers are right here, but I screwed up the numbers, which is fine. We're just doing simple math, but yeah, you can't see it. So these numbers are totally correct. So the coarse ag, it's a crushed rock that has a moisture content of 1.3 % and it an absorption of 0.7%. The sand has an absorption of 1.2%, but a moisture content of 6.3%.

Seth Tandett (06:51)
⁓

Okay, what I'm asking is where do you get those numbers from? Is that from the guy that you buy your rockets from?

Dr Jon (07:13)
Oh, these numbers.

So absorption is normally given to you by your aggregate provider or you can hire a third party who does ASTMC 33 and then what is it ASTMC 136. There's all these ASTMs you use, but you're basically drying out the aggregate, then saturating it, then drying it, and you're taking weights in between to give you what that absorption is. And then the moisture content

The moisture content should be listed on the batch ticket and the folks at the plant should be testing the moisture content not only through moisture probes, but they should be running their own internal calibration. And it's a very easy thing to do by taking your aggregate, having an initial weight, drawing it back until it doesn't change by more than one gram or 1 % and then doing a ratio of the final weight minus the initial weight over the final weight, final minus initial over final.

times 100 % and then I'll give you your moisture content.

Seth Tandett (08:13)
Okay.

Dr Jon (08:13)
So I screwed up my math, but these numbers are kosher. So I screwed up this math, but it's no big deal. So the first numbers that we want to do is the new weight of the sand and the rock. So let's start out with our sand. We have 1,280 pounds of sand.

And according to this, our moisture content is 6.3%. So what we're going to do is we're going to multiply 1,280 pounds, our original standby design, multiplied by the quantity 1 plus our moisture content in percent. So 1 plus 6.3 % divided by percent.

And of course everybody has their calculators out. That means we're taking 1,208.

Seth Tandett (09:05)
Check out this, is

this a TI? Check that out.

Dr Jon (09:08)
No, that's older than sin. Times 1.

Seth Tandett (09:14)
Can you stop sharing

that screen real quick? No, you're good. All right, cool. I want everybody to see your face. know, we're on with the encouragement of my wife, who's a producer of the show. We're now on Instagram, and she wants to see your face. So yeah, you guys got to look at stuff. What is the kids' call to Instagram now? Is it the Gram?

Dr Jon (09:17)
Yeah, yeah, buddy, sorry,

We said.

Lemme see.

Bless.

My dad!

Insta.

Seth Tandett (09:41)
Insta, Okay. Anyhow. Yeah, that's right there. That's pretty sweet.

Dr Jon (09:43)
Let me see that calculator.

Nah dude, you need to get one of these. They're like eight bucks.

Seth Tandett (09:51)
Yeah, had one of those in high school. I don't think I have one of those anymore.

Dr Jon (09:55)
Alright, I'm getting, you know what? The academy can afford to get you and you deserve it. It's a fucking... Anyway. So, doing that math you get 1280 times 1.063. What did you get?

1288 times 1.063. Well, nobody judging here. Whitney's judging.

Seth Tandett (10:15)
I'm sure she is. She's much smarter than me. 136? Is that what we're trying to get? 136?

Dr Jon (10:20)
What... What did you get?

Well, it's 1280 pounds times 1.063, so it's got to be a little bit bigger than that.

Seth Tandett (10:34)
so it's a legit 1.063. Instead of making that into a decimal, you're using that? OK, gotcha.

Dr Jon (10:42)
Right. So it's one, right,

because that stands for 100%. So it's 100 % of the weight plus that 6.3 % moisture.

Seth Tandett (10:49)
Yep, you're right.

1360.

Dr Jon (10:54)
Yes, 1,360 pounds per cubic yard is our new sand weight.

Now we're going to do the same for the rock weight where we take 1830 pounds per cubic yard and we multiply it by the quantity of 1 plus our 1.3 percent divided by percent.

So again, we're doing 1830 times 1.013.

1.013

Well, you should see where those, say it again, sorry. Perfect. You should also see where those numbers should come from. The reason we're doing one plus that moisture content is because the moisture is based on how much the aggregate can absorb in its own dry weight. So when I say it absorbs 6.3 % water,

that's of its own dry weight.

