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‘Self-healing’ concrete is being developed. Researchers are using a ground-borne bacteria – bacilli megaterium - to create calcite, a crystalline form of natural calcium carbonate. This can then be used to block the concrete’s pores, keeping out water and other damaging substances to prolong the life of the concrete.

Self-healing’ concrete is being developed by researchers at Northumbria University which could see cracks in concrete buildings become a thing of the past.

Dr Alan Richardson, a Senior Lecturer in Construction in the School of the Built and Natural Environment, is using a ground-borne bacteria – bacilli megaterium - to create calcite, a crystalline form of natural calcium carbonate. This can then be used to block the concrete’s pores, keeping out water and other damaging substances to prolong the life of the concrete.

The bacteria is grown on a nutrient broth of yeast, minerals and urea and is then added to the concrete. With its food source in the concrete, the bacteria breeds and spreads, acting as a filler to seal the cracks and prevent further deterioration.

It is hoped the research could lead to a cost-effective cure for ‘concrete cancer’ and has enormous commercial potential.
While further research is needed, Dr Richardson is hopeful that the repair mortar will also be effective on existing structures.

So-called ‘concrete cancer’ may be caused by the swelling and breaking of concrete and is estimated to cost billions of pounds worth of damage to buildings.

Dr Richardson said: “This project is hugely exciting. The potential is there to have a building that can look after itself.”


http://www.sciencedaily.com/releases/2012/04/120426105001.htm

Steel fiber reinforced concrete (SFRC) is a practical construction material that is quick and easy to use. But monitoring SFRC quality is difficult, and this has kept industry acceptance low. A new method offers a quick way to examine its composition.

Steel fiber reinforced concrete (SFRC) is a practical construction material that is quick and easy to use. But monitoring SFRC quality is difficult, and this has kept industry acceptance low. A new method offers a quick way to examine its composition.

Concrete is the world's most popular building material: we use it to bridge rivers and valleys, build walls and line tunnels. The most common form of concrete is steel reinforced -- a principle that will be familiar to anyone who has ever taken a closer look at a building site. Long steel rods, also called rebars, are bent into a dense framework, known as the reinforcement, which is then filled with concrete. But building with steel reinforced concrete is time consuming. It can take days or even weeks before the reinforcement for large buildings is fully assembled, the rebars bound together, and everything ready for the concrete pour.

Steel fiber reinforced concrete is a much quicker alternative, as steel fibers about the length of pine needles are simply mixed in to the liquid concrete. Once the concrete sets, this network of fibers does exactly the same job as traditional rebar reinforcement, increasing the concrete's tensile strength and counteracting cracks. Despite this, SFRC is not very widely used in the construction industry. The reason is that it was always very difficult to determine the quality of the material in the past, as there was no method for simply and reliably analyzing the distribution of fibers in the concrete. And yet it is this distribution that determines the material's load bearing capacity. If there are zones within the concrete where fibers are clumped together, or if certain sections of a slab contain no steel fibers whatsoever, the material is much less able to withstand stresses. This represents an element of risk that many construction companies are not willing to take, causing them to shy away from using SFRC.

Help has now arrived in the form of a new analysis method developed by mathematicians at the Fraunhofer Institute for Industrial Mathematics ITWM in Kaiserslautern. It uses probability calculations to work out the distribution of all the fibers within concrete samples in a matter of seconds. Project leader Dr. Ronald Rösch and his team of experts use X-ray computed tomography in a way he describes as not dissimilar to how CT scans are used in medicine. "The only difference is that we use it to examine samples taken from finished concrete components, not people," Dr. Rösch explains. Scientists take a core sample about ten centimeters in length from the concrete to be tested. The sample is then X-rayed using an industrial CT scanner at a resolution around a thousand times finer than that achieved by medical scanners. This system reveals even the finest micrometer-sized structures within the material, and generates a high-resolution 3D data set for the concrete sample that contains some eight billion pixels -- a huge file. Rösch and his team then use their new software to analyze this image data. By assessing differences in contrast, the software is able to assign each pixel to a particular structure within the material, be it concrete, a small stone, a trapped air bubble or a steel fiber. As the software works its way through the data set, all the fibers gradually become visible in the image.

