Posted on 05/06/2017 7:38:09 PM PDT by Lorianne
It's the world's most popular building material, and ever since the Romans built the pantheon from it some 2,000 years ago, we've been trying to find ways to make concrete more durable.
No matter how carefully it is mixed or reinforced, all concrete eventually cracks, and under some conditions, those cracks can lead to collapse.
"The problem with cracks in concrete is leakage," explains professor Henk Jonkers, of Delft University of Technology, in the Netherlands.
"If you have cracks, water comes through -- in your basements, in a parking garage. Secondly, if this water gets to the steel reinforcements -- in concrete we have all these steel rebars -- if they corrode, the structure collapses."
But Jonkers has come up with an entirely new way of giving concrete a longer life.
"We have invented bioconcrete -- that's concrete that heals itself using bacteria," he says.
"We have invented bioconcrete -- that's concrete that heals itself using bacteria," he says.
(Excerpt) Read more at edition.cnn.com ...
Solution: MORE IMMIGRATION!!!
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>> “No matter how carefully it is mixed or reinforced, all concrete eventually cracks” <<
This is definitely not so!
Only concrete that is subject to tensile stress can crack.
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>> “Interesting if it works.” <<
It can’t!
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Its not wet.
The water became a part of the crystalline lattice after about 10 minutes, except where it was in motion.
Its an exothermic process.
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Romans used pumice, volcanic dust, in some of their concrete formulations and where they did it has held up much better.
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Hell will be psycho-thermic.
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Hillary
Hmmm, been a few years, but I swear some of the first words out of my instructors mouth when prepping for ACI concrete inspection certification was “All Concrete Cracks”.
I do know concrete shrinks as it cures and was taught it continues to cure or get harder which makes it more brittle forever
I am a structural drafter and when we do slabs on grade, we put in control joints to make the slab crack there... i.e. the little lines in the sidewalk, those are control joints. we know in general, as soon as a slab starts approaching a 2:1 ratio you are almost guaranteed a crack in the middle, so we put a control joint there.
We did a bunch of tract homes in terrible soil areas and used post tensioned slabs, the concrete cracked after initial 28 day cure time, then 1/2” cables that were laid out about 3 feet apart each way, before pouring the concrete were pulled to like 80,000# and clamped off which closed up all those shrinkage cracks. A lot of our bridges are built like this “post tensioned”.
I just did a set of concrete stairs for a custom house that the treads all look like they are floating, the individual stair treads are 5” thick, 11” wide and cantilever 36” out from the concrete support wall. The engineer specified epoxy coating the concrete surface after shrinkage cracking, so the reinforcing does not rust when it rains and water gets into the cracks.
Concrete is very interesting I learned in a book titled STUFF MATTERS, which goes into interesting details about concrete, stainless steel and other substances. Not only does he discuss this self-healing concrete, he also describes concrete that combats air pollution and self-cleans.
A number of years ago they discovered that the Romans used powdered volcanic ash in their concrete to make it stronger. Most concrete today has volcanic ash mixed into it.
The Pantheon is interesting. How did they pour so much concrete without getting a cold joint?
OH yeah. I see we have a BIG Concrete proponent here. It is not an exothermic reaction. That is sun energy. Granite is the natural way.
A very good and interesting bit of information.
I’m in need of a new patio and walkway and “open” to someone who wants to create a test case right here. PM me if you willing to do the job.
I love how the article starts with a reference to the 2,000 year old roman Pantheon, which is still standing and perfect, and then say how all concrete eventually falls apart. Eventually, perhaps, but eventually comes much sooner with modern concrete!
Would galvanized re-bar be better? How much more would it cost?
That’s not me. AzNASCARMan is the expert here.
Galvanized steel still corrodes, the zinc coating just corrodes first. That could cause spalling and stress cracking, seriously weakening the structure.
I watched a documentary on the construction of the new Bay Bridge a few months ago. All the rebar was epoxy/plastic coated to prevent corrosion. Even the tie wires were coated.
Watching the rebar cages being placed into the forms must have been a hair-pulling moment for the design and construction teams.
Probably because of EPA environmental restraints on the manufacturing. Locally, the city forced many residents to replace cracked concrete squares on the sidewalks, concrete that was maybe 70 or 80 years old but cracked due to tree root growth and shifting ground. The newer concrete just poured within the last year is whiter, and is already cracking after only six to twelve months. Weak stuff.
I am not an expert on concrete.
We had new concrete poured to extend our patio.
We put ice melt from big home repair store on the patio one time.
The old concrete flaked up and then the new concrete flaked up.
I repaired and then covered with sealer and concrete paint.
The repairs all came up and there is additional flaking.
I think that the chemicals from the ice melt (it’s not NACL) are transported by melting snow into the concrete and then aid the water in expanding as it refreezes.
We now put down cat litter as it won’t penetrate into the concrete and cause it to flake.
It’s been an expensive lesson for me.
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