Influence of Aggregates on Concrete Design

Welcome concrete fans! Today we're going to talk about again concrete mix design but how aggregates has an impact on it. We're not going to cover everything about aggregates today. We're going to give you an introduction, the basics. Don't worry, more aggregates in future videos. Aggregates make up roughly 70% of the volume of your concrete mixture. Because of that they're really important and you need to understand kind of how they work and what they're all about. The aggregate Size and distribution is very important. The shape and the texture. There's something called the surfness roughness. This is like how smooth or how rough the outside surface of the aggregates are. All of these things tell us are important and they tell us how the aggregate itself is going to impact the workability of our concrete. Let's see what I mean. Let's look at some pictures. On this slide, I'm showing five different concrete mixtures. Now these concrete mixtures are all the same. Every one of them is the same, except the gradation, that the size distribution of the aggregate is different. It's the same coarse aggregate, it's the same fine aggregate, it's the same volume of paste, it's the same water to cement ratio, same add mixtures, everything is the same, but the gradation of the aggregate is different. And the point of this slide is, these are slump tests, and the point of this slide is that aggregates have a huge impact and the gradation have a massive impact on the workability and the constructability of your concrete. For example, the upper left-hand corner here, I've got a picture of a concrete mixture with deficient fine sand. If you remember when I talked about slump, I told you that just because you get a certain number of a slump, That doesn't necessarily mean that concrete mixture is right. It may be that something's kind of wrong with it. Look at that. Look how it just kind of disintegrated. That's not good. It had deficient amount of sand so it had almost no cohesion. Let's look in the upper right hand corner. Now, here's a mixture where it's not very much slump at all, yet the total amount of sand is the same. Now the gradation, the size distribution of the sand is different, but the total amount is the same. And look. You get almost no slump out of that concrete. It's so stiff. That's not good. In the lower left hand corner, I say high amounts of intermediate aggregate. What's that mean? Intermediates are not large rocks, mid-sized rocks. There's a lot of those, too much of those in that mixture. Look how stiff it is. And let's look in the lower right-hand corner. Look at that concrete. It just doesn't look right. Look at that. Look at that. It just doesn't look right at all. It slumped. It got a decent slump. But it's kind of falling apart. Corsagra is trying to, like, come out of it. That's a high amount of Corsagra in the middle here. This is just right. This is just the right amount of everything. And that's what you're shooting for. This is all work done from a former PhD. used to in my name, Dan Cook, and Dan is a superstar. He is a concrete awesome guy, and we were super lucky to have his work to share with you today. Let's talk about workability, how finishable the concrete is. Let's look here. Same mixtures. This is if you were trying to make the concrete smooth, you're trying to run like a trowel, a tool over it to, again, smooth it out. This is what you'd see. Upper left-hand corner. This is deficient amount of fine sand. Look at that. It looks like there's just paste covering rock. That's not good. And then on the upper right-hand corner, now we have too much fine sand. Look at that. It looks like hairy concrete. That'd be so hard to finish and get smooth. And then we have the lower left-hand corner, excessive amounts of intermediate aggregate. And the lower right-hand corner, excessive amounts of corn. aggregate. You can see the aggregate trying to come out of the mixture as you're trying to finish it. And in the middle it's just right. Now maybe you have a hard time seeing the differences between these five mixtures, but I hope you get, I hope you understand that all these mixtures are exactly the same. The amount of coarse, fine, paste, water, everything is the same, but the gradation is different and the gradation has a huge impact on how your concrete's going to perform. Now, another thing that can happen is segregation. This is where the rock goes one way and the paste goes another way. This usually happens when you have too much of a single size or multiple sizes inside your concrete. I'll talk more about that coming up. Again, you can see that the concrete is going to be a little bit more If you just had too much of one size, you wouldn't know that if you only looked at the total amount of coarse aggregate you have. Okay? This isn't good. This doesn't make constructible concrete. This doesn't make durable concrete. You don't want this. Okay? Now, does the shape of the aggregate matter? People always ask that question. And yeah, the answer is yes. We took three different aggregates. We have pictures shown here. This one is cubic. It's got a little bit of angularity. We'll talk about how to measure size in a second. It's got something called low amounts of texture. That means it's not real smooth, but it's not real rough. And then we've got something here in the middle. This is a crushed gravel. This is slightly flat shaped. It's not cubical, slightly elongated. It's got very low angularity. It's kind of rounded. And it's got a very low amount of texture. It's pretty smooth, okay? Not perfectly smooth. Then on the far right, it's another limestone crushed in a different way. It's another type of limestone as well. And it's really flat. Look at these pictures. See how flat it is? And the angularity, that means it's not quite cubical. It's got some non... Uniform corners, little kind of angular, weird, strange corners. It's got a little bit of medium texture to it, a little bit more roughness to the surface. Now what we did is we made concrete, exact same concrete mixture, the exact same gradation, that means size