Now, the next thing we have to figure out is how much water, free water, the rock and sand bring. Now, the first question is what the hell is free water? And how do you determine it? If we have our aggregate, Whitney, do I have an aggregate around here? If we have our aggregate, I don't have an aggregate. here we go. Duct tape, roll tape. So we have our aggregate.

and we drop it in water, it absorbs water, right? Or it got rained on. Let's say it got rained on, right? It has an absorption of 3%, right? That means the rock will absorb up to 3 % of its own weight in the weight of water into the rock. Well, if the rock has a moisture of 5%, so that means I took...

a thousand grams of rock, I weighed it out, then I microwaved it for 20 minutes and I got the new weight and it says, hey, you have 5 % moisture. That means there is 2 % free water on the surface of the aggregate. Because 5 % water minus 3 % absorption equals 2 % free water on the surface. Now that free water will directly impact our water cement ratio.

And what that means is we have to account for the free water that the rock, the sand, and the admixtures are bringing to the concrete that will immediately impact our water cement ratio. Does that make sense?

Okay, so to do that, we take our original weight, so we're gonna start with our sand. We're gonna have 1,280 pounds per cubic yard times the quantity 6.3 % minus 1.2%. The free moisture, which is 6.3%,

minus the absorption, which I believe was 1.2. Let me double check that my numbers are right. Yeah, 1.2 minus 1.2.

gives me, well, I'll let you.

What's that?

Seth Tandett (14:00)
You're saying 6.3 minus 5.1?

Dr Jon (14:01)
5.1, yeah. 1.2,

then you gotta divide that by 100 % and multiply that whole thing by 1,280.

Yes, sir.

.28

Cool. That's what I got. And just hold that 65.28 for a second. We're not going to use that in the end, but now we need to do the same thing for the rock, where we take 800 or 1,830 pounds times the quantity 1.3 minus 0.7 divided by 100%. And that's our free moisture of the rock minus the absorption of the rock.

divided by 100 % and we multiply that whole thing by 1830.

jeez.

Yes,

Yep, same thing. Not the same thing. Now add the original water that we got the sand, 65.28 plus 10.98, because that's all the free water that the rock and sand are bringing to the mix.

Yes, sir.

We're gonna put that off to the side, correct. So we're hold that off just for a second, okay? Uh-oh, now you're in trouble.

How we doing?

Okay, the next thing that we're going to do, item number two, is the admixture dosage.

Now the... cool, Whitney look Seth has got a new nickname for me. Look what it is. Look at that. How did you do that Seth?

Nothing. So item number two is add mixture dosage. Now in the customer specification, it said the maximum slump allowed. We determined that to be five inches, but we wanted to push it to a six to seven inch slump. And to do that, we're going to be using a mid-range water reducer. And the back of the soup can, manufacturer recommends four fluid ounces per cementitious hundred weight.

So we're going to go through that calculation. and the mid-range has 50 % solids, which means it also has 50 % water. So not only are we going to figure out the admixture dosage, we're also going to figure out the amount of water that it brings to the mix to add it to that free water. Does that all make sense?

Seth Tandett (16:11)
Yeah, sounds like two ounces of water.

Dr Jon (16:13)
Ummm...

No.

Seth Tandett (16:15)
No?

Dr Jon (16:16)
No, no, no, no, close, close, but you're 10 off. So the way that we figure that out is you take our recommended dosage rate, four fluid ounces per hundred weight, and then you multiply it by your hundred weights of cementitious or cement, depending on the type of admixture and the manufacturer's recommendation. So here we're using cement. So determine our cement hundred weights.

We divide 550 pounds per cubic yard by 100 pounds per cement hundred weight. Our pounds and pounds cancel out and now we're left with cement hundred weight in the numerator and cubic yards in the denominator. So it's 4 times 5.5 cement hundred weight per cubic yard and we're left with 22 fluid ounces per cubic yard.

that make sense?

Okay, so 22 fluid ounces per cubic yard is a dosage that we'll use per cubic yard in the back of the truck, but now we want to determine the water. And this is a little bit tricky because you got to do a little bit unit conversion. The first thing is we take our 50 % solids, we multiply it by our 22 fluid ounces per cubic yard, and we get 11 ounces per cubic yard, fluid ounces per cubic yard of water.

Now what we do is we divide that fluid ounces, that 11 fluid ounces by 128 fluid ounces per gallon. This converts us to gallons. Now when we do that, what is that? 11 divided by 128, oops, divided by 128, oops, gives us 0.086 gallons per cubic yard of water.

