Using bacteria to make self-healing cement | Hacker News Reader

Using bacteria to make self-healing cement

thestructuralengineer.info

156 pointsvinnyglennon68 comments

>Being mixed with concrete and distributed evenly throughout it, they can lay there in a dormant state for up to 200 years; only when the concrete cracks, air and moisture awaken the bacteria which use the calcium lactate as a food source and start to produce limestone, sealing off the cracks in 3 weeks’ time. The technology, currently able to seal cracks of any length but only up to 0.8 mm wide, was a finalist for the European Inventor Award 2015, an initiative of the European Patent Office (EPO).

That's brilliant. I wonder what the cost increase would be for including this solution v. the cost of traditional repairs.

The article says it costs about twice as much.

> Currently the cost of this new technology is still considered prohibitive, as it is twice the cost of regular concrete manufacture (70-80 € / m3), making it only viable for projects where leakage and corrosion are particularly problematic, such as underground and underwater structures.

What's funny to me though is that they consider this cost prohibitive despite the expected theoretically longer life without replacement or maintenance.

How often do you think most concrete structures (with only minor cracking like in the article) undergo serious rehab? Maybe once in their service life.

Also, when planners are choosing between alternatives, net present value (NPV) is calculated which takes into account predictable maintenance, so the cost of future repairs is already considered in these decisions.

Civil engineering is also not computer engineering. There is no agile development and you have to get it right the first time. The industry as a whole is not quick to adopt new technologies without seeing them proven in the field relatively thoroughly.

May be it's true for Europe, but in my country they're re-building roads every few years. Not sure if they are agile or just corrupt...

Qualification: I can't really confirm this fiscal responsibility of this.

Vermont is of the opinion that resurfacing roads frequently (like every two years) is cheaper than investing in anti-frost heavy road beds and cement... The reasoning behind this is that intense ground freezing can end up upsetting the best bedding techniques and causing frost heaves anyway - that coupled with frequent ploughing to deal with heavy snow fall makes long term road investments fiscally irresponsible. Also the state has frequent flooding issues which can upset road bedding in more different and fun manners.

depending on how plastic the soil, replacing it with the road base doesn't stop deformation just slows it down. If the base material is heavier than the native material it will speed the whole thing up.

Then you get into the territory of lightweight fills and it gets really expensive very quickly even beyond basic roadbuilding.

the complexities of road construction depend on all sorts of factors from weather, subgrade composition, labour and material costs, traffic weight, total traffic, availability of capital, willingness to take risks, etc etc.

Most likely the roads are not being "rebuilt" but rather getting microsurfacing, and occasionally a mill and inlay of just top layers of the road surface. Fully rebuilding roads is more time consuming.

Ive been enduring a rebuild of I-294 around Chicago. It's around a 40 mile rebuild (ripping everything out down to dirt), IIRC. They're widening the highway in stretches, completely redesigning interchanges as well to remove sharp turns so that semis can keep speed and better merge. Lots of overpasses and other bridges being rebuilt to accommodate the extra lane each way. They completed the stretch around Ohare airport pretty quickly, in about a year, but seeing the materials used, I doubt it will hold up over time. I expect it will need maintenance on the first completed stretch before the 10 year project is complete. They went from concrete to an all asphalt layering from what I saw. Doubt it will hold up.

Edit: designing -> redesigning.

I’ve been seeing a lot of concrete get torn up and replaced with asphalt here in Illinois, all over the Chicagoland region. It’s a shame.

Additionally, something I’ve noticed is cutting out squares of broken asphalt around a pothole and filling that, only repeated every few feet to make it look like a patchwork quilt. I get that it is cheaper, but it’s not even going to last through a single winter...

asphalt can be designed for similar loading to concrete, and can be easier to repair and replace. Oil may have been cheap so asphalt may have been cheap reducing the cost significantly even with future maintenance.

Hard to say without knowing the details. Asphalt is not garbage and the only people I know who can evaluate it by sight work with it routinely.

