cc >> Tom Zinnen: Welcome,
everybody, to Wednesday Nite at the Lab.
I'm Tom Zinnen, and I work here at the University of
Wisconsin-Madison Biotechnology Center and for the UW Extension
Cooperative Extension. And on behalf of our partners
at the Wisconsin Alumni Association and Wisconsin Public
Television, welcome again to Wednesday Nite at the Lab.
We do this every Wednesday night, 50 times a year.
This is a very special night because this is the
start of our sixth year, and I'm pretty pleased that
we've been able to flourish this long, and I'm looking
forward to doing this for many more years to come.
The talk for tonight is appropriate, I think, because it
talks about the durability of a material, the endurance of an
idea, and the foresight to launch an exploration into the
future. Tonight's speaker
is Steve Cramer. He's an Associate Dean for
Academic Affairs at the College of Engineering.
And he leads the undergraduate and graduate programs in related
activities there. As a researcher, Cramer studies
structural engineering with primary expertise in the
mechanical behavior of wood and wood-based materials, the design
and analysis of wood structures, and the performance of concrete
construction materials. He's a member of the UW Madison
Teaching Academy. In 2002, he earned the
Chancellor's Distinguished Teaching Award.
He received his bachelor's in civil and environmental
engineering from UW Madison in 1979, and then he headed to
Colorado state for his masters and his PhD.
He joined the College of Engineering faculty in 1984.
And you can see the title of his talk is going to be the
Centennial Study of Concrete. And, again, I'm very pleased
that he is going to do it tonight because I think it's an
appropriate set of themes for all of us.
They're celebrating a hundred years; we're celebrating
starting our sixth year. I'd like to welcome you to the
lectern. [APPLAUSE]
Steve Cramer: Thank you. So with all of the things going
on in the world and all of the things going on in the state,
you're here to learn about concrete tonight.
[LAUGHTER] That is absolutely wonderful.
I don't think I could ever have such a great audience.
We want to know what's going on in Walker's head.
[LAUGHTER] >> Well, now, we're going to
take a break from the politics tonight, and we're going to talk
about concrete. The other folks in my team are
Jess Silva, a PhD candidate in the material science program.
And Jess is actually in the audience towards the back, and
when I get into trouble she's going to bail me out.
And then Jake Effinger is a master's candidate in civil and
environmental engineering, and he was active in this project as
well. I want to acknowledge
Jim Schmitt, the president of Schmitt Technical Services.
He helped us do the petrographic analysis.
Ruipeng Li is a graduate assistant working with me, as
is Ramsey Kropp. Bill Lang works in our
structures and materials lab. He helped with the tests.
And I could go on for quite a while if I acknowledged everyone
who worked on this project over the past 100 years.
You'll see some of the names later, so I won't list them.
But certainly this isn't a study that we began, it's a study that
we're completing. Now, there's some preliminaries
here before we get started. I'd like to pass out my cement
grains. My cement grains are atomic fire
balls. If you like an atomic fire ball,
please take one. If you don't, that's fine.
You can still get the gist of what I'm going to talk about
today without taking one. But I have mine up here, and at
a certain point in my talk I'm going to ask you to plop that
into your mouth. But not now.
So I'm going to pass this out and get this going and please
help yourself. And at the appropriate time I'll
say go, and if you'd like to take one.
Now an atomic fire ball, if you've never had one, generates
a little bit of heat. It's kind of a red hot cinnamon
candy. So if you're not up for that
tonight, that's all right. And don't open them yet.
Now I'm watching. [LAUGHTER]
No one eats them yet. >> What does the word atomic
have reference to? >> Well, that will become
apparent when you put it into your mouth.
[LAUGHTER] It kind of explodes.
And it will create a hot tingly sensation.
And are you going to put it in your mouth?
I am. I am.
At the appropriate time. We're not there yet.
Now, one of the beauties of Portland cement concrete is it
can be formed to really any shaped desired.
And that's why it's the most widely used construction
material in the world, but at times the general public doesn't
really understand this concept very well.
[LAUGHTER] They think it's hard.
They think it's durable. They think it lasts forever.
