The material that could change the world... for a third time
Thousands of years ago,
the Romans invented a material
that allowed them to build
much of their sprawling civilization.
Pliny the Elder praised an imposing
sea wall made from the stuff
as “impregnable to the waves
and every day stronger.”
He was right: much of this construction
still stands,
having survived millennia of battering
by environmental forces
that would topple modern buildings.
Today, our roads, sidewalks, bridges,
and skyscrapers
are made of a similar, though
less durable, material called concrete.
There’s three tons of it for every person
on Earth.
And over the next 40 years,
we’ll use enough of it
to build the equivalent of New York City
every single month.
Concrete has shaped our skylines,
but that’s not the only way
it’s changed our world.
It’s also played a surprisingly large role
in rising global temperatures
over the last century,
a trend that has already
changed the world,
and threatens to even more drastically
in the coming decades.
To be fair to concrete, basically
everything humanity does
contributes to the greenhouse gas
emissions that cause global warming.
Most of those emissions come
from industrial processes
we often aren’t aware of,
but touch every aspect of our lives.
Look around your home.
Refrigeration—
along with other heating and cooling—
makes up about 6% of total emissions.
Agriculture, which produces our food,
accounts for 18%.
Electricity is responsible for 27%.
Walk outside, and the cars zipping past,
planes overhead,
trains ferrying commuters to work—
transportation, including shipping,
contributes 16%
of greenhouse gas emissions.
Even before we use any of these things,
making them produces emissions—
a lot of emissions.
Making materials—
concrete, steel, plastic, glass,
aluminum and everything else—
accounts for 31%
of greenhouse gas emissions.
Concrete alone is responsible for 8%
of all carbon emissions worldwide.
And it’s much more difficult to reduce
the emissions from concrete
than from other building materials.
The problem is cement,
one of the four ingredients in concrete.
It holds the other three ingredients—
gravel, sand, and water— together.
Unfortunately, it’s impossible to make
cement without generating carbon dioxide.
The essential ingredient in cement
is calcium oxide, CaO.
We get that calcium oxide from limestone,
which is mostly made of calcium carbonate:
CaCO3.
We extract CaO from CaCO3
by heating limestone.
What’s left is CO2— carbon dioxide.
So for every ton of cement we produce,
we release one ton of carbon dioxide.
As tricky as this problem is,
it means concrete could help
us change the world a third time:
by eliminating greenhouse gas emissions
and stabilizing our climate.
Right now, there’s no 100% clean concrete,
but there are some great ideas
to help us get there.
Cement manufacturing also produces
greenhouse gas emissions
by burning fossil fuels
to heat the limestone.
Heating the limestone with clean
electricity or alternative fuels instead
would eliminate those emissions.
For the carbon dioxide from
the limestone itself,
our best bet is carbon capture:
specifically, capturing the carbon
right where it’s produced,
before it enters the atmosphere.
Devices that do this already exist,
but they aren’t widely used because
there’s no economic incentive.
Transporting and then storing
the captured carbon can be expensive.
To solve these problems,
one company has found a way to store
captured CO2 permanently
in the concrete itself.
Other innovators are tinkering with
the fundamental chemistry of concrete.
Some are investigating ways
to reduce emissions
by decreasing the cement in concrete.
Still others have been working
to uncover and replicate
the secrets of Roman concrete.
They found that Pliny’s remark
is literally true.
The Romans used volcanic ash
in their cement.
When the ash interacted with seawater,
the seawater strengthened it—
making their concrete stronger and more
long-lasting than any we use today.
By adding these findings to an arsenal
of modern innovations,
hopefully we can replicate their success—
both by making long lasting structures,
and ensuring our descendants can admire
them thousands of years from now.