Why do we NEED air bubbles in concrete? | air entrained concrete

Summary

In this informative video, Tyler Lai explores the critical role of air bubbles in concrete, emphasizing their importance for freeze-thaw durability. He explains that not all air bubbles are equal, with smaller bubbles being more beneficial than larger ones. Lai challenges the conventional wisdom that a 6% air content in concrete guarantees durability, highlighting that the size of air bubbles is crucial. He discusses the historical basis for current concrete specifications, which were established by Paul Kleeger in the 1950s, and argues that these standards may be outdated given the advancements in concrete mixtures. Lai introduces the concept of the spacing factor, a measure of air void distribution, and explains how it is a more accurate predictor of concrete performance than air content alone. The video concludes with a call for a reevaluation of concrete specifications to account for the size of air bubbles.

Takeaways

• 🏗️ Air bubbles in concrete are crucial for its durability, contrary to common belief that they indicate poor construction.
• 🔍 Smaller air bubbles within concrete are more beneficial than larger ones for enhancing freeze/thaw durability.
• 🏡 A project's success can hinge on the size of air bubbles; smaller bubbles lead to better performance over time.
• ❄️ The freeze/thaw cycle's impact on concrete is mitigated by the presence of small air bubbles that allow for water expansion without causing damage.
• 💭 The volume of air in concrete does not directly correlate with freeze-thaw performance; it's the size of the air bubbles that matters.
• 🔬 Historical standards for air content in concrete, like Paul Kleeger's 6% recommendation, may not be applicable to modern concrete mixtures.
• 📚 Modern concrete often includes various admixtures that change its characteristics, unlike the simpler mixtures of the past.
• 🔍 The ASTM C457 method is used to analyze the hardened concrete's air void system, providing insight into the bubble size and distribution.
• 📏 The spacing factor, an average distance between air voids, is a key metric, with a target of less than 0.08 inches for optimal performance.
• 📈 Durability testing, such as freeze-thaw cycles, shows that small bubble mixtures require less air content for success compared to large bubble mixtures.
• ⚠️ Current specifications for air-entrained concrete may be flawed and outdated, emphasizing the need for updated standards that consider bubble size.

Q & A

Why are air bubbles important in concrete?

Air bubbles in concrete are critical for enhancing freeze/thaw durability. They provide a space for water to expand when it freezes, preventing damage to the concrete structure.

What is the difference between small and large air bubbles in concrete?

Small air bubbles are more effective at providing freeze/thaw resistance than large ones. They allow water to reach the boundary of the concrete before it expands and causes damage.

Why do some people think air bubbles in concrete are a mistake?

Some people might associate air bubbles in concrete with poor construction or a mistake, not realizing that they are intentionally added for durability purposes.

What is the significance of the spacing factor in air entrained concrete?

The spacing factor is a measure of the average distance between air bubbles in concrete. A lower spacing factor (less than 0.008 inches) indicates a more uniform and effective distribution of air bubbles, which is desirable for freeze/thaw resistance.

Who is Paul Kleeger and what is his contribution to concrete technology?

Paul Kleeger was a researcher who conducted extensive studies on concrete and discovered that adding air bubbles using soap improved its freeze/thaw durability. His findings have been foundational in the development of air entrained concrete.

How does the addition of air-entraining admixtures affect concrete?

Air-entraining admixtures create a system of small air bubbles within the concrete, which is crucial for improving its freeze/thaw durability and overall performance.

What is the ASTM C457 analysis and how is it used in concrete testing?

The ASTM C457 analysis is a method for examining the hardened air-entrained concrete. It involves cutting, polishing, and examining the concrete under a microscope to measure the size and spacing of air bubbles.

Why is it insufficient to rely solely on the air content percentage to determine freeze/thaw durability?

The air content percentage alone does not indicate the size distribution of air bubbles. Smaller bubbles provide better freeze/thaw resistance, so both the volume and size of the bubbles are important.

What is the significance of the 4% and 7% air content in relation to freeze/thaw durability?

In the context of the video, 4% air content is sufficient for concrete with small air bubbles to pass freeze/thaw tests, while 7% is required for concrete with large bubbles, indicating that smaller bubbles are more effective.