And by the time you leave here, in a short while, I think you'll
find that it's a much more delicate material and complex
material than probably what you imagined.
So cement is any material that acts to bind other materials
together. I have to give you some of the
basics here first before we get into the meat of the research.
We generally refer to mortar as Portland cement plus water plus
fine aggregates plus, in this day and age, add mixtures.
They didn't have add mixtures in 1910.
And cement paste we'll think of as Portland cement plus water.
So what do you see here? What do you see?
[INAUDIBLE] Okay.
I'll be giving you a quiz throughout this presentation.
There's a couple things you should see here.
Many would refer to this as oh, look at they're doing a cement
project. They're making a cement road.
No. No, this is a concrete project.
They're making a concrete road. The distinction is important
when it comes to engineering. The second part of this is you
might think to yourself: this will be ready to drive on when
it dries. No.
Concrete does not dry, it hardens by hydration.
And we're going to get into some of the hydration aspects today.
Now, these lessons here are basic.
My children had the distinct pleasure of knowing this by the
time they were five. [LAUGHTER]
It's just the way it is when your dad's an engineer and a
faculty member. You'll often see these referred
to as cement trucks. They're not cement trucks.
They're concrete ready-mix trucks.
They're moving along and mixing the cement with other
constituents down the road to a job site.
Perhaps the most common mischaracterization is this is a
cement sidewalk. No, it's not.
It's a concrete sidewalk. And it's a chemistry experiment.
Really, all of these pictures that I've been showing you
there's a vast amount of chemistry going on in the truck,
on the highway, on the sidewalk. It's all chemistry.
And if we could perfect the chemistry, probably concrete
would last even longer than it does now.
So this is a cement truck, and there's one at a job site.
And, of course, cement is the powdery material that's added
with water, fine aggregates, coarse aggregates, and add
mixtures. What else do you see there?
[INAUDIBLE] Fruit cake.
Cement is to concrete as flour is to fruit cake.
So getting the terminology right is an important aspect here of
talking about concrete. Now, Portland cement is a
hydraulic cement, and that means it's going to harden due to the
chemical reaction to water. Tends not to degrade when
exposed to water. In fact, many projects are done
where you pour the concrete directly into water, and it will
harden under those conditions and function just fine.
If we look at what Portland cement actually consists of, it
consists of tricalcium silicate, which in cement chemist's
language we call C3S, and that's the largest portion of Portland
cement today. It will have dicalcium silicate,
which we call C2S, and around 19%-20% of Portland cement will
be that compound. It will have tricalcium
aluminate, C3A, relatively small amount.
And tetracalcium aluminoferrite, an even smaller amount.
And you can see the depiction there of some of these compounds
that would be in a cement grain. And cement grain, of course, is
much smaller than my model that I've given to you.
What's the significance of the word Portland?
We will come to that. That will come shortly.
So, we don't have time tonight to go into exactly how Portland
cement is manufactured. Raw materials include calcium
carbonates. Those could be limestones, those
could be seashells. They could be a variety of
different kind of calcium type materials: silica, alumina, iron
oxide. And we find that the C3S
hydrates and hardens most rapidly.
And that's responsible for the initial set of the concrete and
the early strength of the concrete.
C2S hydrates and hardens a bit more slowly and that tends to be
more of a contributor to strength after seven days.
C3A has a high heat release in its early age.
Really doesn't do much to the structural performance of
concrete but it's necessary for the manufacturing, and similarly
with the C4AF, it's really more of a manufacturing issue.
Now there are some other compounds as well.
They're in rather small quantities, but they can have a
significant impact on the outcome of the concrete product.
Okay, so the time has come. If I can get the package open.
There we go. So we're going to talk about the
exothermic reaction here, and you have the model, the atomic
fire ball is my model of the cement grain.
