Built Environment Materials

Concrete is the most widely used construction material in the world. Sabbie Miller, an Associate Professor at the University of California, Davis, discusses the built environment and optimizing infrastructure materials.

Episode Transcript

(00:03):
This is the Discovery Files podcastfrom the U.S.
National Science Foundation.
Concrete
is the most widely used constructionmaterial in the world.
It is the backbone of what is calledthe built environment.
A crucial ingredient for housingand infrastructure development.
Advances in materials scienceand processing can enhance the long term
durability of many building materials,including concrete,

(00:26):
enabling significant economic and societalbenefits.
We're joined by Sabbie Miller,an associate professor in the Department
of Civil and Environmental Engineeringat the University of California, Davis,
whose research is dedicatedto advancing the built environment
through the development and optimizationof infrastructure materials.
Professor Miller,thank you for joining us today.
Thank you so much for having me.

(00:46):
So I want to start with kind of definingone of the terms
that’s kind of key to whatwe're going to be talking about today.
What is the built environment?
So folks do use the built environmentin a couple of different ways.
But typically what they're referring tois basically all of our buildings.
So houses apartment buildings,hospitals, school buildings, offices,

(01:07):
as well as all of our infrastructuresystems and roadways.
So sewers and highwaysand all of those things together
are the environment that we as humansare building for ourselves.
And so it's oftenreferred to as a built environment.
The most common material is concrete.
So we're going to be talkingabout a lot of concrete today.
I want to startwith the manufacturing process.

(01:27):
What are kind of the problemswith manufacturing currently?
So there's a couple of thingsto think about with concrete.
Yes, it is our most consumed buildingmaterial worldwide.
It's actually a composite material.
So it's made out of cement, water
and crushed rocks,which we refer to as aggregates.
So sometimes cement and concreteare used as synonyms.

(01:48):
But in reality, cement is this powderthat reacts with water and holds together
rocks to make the synthetic rockthat we refer to as concrete.
And some of the manufacturing challenges
associated with the production of concreteare actually tied to that cement.
So when we're worried about thingslike the environmental burdens
for concrete,it's a function of a couple of things.

(02:08):
One, we use a heckof a lot of this material.
So whenever you use a lot of something,it's impact scale accordingly.
The other side of thatbeing that the production of cement
requires the utilization of limestone,that's our main ingredient
in the production of cement.There are other ingredients as well.
But that limestone,
to create that reactive compoundthat could interact with water,
we actually have to carbonate it.

(02:29):
We actually have to break off effectivelycarbon dioxide from that limestone.
And that leads to a direct emissionsfrom a chemical conversion.
And then on top of that,to get the reactions to take place,
we require thermal energy.
So then we also have energy derivedemissions tied to the production
of cement.
So when we're talkabout the impacts of concrete,

(02:50):
oftentimes the impacts are thingstied to cement that we're worried about.
We hear about a lot of buildingswhen they get torn down
going straight to the landfill.
Can we crush them and reuse them?
As an aggregate,let's say in any new concrete?
Or is there issues with that carbon cycleand the bits of the cement that you just
explained chemically that make itso we can't really do that?

(03:10):
It's a yes and no response to that.
We can crush our concreteand get some benefits out of that product.
One of the benefits,
actually, is that we really increasethe surface area to volume ratio.
And if we have proper exposureto atmospheric CO2,
the hydrated cement in that concreteactually has a chance to interact
with the CO2 that's in our atmosphereand pull a wee bit back out.

(03:31):
The other thing, though,
that we end up seeing from our crushedconcrete is exactly as you mentioned.
It's made out of hydrated cementand aggregates,
which means it's not the same performanceas the aggregates alone.
It's now got this like caked on
hydrated cement stuck on the materialso it doesn't have the same performance
as our normal aggregates that we wouldnormally crush and use in our concrete.