Why are current concrete specifications considered flawed according to the video?

Current specifications are based on research from the 1950s and do not account for the advancements and variations in concrete mixtures today, particularly the use of multiple admixtures and supplementary materials.

Outlines

00:00

🏗️ Importance of Air Bubbles in Concrete

This paragraph introduces the topic of air bubbles in concrete, emphasizing their critical role in enhancing freeze-thaw durability. The speaker, Tyler Lai, explains that smaller air bubbles are more beneficial than larger ones for concrete's longevity. The discussion contrasts two structures built with the same materials but differing in bubble size, illustrating the impact on durability. The video also touches on the historical use of air entraining admixtures, pioneered by Paul Kleeger, and how modern concrete mixtures have evolved beyond the scope of Kleeger's research, necessitating a reevaluation of air content specifications.

05:02

🔍 Analyzing Air Void Systems in Concrete

The second paragraph delves into the technical aspects of air void systems in concrete, focusing on the importance of bubble size and distribution. It introduces the concept of the spacing factor, developed by T.C. Powers, which measures the average distance between air voids. The ideal spacing factor is less than 0.08 inches, as per ACI 201. The paragraph contrasts two air void systems, one with small bubbles and the other with large, highlighting the preference for the former due to its superior freeze-thaw resistance. The discussion also includes graphical representations of bubble size distribution and their correlation with concrete durability. The speaker concludes by emphasizing the inadequacy of air content alone in assessing freeze-thaw durability, advocating for a more nuanced understanding of bubble size and distribution in concrete mixtures.

Keywords

💡Air Bubbles

Air bubbles in concrete are intentionally introduced to enhance its freeze-thaw durability. These microscopic pockets of air within the concrete help to accommodate the expansion of water as it freezes, preventing the concrete from cracking. In the video, it is emphasized that not all air bubbles are created equal; smaller bubbles are more beneficial than larger ones for the concrete's integrity.

💡Concrete Durability

Concrete durability refers to its ability to withstand various environmental conditions and maintain its structural integrity over time. The video discusses how the presence of air bubbles, particularly their size, significantly impacts the durability of concrete, especially in freeze-thaw cycles.

💡Freeze/Thaw Durability

Freeze/thaw durability is a key aspect of concrete performance, especially in climates where temperatures fluctuate above and below freezing. The video explains that small air bubbles in concrete provide better freeze/thaw durability because they allow for water expansion without causing cracks.

💡Air Entrainment

Air entrainment is the process of intentionally introducing air bubbles into concrete during mixing. This is done to improve the workability and durability of the concrete, particularly against freeze-thaw cycles. The video highlights that air entrainment is crucial for creating 'good' concrete.

💡Spacing Factor

The spacing factor is a measure used to evaluate the distribution of air voids in concrete. It is defined as the average center-to-center distance between air voids. The video mentions that a spacing factor less than 0.008 inches is desirable for good freeze-thaw durability.

💡ASTM C 457

ASTM C 457 is a standard test method for evaluating the air void characteristics in hardened concrete. The video describes this method, which involves cutting and polishing a sample of concrete, then examining it under a microscope to measure the size and spacing of air voids.

💡Air Content

Air content in concrete refers to the total volume of air voids expressed as a percentage of the total volume of the concrete. The video points out that a higher air content does not necessarily correlate with better freeze-thaw performance; the size and distribution of the air bubbles are more critical.

💡Paul Kleeger

Paul Kleeger was a researcher who conducted extensive studies on concrete in the 1950s. His work led to the understanding that adding air bubbles to concrete could improve its durability. The video notes that while Kleeger's findings were groundbreaking, the specifications based on his research may not be entirely applicable to modern concrete mixtures.

💡Aggregate Size

Aggregate size refers to the size of the particles of stone, gravel, or crushed rock that are used in concrete. The video mentions that specifications for air content in concrete are often based on aggregate size, which can influence the required amount of air entrained to achieve optimal performance.

💡Admixtures

Admixtures are substances added to concrete to modify its properties, such as workability, strength, or durability. The video discusses how modern concrete often contains a 'cocktail' of different admixtures, unlike the simpler mixtures used in Kleeger's time, which had only one type of admixture for air entrainment.