> Civil engineering is also not computer engineering. There is no agile development and you have to get it right the first time.

Eh, that's a little overstated. You'd be surprised how many buildings and bridges have major refits when it becomes obvious that their design didn't live up to expectations.

design flaws can't be fixed by bacteria, so will not be stopped from using this concrete.

Predictable maintenance is already factored into decision making.

Fixing mistakes in structures you have to take apart gets very expensive quickly.

There's a youtube video about a hybrid version of that, some famous civil engineer forgot a tiny detail in a massive project. Student of his raised the issue, he actually listened, and managed to plan a last minute redesign/overhaul without anybody knowing (at first).

It's the Citicorp tower you're talking about.

most probably, and thanks to you, I found the video again

https://www.youtube.com/watch?v=Bv2YQnT6pSo

There's this youtube video, I won't link to it, but its awesome. I haven't seen it myself, my wife has, and she told me it was amazing. Its youtube, the video, super student vs teacher thing, overly amazing, much overhaul, legit story.

> What's funny to me though is that they consider this cost prohibitive despite the expected theoretically longer life without replacement or maintenance.

Unless almost all maintenance and replacement needs are due to cracks that don't rapidly become more than 0.8mm wide, this reduces maintenance costs but doesn't let it go an extended time without normal maintenance and replacement. At double manufacturing cost, that could well be a losing trade-off for most applications.

>What's funny to me though is that they consider this cost prohibitive despite the expected theoretically longer life without replacement or maintenance.

Time value of money plays a big part here. The extra cost is now, the maintenance costs are paid later. Costs paid immediately are significantly more expensive than costs paid a long time from now.

With current low interest rates, I'd say this effect is sharply reduced. The twenties will produce infrastructure that will last a really, really long time because those maintenance costs will be incorporated almost without discount.

A lot of public budgets don't have room for a big upfront cost, but a longer pay period can be incorporated more smoothly and disturb fewer other parts of the budget, even if it ends up costing more in the long run. Sometimes there are federal grants to provide quick windfall for public works.

To be honest I really don't want concrete repaired. It's not like a steel girder that get exposed to rust but can otherwise be swapped out with a new piece. If concrete is cracked there is a reason why: something shifted. Raze and rebuild because the earth will never stop settling and/or shaking. Don't they bust up old concrete into new gravel and concrete as well? Probably cuts down on how much land needs to be quarried.

The cost of replacement or repair is not something the current buyer will have to deal with, so the cost saving are also not his cost savings...

I interpret that as twice the cost of a traditional initial pour, but I think the question was how much that premium is offset by savings on repairs and maintenance over the life of the structure. The article implies it's currently only viable where where leakage and corrosion are particularly problematic, but mentions they're working on an alternative strain of bacteria grown from a sugar-based nutrient rather than more costly calcium lactate.

Fun Fact: Much of the Great Wall is still in very good condition thanks to its amazingly resilient mortar. The secret ingredient: sticky rice.

https://www.telegraph.co.uk/news/worldnews/asia/china/778584...

I love hearing about possibly competitive low-tech solutions.

"Are you double-dog sure this stuff can never get out in the wild?"

I think that Belyaev's "Eternal Bread" (1928) is much more relevant because it's about actual biotechnology and the scientist had good intentions.

I think a) the bacteria aren't novel. b) Calcium Lactate is what enables this.

There is absolutely no way this could possibly go wrong.

While I'm sure I agree with you, this comment reads like some famous last words!

The materials scientist Mark Miodownik discusses this and other miracles of modern, well, materials science in his marvellous book "Stuff matters" (https://books.google.com/books/about/Stuff_Matters.html?id=_...). I found it fascinating—though, fair warning, the material on cement was by far the most fascinating to me.

By the way, I just discovered he's got a new (to me) book, my copy of which is titled "Liquid rules" (apparently a later printing of a book originally just called "Liquid") (https://books.google.com/books?id=7p_FwQEACAAJ ).

