Researchers at Worcester Polytechnic Institute (WPI) have developed a new self-healing concrete that could multiply structures’ lifespans and slash CO2 emissions.
Most infrastructure is composed of concrete, and indeed, in its many forms, it is the single most used material in the world. However, the use of concrete comes at an environmental cost. While the production of concrete materials does not produce a large volume of carbon emissions by itself, its sheer volume is responsible for almost 8% of human made global carbon emissions and 3% of global energy demand. Therefore, healing rather than replacing concrete offers a significant benefit to the environment. Here, we present a new paradigm by introducing a novel mechanism to naturally heal cement paste that actively consumes rather than generate it.
This will eliminate the need for expensive repairs or replacements. The work, published in the peer-reviewed journal Applied Materials Today, uses an enzyme that automatically reacts with atmospheric carbon dioxide (CO2) to create calcium carbonate crystals, which mimic concrete in structure, strength, and other properties, and can fill cracks before they cause structural problems.
“We looked to nature to find what triggers the fastest CO2 transfer, and that’s the CA enzyme,” said Rahbar, who has been researching self-healing concrete for five years. “Since enzymes in our bodies react amazingly quickly, they can be used as an efficient mechanism to repair and strengthen concrete structures.”
The process, which Rahbar has patented, can heal millimeter-scale cracks within 24 hours.
Inherent brittleness of concrete leads to damage through several mechanisms such as freeze-thaw cycles pervasive in our environment. Current repair processes for cracked and damaged concrete rely on matching dissimilar materials, such as the inorganic C-S-H of concrete with organic petroleum-derived epoxies. The success of repairing concrete by patching and resurfacing processes relies upon the removal of the damaged material, which can cause further damage. Universally, rehabilitating concrete with mismatched materials creates additional flaws in the repairs, undermining the process. The repair process can take several forms, but the general first step is to chip away until only sound concrete remains, often exposing the reinforcing steel bar. One study found that only around 50% of repairs are durable while around 25% failed. Furthermore, only after 5–7 years, most repairs failed. The main mechanisms of failure here are the bond breakage between materials due to chemical attack, thermal fluctuation, and inadequate preparation or application.
Applied Materials Today – An enzymatic self-healing cementitious material
Highlights
• Inspired by the extremely efficient process of CO2 transport in cells, a self-activated healing mechanism for a cementitious matrix is proposed using Carbonic Anhydrase (CA) enzyme.
• The CA Enzyme, a protein, is used here as a catalyst; hence it is not consumed in the process.
• The rate of crystal precipitation in the proposed enzymatic mechanism can be can be up to four orders of magnitude higher than bacterial concrete.
• Comparing to bacterial concrete the process is entirely safe and odorless. It removes the use of bacteria/microbes in civil infrastructure.
• The healed crack sizes (larger than 1 mm) are significantly larger than bacterial concrete, due to the enhanced crystal precipitation rate.
Abstract
Concrete is the most widely used material in the world and is responsible for 8% of global carbon emissions. It is inherently brittle, and it requires frequent repair or replacement, which are expensive and generate large volumes of CO2. Current methods of repair by agents such as mortar and epoxies result in structures with reduced strength and resiliency due to material mismatch, therefore, a self-healing cement paste (concrete’s main matrix) is needed to overcome this problem. The leading self-healing mechanism is based on the use of bacteria and microbes, which are slow and have limited applications, as well as unknown health effects. Inspired by the extremely efficient process of CO2 transfer in biological cells, this study introduces a method to develop a self-healing mechanism in a cementitious matrix using trace amounts of the enzyme Carbonic Anhydrase (CA). CA catalyzes the reaction between Ca2+ ions and atmospheric CO2 to create calcium carbonate crystals with similar thermomechanical properties as the cementitious matrix. The crystal growth rate using this method is orders of magnitude faster and more efficient than bacterial methods, resulting in the healing of large flaws on timescale orders of magnitude shorter. This method is capable of self-healing samples with millimeter-scale flaws within 24-hours and is significantly faster than all current methods that need a minimum of 28-days for strength recovery of microscale cracks. This inexpensive method is biologically safe, actively consumes CO2, and avoids using unhealthy reagents. It can be an efficient mechanism to repair and strengthen the existing concrete structures.
SOURCES – Applied Materials Today, Worcester Polytechnic Institute
Written By Brian Wang, Nextbigfuture.com
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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Makes sense. Also, I did mean to say Shanghai, not Singapore. The problems with 3 Gorges Dam are reputedly many and include the problem with much of the heavy construction in Shanghai, in that both suffered from corrupt builders/suppliers using too little cement, and too much sand, in their mix, as they surreptitiously cut costs so as to pocket the difference.
Yea, everything is subject to some kind of decay, maybe even protons.
You might be forgetting some of the early advocacy of the Foresight Institute. Structural proteins was one of their pathways to nano-tech. I recall a line like ~"Don't think wet meat, think cow horns"
nothing happens…nothing happens…after 6 hrs…all fixed.
