MIT Researchers Discover Why Concrete Breaks Down
The old saying “step on a crack, break your mother’s back” may not apply to sidewalks for much longer now that MIT researchers have figured out why concrete breaks down. As a result of the discovery, structures like buildings, bridges, and yes, sidewalks, could last for hundreds of years longer than they currently do. A nuclear waste container built to last 100 years could, for example, last 16,000 years.
According to MIT professor Franz-Josef Ulm, creep (the process that create cracks) is created when calcium-silicate-hydrates (CSH) rearrange at the nano scale. When mixed with water, CSH particles change in density from 64% to 74%. By adding silica fumes–a waste product from aluminum production–to concrete, overall density can increase to 87%. That’s a change that could eventually lead to longer-lasting, lighter structures.
If Ulm’s theories are put it into practice, the concrete industry and the planet could benefit immensely. 5 to 8% of all manmade CO2 comes from manmade concrete construction, so any reduction in the need to produce more of the stuff would slow global warming. And with twenty billion tons of concrete churned out annually, there’s plenty of room to cut down on production.
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June 17th, 2009 at 2:07 pm
Interesting
June 17th, 2009 at 3:27 pm
How much does it cost for each ton?
Just because they say it is a way to use a waste product, it doesn’t mean it’s low cost.
All solutions need to be used worldwide and that means at a competitive cost.
June 17th, 2009 at 4:47 pm
You’re telling me that increasing the concrete density from 74% to 87% will increase the life span of a concrete structure from 100 years to 16,000 years? Any increse in lifespan is good but it appears the projections are a little generous.
June 17th, 2009 at 4:52 pm
This is news? Silica fume has been used in concrete for decades, beginning in the 1940’s. It is very beneficial in reducing concrete permeability and mitigating chloride attack; it doesn’t increase density significantly. Creep is not what causes cracks either. There really isn’t much accurate information anywhere in the article. 16,000 years? Dream on.
June 17th, 2009 at 5:11 pm
Do some research, silica fume has been used for years. The American Concrete Institute (ACI) started advocating its use in the mid 1980’s, there is an ASTM standard (ASTM C1240) concerned with this use of it. ACI has published ACI 234R-06. Guide to Silica Fume in Concrete. This is not news but standard good practice and it is not a new green miracle.
June 17th, 2009 at 5:43 pm
Please get facts checked before publishing a story. Use of silica fume in concrete is almost 25 year old practice and its benefits and disadvantages on concrete are well published.
June 17th, 2009 at 5:47 pm
This is not new, but nice to see confirmation of what is now available. Concrete industry has been using silica fume for 15+ years to make high-strength concrete, especially in factory precast concrete, to get 8000-12000 psi compressive strengths. High strength means less concrete needed. It does add cost, but extra strength balances it out. Better durability is known. Wonder if they are dosing are higher rates than we normally see.
June 17th, 2009 at 6:06 pm
How can increasing the density of concrete reduce lead to lighter structures? And creep does not itself cause concrete to crack. In fact, in many cases creep can reduce cracking by relieving stress.
June 17th, 2009 at 6:18 pm
Silica fume has been used in concrete production for years. FHWA’s High performance concrete program featured it to improve concrete durability, and virtually all high strength concrete uses the material. Silica fume is the by-product of producing silcon metal of ferrosilicon alloys in smelters. Costs in the neighborhood of $400 per ton compared to $100 a ton of ordiary portland cement. FHWA and the Silica Fume Association have published an excellent reference manual. I’m afraid the researcher is a little behind the times!
June 17th, 2009 at 7:56 pm
Articles like this don’t do anything for CleanTechnica’s credibility. Silica fume isn’t new, nor is knowledge of its performance.
June 17th, 2009 at 9:18 pm
another nitpick: the 5-8% figure is usually attributed to the production of cement, not concrete itself. So really, an improved method for producing cement is needed.
June 18th, 2009 at 12:58 am
The original item from MIT.
http://web.mit.edu/newsoffice/2009/creep-0615.html
Seems the 16000 year number comes from mathematical modelling.
June 18th, 2009 at 12:22 pm
The information is not adequate, and does not highlight the breakthrough of the MIT researcher. It needs clarifications.
June 19th, 2009 at 2:32 am
“Seems the 16000 year number comes from mathematical modelling.”
Bull hooey! My pappy’s great-great-great-great-great-great-grande-great-grate-gyrate-great-grand-father had that study passed down to him from his great-great-great-great-great-great-grande-great-grate-gyrate-great-grand-father!
I finally saw degradation in the sample so I reported it as it was my and my family’s sworn duty to the tribe, the elders, and the shaman.
July 19th, 2009 at 9:53 pm
[...] is estimated to account for about 5% of all carbon dioxide emissions from human activity, with concrete accounting for about 8% overall. Though rubber surfaces do involve some greenhouse gas in the manufacturing process, [...]
August 12th, 2009 at 12:16 pm
Scientifically we can’t judge on this article if we didn’t see any results and trends, like what is the becoming compressive strength,expansion test during a certain period of time with different % of silica fume mixed with the concrete. Also what is the future of the silica fume after being solidified inside the concrete, is there any study done concerning the permeability of the silica and its content such as heavy metals when they are facing acidic environment like acid rain or in Alkali environment.
September 7th, 2009 at 10:27 am
this is landmark achievement by researchers.i would
add it further by further curbing global warming .
csh particle can be neutralize by adding gravel and sand process in bricks kiln and closing it mouth.then adding in concrete.moreover collecting the smoke from all industries and adding in concrete alongwith lime then that would also reduce global warming.
ur sincerely
kashif