How we could make carbon-negative concrete | Tom Schuler

Transcriber: TED Translators Admin Reviewer: Rhonda Jacobs

Concrete is all around us,

but most of us don't even notice that it's there.

We use concrete to build our roads, buildings, bridges, airports;

it's everywhere.

The only resource we use more than concrete is water.

And with population growth and urbanization,

we're going to need concrete more than ever.

But there's a problem.

Cement's the glue that holds concrete together.

And to make cement,

you burn limestone with other ingredients in a kiln at very high temperatures.

One of the byproducts of that process is carbon dioxide, or CO2.

For every ton of cement that's manufactured,

almost a ton of CO2 is emitted into the atmosphere.

As a result,

the cement industry is the second-largest industrial emitter of CO2,

responsible for almost eight percent of total global emissions.

If we're going to solve global warming,

innovation in both cement production and carbon utilization

is absolutely necessary.

Now, to make concrete, you mix cement with stone, sand, and other ingredients,

throw in a bunch of water, and then wait for it to harden or cure.

With precast products like pavers and blocks,

you might shoot steam into the curing chamber

to try to accelerate the curing process.

For buildings, roads, and bridges,

we pour what's called ready-mix concrete into a mold on the job site

and wait for it to cure over time.

Now, for over 50 years, scientists believed

that if they cured concrete with CO2 instead of water,

it would be more durable,

but they were hamstrung by Portland cement's chemistry.

You see, it likes to react with both water and CO2,

and those conflicting chemistries just don't make for very good concrete.

So we came up with a new cement chemistry.

We use the same equipment and raw materials,

but we use less limestone,

and we fire the kiln at a lower temperature,

resulting in up to a 30 percent reduction in CO2 emissions.

Our cement doesn't react with water.

We cure our concrete with CO2,

and we get that CO2 by capturing waste gas

from industrial facilities like ammonia plants or ethanol plants

that otherwise would've been released into the atmosphere.

During curing, the chemical reaction with our cement breaks apart the CO2,

capturing the carbon to make limestone,

and that limestone's used to bind the concrete together.

Now, if a bridge made out of our concrete were ever demolished,

there's no fear of the CO2 being emitted because it doesn't exist any longer.

When you combine the emissions reduction during cement production

with the CO2 consumption during concrete curing,

we reduce cement's carbon footprint by up to 70 percent.

And because we don't consume water, we also save trillions of liters of water.

Now, convincing a 2,000-year-old industry

that hasn't evolved much over the last 200 years,

is not easy;

but there are lots of new and existing industry players

that are attacking that challenge.

Our strategy is to ease adoption

by seeking solutions that go beyond just sustainability.

We use the same processes, raw material, and equipment

that's used to make traditional concrete,

but our new cement makes concrete cured with CO2

that is stronger, more durable, lighter in color,

and it cures in 24 hours instead of 28 days.

Our new technology for ready-mix

is in testing and infrastructure applications,

and we've pushed our research even further

to develop a concrete that may become a carbon sink.

That means that we will consume more CO2 than is emitted during cement production.

Since we can't use CO2 gas at a construction site,

we knew we had to deliver it to our concrete

in either a solid or liquid form.

So we've been partnering with companies that are taking waste CO2

and transforming it into a useful family of chemicals

like oxalic acid or citric acid,

the same one you use in orange juice.

When that acid reacts with our cement,

we can pack in as much as four times more carbon into the concrete,

making it carbon negative.

That means that for a one-kilometer road section, we would consume more CO2

than almost a 100,000 trees do during one year.

So thanks to chemistry and waste CO2,

we're trying to convert the concrete industry,

the second-most-used material on the planet,

into a carbon sink for the planet.

Thank you.