And probably the only moisture you have available is in your
mouth. So that's where your cement
particle is going to go. And we're going to see that the
C3S plus the water produces this chemical compound plus this
compound, and that's notation for calcium silicate hydrate and
calcium hydroxide. Similarly but slower,
(coughs), excuse me. [LAUGHTER]
The C2S plus water is going to produce calcium silicate hydrate
and calcium hydroxide. Now, it's very important you pay
attention as well not only to the screen but what's happening
in your mouth. Keep track of the timing of what
happens. Now the calcium silicate hydrate
is not a well-defined compound, so we can't chemically control
this in a very precise way. The stoichiometry is going to
vary depending on the temperature of hydration, the
ratio of water to cement and so forth.
But it does make up a large percentage of cement paste,
which, of course, is cement plus water.
Now here's what's going on in my mouth, if not yours, we plopped
this in our mouth a couple of minutes ago and there was a nice
little sweet taste right off the bat.
Kind of enjoyable. And then for a few minutes
while I was talking, not much happened.
We were in this stage two, which is sometimes called the
induction period. Right about now, for me, I am
in this acceleration phase. [LAUGHTER]
I am too. >> Yeah, and it's really going
to take off. >> We need water.
Yeah, and it's going to generate quite a bit of heat.
This would typically with concrete occur in
the two and a half hour to three and a half hour timeframe.
We don't have that kind of time here.
So the model works a little bit faster than that.
And if you bear with us here a little bit longer, this will
subside. I don't think I've reached the
peak yet, personally. And then it will have this long
kind of deceleration, if you might, or period where it's not
generating so much heat. And it will just kind of
peter out. And what's happening is it's
creating calcium silicate hydrate around the particle as
we get down in here. And the hydration process is
going to continue, but it's going to become diffusion
controlled. It's going to be the ability of
water to penetrate the hydration products that are forming around
the cement grain which is going to control how fast it gains
strength. Back in here, it's just the
availability of water. The water is getting to that
cement grain and that cement grain is exploding with crystal
growth. I think I got the larger ones
this time which means that they last a lot longer.
[LAUGHTER] >> How can you talk with it
in your mouth? [LAUGHTER]
Well, we're not through yet. We'll see how long I go.
Practice. You've done this before.
I've done this before. Sometimes I'm not very
successful in keeping the lecture going while I'm talking,
but that's usually to the delight of my audience.
Do you have water? >> Nope.
So here we see these different phases illustrated pictorially.
The large red pieces here represent the C3S in a concrete
matrix, or a cement paste matrix maybe more appropriately.
The C2S is the light blue parts like right in there.
The C3A is the bright green. And the C4AF, which I don't,
oh, yeah there's some right up in here, is the orange.
And then as it progresses through these different stages,
it's going to produce calcium hydroxide, which is dark blue,
and the calcium silicate hydrate, which is the yellow.
So you can see that the C3S shrinks and instead we get these
hydration products forming. And that's what going to give us
our strength to the concrete. So really the only reason that
we put stone in it is so that we don't have to use so much cement
because the cement is expensive. Now, our primary measure of
quality is the compressive strength.
And compressive strength is measured by creating the
samples, which these gentlemen here are forming, and typically
that's sample is a six by 12-inch cylinder.
And there's a very appropriate way to make these and you take
them back to the laboratory and you push on them and you crush
them and that's just universally across the world the primary
measure of concrete quality. Now what controls the
compressive strength is the water/cement ratio.
And that was discovered in 1918. I'm going to talk about the
history of Portland cement a little bit more.
It was discovered, at least in its most relatively modern form,
in 1845. So for about 50 some years, 60,
70 years, they really didn't understand quite how it worked.
And in 1918, Ben Abrams discovered that water, the
amount of water to the amount of cement was very, very important.
Now we only need about .22 to a quarter pound of water
to hydrate all the cement. For one pound of cement you only
need about a quarter pound of water.
So what you'll find, though, is they always add much more than
that. And the reason they add much
more than that is to gain workability.
To finish it off, to make it look smooth, to be able to move
it into position, they add more water.
So that, in essence, it almost flows into place.
So that would be fine, but once you have more water than you
need, it works against you. It creates a void system where
the water displaces the solid cement material and, thus, you
have a more porous, more void-filled solid than you'd
have if you add less water. And if only a quarter pound of
water is needed to hydrate the cement, then where's the other
water go? Well it dries out eventually, it
migrates, and behind it will leave voids.