distribution was exactly the same. But because of these inherent differences in shape of the aggregates, all of the mixtures require different amounts of admixture. water reducer to reach the same slump. For example, this one required zero ounces per hundred weight of admixture. This one required three ounces per hundred weight of admixture. And this one required 6.9 ounces per hundred weight of admixture. We want concrete mixtures that use less admixtures. If we had our choice, we would choose this one. the one that needs zero ounces per hundredweight. People might think that one thing is better than another. It's best just to test it and see and quantify it. Another way to quantify how the shape of aggregates is with a test called ASTM D4791. This is like a big caliper and it measures the flatness elongation, and overall shape of an aggregate particle. Let's show you how it works. You take an aggregate, and you measure the minimum dimension that you can find. And you take that same aggregate, and you measure the maximum dimension, or you compare the maximum dimension. And you get something called the flatness ratio. And Dan found, in his research, that he would recommend that you have 15% of your particles with a flatness ratio of 1 to 3 or less, or less than 15%. You don't want a lot of particles with a flatness ratio greater than 1 to 3. And again, about 15% was like the magic number that Dan found. So there's a tip for you. Now, does that mean we can't make concrete with flat and elongated particles? No, no, it doesn't. You can, but you might need more paste. You might need more cement and water. that may impact your cost, your durability, maybe strength. These are things you have to think about. These are the trade-offs that come up over and over and over again when we talk about concrete mixtures. The most common way to investigate an aggregate for concrete is to usually describe it by two parameters. One, the mineralogy. That's what type of rock is it. Is it a limestone? Is it a river gravel? Is it a granite? Is it a sandstone? Chord site? That type of information. And the other is the gradation. That's the size distribution. That's what I was talking about previously. It's kind of important. The type of rock is going to determine the density of it. Something called the specific gravity, or SG, specific gravity. That's going to be really important. That's the density compared of the aggregate, compared to the density of water. The hardness and the strength is also determined by the mineralogy of the aggregate. The gradation and the shape are determined about how the rock is processed. Now that doesn't mean that the meteorology doesn't have some impact on these, but the method that the rock is produced or crushed has a huge impact. There's many, many things. ...you can do to improve the gradation and the shape of the aggregate by the crushing process. Now, we're not always talking about rocks. Sometimes we're talking about sand. But the gradation of sand, sand doesn't usually come, I guess there's two types, but natural sand doesn't come from the crushing process. It comes from a river. It comes from a stream. scoop it out. If you find the right spot, you're going to get the right shape and gradation of sand particles. And as you change different spots in the river, these things will change. Now we're not always blessed to have have natural sand. We're not always blessed to have this beautiful river sand. And sometimes we have to use whatever we have locally. And this is sometimes called a man sand or manufactured sand. This comes from the crushing of the rock. This leftover material, these small fine material, you can use as sand and concrete. The problem is that the shape isn't quite right. It's kind of angular. It doesn't work as well with our finishability and our workability. ability. That's something that needs more work to better understand. Something you should think about though. Three, two, one. The aggregate gradation is usually expressed by using something called a sieve analysis. It's where you have a bunch of screens of different sizes and you put rock on top and you shake it and shake it and shake it and shake it and you see which ones got caught on a screen and which ones didn't. Well, from this sieve analysis, you can actually calculate something called the percent retained. And that's how much material was caught on a certain sieve. And then by that information, you usually produce these two plots. This plot on the top is the percentage passing versus sieve number. This is the percent that made it through a certain sieve size. And then this down at the bottom is the percent retained versus a different sieve size. This is again the amount that was caught on each one of the sieves. Now I've shown these two graphs and I've labeled them. This is number three, number three, number two, number two. These are the exact same. exact same aggregates, just shown in two different ways. I'm gonna try to explain kinda how this works. For example, this percent passing says at a sieve size of a number 50, that 10% of my material is passing. That means below the sieve size of a number 50, there is 10% of that material. Let's show you that. Here's a number 50, that means below it, That means the number 100, look at that, there's 10% on the number 100, 0% on the number 200. There you go, 10%. passing the number 50. Let's keep going. Let's look at the number 30. Number 30 here says 50% is passing through the number 30. It means 50% is below the number 30, but we don't really know what it is. Is it caught on the 50? Is it caught on the 100? Is it caught on the 200? We don't really know. But if you come down and look here, again, it just says 50% is below this point. And again, this is the true gradation. This is one reason why I'm a big fan of percent retained. Now the industry, the concrete industry is not. The concrete industry talks in percent passing and they think in percent passing and I think differently. I don't think percent passing is nearly as helpful because it's hard for me to imagine kind of what the gradation looks like just by looking at these funny