Now we don't need that in gallons, we need it in pounds. So the conversion from gallons of water to pounds per water is 8.345 pounds per gallon. And we are left with 0.72 pounds per cubic yard of water that the admixture brings up.

Now please bear in mind the computer is going to, the batching computer is going to do this, but as a contractor, as an engineer, you should know how to recognize things and do the math to be able to figure this out with a calculator in the field. So altogether, when we add up our 76.26 and our 0.72 pounds per cubic yard, we come up with the total water of

76.97 and we are going to call that 77 pounds per cubic yard.

Did you get that?

Great, I just called it 77. This is when we round it up.

Original water was 314 pounds per cubic yard. That's our design water. So to get our batch water, we take 314 pounds per cubic yard minus our free water, which is 77 pounds per cubic yard. And we are left with 237 pounds per cubic yard for our batch water.

So what's our final mix design?

final mix.

Can hear the train?

Material and then content.

So we got our cement at 550 pounds per cubic yard. We got our rock at 1,854 pounds per cubic yard. Our sand was at 1,360 pounds per cubic yard. Our water.

is at 237 pounds per cubic yard. And our high range water reducers is at 22 fluid ounces per cubic yard.

Sweet.

So what I'll do is, part of your podcast thingy, I'll take pictures of my notes and I'll send them to you. Or do you want me to take pictures of my notes, put them in chat GPT to make them look pretty and send them to you? Or do you want me to just send it to you as is?

So mean. He's so mean, Whitney.

Seth Tandett (20:38)
Okay, so we got our batch mix, now what do we do? I'm still getting over the fact that the admixtures are 50 % water. I'm still trying to get over that.

Dr Jon (20:41)
Now what we do is we go dial in at the plant.

Okay, go ahead. What was the problem with that?

Seth Tandett (20:54)
I don't know, I thought it'd be less. I thought there was more. I don't know.

Dr Jon (20:58)
You thought there was more what?

Seth Tandett (21:00)
be more admixture my admixture versus water.

Dr Jon (21:03)
no, no, I mean, there are some admixtures out there that only have 2 % solids.

I mean, yeah, yeah, there's not many admixtures that can go above 50 % solids. And most of those are hard to keep in suspension. You got to remember an admixture normally is a distilled or what deionized water with food coloring or some type of dye, you know, a, and then other active ingredients, some of which could be suspension agents, defoaming agents, or fugitive dyes. The active ingredient.

There's not a lot in there. Like you don't need a lot of polycarboxylate wax in the emulsion to kick off the plasticizing effect. Shit, look at air. Air, I mean, if you really dried it back, I think there's like 15 or 10 % solids in air and you only use one fluid ounce per hundred weight or two or three. You put so little in there and there's so little solids and it does such an amazing.

Seth Tandett (22:07)
Yeah. Cool.

Dr Jon (22:10)
That's the problem with dry air additives. We used to use one way, back in the day and we don't use it anymore. It's called Haustapur. Haustapur is a German technology. And when we'd use it, you would use it in 80-pound batches that were made from a 3,000-pound batch. For a 3,000-pound batch, you would need like 0.04 pounds.

and you only get two minutes of mixing in this blender. And it's like, the crap. There's no way you're to get that little powder to mix in that much of a batch in two minutes. And this is most of the air and training agents. You'd have to cut them with a titanium dioxide, excuse me, a limestone fine, like a cheap material as a cutting agent, and then take that, you know,

cut agent or cut air and training agent in a limestone fine and then put that in your mix because that was easier to blend in that short period of time. But yeah, don't be surprised. There's like, again, carbon nanotubes because they don't like to stay in stability. Most of those, you're only using 0.1 to 0.5 % solids in your solids or in your liquid because anything more is going to settle out.

What were you expecting it to be?

Seth Tandett (23:33)
I don't know. I guess I never really thought about it.

Dr Jon (23:38)
Okay, so

right now with our mid-range water reducer, you're at four ounces per hundred weight, which is a lower dosage, but it's a standard dosage. If we doubled that dosage, if we said, we're going to make it eight ounces per hundred weight. Now we're up to 44 fluid ounces per hundred weight, which if you can't tell by my voice, that's a lot to me, but I'll put it in other terms, that's a third of a gallon for one cubic yard.