And those voids are doorways for bad things to happen to the
concrete. Chemicals can get in and
destabilize the matrix that has been created, and you see this
every day when you see concrete spalling or breaking down out in
the real world. So concrete lasts forever,
right? Wrong.
The processes of degradation could be physical or mechanical,
abrasion, expansion and contraction.
You hear about in the summer, these blowups on the highway
that occur as the concrete expands.
Freeze/thaw attacks, a big deal in Wisconsin.
Water gets in, it freezes, it expands, creates expansive
pressures. Chemical attacks too.
This is a chemistry experiment. You have acids that can break
down the concrete. You have salts, you have
sulfates, and you have just simple carbon dioxide that's in
the atmosphere can cause carbonation and break down the
concrete. So these are the enemies of
concrete. If you drive your car into the
garage, salt comes off your car, you're starting to see your
concrete garage floor start to spall, the thing you could do
during the summer is get a good sealer on that so that salt
can't penetrate and affect the chemistry.
So it's time for some history now.
As I mentioned, 1845 was really the discovery of Portland cement
concrete. And it was called Portland
cement because it looked very similar to a popular building
stone quarried in Portland, England.
So there's your answer to your question.
It's been produced in the United States since 1871.
And today we use five to six sacks, a sack is 94 pounds, per
person per year in the United States.
Now it's time, you kind of have gotten the basics, I've given
you a little bit of the chemistry, it's time to think
about the history here as it relates to the University of
Wisconsin and the state. The study began with
Morton O. Withey, and in 1905 he became a faculty member
in the College of Engineering. I don't think it was even called
the College of Engineering at that time.
And what's interesting is in 1910 he didn't launch
a hundred-year concrete study, he launched a 10-year concrete
study. He made a whole slough of
specimens for testing with the idea that after about 10 years
the study would wrap up. Okay?
He won a number of awards, and this may become apparent why in
just a second. He won the Wason Medal, the
Turner Medal, 1932, 1947, respectively, from the American
Concrete Institute which was formed in 1904.
He then served as the ACI president in 1943.
And in 1946, he became the dean of the College of Engineering.
He retired in 1953. He's the gentleman on the left
in the picture. And in 1961, he describes how
the 1910 study had been expanded to a 50-year study.
So, you know, I like to talk about the extraordinary vision
that he had for a hundred-year study, but quite honestly it
wasn't planned to be a hundred-year study in the
beginning. But he did make enough specimens
such that it could become a hundred-year study and we have
to give him credit for that foresight.
Now, what's going on at the same time in the United States?
In 1902, Thomas Edison introduced the first large scale
cement kiln. So prior to 1902, while it was
being produced in the United States since 1871, it wasn't
really being used in a broad scale.
There just wasn't a ready means to produce it in those
quantities. Two years later the Wisconsin
Idea is established and the American Concrete Institute is
founded. In 1909, horse-drawn
concrete mixers appear. So you think about the ready mix
truck that I showed you earlier in the slide, now we have a
horse-drawn mixer starting to appear.
What did the mixing? >> The wheel power, as I
understand it. So they pulled, the horses
pulled the mixer along, obviously on a much smaller
scale than the trucks I showed earlier, and the wheels as they
turned had some sort of paddle or so forth to mix the concrete.
Cement demand in 1910 when the study began is 20 kilograms
per capita worldwide. Now, we're going to look at this
statistic through time. Remember the population of the
world is growing at the same time.
So in 1916 we begin to pave streets with concrete.
And we're probably still using horse-drawn concrete mixers and
very manual methods. And that's a big undertaking
because a concrete street or road takes a heck of a lot of
concrete. If any of you have ever done
your own sidewalk, it's a lot of work.
And then in 1916, the Portland Cement Association is founded.
The Portland Cement Association is an association of cement
producers. So the cement producing
infrastructure or industry of the United States had now grown
to where they can organize. So eventually Morton Withey
passes the study on to Kurt F. Wendt.
Kurt F. Wendt might be a familiar name to you because
the engineering library is the Kurt F. Wendt Library.
The picture shows him standing in front of the library.