What’s cool about this is could it save the cost of making expansion joints?

Edit. What I mean is you could do really big pours instead of sections. Think a mile long sidewalk with no sections.

But you would need a long queue of cement trucks :)

I don't believe so - those expansion joints exist IIRC to account for the fact that cement is quite temperature volume stable... but it isn't temperature inert. The seasonal temperature swings cause expansion and shrinking of cement and, especially on the scale of a bridge, those slight volume changes add up.

I imagine this tech would allow shrinkage during the winter to be automatically repaired if it manifested as hairline gaps - but when summer rolled around you'd get a severe amount of buckling the cement expanded... then those buckles might partially repair - be reinforced when gaping occurred in winter - then buckle even more come next summer.

I don't think so. It takes weeks for this cement to heal itself, whereas the sort of temperature swings that would cause very long pieces to crack happen in hours. You'd have frequent cracking and re-cracking without enough time to heal.

I think this is better suited for damage from infrequent events (earthquakes, temperature swings from 10-year storms, human accident, etc.).

I would like to understand the science behind how bacteria can live under the 50 gigapascals of pressure that one would find in the base of a skyscraper.

My intuitions currently tell me that finding life underneath such mechanical stress is comparable to finding life inside the lava of a volcano or on the surface of the sun.

Well, there are bateria living on chemical energy deep down in the oceans near volcanoes, that's not far from your example.

There are actually bacteria living in rocks thousands of feet below the surface.

>the 50 gigapascals of pressure that one would find in the base of a skyscraper.

I guess you will need to rethink about the order or magnitude of the pressure you cited:

https://en.wikipedia.org/wiki/Orders_of_magnitude_(pressure)

Easy comparison terms are pressure to create artificial diamonds 18 GPa, pressure at the bottom of the Mariana Trench 110 MPa.

Compression resistance of concrete is between 20 and 80 MPa:

https://en.wikipedia.org/wiki/Compressive_strength

Where 20 is "common" concrete, 30-50 is typical reinforced concrete, anything above is specisl, high strength concrete.

Check out pascalization, an alternative to pasteurization that uses extreme pressure.

https://en.wikipedia.org/wiki/Pascalization

Ancient Romans had kinda similar technology, although chemically not bacteria based.

https://www.nature.com/news/seawater-is-the-secret-to-long-l...

Wasn't it discovered that these bacteria are what make "Roman Cement" so much better then modern 'Portland Cement'? (or was I supposed the RTFA?)

The primary difference between Roman and modern cement is that Roman cement does not have reinforcing steel in it and cannot support loads that put it under tension stress. This reinforcing steel is what fails with age - cracks develop, let in air, and corrode the steel. No steel, and what you have is basically a shaped rock, and that can last a really long time.

The downside, of course, is that not being able to resist tensile loads severely limits the designs you can make with concrete. Reinforced concrete is significantly more useful than unreinforced concrete.

and to add to this, all reinforced concrete cracks. Otherwise it doesnt need to be reinforced.

I wonder if it would be feasible to replace the steel reinforcement rods with ceramic? No iron no rust.

I also wonder if concrete might bond better with ceramic. My understanding is that concrete does not bond well with steel.

It looks like some effort was made in 2010 to coat the reinforcing steel with a porcelain enamel [1]. I believe the enamel's primary function was to provide a bond with the encasing concrete. Naturally, it would also help to protect the steel from water and oxygen.

There must be a reason why ceramic cannot fully replace steel. Cost perhaps.

Maybe these technologies would be better combined.

[1] https://www.ceramicindustry.com/articles/90943-improving-ste...

A big part of the problem with coated steel rebar is that rebar is treated very roughly on construction sites, and any nick or failure of the coating is really bad news when the chemical isolation provided by the concrete fails. Instead of the corrosion happening relatively uniformly at a slow rate across the entire length of the reinforcing bar, it'll happen at a few select sites at a significantly higher rate.