S-shaped curves. But for example, see this big jump here? That means that on one sieve size, that there's a huge amount of material. Look at that. 80% of aggregate number 2 is caught on the number 4 sieve. Again, I'm a big fan of the percent retained. I just think it makes more sense. I think it's easier to follow, and easier to understand. Based on the percent passing information, that's the S-shaped curves I just showed you, people use ASTM C33 to group different sizes of aggregates, different types of aggregates, different size distribution of aggregates. And I've shown you some typical ones here below. Here I'm showing you different sieve numbers, okay? And this is actually the opening for the sieves. Okay, and then here are different categories of aggregates that are sold. This is a kind of an idea you could call someone up, an aggregate producer up on the phone, and you could ask for a number 57 stone, and they know what that means. Everyone knows what that means. That means that on the one inch sieve size, that between 95 and 100 percent of the material is passing. And that means on the half inch that between 25 and 60 percent, isn't that kind of a big number? I think it is. But between 25 and 60 percent is passing. And again, number four and number eight, there's criteria. This is helpful. So when some people are calling up on the phone to order, they kind of have some idea what they're getting. Another thing that's really critical about these different numbers is something called the maximum nominal aggregate size. This is also important, which I'll explain coming up. But this is for certain times, I can't have aggregates that are too big. Okay? They'll wreck my construction practices. And again, a number 57 stone is a way to order an aggregate that has a one inch maximum nominal size. If you want to drop down to a number 67, there's a three quarter inch maximum nominal size. Let me tell you another secret though. There are many different products out there, aggregates, that are sold that meet multiple of these categories. What? How could that be? Like, if I'm ordering a hamburger and I'm ordering, like, a turkey sandwich, they're two different things, right? Well, in aggregates... It's not that simple, okay? Both a hamburger and a turkey sandwich are both a sandwich, just different types. Many different types of aggregates that are out there fit into multiple different categories. This is a very, very broad category here, like sandwich. Kind of a broad category. And you need to look at the specifics. You need to look at the specific gradations. Okay? Before you just order, like, a number 57, would you just order a sandwich? It could be, like, an egg sandwich or an egg salad sandwich or a turkey sandwich or something we call a hamburger sandwich. sandwich. Some people call it a bunch of other nasty stuff, sandwiches. You need to know specifics. That's important. Again, we'll talk more about that coming up. Let's jump in more at this maximum nominal aggregate size. Typically, this is defined as the amount of material that has 85 to 95% pass that sieve size. That means there's only about, supposed to be about, between 5... and 15% of this one size. Usually it's around 5%, 5 to 10% of that size. That's kind of like the maximum top end. And this is critical when we look at the constructability of different types of structures. For example... The maximum nominal aggregate size is kind of important when you're looking at pouring concrete between two forms. It would kind of be bad if all of your aggregates kind of clumped up and formed like a bridge or like kind of an archway. inside, in between the forms. That's not what you want. You want aggregate and paste to be inter-dispersed together. You don't want just aggregate on aggregate contact, because you might have a bunch of voids in there as well. And voids aren't good for anybody. So because of this, if you're making a wall, there's a criteria or an actual requirement by the building code that your maximum nominal aggregate size will be less than one-fifth the minimum dimension between two formed surfaces. Therefore, if I was trying to pour a wall that's five inch thick, that's a pretty thin wall. But if I did, I would have to use a one inch or lower, actually a lower, smaller, less than one inch maximum nominal aggregate size. Let's say I'm pouring a slab. Again, it would be bad if I have three aggregates that stacked up on top of one another, okay? Again, form this kind of pocket. That wouldn't be good. So again, there's a rule that the maximum normal aggregate size has to be less than one-third of the minimum thickness of a slab. So if I'm pouring a six inch slab, then one third of that would be two inches. That means my maximum nominal aggregate size would have to be less than two inches. Let's say I'm pouring within a reinforcing mesh, like a grid like this. It would be really bad if I got an aggregate that got stuck inside the grid. For example, if I was pouring concrete here and the concrete, the aggregates got stuck. and wouldn't travel through the grid to the forms, to the cover, I'm sorry, through the grid to form the cover and meet the forms on the outside. That'd be bad. If I could clog that up, that would be horrible. So because of that, the minimum clear spacing between rebars, the minimum, could be S1, could be S2, whichever the minimum is, your maximum normal aggregate size has to be less than three quarters of that value. And also, if you have concrete where you're really concerned about the look or the aesthetics, or also if you're concerned about the quality of the cover. Cover is the area between the steel and the surface of the concrete, and the cover is very important for durability. Again, if you're pouring this type of structure, the minimum cover between the rebar and the forms, the minimum, the minimum dimension between the rebar and the forms, Three quarters of that, your maximum aggregate size has to be less than that. Or again, your aggregate can hang between the forms and rebar and will ruin the surface finish and reduce the effective cover on your steel. Again, this is important. Thanks.