In 1910 when the project started, he was four years old
at the time. Hardly could he imagine at that
age where his career might go and how he might fit into this
study. In 1936, he joins the UW.
In 1941, he joins the one hundred-year concrete
project, as I call it. In 1953, he's appointed dean of
the College of Engineering. In 1963, he's elected president
of the American Society of Engineering Education and '71 he
retires. What's going on in the world at
that time? In 1930, air entraining concrete
is discovered which greatly enhances the freeze/thaw
durability. So I won't go into all of the
details, but they learned that if you purposely put small
bubbles into a concrete mix, it acted like a pressure reservoir
for the expanding ice that would get into the concrete.
And the durability was greatly enhanced.
It was discovered completely by accident, by the way.
I'd like to be able to say a purposeful research project
discovered it, but it was really an accidental discovery based on
a contaminated mixer mixing in a material that generated bubbles
unintentionally in the concrete mix.
And to everyone's amazement, the concrete lasted a very long time
in freeze/thaw. In 1936 the Hoover and
Grand Coulee dams were generated.
And as those dams were built controlling the heat, now
I'm in the deacceleration phase, I don't know about you.
It's getting a lot better. [INAUDIBLE]
Yep, there you go. So the Hoover and Grand Coulee
dams were built, and these large dams controlling that heat that
you experienced a few minutes ago was one of the design
challenges that they faced. Also in the 1930s and later,
changes were made to the cement grinding to make it finer and
with a higher C3S content. And now by this time in 1940
cement demand is six times per capita in the world compared to
what it was simply 30 years ago at 180 kilograms per person.
So the study was eventually passed to George Washa.
In 1910, he was one year old as the project commenced.
In 1930, he joined the college as an instructor while in
graduate school. If you're keeping track of these
time frames he's almost a contemporary of Kurt F Wendt.
In 1941, he joins the hundred year concrete project.
Receives a number of awards from the American Concrete Institute.
In 1942, joins the college as an assistant professor.
Along in there he becomes the chair of the Department of
Engineering Mechanics. And in 1978, he retired.
And then I come along. In 1961, I was four years old.
And that was when the 50-year results were published.
I came to the College of Engineering as an undergraduate
in 1975, and lo and behold in 1977 I have a class with George
Washa where he teaches me concrete mix design.
I go off to graduate school and to go on to have my career, and
somewhat by chance, maybe by chance, maybe not, in 1984 I
come back to Madison and I join the faculty in the College of
Engineering. In 1987, George Washa and
another professor by the name of Jeff Seaman come to me and say,
why don't you work with us, we're going to test some
long-term concrete. And thus I become involved.
In 2003 cement demand is now 320 kilograms per capita,
worldwide. So, again, you need to think not
only about this demand of cement that's increasing but the
population of the world is increasing too.
And then in 2006 I joined the Dean's Office in academic
affairs. And that's a picture of yours
truly and Jim Ottlane, who was a technician in the college,
setting up to do one of the 50-year tests in 1987.
Right, that's me just yesterday. No, not quite.
[LAUGHTER] So now let's talk a little bit
about the hundred-year test program specifically.
There were three series that were developed over the years.
In 1910, series A was made. The test concluded as we
conducted them here in 2010. There's also a 1923 series B,
and we still have cylinders to do that and those tests will
conclude in 2023. Let's see, that's 11 more years,
I don't know if that's me or not.
1937 was series C. Those were just 50-year tests.
And those tests concluded in 1987, and that's what I alluded
to a minute ago. The tests have included, in our
most recent go around, petrographic examination, cement
chemistry, compressive tensile strength.
There was in some earlier work looking at the expansion and
shrinkage of concrete and freeze/thaw durability.
The series A tests broke into two kinds of specimens.
Those that were submerged in water.
So there was these specimens sitting in water for essentially
a hundred years. And then there were some
specimens "in the cellar." "In the cellar" is in the
basement of Engineering Hall. Now, there were probably other
locations of that cellar over time but they were in the
basement. Now, the reason I call it "in
the cellar" rather than just out in air is I know that basement
in Engineering Hall gets pretty damp in the summertime.
