Why do we NEED air bubbles in concrete? | air entrained concrete
Summary
TLDRIn 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concrete specifications, which were established by Paul Kleeger in the 1950s, and argues that these standards may be outdated given the advancements in concrete mixtures.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- ⚠️ Current specifications for air-entrained concrete may be flawed and outdated, emphasizing the need for updated standards that consider bubble size.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
🏗️ 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.
🔍 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.
Mindmap
Keywords
💡Air Bubbles
💡Concrete Durability
💡Freeze/Thaw Durability
💡Air Entrainment
💡Spacing Factor
💡ASTM C 457
💡Air Content
💡Paul Kleeger
💡Aggregate Size
💡Admixtures
💡Durability Factor
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
thumbs up subscribe to my channel if you
haven't yet and leave me a comment below
take care bye
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