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September 19, 2008

Concrete Solutions

Posted: 12:13 PM ET

Hard, flat, tough, solid. These are all words that you could use to describe concrete. But green? That’s not usually an adjective many people would apply to cement – unless, of course, they knocked over a can of emerald paint on their driveway… But here’s a rundown of some new environmentally friendly products that are paving the way to greener, well, pavement.

Workers lay Filtercrete (left) and Flexi-Pave (right) instead of regular concrete. Source: CNN/KBI

Recently used to green Chicago’s alleys (watch story here), Filtercrete is one of a few products that help improve normal pavement by making it porous. It is filled with tiny holes that allow water and air to flow between the surface and the soil. This reduces the runoff to local waterways, while increasing water input to local underground aquifers. Because water is less likely to be trapped in the porous concrete, there is a reduction in cracks caused by water freezing to ice. Filtercrete’s holes also harbor bacteria that break down contaminants like oil and grease, so water is cleaned as it passes into the ground.

Flexi-Pave: KB Industries’ flagship product Flexi-Pave adds one more green aspect to porous pavement. Used for ‘low-speed’ surfaces like sidewalks, trails, and parking lots, Flexi-Pave is made primarily of recycled tires. Considering they are used at a rate of one per person per year, there are a lot of worn-out rubber tires out there that could be diverted from landfills and recycled into pavement.

Because it’s made of rubber, Filterpave can expand with any freezing water that happens to be caught in the product’s pores, further reducing the chance of cracking. Also, the product can be outfitted with subsurface heated water pipes to help melt snow lying on the pavement’s surface. “[It] causes any snow to immediately turn to water and pass through the product,” says Chief Operating Officer Trey Wylie, “[Clients] have eliminated snow removal costs and no longer have to apply chemicals throughout the winter.”

Air-Purifying Concrete: It’s still in the research stage, but scientists at the University of Twente in the Netherlands are developing a form of concrete that could help clear nitrogen oxides from the air. Nitrogen oxides are those chemicals that cause problems like smog and acid rain, but this new concrete will contain a chemical – titanium dioxide – that converts nitrogen oxides into harmless nitrate salts.

The salts are rinsed off the surface and into drainage systems when it rains, and the concrete should continue to perform over time. “[Titanium dioxide] is a catalyst, so it is enabling the reaction, but not participating, not consumed, so it never wears out,” says researcher Jos Brouwers. He adds that the air-purifying concrete could potentially be combined with porous concrete products like those mentioned above or even used in decorative facades of buildings. Results on how effectively the concrete performs in field tests are expected in 2009.

So what do you think of these products? Where can green pavement go from here?

Julia Griffin, CNN Science & Technology

Filed under: Cars • environment • Materials • recycling • Tires

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Garry Minor   September 19th, 2008 1:03 pm ET



S Callahan   September 19th, 2008 1:20 pm ET

Wow Julia..great article. Being a severe asthmatic very sensitive to the enviroment I would love to advocate to my city for the air purify concrete. Curious question, what happens to the salts that drain off?

PD. I see that CNN acnowledged through a posted TIME article by M.J. Stephey that CERN is locking at the spiritual aspect of life (consciousness after body stops). As well, other articles telling of the breakdown and now repair of CERN that is set to go again. Can we hear more of the two stories through blogs?

Franko   September 19th, 2008 4:53 pm ET

Fascinating are all the new materials, some from waste products.
Epoxy concrete, sanded to make extremely durable items.
Shopping mall sidewalks, fountains, specialized concrete.
Particle board, cheap compared to plywood. Some amazing paints.

Patrick   September 19th, 2008 5:16 pm ET

These all sound like wonderful products but, if I am a developer, school, or a municipality that wants to build green, the most important items I would want to know first:
1. Initial cost premium if any.
2. Durability and maintenance cost premiums if any.
3. Quality and performance compared to normal hard suface material.

If all of these criteria are satisfied, the product is a worthwhile investment.

Jason   September 19th, 2008 6:14 pm ET

Two problems I see.

1. Air purifying concrete uses titanium dioxide. Titanium dioxide is acquired through mining. Those who are truly green would consider mining a big no-no. Trying to be green is an unattainable fantasy that weakens economies and lowers the standard of living.

2. Porous Concrete. The transition between fall and winter and winter and spring in areas that have snow and ice will provide ample opportunity for water to become frozen as temperatures dip at night. The freezing and unfreezing during these periods inside the porous cavities will cause the concrete to break apart.

Big Foot   September 20th, 2008 2:31 am ET

Just checking. No conspiracy theory postings yet? Or is the media censoring them? 🙂

Franko   September 20th, 2008 4:14 am ET

"porous concrete is a form of concrete which is permeable, rather than solid. Porous concrete is made by mixing large aggregate material with mortar, creating lots of voids in the cast concrete"

Large surface area. Low in strength, special effects for special places. Tradeoff weakness for adwantages. Still need grawel bed, drainhole for downpour.

"Concrete Solutions" - Water is a solwent, dissolwing, lifetime reducing.
Increase lifetime, special insoluble binder, instead of plain mortar ?

S Callahan   September 20th, 2008 10:22 am ET

Julia i love this article but Still waiting for a Haldron blog to go up.
I see CNN reported today that CERN is out of commission for at least two about some more the truth of what really went wrong, still going wrong...the Scientists know....remember, to give credience to our God..this time it was mercy...

Franko   September 20th, 2008 5:56 pm ET

Porous concrete has similarities to sponge foam, metal, glass, rubber, or plastic
Warious mixing possibilities, ewen plastic washable filter in your air cleaner.