So there's probably a higher humidity and higher moisture in
that environment than you might see just outside.
There were two water/cement ratios, .63 and .90.
Those are high by today's standards.
We're doing some concrete experiments for the Wisconsin
Department of Transportation. We typically work with a water
to cement ratio of .4, .42, somewhere in there.
If we look at the cement chemistry, and they measured
this at the time they made the specimens, the C3S, the alite
remember that generates that early strength.
That was about 29% in 1910. It was Atlas Cement.
Medusa Cement from 1937 had 53%. And then if you look at a modern
cement, it's like 60%. So remember I mentioned that in
the '30s on, they started to make the cement finer and put
more C3S in it. And indeed we see that here.
And, conversely, the C2S, and an impure form of that would be
belite, had 44%, and you can see now it's decreased down to 12%.
Also, as I indicated, the fineness has changed.
In 1910 that cement only about 60% of it passed the number
325 sieve. The number 325 sieve has a
.045-millimeter screen opening. So that's pretty small.
And then you can see that today that number has increased to
pretty much 95%. Almost all of the cement will go
through a 325 sieve. Jess did the petrographic
analysis. She took thin sections for
optical mineralogy. She looked at polished surfaces
to look at the structure, and she looked at fractured
surfaces. And, you know, some of the
general findings she had was that the wet stored concrete
was harder and less fragile than the concrete
that was "in the cellar." And the overall matrix
contained a lot more binder than concretes today.
I had mentioned earlier that CO2, just the CO2 in the
atmosphere can chemically degrade concrete, and the way
that that works is the CO2 on the surface will attack the
calcium hydroxide first, combining with the CO2, and it
will generate calcium carbonate plus water.
And you all know calcium carbonate is pretty chalky,
pretty crumbly, there's not much strength to that structure.
So that's not a good thing. Once the CO2 consumes the
calcium hydroxide and if it's still continuing to penetrate
into the concrete, next it will attack the calcium silicate
hydrate. So that, again, will create
calcium carbonate, and of course this is the main strength
component of the concrete, so as that calcium silicate hydrate
gets degraded and is replaced by calcium carbonate, you see a
degrade then in the strength. She found that there were poorly
graded materials. There wasn't much size diversity
in the sand. You have to remember concrete's
a brand new material in 1910 when they made these.
So many of the rules and refinements that exist today,
they didn't know then. That's part of why they were
doing the experiment. They wanted to learn more about
how these properties changed in near term and in long term.
This specimen, C340, C stands for cellar, that's why the using
the term, was completely carbonated to the point that
carbonation products were replacing the concrete products.
In the water-cured specimens, the cement particles in general
were very large, some unhydrated cement compounds.
Very interesting. After a hundred years she's
still finding some unhydrated cement compounds in the
concrete. One would think at some point
that process would end. But the particles are larger
than they are today so it takes a little bit longer to react.
She found in the alite and belite there were hydration
rings, and some of those were even visible with a stereo
microscope. So, again, the C stands for
cellar and the W stands for water.
And different observations could be made here, but based on these
observations she could see that those in the cellar were going
to be weaker than those cured in the water.
And as I mentioned, there's two water/cement ratios occurring
here as well, .63 and .9, and from the microstructure she
could see that the ones with a higher water/cement ratio are
going to be more porous and the CO2 is going to be able to
penetrate them more easily and the carbonation is going to
occur. There's not as much CSH, calcium
silicate hydrate, there to begin with.
So she also did some scanning electron microscope analysis.
She found a very well-bonded matrix in some cases, but then
there'd be these little dolomite particles in others kind of
indicating that there was an excessive amount of fine
particles in some of the aggregates that were used.
And you can see cracking that's occurring here because that
aggregate's not as clean and hard as we'd like it to be.
And as she went into some of the voids, the ettringite was
present. Ettringite is a secondary
hydration product that can occur.
And actually if there's, ettringite will only form when
there's water and moisture present.
So if you're out and there's water getting in your concrete,
likely some ettringite is forming.
And if it fills all the voids, it will begin to expand and
break your concrete up. Cement with a reaction ring.
