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Comment by samgtx | Hacker News Reader

>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.

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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.

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