(03:54):
As a result of that,
it doesn't always necessarily performthe way we want it to in a new concrete,
but we are able to use it for surein certain applications.
So for example, in California,where I am, I know that our Department
of Transportation actually uses theconcrete from the roadways that we have,
crushes it up, and uses a road basefor the new roadway
that they're about to put in,

(04:14):
because it has greatperformance characteristics for that.
So we can use it in some ways,but not all ways.
So thinking about potentially reusing itfor structural purposes,
it might have a weakerfracture value or something.
Yeah.
The paste itself can have certainperformance characteristics
associated with it.
The cement
that's interacted with the waterand created this kind of binder material,
the aggregate is goingto have certain performance.

(04:35):
And then there's what's referred toas the interfacial transition zone.
This region where the cementis actually bound onto the aggregates
that has its own micro structureassociated with it.
So yes,
we end up with potentially differentfracture performance associated with that.
Other types of durabilityissues can also be tied to having
this effectively, like a three phasematerial as opposed to just the aggregate.

(04:56):
So yeah,there's a couple of different issues
that could happen that might hinderuse in certain applications.
So the paper that kind ofbrought your work to my attention
is looking at using buildingmaterials for carbon storage.
So how might that be possible?
There's many different ways.
So many of our buildingmaterials are already carbon based right.
They're already using carbon.

(05:17):
It's not necessarily carbonthat we've pulled out of the atmosphere,
but it is carbon.
So part of what could happenis if we're able to re-engineer
those materialssuch that the carbon that's in
the material is coming from a direct aircapture system, or we're basically pulling
atmospheric CO2, concentrating itand then using it in those materials.
Then we could potentially store them

(05:38):
for a really long timein the built environment.
The other way we could dothat is capturing flue gas.
So carbon capture, actually trying to capture the CO2
as it's coming out of industrialprocesses, energy generation processes,
and then again, concentrating it,using it in our built environment
as the carbon sourceand potentially even having the materials

(05:59):
themselves directly capture carbondioxide from the atmosphere.
This happens a little bit morewith our biogenic materials, materials
that are living organisms,like our photosynthetic materials.
So if they're able to already interactwith the atmosphere
through photosynthesis,they can pull in carbon.
And then we could use that materialas something in the built environment.
So there's a couple of different ways toget that carbon stored in our materials.

(06:22):
But it depends on the materialthat you're talking about.
I know part of the studyyou were looking at the effectiveness
of different kinds of blocks likeconcrete, brick, asphalt, plastics, woods.
Can you talk a little bit about theeffectiveness of these different forms?
Yes. So depending on the amount of carbonthat you could put in any material,
you're going to have a certain degreeof potential effectiveness

(06:44):
based on the carbon content. Right.
So this is a very high level of carbonfor this material.
So in theory we could store more carbonin this material on a weight basis.
The other thing though that we foundwas a much larger driver than that
component was how much of this materialdo you plan on using?
So even if you're getting lesscarbon stored in the material,
but you could scale itto an enormous quantity, like concrete,

(07:08):
then potentially you have this huge bodythat could store carbon dioxide
as long as you're gettingdesired performance out of the material.
So if the material has any lossin strength or the ability to place it
during construction, or if it failsearlier than our conventional material,
then you could end upnot seeing these benefits.

(07:28):
So the performance of the materialis always priority.
The idea, though, is thatif we're able to get equivalent
or better performanceout of these materials and store
atmospheric CO2 in them,we could have this really net benefit
of leveraging this huge mass of materialsthat is available to us.
One of those materials that I was curiousto ask you about is bioplastics,

(07:49):
because we hear about plasticand think about it
being likemore of a manufactured toxic thing.
What is a bioplastic?
So bioplastics are plasticswhere the carbon and the long
chain molecule that makes upour plastics is coming from a bio resource
as opposed to a petroleum based resource.
So the vast majority of our plasticsthat we interact with are coming from
petroleum based resources.That's where their carbon is coming from.

