Comments on: IS IT GREEN?: Concrete

By: concrete_fan

concrete_fan — Tue, 25 Aug 2009 20:11:29 +0000

the terms ‘concrete’ and ‘cement’ need to be defined more clearly and not used interchangably. That’s the huge issue here. Most concrete products manufacturers pick their cement supplier based on their sustainability initiatives. Every major cement producer in the world is working as hard as possible to reduce their carbon emissions. The fact is, concrete structures use fly ash to reduce cement volume, and the fly ash would normally be landfilled if not used for this purpose. Also, most concrete mixes use less than 1% admixtures- most if not all of which are completely contained in the concrete and won’t leech out into the soil if buried. Concrete structures also use 90%-100% recycled steel for the reinforcement they require. The rest of the concrete structure is sand and stone, and again, most major concrete products manufacturers are or should be picking their aggregate and sand suppliers based on the suppliers’ committment to rehabilitating the quarry once it is no longer useful. Subdivisions, commercial parks, etc. can be built, without issue, on a rehabilitated quarry.

Just remember, CEMENT only makes up approximately 15-17% of a CONCRETE structure, and according to the UK concrete industry sustainability report, the embodied CO2 associated with the production and transport of an average tonne of concrete is 95 kg. Very small compared to alternative materials.

By: Hendrik

Hendrik — Thu, 07 May 2009 22:21:27 +0000

1 cubic meter is about 35.3 cubic feet–to correct one of the commenters’ comments.

The article is basically sound until they get to the part concerning how much concrete is made worldwide. We are making about 2.7 – 2.8 billion metric tons of hydraulic cement each year worldwide, not concrete. The concrete made using this cement (I will include mortars in this figure) would be on the order of 19 – 25 billion metric tons (let’s say, 22 Gt for a middle of the range)–this is about 3 metric tons per person on the planet–each year.

Carbonation of concrete (i.e., the calcium silicate hydrate component) is extremely slow and usually very incomplete, even after decades to centuries. But during the hydration of the cement, free lime (becomes hydrated lime) is released and this lime amounts to roughly 20-30% of the original CaO in the cement analysis. It is this free lime that can readily carbonate if exposed to atmospheric CO2. The problem is getting the CO2 in contact with the lime–it’s a slow process (absent high pressures) in thick, intact structures. It is relatively rapid in high surface area applications (thin walls, stuccos, sidewalks, etc…) and can be fairly fast in demolition debris.

By: cretzler

cretzler — Mon, 09 Mar 2009 18:10:38 +0000

Don’t forget about the hundreds of admixtures possible with concrete, including the ones from recycled sources such as fly ash. These can have a huge impact on the performance and environmental impact of the material. Fly ash is a byproduct of coal power plants that can be used to replace significant portions of the portland cement. It is also important to consider the vast amounts of steel reinforcement that go into concrete structures. Alternative reinforcing materials and details can help decrease the steel tonnage on a job and make the material more “green”.
And like billolive said, we must think about what alternatives there are to concrete as well. In most cases where concrete is used, structural steel is the only viable alternative and it requires much more energy to produce.

By: Budi Waluyo

Budi Waluyo — Mon, 09 Feb 2009 17:50:35 +0000

As if a sword, technology advancement has two edge. One edge it can enhance human life quality but another side it tend to destroy natural environment. I believe they will find their balance. I, personally appreciate all the company effort to decrease the negative effect of natural sources exploration and the streamline of building material production. While the natural sources exploration should be in tight supervision.

By: mk

mk — Sun, 08 Feb 2009 09:54:48 +0000

After visiting Malaysia where a lot of limestone is collected for use in concrete, it makes me cringe inside when I see concrete being used. Beautiful natural limestone hills, with trees growing all over them and around are cut down so that they can get all the limestone out of them. The end result is a flat landscape with nothing but desolate land underneath.

I talk of this hills like the ones of the famous Batu Caves: http://www.flickr.com/photos/creazione/2592470217/

I can see the need in our modern lives for such a material, but honestly, it puts it into perspective whenever I see it being used anymore. Beautiful landscapes being flattened so that we can build bigger buildings? The destruction of a beautiful thing.

By: raunchpaunch

raunchpaunch — Sat, 07 Feb 2009 04:14:45 +0000

hyssil is an alternative to precast concrete panels, aerated and thus lightweight, and it doesn’t require autoclaving and can be wet set.
check it out here.
http://www.hyssil.com/index.htm

By: cpine

cpine — Fri, 06 Feb 2009 20:44:57 +0000

Another factor to consider in concrete construction is form work. Before the “mud” can set, it must be molded, either as blocks at a plant, or on-site as form work. Slip forms can be made of steel, plywood and framing timbers, or even cardboard. Tilt-up construction, in its crudest form, simply uses the earth trenched out to the appropriate shape. It can also be used in rubble or wattle and daub construction as a binder and finish, or simply as mortar for brick and stone construction. Each of these considerations reflect local sourcing, use of other materials, transportation, waste, WATER USE, and factors frequently overlooked or “externalized” when evaluating the “greenness” of concrete alternatives.

By: marko

marko — Fri, 06 Feb 2009 16:17:06 +0000

Well, if the new cements require less energy to produce, they could/should also be cheaper?
Also, it is the amount of cement in concrete (kg cement per m3 of concrete) that determines the strength of concrete, much more than the water/cement ratio. Water/cement ratios is more of a workability/strength ratio.

By: renschede

renschede — Fri, 06 Feb 2009 14:16:46 +0000

Kudos for this kind of reporting – I would love to have much more like this.

I believe if we are to be serious about creating “sustainability” then we must take the time to underpin our discussions and decision-making with just this kind of basic analysis – sadly lacking from most media coverage of “green” design.

Again, thank-you.

Ryan Enschede
Architect, Brooklyn NY

By: InvertedPantsMan

InvertedPantsMan — Fri, 06 Feb 2009 08:45:32 +0000

Nice article. 1 cubic meter is a cube of (roughly) 3.5 feet in stead of 35 however.

By: billolive

billolive — Fri, 06 Feb 2009 07:50:56 +0000

One thing I always see missing in the “concrete is not green” argument is the simple fact that, in many cases by using concrete you don’t cut down trees! Concrete is faster, easier to use, longer lasting and replaces wood in many cases where it would take incredible amounts of lumber to achieve the same structural integrity. Translate 2.35 billion tons of concrete per year into the same number of trees being cut down and run those numbers would ya? We should just work on upping the efficiencies of its creation. A replacement might be nice, but then so would zero point energy, 150mpg cars, technological advancements instead of technologic suppression, hmmm come to think of it this list could go on and on and on………..

By: elepski

elepski — Thu, 05 Feb 2009 23:36:25 +0000

I feel Concrete is so important to our lives now that considering an alternative is futile. Honestly, What can you replace it with?

By: goooglemonster

goooglemonster — Thu, 05 Feb 2009 22:02:35 +0000

This doesnt cover supercritical concrete that is made using co2 which draws out the water and cures the concrete. Supercritical concrete also offers the ability to absorb large amounts of co2 in the finished products.