Don't worry, more aggregates in future videos. Aggregates make up roughly 70% of the volume of your concrete mixture. Because of that they're really important and you need to understand kind of how they work and what they're all about.

The aggregate Size and distribution is very important. The shape and the texture. There's something called the surfness roughness.

This is like how smooth or how rough the outside surface of the aggregates are. All of these things tell us are important and they tell us how the aggregate itself is going to impact the workability of our concrete. Let's see what I mean.

Let's look at some pictures. On this slide, I'm showing five different concrete mixtures. Now these concrete mixtures are all the same.

Every one of them is the same, except the gradation, that the size distribution of the aggregate is different. It's the same coarse aggregate, it's the same fine aggregate, it's the same volume of paste, it's the same water to cement ratio, same add mixtures, everything is the same, but the gradation of the aggregate is different. And the point of this slide is, these are slump tests, and the point of this slide is that aggregates have a huge impact and the gradation have a massive impact on the workability and the constructability of your concrete. For example, the upper left-hand corner here, I've got a picture of a concrete mixture with deficient fine sand.

If you remember when I talked about slump, I told you that just because you get a certain number of a slump, That doesn't necessarily mean that concrete mixture is right. It may be that something's kind of wrong with it. Look at that.

Look how it just kind of disintegrated. That's not good. It had deficient amount of sand so it had almost no cohesion. Let's look in the upper right hand corner.

Now, here's a mixture where it's not very much slump at all, yet the total amount of sand is the same. Now the gradation, the size distribution of the sand is different, but the total amount is the same. And look. You get almost no slump out of that concrete.

It's so stiff. That's not good. In the lower left hand corner, I say high amounts of intermediate aggregate. What's that mean? Intermediates are not large rocks, mid-sized rocks.

There's a lot of those, too much of those in that mixture. Look how stiff it is. And let's look in the lower right-hand corner. Look at that concrete.

It just doesn't look right. Look at that. Look at that.

It just doesn't look right at all. It slumped. It got a decent slump. But it's kind of falling apart. Corsagra is trying to, like, come out of it.