(08:11):
But instead, if we're able to use thingslike food waste, not priority food,
not food that we would otherwise eat, but waste that we would have otherwise
disposed of, or residues from, differentagricultural or forestry practices.
So a biomass that we otherwiseneed to get rid of isn't
going to be a priority for something elsein terms of its utilization.
If we could use thoseas the source of carbon,

(08:34):
then we could potentially reduceour dependency on petroleum
and leverage a bio resourcethat has pulled CO2 out of the atmosphere.
We might have access to ita little bit more
locally because of the abilityto use different types of bio resources.
So there's a
couple of different strategiesthat one could use, basically leveraging
that source of carbon to replace

(08:56):
our more petroleum based carbonsand those materials.
Would this be like,
say in the corn industry,like the husks or something that probably
you don't have a lot of use otherwisebut could potentially be used in this way?
Exactly.
So it's not the kernels that we wouldotherwise want to eat.
But yes, the husks, straw leaves,all of those sorts of things
that would otherwise be cultivatedbut not necessarily have as much value.

(09:19):
Now, I will note that we don't wantto take all of that off of the farmland,
because farmers actually do need some ofthose nutrients to go back into the soil.
But if it is already being removed,
then that type of biomass can be reallyvaluable for products like bioplastics.
Interesting.
One of the other things I wanted to ask
you about was geo polymers and their usein kind of alternate cements.
Can you talk a little bit about whatthese things are?

(09:40):
Yeah.
So there's a class of alternate cementsthat are referred to as alkali
activated materials.
Basically it's leveragingtwo main components a aluminum silicate
solid precursor.
So something that has a lot of aluminumand silica in an amorphous
kind of like a chaotic, crazy state,not very well
aligned in a crystalline state,along with alkali activators.

(10:02):
When those are combined appropriately,
then we can actually create somethingthat acts like a binding material,
just like our regular conventional cementwith water.
So we're basically ableto replace our normally highest CO2
component of concrete
with something that doesn't requirethe same decarbonization of limestone, nor

(10:23):
does it require that same energy demandthat our conventional cement requires.
So if we're able to replace that,
there's this idea that potentiallywe could reduce a lot of the impacts
that we would normally associatewith our cement and our concrete.
Geo polymers are a subclass of alkaliactivated materials.
So they happen to be one of the onesthat's really well studied.
But it's in that class of materialsthat have these two key components

(10:47):
associated with them.
And there's a lot of work going onright now trying to understand
where can we get those aluminumsilicate solid precursors,
where can we get those alkaline resourcessuch that they are globally available
and they themselvesdon't have high impact?
Because if we have to process them a lot,
then we could kind of counterour own benefits.
That was going to be my next question,like trying to think about that for people

(11:08):
that aren't too specificabout the chemistry there,
can you talk about something
that might be an example of whatthat ingredient would be?
So our most commonly used alkali
activators would be things like sodiumsilicates and sodium hydroxide.
We use those kind of alkali resourcesin a bunch of other applications as well.
In terms of the solid precursors,a lot of work is looking at things

(11:31):
like the utilization of coal flyash and, ground granulated
blast furnace slag, which we already usein the cement and concrete industry.
Coal fly ash is actually it'sexactly what it sounds like.
So we use coal for the generationof electricity in many parts
of the world,and the vast majority is carbon.
That's what we're trying to oxidizeto get our energy resources.

(11:52):
But there's a bit of mineral in that coal,and the minerals are going to contribute
to the formation of ashes,and some of the ashes
will settle down to the bottom,others will fly upwards.
And the ones that fly upwardsare a bit fly ash.
And those ashes actuallyhave a really desirable characteristics
associated with them.
For this kind of perspectiveof utilization of aluminum silicates,

(12:12):
they have great characteristicsfor reactivity, a nice disordered
structure, etc..
So that's one class of these typesof materials.
The blast furnace slagthat I mentioned is actually a byproduct
of the treatment of ironoxide to form iron.
So iron is our main precursorto the formation of steel.
But we use iron and other things as well.
Steelobviously has like a wee bit of carbon,

(12:34):
so we get better performanceout of that material
when we're trying to make thingslike iron.
We usually start off with somethinglike iron oxide,
and then in order to make thatiron product,
we actually have to send itthrough a furnace.
The utilization of,certain types of compounds
within the furnace, particularlya lime to purify that overall material,

(12:55):
leadsto the formation of a slag byproduct.
So we're still getting our iron,but we've also got this
byproductassociated with the general process.
It also has fantastic characteristicsthe slag does for use in things
like the productionof our alkali activator materials
or the use in concrete, because it caninteract with the hydration process.
So there's a couple of usesof these industrial byproducts

(13:16):
that can get leveraged.
There's also a bunch of other resourcesthough as well.
So a lot of our agriculture productshave a wee
bit of mineral in the biomass itself.
So again,
not the food, but those residues likethe corn husks, like rice straw, etc..
When we use those biomass products, it'spredominantly carbon again.