Does that sound like enough admixture for you?

per cubic yard. Now, it sounds like a lot. Now, if you never sell a cubic yard, normally you sell five, let's go 10 cubic yards, so you times that by 10, and now that's 3.4 gallons just for that one admixture per cubic yard, but normally they have them in bottles with fluid ounces, and you can look down and see them, and that comes up to 440.

ounces per cubic yard. Let me see if I can pull up what an admixture container looks like. Is that okay?

Seth Tandett (24:41)
sure why you're doing that. Most of the time when you send a truck out, the contractor asks you to withhold water because they want to add it at the site. Is there any adjustments needed for that at all or?

Dr Jon (24:51)
Right. Right.

Oh yeah, when

the batch man is working at the computer, they might do that just because that's how they roll or that's the technique that they've been going with or they have an RPM gauge that tells them how much energy is required to turn the mix. And for a certain mix, if the energy is too high, that means there's not enough water or maybe the slump isn't high enough so they can add water. But yeah, at the batch computer, you have this trim.

or add function. And yeah, you can totally trim and add water based on the customer's needs.

Sorry, I'm looking, is that it?

got this wonderful picture of an admixture in Connex or not a Connex, what are they called? Shipping containers? And yeah, let's see.

Nope, that's not it. You know it always happens. You want that perfect presentation and you can't find it when it counts.

What editing are you gonna have to do, sir? You're being mean with me. He's being mean today. Here we go. I found it. Jeez. Okay, so... Let's see. Let me take this out. Let me take this out, and then I'll just make this a big old picture.

Why do you have to do- because I'm wasting time?

You know I'm worth it.

Tell your wife I said thank you. Is she the one who edits?

Okay, so this is an admixture dispensing system, and on the opposite wall you have cameras that are looking at these. And those metrics, so these are, I believe these are Crezo admixtures. Yeah, they're Crezo right there. The Tard 125, the Optima 2, whatever, 256. So this is an older picture. But all these markings on here are in fluid ounces.

So there's a camera on the opposite wall. top of these pumps or top of these bottles, pony bottles or way up bottles are connected to much larger tanks. And you can see like the pumps are right here on the bottom right. So these get filled up for every batch of concrete, five cubic yards, 10 cubic yards. And before the plant manager releases it,

he'll make sure, or the batch man releases it, he'll make sure that the correct amount of admixtures are weighed up from the video camera. And then he'll press the release button.

So if you went anything higher than about, I don't know, we went to, what did I say, 10 ounces per hundred weight? If you went anything higher than, shoot, let me just do the math right quick. So that's 600. So you see the highest number here is 900. Looks like 950 fluid ounces on the Optima 256. So 950 fluid ounces per batch is...

and we have a 10 cubic yard batch, let's say we do a 5 cubic yard batch, that means we're going to ⁓ need 190 fluid ounces per cubic yard. And if we did that ⁓ in our current cement hundred weight, that's 35 fluid ounces per hundred weight. So if we went above 35 fluid ounces per hundred weight, which, hey, I've used admixtures that gone up to 165,

You can't use this current admixture dispensing system. You'd have to design, and they have things out there, but you have to use something that's not off the shelf. So 8 to 12 ounces per hundred weight. Sometimes you'll see stuff go up to 32, and that's normally your accelerators. They go in percentages. 1 % can be 12 to 16 ounces per hundred weight. So if you have 2%, that's 32 ounces per hundred weight.

Well, if they're putting that much in, they can't do a 10 cubic yard batch because they don't have the bottle size for it. So they'll go all the way down to a three or five cubic yard batch so they can fit it in the bottle. Does that make sense what I just said?

Seth Tandett (29:04)
Sure did.

Dr Jon (29:05)
That's why they call me Concrete Adamus.

Seth Tandett (29:07)
Whoever they are. Okay. Yeah, I see it. see it. All right. Well, did we, I think we covered everything we said we're going to cover today. That was interesting. We did have someone reach out and wanted to know about the adjustments you make for admixture. So I think we checked that one off and we so that appreciate you explaining that and coming on.

Dr Jon (29:10)
It's right there.

You know, we did

want to talk about that chart, but I kind of closed that out. So if you want to bring that next time or the next time we have a talk, that would be awesome.

Seth Tandett (29:44)
Yeah, we can certainly do that. All right. Dr. Jon, thanks again for coming on the show. I appreciate it. And folks, until next time, let's keep it concrete.