That's a high amount of Corsagra in the middle here. This is just right. This is just the right amount of everything. And that's what you're shooting for.

This is all work done from a former PhD. used to in my name, Dan Cook, and Dan is a superstar. He is a concrete awesome guy, and we were super lucky to have his work to share with you today. Let's talk about workability, how finishable the concrete is.

Let's look here. Same mixtures. This is if you were trying to make the concrete smooth, you're trying to run like a trowel, a tool over it to, again, smooth it out.

This is what you'd see. Upper left-hand corner. This is deficient amount of fine sand.

Look at that. It looks like there's just paste covering rock. That's not good.

And then on the upper right-hand corner, now we have too much fine sand. Look at that. It looks like hairy concrete.

That'd be so hard to finish and get smooth. And then we have the lower left-hand corner, excessive amounts of intermediate aggregate. And the lower right-hand corner, excessive amounts of corn.

aggregate. You can see the aggregate trying to come out of the mixture as you're trying to finish it. And in the middle it's just right.

Now maybe you have a hard time seeing the differences between these five mixtures, but I hope you get, I hope you understand that all these mixtures are exactly the same. The amount of coarse, fine, paste, water, everything is the same, but the gradation is different and the gradation has a huge impact on how your concrete's going to perform. Now, another thing that can happen is segregation.

This is where the rock goes one way and the paste goes another way. This usually happens when you have too much of a single size or multiple sizes inside your concrete. I'll talk more about that coming up. Again, you can see that the concrete is going to be a little bit more If you just had too much of one size, you wouldn't know that if you only looked at the total amount of coarse aggregate you have. Okay?

This isn't good. This doesn't make constructible concrete. This doesn't make durable concrete.

You don't want this. Okay? Now, does the shape of the aggregate matter?

People always ask that question. And yeah, the answer is yes. We took three different aggregates.

We have pictures shown here. This one is cubic. It's got a little bit of angularity. We'll talk about how to measure size in a second.

It's got something called low amounts of texture. That means it's not real smooth, but it's not real rough. And then we've got something here in the middle.

This is a crushed gravel. This is slightly flat shaped. It's not cubical, slightly elongated. It's got very low angularity. It's kind of rounded.

And it's got a very low amount of texture. It's pretty smooth, okay? Not perfectly smooth.

Then on the far right, it's another limestone crushed in a different way. It's another type of limestone as well. And it's really flat.

Look at these pictures. See how flat it is? And the angularity, that means it's not quite cubical.

It's got some non... Uniform corners, little kind of angular, weird, strange corners. It's got a little bit of medium texture to it, a little bit more roughness to the surface. Now what we did is we made concrete, exact same concrete mixture, the exact same gradation, that means size distribution was exactly the same. But because of these inherent differences in shape of the aggregates, all of the mixtures require different amounts of admixture.

water reducer to reach the same slump. For example, this one required zero ounces per hundred weight of admixture. This one required three ounces per hundred weight of admixture.

And this one required 6.9 ounces per hundred weight of admixture. We want concrete mixtures that use less admixtures. If we had our choice, we would choose this one.

the one that needs zero ounces per hundredweight. People might think that one thing is better than another. It's best just to test it and see and quantify it.

Another way to quantify how the shape of aggregates is with a test called ASTM D4791. This is like a big caliper and it measures the flatness elongation, and overall shape of an aggregate particle. Let's show you how it works. You take an aggregate, and you measure the minimum dimension that you can find. And you take that same aggregate, and you measure the maximum dimension, or you compare the maximum dimension.

And you get something called the flatness ratio. And Dan found, in his research, that he would recommend that you have 15% of your particles with a flatness ratio of 1 to 3 or less, or less than 15%. You don't want a lot of particles with a flatness ratio greater than 1 to 3. And again, about 15% was like the magic number that Dan found. So there's a tip for you.

Now, does that mean we can't make concrete with flat and elongated particles? No, no, it doesn't. You can, but you might need more paste. You might need more cement and water. that may impact your cost, your durability, maybe strength.

These are things you have to think about. These are the trade-offs that come up over and over and over again when we talk about concrete mixtures. The most common way to investigate an aggregate for concrete is to usually describe it by two parameters. One, the mineralogy. That's what type of rock is it.