"In and of itself this picture isn't much use, however, as the tangled network of fibers is so dense that it's almost impossible to make out individual ones with the naked eye," explains Rösch. This led the experts in Kaiserslautern to develop software that brings order to the chaos by analyzing the system as a whole rather than evaluating each individual fiber. The program simply decides whether a particular pixel represents part of a steel fiber, and calculates the orientation of that fiber.
For each pixel, the program calculates the composition of the material adjacent to it. Is it a fiber, or not? Instances where numerous fibers touch or cross over each other are the most interesting, as to begin with it is unclear which of all the adjacent pixels actually belongs to which fiber. Does that pixel belong to the fiber coming in from the top left, or to the one crossing the others directly from above? This is where the probability calculation comes in. It weighs up the location of each pixel, and attributes it to a particular fiber based on what makes logical sense. The results tell the experts everything they need to know, revealing not only the proportion of steel fibers in the sample, but also their orientation. "This is especially important when the concrete component has to absorb forces coming from a particular direction," says Rösch. An example of this is bridges carrying cars and trains at high speed.

It goes without saying that Rösch is aware of the system's current limitations; a CT scanner the size of a small wall closet is simply too big for practical use on a building site. "But this is an obstacle we can overcome," he says. "Our colleagues at the Fraunhofer Development Center for X-ray Technology EZRT in Erlangen have already developed a machine the size of a beer crate." A prototype for practical application could be available in five years, Rösch estimates.


http://www.sciencedaily.com/releases/2013/11/131113080217.htm
 

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A nice sugar coated summary of theoretical concrete.

Bottom line is that fibers do not replace conventional rebar, but they do reduce the micro-cracking. Fibers have been tried in Europe for many years because they have the systems to introduce them and monitor everything (to an excess) and general concept has improved, but it (FRC-fiber reiniforced concrete) is not a viable material for most uses especially with the required mixing time a time of dosing.
 

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You should check out a product called Helix Micro Rebar. It is a steel fiber concrete additive that is a complete rebar replacement. It can be used for structural concrete as well as slabs. They use it in their interstate systems in Australia and NO rebar. There has been multiple story concrete/ICF buildings built with the only rebar located at cold joints and concentrated stress points. It's been on the market for 10 years or so with ZERO failures. We are currently building a 10,000 sqft ICF home using it in walls and suspended concrete floors. And we don't have to spend hours installing rebar. Awesome stuff, and will be a game changer in the concrete industry.
 

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Discussion Starter · #4 ·
I can't see the fibers working either. From what I know of bacteria (only Microbiology 101) I wouldn't see the 'healed' areas as being as strong as a patch. They are interesting theories though.
 

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Interesting articles............. On the bacteria one there is another technology using bacteria where it is used with a material in a mold and transforms the mold into a solid shape that is supposed to be able to be used in place of concrete blocks. I can't remember what it's called but it sounds similar to the bacteria mentioned.

Regarding steel micro fibers, in addition to what Concretemasonry mentioned a couple of other considerations came to mind, namely the need when placing rebar to keep the steel minimum distances from the earth and air (we usually call out 3" from earth and 2" from air). How would this be accomplished if the fibers are throughout the mix? Also, finishing the surface with microfibers can be a big PITA and this could be an issue.

Just saw the post from Ps and will have to check it out.
 

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Discussion Starter · #6 ·
Also, finishing the surface with microfibers can be a big PITA and this could be an issue.
Good point. Bill says when he worked with the steel fiber (commercial) they used a 4' ride on trowel to burn that stuff down and it would chew up the blades. Not nice.......
 

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Actually, it finishes the same as any other concrete. And doesn't affect finishing equipment in the least. Here's a few things to check out regarding helix. I've personally seen the 2" thick parking lot with ZERO conventional rebar in it, poured with helix. Not a crack in it. This isn't the standard steel fibers that you've used in the past. I know I sound like a salesman, or someone with something to gain by pushing the product, but I'm just a contractor that has found a product that really is amazing. I've got 2 pallets of the stuff sitting in the warehouse right now.

http://www.helixsteel.com/projects/precast

http://www.modernarchstructures.com/wp-content/uploads/2011/09/Why-Use-Helix-Helix-FAQ.pdf

http://icfmag.com/articles/features/2013-11_Reinforced-Concrete.html
 

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I read the articles on the zinc coated corkscrew fibers used and the number of projects its been used in and it sounds very promising but I also find it a concern that it has only been in use for 10 years.