Worst. Timelapse. Ever.
I think "hydraulic cement" is a kind of cement that you can literally put in the water such as for making a dock or securing a post down there before they had big machines to pound them in.
I has some convenience advantages too. You can put a lot more of it on a truck, because it is much lighter than steel. And being lighter makes it easier to put in place and tie up. Probably less back injuries and finger pinches too.
I have to admit this hydraulic/non-hydraulic concrete terminology sent me for a bit of a loop, until I looked into it. Where and when I was raised, (A lot of my relatives were in the building trades.) "hydraulic cement" was a cement product that you mixed with water to form a putty that expanded slightly on curing. Great stuff for plugging leaks in concrete walls, but too expensive to actually build things out of.
What you're calling "hydraulic cement" would have been called "Portland cement", or usually just "cement", the 'hydraulic' cement was exclusively the leak stopping cement.
https://www.quikrete.com/pdfs/data_sheet-hydraulic%20water-stop%20cement%201126.pdf
I'm going to guess that the reticence of the government building codes to innovate is also a major factor.
The inability to modify it on site contributes, I think. It's not like steel rebar, where you can just heat a spot with a torch and bend it, and retain the properties.
I was wondering that myself. Also, most enzymes denature if they're dehydrated. Maybe they extensively crosslink it first?
The concrete's cement may absorb CO2, but until some other source of heat is used, I suspect more is released in making the cement. The cement ingredients must reach temperatures of 1500-1700C to create cement.
Using heat from a fission reactor, perhaps a HTGR(High Temperature Gas Reactor) would likely render the use of nonhydraulic cement "carbon negative", and hydraulic cement "carbon neutral" depending on mining emissions. I believe it would be difficult to use a MSR due to materials temperature constraints.
Water does not cause the deterioration of hydraulic concrete, in fact it must have water to cure. Water curing is a technique where concrete is kept wet, long after it hardens to ensure complete reaction of the cement, and eliminate cracking due to drying before a complete cure.
Large dams like Hoover are designed so they are at all points in compression, once loaded by water pressure. As a result they do not require any sort of reinforcement. The corrosion of steel reinforcement is almost always the reason properly designed concrete structures fail, particularly in salty(maritime) environments.
Basalt fiber, rebar, and grids should be used in any concrete you want to last. It's use is common in China, but rare in the US. The only reason I can think of is the reticence of the construction industry to innovate to any great degree.
Large nonhydraulic concrete structures take a long time to fully cure(harden), because CO2 has a difficult time getting inside the concrete. A structure many meters thick, like the three gorges dam might take millennia to cure.
A good solution is to use hydraulic concrete, and give it a veneer of nonhydraulic concrete, particularly in salty environments where the intrusion of salts through cracks leads to corrosion of steel reinforcement.
So, these folks have found a way to speed up the curing of non-hydraulic concrete. It's not widely known that the Romans used nonhydraulic cement/concrete two thousand years ago, or that it is self healing as far as small cracks go.
I've worked on using carbonic anhydrase to heal cracks also. How did they solve the pH incompatibility problem? Cement is extremely basic; pH 11 before curing. How is the enzyme protein protected from degradation?
It's a shame the Three Gorges Dam and its brethren weren't made from this stuff. Or a lot of Singapore, for that matter. Big things cracking is never really a good thing.
but it has to be applied, post-issue. This appears to be 'baked in'.
Agreed. Modern structural design is very efficient – mostly because labor is so expensive and tech has allowed structures otherwise impossible or impractical.
Roman 'mass' building is certainly a 'legacy' in its own right – thick, heavy, and everywhere – and why not? labor is cheap, disposable, ubiqutious (and often forced) with loose deadlines and simple (in concept) projects. If it didn't fall down in the first few months, it's likely there forever.
What an offensive notion.
It's not new, it's better.
The article actually directly addressed those sorts of attempts, which use live bacteria. This new one uses enzymes only, nothing alive. This removed some environmental safety concerns, and apparently is also more effective.
That video from 2009(!) led to over half a dozen others in my feed, including this one: https://www.youtube.com/watch?v=xJxf2rf3_ng So, why is this not better known by now? It seems like the bacteria needs water, but that is readily available in the same environment that caused the crack in the first place. But maybe on roads and sidewalks, there is too much other pollution for the bacteria to survive? What about in building foundations? It's a lot better than digging them up again to repair foundations!
How do giant dams, like Hoover Dam, manage not to deteriorate over decades, almost a century now, of water and pressure?
Why isn't this used everywhere by now, perhaps with the new graphene-laced concrete?
This is not new and was developed by others
https://youtu.be/PyBR3PDPa-c
It also has to be pointed out that the Romans would typically use FAR more concrete that a modern design would. With associated far greater expense (and CO2 output for those concerned about such things).
Modern bridges for example, using steel reinforced (and prestressed, a very important technique) concrete would have one graceful curve spanning a valley where the Romans would have dozens of supporting columns feeding into rows of arches to support a span of the same size.