Closed cell structures, such as styrafoam and astrogel make good insulators
Composite building materials, optimized to fill the design need.

Brian, Detroit, MI   September 21st, 2008 5:37 am ET

Sounds like a good idea.

Tom from Vienna   September 21st, 2008 8:02 am ET

The porous concrete will be destroyed in the first "freezing rain" weather due to the water freezing in the pores before it has a chance to pass through.

And porous concrete may look good on a level area, But, on uneven terrain (most on the earth), the movement of water over concrete prevents the slow errosion of the ground beneath. Porous concrete roads will shift downhill over time faster than normal concrete.

If scientists and environmentalists want to work on better roads, consider replacing black asphalt with something that reflects sunlight rather than absorbing it as heat.

Franko   September 21st, 2008 9:58 pm ET

Large particle aggregate, insufficient binder to fill the gaps.
Passes water, untill gets clogged up. The plumber has miniature plunger ?

Bumpy, badly scrape your kneecaps on a permeable tennis court. Not for disabled or high density commercial traffic. Too complex to mix for the average Henry the Handyman. Somewhere in between high maintenance useful.

Andrew   September 21st, 2008 11:49 pm ET

There were tests done on the porous concrete in Wisconsin. Freezing was indeed a concern. However, some of that stuff has been laid down for 4 years of freeze-thaw cycles and is pretty much undamaged. One reason for this could be that the holes do not completely fill with water, allowing some compliance when freezing/thawing occurs. However, the designers did consider this, and had suggested this stuff would perhaps work better where it doesn't get too cold.

Dan Hassett   September 22nd, 2008 11:14 am ET

Note to editor: In the 4th graf, you call it "Filterpave" when it should be "Flexi-Pave" - unless I missed something.

teenager in skool   September 22nd, 2008 11:54 am ET

i think that that is sme cool concrete they should use it all over the world especially here where out economy is slowly crashing. oh well we will get back on out feet eventually. 😀

KLF   September 22nd, 2008 12:00 pm ET

Holy cow, what a bunch of nay-sayers...

FYI... porous/pervious concrete has been in use for several years with great success. Read about it:

Nay-sayer   September 22nd, 2008 5:08 pm ET

Porous/pervious concrete has been used for several years now. One of the problems that has been encountered is that along with water getting back into the system, so do unwanted contaminates (e.g. oil from the roads). Regardless, permeability rates vary greatly depending on the volume of discharge (rain). May be we should make our cities denser and leave the country side as country.

Franko   September 22nd, 2008 11:10 pm ET

In your living room. Suck up dirt to a centralized vacum system. Add heating, cooling, perfume, negative ions, humidity controls. What way to control cat fleas.

Bill (Raleigh, NC)   September 23rd, 2008 10:01 am ET

Regardless of the performance of these particular products, it's great that teams around the world are innovating in all areas of human endeavor to preserve our planet and increase the quality of life for its inhabitants. It's a sure bet that we'll be in deep trouble if no one is trying to make a difference in these areas. It takes many projects like these to create successful products that can make a difference. This is how it's done, folks. To throw stones at that intent is just weird. Three cheers for these innovators!

Franko   September 23rd, 2008 12:51 pm ET

A material that needs extra care in preparation, application, and maintenance
Special effects, under certain conditions,, can outlast ordinary concrete.

Mixing ordinary concrete for the application, I can do.
Try a small porous batch ? will have to really think hard

info on greener concrete |   September 24th, 2008 8:32 am ET

[...] Filled under: Building materials | You can follow any responses to this entry through the RSS 2.0 feed. [...]

smoky   September 25th, 2008 1:43 pm ET

Yeah, people! What about cat fleas! We need a concrete solution to cat fleas NOW!

Franko   September 26th, 2008 1:27 pm ET

smoky: you miss the EcoReCyclePossible
Collect the fleas, feed to goldfish, cat likes live fish, more fleas

Gen Utopia   September 27th, 2008 8:48 pm ET

I once had an eco-nut roommate that refused to put a flea collar on his cat. There were so many fleas in my house they infested my front lawn and came back to haunt me after he left, every summer for three years.

Please put a flea collar on your cat.

Has anyone ever solar fired concrete?

I'd imagine titanium-oxide would be too expensive to use as a building material, unless it provided structural strength advantages as well as filtered the buildings air. If it only filters the air that blows by the building and provides no strength, I can't see anyone ever coughing up the cash for it.

Maybe its possible to convert these polluting oxides into harmless salts using a metal or mineral that is less expensive than titanium.

Or is titanium onlly expensive because it takes a lot of energy to smet? (maybe we could solar fire titanium...)

Gen Utopia   September 27th, 2008 8:53 pm ET

Smet? (I meant smelt of course)

A third possible advantage of air-cleaning concrete may be that it prevents corrosion of the building and thus increases its expected life-span.

johnell deloach   September 27th, 2008 9:31 pm ET

wow i am feeling this new concrete that they have on the market especailly for the snow

bigger picture   September 29th, 2008 11:23 am ET

Good to get the ideas out there, but there are many limitations with porous pavements, especially from particles filling in the small holes.

See, e.g.:

Re: the pavement releasing nitrogen, to waste water, this sounds risky, as can lead to algal blooms in open water. Info, e.g. at :

Fred Thompson   December 9th, 2010 3:03 pm ET

I have seen flexi-pave in Syracuse, NY . It looks great and holds up to all the snow they get. Theres a park down the street that has it and in the winter the snow melts faster than on the concrete walks

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