💡Durability Factor

The durability factor is a measure of a concrete's ability to resist degradation under specific conditions, such as freeze-thaw cycles. The video uses data points on a plot to illustrate how different air contents and spacing factors affect the durability factor in concrete mixtures.

Highlights

Air bubbles in concrete are critical for its durability, contrary to appearances.

Smaller air bubbles are more important for the concrete's freeze/thaw durability than larger ones.

A project comparison shows that concrete with small bubbles lasts longer than that with large bubbles.

The freeze/thaw process and its impact on concrete durability are explained through a water pocket analogy.

Air entrained bubbles are key to freeze-thaw resistance in concrete.

The volume of air in concrete does not directly equate to freeze-thaw performance.

Paul Kleeger's research from the 1950s is the basis for many current concrete specifications.

Modern concrete mixtures have evolved significantly since Kleeger's time, necessitating updated specifications.

The preference for a specific air void system in concrete is based on the size of the bubbles.

ASTM C457 analysis is used to measure the size and distribution of air bubbles in hardened concrete.

The spacing factor, introduced by T.C. Powers, is a critical metric for air void distribution in concrete.

A low spacing factor indicates a more effective air void system for freeze-thaw durability.

The relationship between air content and spacing factor is crucial for achieving the desired bubble spacing.

Air content alone is not sufficient to determine freeze-thaw durability; bubble size is also essential.

Concrete with small bubbles requires less air content to achieve a good spacing factor compared to large bubbles.

Specifications based on Kleeger's research may not be applicable to modern concrete mixtures.

The video suggests the need for new tools to assess air bubble size in concrete for current mixtures.