Is it a limestone? Is it a river gravel? Is it a granite? Is it a sandstone? Chord site?

That type of information. And the other is the gradation. That's the size distribution. That's what I was talking about previously.

It's kind of important. The type of rock is going to determine the density of it. Something called the specific gravity, or SG, specific gravity. That's going to be really important. That's the density compared of the aggregate, compared to the density of water.

The hardness and the strength is also determined by the mineralogy of the aggregate. The gradation and the shape are determined about how the rock is processed. Now that doesn't mean that the meteorology doesn't have some impact on these, but the method that the rock is produced or crushed has a huge impact. There's many, many things.

...you can do to improve the gradation and the shape of the aggregate by the crushing process. Now, we're not always talking about rocks. Sometimes we're talking about sand.

But the gradation of sand, sand doesn't usually come, I guess there's two types, but natural sand doesn't come from the crushing process. It comes from a river. It comes from a stream.

scoop it out. If you find the right spot, you're going to get the right shape and gradation of sand particles. And as you change different spots in the river, these things will change.

Now we're not always blessed to have have natural sand. We're not always blessed to have this beautiful river sand. And sometimes we have to use whatever we have locally.

And this is sometimes called a man sand or manufactured sand. This comes from the crushing of the rock. This leftover material, these small fine material, you can use as sand and concrete.

The problem is that the shape isn't quite right. It's kind of angular. It doesn't work as well with our finishability and our workability.

ability. That's something that needs more work to better understand. Something you should think about though. Three, two, one. The aggregate gradation is usually expressed by using something called a sieve analysis.

It's where you have a bunch of screens of different sizes and you put rock on top and you shake it and shake it and shake it and shake it and you see which ones got caught on a screen and which ones didn't. Well, from this sieve analysis, you can actually calculate something called the percent retained. And that's how much material was caught on a certain sieve.

And then by that information, you usually produce these two plots. This plot on the top is the percentage passing versus sieve number. This is the percent that made it through a certain sieve size. And then this down at the bottom is the percent retained versus a different sieve size. This is again the amount that was caught on each one of the sieves.

Now I've shown these two graphs and I've labeled them. This is number three, number three, number two, number two. These are the exact same.

exact same aggregates, just shown in two different ways. I'm gonna try to explain kinda how this works. For example, this percent passing says at a sieve size of a number 50, that 10% of my material is passing.

That means below the sieve size of a number 50, there is 10% of that material. Let's show you that. Here's a number 50, that means below it, That means the number 100, look at that, there's 10% on the number 100, 0% on the number 200. There you go, 10%. passing the number 50. Let's keep going. Let's look at the number 30. Number 30 here says 50% is passing through the number 30. It means 50% is below the number 30, but we don't really know what it is.

Is it caught on the 50? Is it caught on the 100? Is it caught on the 200?

We don't really know. But if you come down and look here, again, it just says 50% is below this point. And again, this is the true gradation.

This is one reason why I'm a big fan of percent retained. Now the industry, the concrete industry is not. The concrete industry talks in percent passing and they think in percent passing and I think differently. I don't think percent passing is nearly as helpful because it's hard for me to imagine kind of what the gradation looks like just by looking at these funny S-shaped curves.

But for example, see this big jump here? That means that on one sieve size, that there's a huge amount of material. Look at that.

80% of aggregate number 2 is caught on the number 4 sieve. Again, I'm a big fan of the percent retained. I just think it makes more sense. I think it's easier to follow, and easier to understand.

Based on the percent passing information, that's the S-shaped curves I just showed you, people use ASTM C33 to group different sizes of aggregates, different types of aggregates, different size distribution of aggregates. And I've shown you some typical ones here below. Here I'm showing you different sieve numbers, okay?

And this is actually the opening for the sieves. Okay, and then here are different categories of aggregates that are sold. This is a kind of an idea you could call someone up, an aggregate producer up on the phone, and you could ask for a number 57 stone, and they know what that means. Everyone knows what that means. That means that on the one inch sieve size, that between 95 and 100 percent of the material is passing.