A large belite particle. So there's unhydrated cement
that she's finding in here. And there's some ettringite.
The ettringite is going to attract water.
It can actually form a gel which becomes expansive.
You can see a crack forming there.
Here's some calcium hydroxide particles surrounding
aggregates. Calcium hydroxide tends to fill
in some of the nooks and crannies that the calcium
silicate hydrate doesn't form in.
And calcium hydroxide is fine, there's nothing wrong it, it's
strong, but it's less stable. There are more things that can
attack it and break it down. So, no surprise, as she looked
at carbonation depth in the wet curing, she found carbonation
only on the surface only. But when she went to the dry
curing specimens, it was carbonated all the way through.
This is what a compressive test looked like.
And I had indicated earlier that typically compressive specimens
are six inches in diameter by 12 inches long.
Back in 1910 they were six by 18, so they tended to be a
little bit longer. They tended to be very, very
chalky. As you broke them apart there
was just this dust coming out. And, of course, that was the
calcium carbonate forming based on the carbonation.
Okay, finally we get to some results here.
And here we have age on a log scale on the bottom
and compressive strength on the Y axis here.
And here's their first test after about a month.
And the specimen that's been moist-cured after about a month
is just slightly stronger than the specimen that's been put in
the cellar. And that's not surprising
because there's plenty of water in the concrete at that time.
As long as it's not dramatically dried out, there's enough water
there for both specimens to proceed and gain strength.
And they do that all during pretty much that first year.
And then something happens in here.
This is in 1911. I don't know what happened
there, but you can see that the strength actually went down and
then it starts to come back up. What's really interesting is the
water-cured and the cellar-cured specimens tend to kind of
parallel each other. So whatever was going on was
happening to both. Then we get into this period of
one to 10 years. We're seeing some strength gain.
The cellar ones have kind of flattened out.
And then very interesting at the 10-year mark things take off
again, and they're actually parallel to each other but now
the distance is starting to come apart.
And then we see that the cellar ones have dropped off in
strength after a hundred years, and, no surprise, they're
completely carbonated. The CO2 has now, after a hundred
years, taken its toll. This concrete is in decline.
Kind of the opposite situation is occurring in the water.
Of course, they're submerged. So CO2 is not really getting to
them, and even after, from 50 to 100 years, and it's may be not
obvious here in the log scale, but it's still going up in
strength. It's still hydrating, it's still
gaining strength. That's really pretty amazing.
The material is continuing to develop even after a hundred
years. This is the water/cement ratio
of .63. We see a similar result with the
water/cement ratio of .9. But, of course, the strengths
are lower. And they're lower again because
there's less calcium silicate hydrate there, there's more
water voids existing. And, again, we see the same
trend at a hundred years, between 50 and a hundred, we can
now see that the compressive strength is in decline due to
carbonation and yet it's slight, and perhaps barely perceptible
here, but at a hundred years, from 50 to a hundred years we're
still gaining strength in the submerged specimens.
Just looking quickly at some specimens that were made in the
C series, 1987, the 1937 series. First of all, they had a lower
water/cement ratio. So they start out at a higher
strength. These were actually left
outside, not in a cellar, not in water, but outside.
You can see that they peaked out at 10 years, and then just kind
of flatten out after that. Part of that, again, is perhaps
the fineness of the cement. They shot up in strength much
more quickly, and then they didn't have as much C2S or
belite to carry it on longer and longer.
And at some point this was a much finer cement.
The reaction perhaps ceased completely.
So to summarize, concrete's an amazing material.
Truly an amazing material. I hope as you walk out of here
today when you look at, not the cement sidewalk, the concrete
sidewalk, you'll see it in a new way.
Because of its longevity, studying it and testing it
is always a challenge. But what's really unique in this
case is it not only traces the history of what was this new
material at the time in the United States, it actually
traces some of the history of the University of Wisconsin
Madison. Even after a hundred years,
the concrete continues to gain strength, but what you can see
is that when we take it out of the water and put it out in the
air, CO2, simple old CO2, tends to take its toll and essentially
render it structureless or with no structure or strength.
Thank you. [APPLAUSE]