Transcripts

in this video we're gonna talk about why

do we need air bubbles inside of

concrete and then our all air bubbles

created equal and finally did you know

that every specification when it comes

to air entrained concrete is totally

flawed

my name is Tyler Lai and I am cuckoo for

concrete I'm totally obsessed in about

today's video I'm extra obsessed air

bubbles and concrete is one of my

favorite topics you may see this and

think that somebody made a mistake maybe

somebody didn't construct the concrete

correctly you see these voids or bubbles

on the surface and some might think they

look ugly they save the concrete they're

a critical part and these smaller

bubbles these little bitty ones are much

more important than the larger ones

these small 80 bitty ones they're the

good ones here's a project built by the

same contractor using the same materials

and the same specifications but the one

on the right the one that's falling

apart after about five years the bubbles

that were inside of them were mainly

large and the one on the Left had small

bubbles the good ones and it has to do

with the freeze/thaw

durability of the concrete let me show

you what I mean I'm showing a bubble

here and it's surrounded by some water

pockets and as that concrete starts to

freeze that water tries to expand and

it'll try to escape and it tries to find

boundaries around it and it can only go

a certain distance if it makes that edge

of that boundary everything is saved

yeah the concrete is saved if that water

pocket is too far away and as it starts

to expand if it can't reach a boundary

there's only a certain distance it can

travel before it starts to cause damage

before it starts to cause cracks and

to the concrete and that's not good why

do we add air to concrete well these air

entrained bubbles are the key to the

Freestyle resistance but this second

bullet item here is really important the

volume of air in your concrete does not

equal freestyle performance then the

smaller bubbles are much more effective

at providing free saw resistance than

the larger bubbles typically

specifications look something like this

based on the aggregate size they tell

you a certain volume of air and most

people make this even simpler they just

say you need six percent air in your

concrete you know where that's from

well a guy named Paul kleeger god bless

Paul kleeger epic epic guy the Portland

cement Association he did a huge study

huge hundreds and hundreds of concrete's

and he fries and he thought those

concrete's over and over and over again

and he found the secret to making him

last long was putting air bubbles using

soap to put air bubbles inside the

concrete and we've been using that

technology ever since although Paul

clicker did some amazing things his

materials he looked at were very limited

compared to today's mixtures concrete

has changed so much since the 1950s Paul

Klee Gers mixtures didn't have any fly

ash or slag or silica fume in it and

they had mixtures he used he only used

one one an air entraining admixtures

that was the only admixture that existed

back then

how many concrete mixtures can you think

about today they'd only have one

admixture in them almost none I almost

all have a whole cocktail of different

chemicals in it that help make that

concrete better we've got two air voids

systems here one on the left one on the

right both of them have the same volume

of air but as a concrete person we'd

much rather have the one on the right

just because that same reason I showed

you earlier in that picture

there's much more protection out of the

air voids system on the right so how do

you measure this how do we understand

what

going on typically we use a hardened

airborne analysis it's called an ASTM C

four five seven analysis this is where

you cut the concrete you polish it and

you look at it underneath the microscope

and you basically trace over the surface

and align and every time that line

intersects a bubble you measure it and

that's called a cord now on the air

fluid system on the Left we have a bunch

of small bubbles then every system on

the right we have a bunch of large

bubbles we've taken these concrete we've

polished them we've colored them black

we put white inside all of the voids and

you can see on the one on the left

there's just not that many large voids

and the one on the right look at all

those large bubbles we would much rather

have this average system on the left

here's another way to look at this this

is the sizes of the cords this is small

voids this is large voids and this is

the frequency or how often they occur

the green line here is made up of mainly

small bubbles and the blue is made up of

mainly large bubbles if we had to pick

we would much rather have the green now

instead of like in this entire line a

guy named TC powers in 1949 came up with

this really cool concept called a

spacing factor he took all of these

numbers all of these measurements and

said I'm gonna find an average sized

void averagely spaced uniformly inside

the pace there's a lot of averages there

he finds this angular distance here is

something called twice a spacing factor

you don't have to understand anything I

just said you just need to know the

spacing factor is a magic number it has

something to do with the air void

spacing and the number that we want is

less than point zero zero eight inches

that's defined by a CI 201 so we would

say the green line here has a low

spacing and the blue line has a high

spacing factor here's another way to

look at this here's our air volume down

here and here's our spacing factor and

that's our magic number of point zero

zero eight inches and we can see as our

air content goes

our spacing factor goes down as you're

adding more and more air to the concrete

then the spacing of the bubbles has to

get closer and closer and closer

together now if you have small bubbles

if we get about 6% air which is around

most specifications then you get the

nice beautiful spacing factor we care

about if you go to the large bubbles you

have large bubbles in your concrete then

you need much much more higher air

content to get this magical spacing of

your bubbles you cannot tell the size of

your bubbles by just looking at the

volume we're gonna see this over and

over again

now here's another plot that shows air

content down here versus durability

factor this is performance in the

freeze-thaw test this is where we make

concrete and we freeze it we thaw it

over and over and over again and we

actually send a stress wave through it

and we measure how much cracks form on

the inside this is the line that we call

failure and everything above this line

is good everything below the line not so

good and you can see with this small

bubble mixture that if I get enough air

about 4 percent air in my concrete

everything is great but look at this

large bubble mixture I need a lot more

about 7 percent air that's that's quite

a bit different the big takeaway here is

that air content alone air volume alone

is not the way to determine if you're

gonna have freeze thaw durable concrete

you have to know about the size of the

bubbles

here's more data here's air content on

the x axis here is spacing factor that

magical number here and there's that

point 0 0 8 inches and everything that's

a blue dot here these are all mixtures

with small bubbles and everything it's a

filled dot that means it passed the

freeze-thaw test these open dots that

means they failed the freeze-thaw test

all those are small bubbles now if we

look at mixture the large bubbles which

happen all the time look there's an

offset a clear offset and look at these

two bubbles here look at these two data

points right here

they're open they have 7% air these two

data points would pass every

specification in the world when it comes

to freestyle durability and they're

failing the freeze-thaw test put simply

what Paul clicker did was awesome it

worked great for his time but kleeger

his mixes they were old they're from the

1950s they were when Dwight D Eisenhower

was president in the United States and

the specifications that we use today are

still based on Paul Klee Agurs research

they were great in the 1950s but our

concrete's

are totally different today so we need

to know the size of our bubbles in our

concrete and although we can run a hard

neighborhood analysis it's just not

practical to run it regularly it's in

future videos I might talk about some

new tools that can help us with this

thanks everybody for watching leave me a

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take care bye