[bombela]

> It turns out that another chemical reaction, known as carbonation, might also contribute to Roman concrete’s longevity.

Roman concrete was made lime cement (calcium dioxide); which cures via carbonation (hardens with carbon oxide). And adding pozzolan to lime makes it hydrolic (hardens with water). Is it surprising that it can still carbonate some? Modern concrete has steel which rust and crack concrete. You can use fiberglass rebar for longevity, or build without rebar even, but that is more costly and and less efficient.

[Animats]

Stainless steel rebar is a thing. It's expensive, but structures built with it last much longer. Washington State now has a policy that bridges over salt water will be built with stainless steel rebar. Stainless steel costs much more, but total project cost goes up less than 10%.

Epoxy coated rebar looked promising for a while, but it's on the way out. Water gets in at cuts and joints. So all field joints have to have field patching.

There is a great comparison. Two piers were built in the 1940s, side by side, one with carbon steel rebar, one with stainless steel rebar.[1] Go look.

[1] https://worldstainless.org/wp-content/uploads/2025/02/ref19_...

[1] https://worldstainless.org/wp-content/uploads/2025/02/ref19_...

[ErroneousBosh]

> Stainless steel costs much more, but total project cost goes up less than 10%.

I think people are often surprised how little materials cost affects the total cost of a job.

I'm having this argument at work, where I want some more expensive cabling installed in a bunch of offices across Scotland so it doesn't need to be done again in another ten year's time, but "that stuff is so expensive, do we really need it?" is what I'm running up against.

So as it turns out today I'm giving them a breakdown of the cost of the job. Guess what the expensive bits are?

Did you guess "wages for two guys, hotel rooms for two guys, 800 miles of diesel, and a couple of ferry tickets?"

Well, you're way ahead of today's crowd then.

[_n_b_]

I've worked on a few big EPC projects in a specialised industrial sector, including some in the UK. Three things drive the first digit of cost, assuming you've hired relatively competent engineers and constructors:

1. (Design) Building floorplate and architectural complexity (i.e., divergence from 'big box')

2. (Construction) Schedule adherence. Almost any one-off expense to stick to the schedule is worth it, but to your point, these are often challenged or delayed. Building and testing equipment on skids off-site is almost always worth it.

3. (Design/Commissioning) Schedule adherence. For commissioning this is typically driven by design choices (did you pick a high-TRL process, or if not, do all the work required to mature it in parallel to construction?) and by building the right commissioning team (knows their job, knows the plant).

If more expensive plant & equipment gets you ahead on any of these 3, 99% of the time that is an overall optimisation.

[jimnotgym]

I was once working on a one off build and also on a smaller build at the same time. The smaller build was built start to finish as per the plans, the larger one was choices all the way.

The net result, we topped out and roofed the big house, then built the small house in its entirety while the owners of the big house chose their windows. Add that in favour of waterfall design...

[SoftTalker]

Not permitting and regulation? We're told that is the biggest impediment to development.

[tristor]

Permitting and regulation is generally a sub-component to each of the three things mentioned, and can be a major factor in schedule adherence for large scale construction projects. Whether that is the primary impediment or not is often a factor of the specifics of the project (and its design) and the overall environment. During major events (e.g. COVID), materials access and availability was a far more challenging aspect of schedule adherence for most large projects than any other factor.

I've never worked in this field as the GP, but I have family that do and I've heard plenty of stories and made my own observations, but definitely take my two cents with plenty of salt. Maybe GP will reply also.

[_n_b_]

A week late but... in my experience (potentially sector/location specific but I don't think so), most high-risk licensing and permitting activities come before construction starts, and certainly almost always before above-ground construction starts. So regulatory issues may challenge overall project viability, but you tend to know before cash is sunk if you're going to be, for instance, refused planning permission.

[rkangel]

In general, in the UK, labour costs dominate. How do people not understand that?!

This is what's interesting with AI pricing at the moment - it has gone from "a fraction of the equivalent labour cost" and so people have tried to cut staff, and is moving to "on par with labour cost" and all the calculations change.

[bena]

Not just the UK, labor is usually the dominant cost of anything.

Our house flooded about half a foot a year or two ago. I had to replace all the baseboards. The damage was assessed at $40k. I tried to contact contractors to do the work, but the job was so insignificant compared to other jobs in the area, and we were in the middle of getting our house raised, that it was taking forever.