(13:36):
But if we tried to recover energyfrom the biomass
through something like oxidation, we couldthen take the mineral compound
that's left over as an ash formand use it as a solid precursor
for the formationof alkali activated materials.
So there's a couple of different sourcesthat we have worldwide.
And our current estimates suggestthat if we wanted to replace Portland

(13:58):
cement, Portland cementas our conventional cement
with somethinglike an alkali activator material,
about two thirds of our current demandfor cement could, in theory, be replaced.
If we're able to leverageall of these different types of residues
the industrial byproducts,the agricultural residues,
forestry residues, if we're able to reallyutilize those properly,

(14:18):
we can actually start to makea pretty notable dent in the material.
Again, assuming
that we get the right performance,we do need to engineer these things
so that we get what we needout of the materials.
So as you developthese kind of different materials,
is there kind of trouble getting industryto buy in with using byproducts
and using different kind of techniquesto get at these things?

(14:39):
They've traditionally used with limestoneand Portland cement?
Yeah.
So engineers are very focusedon performance for good reason.
We want to create products that work.
That is our main goal
and are a little bit of tweakingto make them work
even better is also one of our big goals.
That said, civil engineerstend to be on the even more risk

(14:59):
averse side than conventional engineers.
We really try to make surethat things are working properly.
The reason for that being thingslike life safety issues,
you don't want to hop on a bridge
and have it collapseor have a building collapse.
We really want to make sure our systemsare working incredibly well,
and we use a few thingsto make sure that we are reducing risk.
A lot of probabilistic modeling,trying to understand exposure conditions,

(15:21):
trying to understand how we could bestdesign these systems to reduce
likelihood of any type of failureassociated with them,
and also our historic knowledge.
I put this material in here 20 years ago.
It's still doing great.
I'm comfortable using it again.
That ends up being a really strong driver.
Also, validation from other partiesthat other person use this material.

(15:41):
It was really successful.
That means I have a higherlikelihood of it being successful.
As you can imagine, incredibly valuable.
We don't want to remove this ideaof minimizing risk.
We want to make sure that safetyand performance are number one always.
But if you come upwith a brand new material
that there's a little bit of a version ofusing it, because this kind of knowledge

(16:02):
of how it's going to perform and comfortassociated with its use
isn't necessarily there.
So we end up seeing that civil engineersare a little bit less likely to rapidly
adopt novel materials, because we needthose materials to perform well.
So that we make safe structures,and we need them to perform
well for a long time.
They have to keep going for decades

(16:22):
because there's a lot of work
going on right now trying to understandhow we improve adoption
of alternative materials,how do we make sure
that we have the proper validationso that we're removing that risk
from the practicing engineer?
They should not be the onewho has to take that on.
Do we changeour overall insurance structure
so that there's more comforttrying to use some of these materials?
Should we changehow we're structuring kind of later

(16:44):
stage testingso we're better understanding durability.
Is there something that we can do
in order to understand any type of barrierfor actually placing the material?
All of that is a really activearea of research.
Everyone's really excitedabout AI right now.
Are you guys using AI in your lab as partof any of that kind of analysis process?
It's a tool. Engineers love tools.

(17:06):
So yes, we do use AI machine
learning algorithms in orderto kind of help predict certain things.
So rather than conducting test overtest over tests
so that we get a battery of information,
there are researchers around the worldwho are collecting fantastic information.
So yes, we are leveraging thingslike AI in order to use many different

(17:26):
data sets that might not all have beenperformed in the exact same way as such,
that we can still predict robustlythe likelihood of material performance.
And we're also leveraging itto inform things where we have otherwise
data poor environments.
So quantifying environmental impacts,for example, is a very and data
intensive field.
And sometimes we have gapsin some of the inputs that are necessary.