And that means on the half inch that between 25 and 60 percent, isn't that kind of a big number? I think it is. But between 25 and 60 percent is passing. And again, number four and number eight, there's criteria. This is helpful.

So when some people are calling up on the phone to order, they kind of have some idea what they're getting. Another thing that's really critical about these different numbers is something called the maximum nominal aggregate size. This is also important, which I'll explain coming up.

But this is for certain times, I can't have aggregates that are too big. Okay? They'll wreck my construction practices. And again, a number 57 stone is a way to order an aggregate that has a one inch maximum nominal size. If you want to drop down to a number 67, there's a three quarter inch maximum nominal size.

Let me tell you another secret though. There are many different products out there, aggregates, that are sold that meet multiple of these categories. What? How could that be? Like, if I'm ordering a hamburger and I'm ordering, like, a turkey sandwich, they're two different things, right?

Well, in aggregates... It's not that simple, okay? Both a hamburger and a turkey sandwich are both a sandwich, just different types.

Many different types of aggregates that are out there fit into multiple different categories. This is a very, very broad category here, like sandwich. Kind of a broad category. And you need to look at the specifics.

You need to look at the specific gradations. Okay? Before you just order, like, a number 57, would you just order a sandwich? It could be, like, an egg sandwich or an egg salad sandwich or a turkey sandwich or something we call a hamburger sandwich.

sandwich. Some people call it a bunch of other nasty stuff, sandwiches. You need to know specifics.

That's important. Again, we'll talk more about that coming up. Let's jump in more at this maximum nominal aggregate size. Typically, this is defined as the amount of material that has 85 to 95% pass that sieve size.

That means there's only about, supposed to be about, between 5... and 15% of this one size. Usually it's around 5%, 5 to 10% of that size.

That's kind of like the maximum top end. And this is critical when we look at the constructability of different types of structures. For example... The maximum nominal aggregate size is kind of important when you're looking at pouring concrete between two forms. It would kind of be bad if all of your aggregates kind of clumped up and formed like a bridge or like kind of an archway.

inside, in between the forms. That's not what you want. You want aggregate and paste to be inter-dispersed together.

You don't want just aggregate on aggregate contact, because you might have a bunch of voids in there as well. And voids aren't good for anybody. So because of this, if you're making a wall, there's a criteria or an actual requirement by the building code that your maximum nominal aggregate size will be less than one-fifth the minimum dimension between two formed surfaces.

Therefore, if I was trying to pour a wall that's five inch thick, that's a pretty thin wall. But if I did, I would have to use a one inch or lower, actually a lower, smaller, less than one inch maximum nominal aggregate size. Let's say I'm pouring a slab. Again, it would be bad if I have three aggregates that stacked up on top of one another, okay? Again, form this kind of pocket.

That wouldn't be good. So again, there's a rule that the maximum normal aggregate size has to be less than one-third of the minimum thickness of a slab. So if I'm pouring a six inch slab, then one third of that would be two inches. That means my maximum nominal aggregate size would have to be less than two inches.

Let's say I'm pouring within a reinforcing mesh, like a grid like this. It would be really bad if I got an aggregate that got stuck inside the grid. For example, if I was pouring concrete here and the concrete, the aggregates got stuck. and wouldn't travel through the grid to the forms, to the cover, I'm sorry, through the grid to form the cover and meet the forms on the outside.

That'd be bad. If I could clog that up, that would be horrible. So because of that, the minimum clear spacing between rebars, the minimum, could be S1, could be S2, whichever the minimum is, your maximum normal aggregate size has to be less than three quarters of that value. And also, if you have concrete where you're really concerned about the look or the aesthetics, or also if you're concerned about the quality of the cover. Cover is the area between the steel and the surface of the concrete, and the cover is very important for durability.

Again, if you're pouring this type of structure, the minimum cover between the rebar and the forms, the minimum, the minimum dimension between the rebar and the forms, Three quarters of that, your maximum aggregate size has to be less than that. Or again, your aggregate can hang between the forms and rebar and will ruin the surface finish and reduce the effective cover on your steel. Again, this is important. Thanks.

Transcript for:Influence of Aggregates on Concrete Design

Transcript for:
Influence of Aggregates on Concrete Design