Including tools I did not have prior, material costs ran about $5k - $7k. I did the work around my job and other obligations, so about one day a week for a couple of months. If I were to honestly guess, it probably took me about two weeks. And that's measuring, cutting, installing, caulking, and painting. And there were some inefficiencies in my process.

[PunchyHamster]

> I think people are often surprised how little materials cost affects the total cost of a job.

It's because they frankly never did it. Nobody that had to contract something around the house is surprised by cost like that, it often costs more than price of renting equipment + you doing it yourself 3 times slower than an expert would did it, even if you're paid well.

There is reason there is so many DIY channels, labour costs are high and install costs of some stuff can be ridiculous (like 2 hour job to install AC costing more than cheap AC unit).

That's also partly the reason the more expensive materials are used - if they offer savings in labour (say way faster to put in), they might be worth it vs paying someone for more hours

[SoftTalker]

It's why plumbers use $25 sharkbite fittings now instead of soldering in a $2 copper fitting. But of course the sharkbite relies on a rubber O-ring and will probably leak in 10 years, the plumber will be long gone or the property probably under new ownership who don't remember.

[giardini]

Softalker is right-on in his warning:

We usually have a few freezes in the winter and some homes' pipes freeze. I was surprised, in speaking to a plumber, to find that pipe clamp installation had come to dominate the repair market (as opposed to repairing/replacing the leaky pipe).

In his first year this plumber had arrived at the plumbing supply house to find all pipe clamp orders backlogged two weeks! He thus determined to, during the warmer months, stockpile a cache of pipe clamps for the coming winter.

Furthermore, as SofTalker states, the fitting is usually left in-place instead of being replaced! Yet one more reason to have a prospective home inspected by someone who is very knowledgeable.

[Animats]

Automated radial welding for pipes seems to be slowly reaching small, plumbing-sized pipes.[1] This has been around for years for larger pipes, but the equipment is now down to home plumbing diameters. Still too expensive, though, at around US$10,000.

[1] https://www.youtube.com/shorts/Jr1TZW8dKCw

[ErroneousBosh]

Yeah. I mean I just had some concrete slabs laid to put a bike shed on (literally bikeshedding, the colour is green, that's what it comes powdercoated in from the supplier, take it or leave it).

It was 300 quid.

I could not buy the materials for 300 quid.

Two guys showed up with eight slabs, half a tonne of Type 2 and half a tonne of sand, and then the next day the landscaper showed up and did about six hours of work to dig it all out, fill it all in, and put the slabs down.

It's absolutely perfect, exactly how I wanted it, and it would have taken me a couple of days and cost far more - and I'm quite good at that kind of stuff, it's just not what I do all day every day so the landscaper will be far better at it.

[jimnotgym]

My experience when i was in the trade is very few people know what perfect looks like, and so are perfectly willing to forego decent workmanship in favour of cheap. One of the reasons I left the trade, you could make more money doing a bad job, and I had no desire to do that.

[cucumber3732842]

>I think people are often surprised how little materials cost affects the total cost of a job.

Because people don't understand how much compliance and box checking and check the guy who checked the last guy's work there is in a "you need government permission for this and not the easy permission they give a homeowner deck project" sized construction project.

[quickthrowman]

> Did you guess "wages for two guys, hotel rooms for two guys, 800 miles of diesel, and a couple of ferry tickets?"

Yes, but I happen to sell and run electrical work so it’s an easy question ;)

[iamflimflam1]

I hope you’re prepared for a huge amount of bike shedding… but if we pick this color, we can save a couple of dollars…

[ErroneousBosh]

It's going in a suspended ceiling so it has to be purple.

[throw0101d]

> Stainless steel rebar is a thing. It's expensive […]

That's an understatement. Fiberglass (GFRP) tops out at roughly US$ 2.50/foot, while SS can get up to $9:

* https://www.wellcoindustries.com/the-cost-of-rebar-and-the-c...

The low-end of plain steel rebar is $0.40.

[IAmBroom]

As the GP noted, it's still only a small bump in overall cost.

[mixmastamyk]

Also lower TCO, total cost of ownership.