How long is the life cycle for concrete? We have sidewalks here that are over 100 years old and look really good and have all sorts of galvanized construction components that are rusting like mad after 10 or so years due to the salt air working on the steel and eating the zinc. Where corrosion isn't such a factor I would feel a lot more comfortable with using such a system but having said that it does sound like it has a lot of wonderful properties; how nice would it be not to have to deal with rebar!
 

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AmeliaP, concrete probelm is very little tensile strength, self healing cracks would help the Road builders/ parking lots, but not so much structual uses.

Most likely $ wise the road solution(pun intended) will be lazy DOTs stopping pouring Brines on 100s of Billions of dollars worth of bridges & Roads &(indirectly a trillion $ worth of vehicles)
The various mini fibers help some but none supply 3-D improvement in tensile strength and lowering shear failures.
the various fibers need a dumbell ends to improve their performance-the first 20-30 diameters of straight refiber don't develope 100% of the fibers/minibars strength...

Maybe a huge 3-d Concrete/steel printer....
 

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concretemasonry said:
A nice sugar coated summary of theoretical concrete. Bottom line is that fibers do not replace conventional rebar, but they do reduce the micro-cracking. Fibers have been tried in Europe for many years because they have the systems to introduce them and monitor everything (to an excess) and general concept has improved, but it (FRC-fiber reiniforced concrete) is not a viable material for most uses especially with the required mixing time a time of dosing.
I don't think the article was talking about fiber reinforcing it was more about the bacteria filling in the pores and keeping water and contaminates out that break down the concrete over time.
 

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Thanks for sharing this Amelia.

We will have to wait and see what the outcome of it all will be and what they come up with and of-course what will be the cost impact.

On the general note proper design, proper drainage, bearing soil condition, and proper sized re-bar design and installation are the keys for a stable structure.

When I was in Spain visiting the Sagrada Família Church which was designed by Antoni Gaudi, the most amassing thing I noticed, was that the old structure which started to be built in the 20's and on forward didn't have any visual structural failures with the materials being used. The new structure which is being built in modern days, with a more modern design, supposedly with more advanced materials, etc already have visual signs of structural failure.
 

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I could see something like this working pretty well with a modified shotcrete setup, but that isn't general purpose or cheap.
 

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I like the science of it and all but it is tough to improve on something with such a long and successful history. If the Romans could build structures that still exist.....they had a good mix. :thumbup:
They sure did...The Colosseum was built sometime in 72 A.D and even when it was struck by an earthquake, most of the structure survived and did not sustained damage to any bearing and supporting memebrs of the structure. With the engineering they had and what ever they used in the mix, still holding up strong :thumbsup:
 

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Regarding Roman construction, And very little frost action....
plus after the invasion of the Goths, VisiGoths, and Vandels, the locals didn't have the tech to demo the monolithic structure, while almost all the smaller Unit system buildings were "recycled" during the various periods of anarchy of the Dark Ages/ City state wars eras.

The one of the biggest probelms with greek buildings is the metal cramps "exploding" as they oxidised. After the lead roofs and wooden timbers were stolen/burned. Similar to exterior/sub grade CMUs walls with ungalvanised dura-wall, easy Demo.

Surviver bias too, all the sub standard construction collapsed some time in the last 18-22 Centuries....

CT scans for rebar placement checks no doubt will become more common place in EQ zones.
 

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I like the science of it and all but it is tough to improve on something with such a long and successful history. If the Romans could build structures that still exist.....they had a good mix. :thumbup:
OTOH, they didn't use Portland cement.

The most common reason old buildings fell down was fire or neglect / abandonment.
 

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Pritch, True the Romans used naturally occouring cements, such as Pozzalans from the local volcanos.
No, the various Pozzalans aren't the "same" as coal fly ashes....
1st or 2cd cousins maybe...

Either can be used as partially replacements for Portland cement in concrete for SOME USES, yes.

Greg24K, The masonry in those pictures have been PAINTED to look damaged/old......
 
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