With the result that the Romans ended up building far, far less than a modern nation over any similar timeframe. It's only because they owned a continent for half a millenium that we ended up with so many roman structures.
Interesting to see if a next stage technology could be used one day as a complete cement replacement applied on a proper matrix. Would be a serious CO2 absorber.
The salt actually aids in the self repair. the seawalls last the longest.
Certain forms are better than others.
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I've gone back and checked and I can't see any way in which that is offensive.
Unless you think it's offensive to show someone in a wheelchair?
capillary action
most times you don't even see a thing.. the concrete will sound hollow if you tap a hammer on it
offensive in so many ways.
https://johnnyoptimism.blogspot.com/2019/08/concrete.html
Concrete… Now there's a hard topic to joke about.
many great Roman structures include 'seawalls' – now that's impressive.
crystalline injection repairs are occasionally used – sounds similar to above. The chemical seeps into cracks and fissures and gaps under pressure – essentially reinstating the matrix of concrete material -and- minimizing those same cracks and gaps that might let water in the first place. Crazy Expensive as I understand it – often used for tunnels, etc.
keeping the water out is the key. Apart from direct precipitation, there is gravity and splash, humidity, (hydrostatic if beneath the ground/ water line) and small-pore/ large-distance water movement (the name of the physical property escapes me). Even the smallest amount of exposure over a brief period causes a remarkable cascading reaction – not noticeable until surface deterioration happens.
to be fair: Romans were lucky, they had access to some quite remarkable local materials – rare ash and stone aggregates – that create a concrete of outstanding durability. Mixed that with smart design – using interior and exterior tensile reinforcement — and voila — in a moderate climate (and probably not to near salty water(??))(and likely protected from the rain) — 'concrete for the centuries'.
Agreed. concrete restoration business is almost in same 'order of magnitude' as the original construction. Durability and service life of reinforce-concrete has changed much over the decades with big-scale solutions (keeping the water away and out) to changing materials properties and techniques. But so many, many foundations and garages and bridges and retaining walls, etc…
Concrete used in buildings, etc., is ubiquitous due to its low cost, easy workability and erection, and shallow learning curve (design and install) — so adding expensive treatments and repairs may make this building concrete system less desirable compared to steel, wood, masonry, etc…
I’ve always been a fan of multigenerational-lasting concrete construction, even with the energy and emissions issues. If you ever have the opportunity to go to Rome and touch and check out concrete structures that are over 2000 years, you’ll be amazed that they’re still around, surviving weather, earthquakes, vandalism and a general lack of maintenance up until only recently. Build it once, build it right, and you won’t have to expend the resources and energy to do it again for hundreds of years or more.
Sort of.
The essence of reinforced concrete is that it is a composite material/ system in most uses – that is, it requires a type of reinforcement that will 'take' the tensile stresses that itself cannot. For example, in a beam, when loaded on top, often bends convex-down and subjects the bottom layer to tensile stess which cracks it – the 'intimate connection' between the rebar embeded in this layer assists the concrete in resisting it – somewhat minimizing the cracks. The main failure of reinforced concrete is when moisture gets through this essentially porous concrete surface layer and contacts the steel, etc., which rusts it – and a wonderful behaviour called 'oxide jacking', an almost 'explosive-like' action from the sudden increased volume of the rusted metal cracks and 'spalls' the adjacent concrete. Salty 'chloride' laden water is worse. Minor spalls due to freeze-thaw (expanding liquid water into 'volumetrically larger' ice within the surface pores) also 'pops' off chunks if it is trapped during freezing. Solutions include non-corroding reinforcement $$$, membranes to stop water from entering the surface $$, and a bunch of nifty-do concrete additives $$ and techs $$$$, which can include current, etc., are the Golden Chalice of reinforced concrete service life, repair, and improved properties. Minimzing 'service cracks' to mitigate moisture entry could be a nice thing.
I'd be a bit concerned about utilizing biological enzymes in this application.
Not because they'd be dangerous, because as proteins, they'd be tasty.
Wouldn't they be subject to biological degradation?
But I have to say that just having it survive mixed with cement is pretty impressive, as cement is an extremely caustic material.
You can actually avoid rebar originated cracking by using basalt fiber rebar, which is superior in most ways anyway. (Except, admittedly, convenience: You can't easily reshape it on site.)
Please correct me if I am wrong. I was under the impression that it was the rebar, and gasses released from it as it rusts, that cause the concrete to crack. This lets in more moisture leading to more rusting and more concrete damage. Usually the rebar is rusted before it is even incorporated into the concrete. I always thought this was a primary reason Roman concrete lasted so long outside of seawater in the mix, because they didn't use steel or iron rebar. This seems like a good idea, but doesn't solve the root issue.
Also, calcium carbonate treatment is already used to waterproof concrete through the same or similar process. How is this an improvement?
Wonderful for intact structures.
When they tear one of them down and dump all of the concrete chunks together for disposal and recycling – does it begin to grow together into one big fused lump?