What exactly is self-cleaning concrete, and how does it work?

The Jubilee Church in Rome is coated in self-cleaning cement. Image: Psidium

In recent months, a new building material that claims to both clean itself and filter pollutants out of the air around has been popping up on new buildings and infrastructure. It's one of those advances in construction technology that does actually seem, well, really good. 

As a result of its self-cleaning abilities, the concrete keeps its colour for far longer than traditional building materials, so doesn't need to be replaced so often; but it can also reduce general air pollution. Which, to be honest, sounds like a bit of a win-win. But how exactly does the magic work? And is there a catch?

How was it invented?

The technology was actually invented pretty much by accident, by Luigi Cassar, an Italian chemist at cement manufacturer Italcementi. He was trying to create a construction material which would keep a bright white colour even in polluted conditions, and hit upon a method called "photocatalysis", which uses the sun's energy to zap away dirt. 

To his surprise, when the air around the treated concrete was tested, it contained up to 80 per cent less nitrous oxide: the concrete was cleaning the air as well as itself.

How does it work? (Warning: science.)

When we clean stuff, we tend to use a substance which can break down dirt so it can be washed from the object's surface, plus a bit of energy to make sure that reaction happens. When you scrub a plate, for example, you use soap and water, plus your own elbow grease, to remove dirt. 


On the surface of self-cleaning cement, the cleaning happens without any scrubbing involved. The secret? The power of the sun.

When light and heat strikes the concrete's surface, catalysts (usually titanium oxides) use that energy to break down the dirt into molecules like oxygen, water, carbon dioxide, nitrates, and sulphates. Gases float away, while liquids or solids are left on surface to be washed away by rain. 

Through a similar process, concrete can also break down pollutants in the air around it: if a pollutant strikes the surface, the titanium oxide reacts with it in the same way.

This diagram shows a nitrogen oxide hitting the surface and being converted into a nitrate:

So what's the catch?

Other scientists have dug into the theory behind self-cleaning cement and found a few problems.

1. Eagle-eyed readers might have already worked this one out: if those new substances left on the surface of the cement are "washed away", where exactly do they go? Unfortunately, the answer is probably "into groundwater, and then rivers and lakes". This is bad news when it comes to nitrates, which cause algae blooms and in turn deplete the body of water’s oxygen levels. 

2. Researchers from Indiana University found that, while the cement does what it says on the tin in specific lab conditions, it reacts quite differently if the humidity or level of pollution is lower. In fact, they found that, in lower pollution levels, the titanium dioxide would catalyse a reaction with ammonia which actually increases nitrogen oxides in the atmosphere.

3. The kilns used to make cement actually give off large amounts of nitrogen oxides and sulphur dioxide, which means the cement would have to be pretty effective (despite the limitations outlined above) to result in a net decrease in atmospheric nitrogen.

So in summary: yes, these compounds do a good job of keeping buildings clean and white. But only time will tell whether they're 100 per cent brilliant for the environment.


 

 
 
 
 

The future is here: Register now for Barcelona’s New Economy Week

Barcelona New Economy Week (BNEW) starts this Tuesday with the goal of turning the Catalan city into the "global capital of the new economy".

BNEW runs from 6 to 9 October, with registration remaining open throughout the event, offering insight from 350 speakers on how businesses can bounce back from the impact of the coronavirus pandemic. It will feature top speakers from the business sectors of real estate, logistics, digital industry, e-commerce and economic zones.

The hybrid, business-to-business event – which is taking place in physical and virtual forms – is organised by Consorci de la Zona Franca (CZFB) and will showcase the way in which Barcelona is preparing for the post-Covid world and the "new economy". It is the city’s first big business event of the year and aims to help revitalise and restart the local economy.

“BNEW will be the first great event for the economy’s global recovery that will allow the redesigning of the productive fabric,” says Pere Navarro, state special delegate at CZFB. “It is an honour to have the participation of renowned professionals and attendees from all around the world.

“As we are not in a position to do a proper ‘in person’ fair, we decided to adapt by creating a disruptive and useful event in this way to relaunch the economy.”

The conference will encompass five interconnected events incorporating real estate, logistics, digital industry, e-commerce and economic zones. More than 8,000 professionals from 91 countries from all over the globe will take part virtually. A further 1,000 delegates are expected to attend the five events in person. Over 200 speakers will take part physically, while the rest will give their talks via a digital platform especially created for the unique event. An advanced digital networking platform – using artificial intelligence – will cross-reference the data of all those registered to offer a large number of contacts and directly connect supply with demand.

The conference will also be simultaneously broadcast in high-quality streaming on six channels, one for each of the five interconnected events and an additional stream showcasing Barcelona’s culture and gastronomy.

BNEW will take place in three venues in the city: Estació de França, Casa Seat and Movistar Centre. All are open, digital spaces committed to the United Nations’ 2030 Agenda. Estació de França will host the BNEW Logistics, BNEW E-commerce and BNEW Real Estate events, while Casa Seat will be home to the BNEW Economic Zones event, and the Movistar Centre will host the BNEW Digital Industry.


Some 36 companies are sponsoring BNEW, and 52 start-up companies will take part and present their highly innovative products and services. A further 128 firms will participate in BVillage, a kind of virtual stand where they can show their products and schedule meetings with potential clients.

Highlight sessions will include: "the era of humankind toward the fifth industrial revolution," by Marc Vidal, a digital transformation expert; "rational optimism," by Luca Lazzarini, a commercial communications specialist; and "future smart cities’ challenges and opportunities," by Alicia Asín, a leading voice on artificial intelligence. Sandra Pina will also talk about how sustainability is transforming us, Jorge Alonso on the humane future of cities and Pilar Jericó on how to face changes in the post-Covid era.

BNEW is described as a new way of developing your know-how, expanding your networks and promoting innovation and talent.

“Networking is always one of the main attractions of the events, so to carry it out in this innovative way at BNEW – with the high international profile it boasts – is a great opportunity for companies,” says Blanca Sorigué, managing director of CZFB.

Readers can register for BNEW for free via this link using the discount code BNEWFREE.