What about using plastic or some flexibly epoxy. Would it have some adverse effect or is there a cost issue?

Epoxy-coated steel rebar has the problem I mentioned, as well as being more expensive than standard rebar. You can remove the steel and use non-corroding materials, but these tend to have significantly less stiffness than steel (and reinforcing stiffness determines the load-to-crack-size ratio)

That is really interesting. I didn't realize that corrosive oxidation would become concentrated and react at a higher rate if the point of exposure was limited.

Why isn't it galvanized like a nail or a porsche?

It can be, but it adds cost to the project, and any galvanized rebar has to be bent before it gets galvanized rather than on-site.

I think concrete bonds with steel just fine. Problem is when it rusts or is exposed to chloride the steel corrodes which expands and cracks the concrete.

I think massive reinforced concrete sections that are kept dry are stable long term.

Some work is being done to find alternatives. Difficult because you need high tensile strength and toughness. And the alkaline environment will wreck other materials. I think ordinary fiber glass turns to gel over time.

A lot of reinforcing bar is coated with epoxy. But I think that's not working out very well in practice. Any nick in the coating directs the corrosion to that point.

Whole thing is an open problem

Stainless steel seems to be working well, though much too expensive for most projects. Maybe part of the problem is that because stainless steel is a proven alternative where it matters, it's hard for other alternatives to break into the market, either at the low-end where there's zero chance your crews are going to apply the new procedures properly, or at the high-end where conservatism and greater access to cash make stainless viable.

If corrosion of rebar is limiting the lifespan of concrete structures then using a resistant rebar could increase the lifespan of a building enormously. Modern buildings could last multiple centuries instead of starting to crumble at 80 years.

It'd be a material engineering feat to get the required plasticity and tensile strength out of ceramics. The plasticity is probably more worrying in practice - the failure mode of rebar rusting is usually visible to inspection and slow enough that action can be taken to ensure that the structure remains safe. The failure mode of a brittle reinforcing member suddenly failing is much more worrying from a safety perspective.

In structural engineering we call this plasticity "ductility", but you're exactly right. We want ductile failures not sudden brittle ones, and that can only be achieved with yielding reinforcing. Ceramics generally will fail brittly, or cause the concrete to crush if the member is over-reinforced.

> the failure mode of rebar rusting is usually visible to inspection and slow enough that action can be taken to ensure that the structure remains safe. The failure mode of a brittle reinforcing member suddenly failing is much more worrying from a safety perspective.

That is an excellent point!

Lots of different materials and techniques have been tried, but nothing so far seems to have really stuck. As an observer I think there are two main factors:

1) The types of steel used coincidentally have nearly identical coefficients of thermal expansion as the concrete used.

2) Everybody in the construction industry and the entire supply chain is familiar with and habituated to steel rebar. The inertia is tremendous.

That's a very high bar to meet to gain a foothold with new materials or new techniques as the entire system has evolved to fit the pros and cons of steel rebar. Anything that departs from standard practice becomes very costly, very quickly, for a gazillion reasons.

I never considered the potential social side to this problem. Thank you for commenting.

Basalt rebar, which is basically like epoxy fiberglass as used in boats, wind generator blades, etc. except basalt fibers and just really long. However, it can't be bent so you have to make joins at every corner and have to order all bent pieces ahead of time.

What about wood?

Wood absorbs water causing it to warp, swell and decay. Having said that, steel rebar is expensive which has motivated some organizations to use wood, as well as other plant materials, as a reinforcement material in concrete with some success [1].

[1] https://www.quora.com/Was-wood-used-as-a-reinforcement-mater...

Roman cement involved volcanic pumice not sand/gravel and did not set quickly (may have needed external heat to set at all).

Sounds like a great material for floating arcologies.

"I'm beginning to think I can cure a rainy day!"

please apply date [2017] to title as the article is old

>Friday, 12 May 2017 01:00cat

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