(17:48):
But we can leverageAI to fill in some of those gaps.
Still with a bit of uncertainty,but better than our just guessing.
And then also we have utilization ofAI for some, overcoming barriers
for adoption, trying to understand, okay,we have very limited data
for these particular typesof performance metrics.
How can we predict what we would expectbehavior to be, or predict what tests
we should be doing in order to fill insome knowledge gaps in that realm as well?

(18:12):
I also wanted to ask youabout NSF support.
What difference has sayyour career award made for you?
NSF support has been the best supportthat I've had in my career.
I realize that that kind of sounds likeI'm pandering.
At the same time though, NSF supportactually allows us to do this
kind of more foundational,understanding type research.
NSF has facilitated my groupactually looking at new areas

(18:35):
where we don't have a solid understandingof how this could pan out,
or wherewe should be focusing our attention.
So it has facilitated work,
like the work that we've been discussingabout what would potentially store carbon
and where could we getthe biggest bang for our buck in terms
of trying to utilize carbonin the built environment?
And we end up seeing that NSFhas actually been incredibly valuable

(18:57):
in trying to supportthat type of really groundbreaking work.
Put on a speculative hat for a secondand think about
where would you like to seecements or concretes in, say, 75 years?
I'm a bit of an optimist,so I would like to see them having
higher performance characteristicsso that we don't need quite
as much of the material.

(19:18):
Obviously, we can't get rid of all of itbecause there's only so much
you can cut backand still get the right amount
of roadways, buildings, etc.,
but higher performance characteristicsout of the material.
I would love to seethe material, obviously, at least at net
zero emissions associated with it,but also ideally something
that could be a net uptake,a net storage system for our environment.

(19:39):
And I would love to see more
on circularity of resourcestied to our use of concrete.
So just like you mentioned,this kind of use of concrete, crushing it
and getting to use it again,
we haven't been big on resourcecircularity in general.
Not calling out concrete,but in general, humans
have been a little bit more linearand the life cycle of our materials.
We’ll extract, we’ll process,we’ll use, we’ll dispose.

(20:00):
I'm really excited aboutthe kind of concept of how we can start
to re-engineer thingsso that when we're taking it out of use,
let's use the resources again such thatthey're circling through our economy.
Perhaps not straightinto the same class of materials
or the same class of productsif we are losing performance.
But how can we start
to reuse those resources so that we don'thave to keep extracting resources,

(20:22):
which would facilitate
our potentially being ableto continue building in a very robust way.
So for the very last question today,
I want to ask you about what's nextin your work.
We actually are continuingdoing work in circularity
because I find it so exciting,
also because there's some issuestied to resource consumption
and localized scarcity.
So we might end up
having areas around the planet wherewe have plenty of the material globally.

(20:44):
But in this particular area,we don't have enough access to it.
Now, we've got to import it fromother areas, which can cause a variety
of different stressors on the environmentas well as other types of stressors.
So trying to better leverage the resourcesthat we're taking out of use,
that circularity is something that we'reincredibly excited about in the group.
We're also looking at pairedmaterial and energy systems.
So humans are fans of energy, electricityin particular, and trying to understand,

(21:09):
okay, if we are going to need to continueto produce electricity,
how can we make sure that we have accessto that electricity while also creating
co products that benefit other typesof systems, such as materials production?
How can we pair those togethersuch that we're able to generate energy
and create a net storagemechanism tied to that energy generation?
So we're getting the benefitof our energy resource,

(21:31):
but also removing CO2 from the atmosphereor undoing air pollutant issues
that we’ve sent into the atmosphere,trying to integrate those together.
And then of course, continuing workon decarbonizing materials production
and creating net uptake,net storage systems,
those are areasthat I'm incredibly excited about.
Special thanks to Sabbie Miller.
For the Discovery Files, I'm Nate Pottker.

(21:52):
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