[yorwba]

> Two piers were built in the 1940s, side by side

As far as I can tell, only one pier was built (using stainless steel rebar) and the presentation is comparing it to a hypothetical alternative as a theoretical exercise: "What if the Progreso Pier was built using carbon steel rebar?"

[boringg]

I think that was the prior pier maybe in the picture? The main pier only has one - it’s massive and goes forever. Pretty beefy construction too given that it takes a lot of heavy trucks.

Progreso - great pier and a great kiteboarding spot.

[world2vec]

There's also Glass Fiber Reinforced Polymer rebar but I don't know much about costs and how good it is vs stainless steel rebar.

[litoE]

As I understand it, concrete has excellent resistance to compression but fails easily on traction, while steel bars are exactly the opposite. That is why you put rebar in concrete: the steel handles the traction loads and the concrete handles the compression. This works well because both materials have similar coefficients of thermal expansion, so as the temperature changes they both expand and contract at the same rate. I suppose you can engineer fiberglass to have the same thermal expansion coefficient and use it to replace steel (assuming it is just as strong on traction). But how would you "build without rebar even"? Wouldn't your beams start cracking at the bottom, where they are subject to traction?

[mikepurvis]

To build without tension you have to build structures that basically look like Roman structures [1]: a bunch of tightly spaces arches so that the entire thing is in compression, with no meaningful tension anywhere.

But it turns out that's pretty inconvenient; we really like doing dozens of feet of span for highway overpasses, building floors, and everything else. So we put rebar in all the concrete and just acknowledge that that means it has an absolute maximum lifespan of a century or two, and will certainly not last for millennia the way pure concrete in pure compression can.

[1]: https://www.theartnewbie.com/blog/rome/roman-arch

[Modified3019]

The “it’s built so everything is under compression” is great thing to bring up, but fyi your link is AI generated, filled with senseless repetition and “it’s not just x, it’s y”.

Looking it up on archive.org shows it was generated this year.

[mikepurvis]

Blah, so you're right. I was just looking for a link with some representative reference pictures, but I should have done more diligence. Thanks for pointing it out.

[cm2187]

They could do large arches too, see https://en.wikipedia.org/wiki/Basilica_of_Maxentius

[throw0101d]

> To build without tension you have to build structures that basically look like Roman structures [1]: a bunch of tightly spaces arches so that the entire thing is in compression, with no meaningful tension anywhere.

Until an earthquake occurs, and then all of those mostly-down forces turn into side-to-side forces.

[Zardoz84]

or go and revive Gothic architecture

[pinkmuffinere]

> Wouldn't your beams start cracking at the bottom, where they are subject to traction?

You have a few mistakes here. I’m not trying to demean you, but I’m going to number them just for clarity, as it can get confusing when there are many misunderstandings.

1. You are intending to ask about tension (which the rebar helps with), not traction (the force your tires exert against a road).

2. Tension is not only experienced at the bottom of beams, the location with the most tension will depend on the geometry. For a vertical beam, I think tension will probably be pretty even through the whole beam in most “normal” designs and loading configurations. But it will really depend on the geometry and on the loads being applied.

3. I think when you say concrete beams you’re meaning columns (apologies if I’m wrong about this). Concrete columns are remarkably good at holding up without rebar, because they experience almost exclusively compression! And indeed, ancient Roman designs did not use rebar at all :). It’s certainly possible.

[litoE]

1.- My apologies for the terminology - I took one overview class on the subject in Spanish, and haven't looked at it in the last 60 years. 2.- Agreed - that's why rebar on horizontal beams (and slabs) sometimes goes on the top edge and shifts to the bottom edge. 3.- By beams I do mean horizontal beams. This also applies to horizontal slabs. However, vertical columns also need rebar, especially in earthquake-prone areas. If the ground moves horizontally in an earthquake, the (vertical) columns have to transmit the motion to the upper parts of the structure. This create huge tension stresses on one side of the columns so they need vertical rebar rods on their perimeter.

[kergonath]

> 1. You are intending to ask about tension (which the rebar helps with), not traction (the force your tires exert against a road).

I don’t know if it is the case here, but it is a common mistake for some non-native English speakers. In some languages traction is a false friend.

[projektfu]

And in English, traction also means pulling, but it got somewhat misapplied to the friction of tires, causing confusion in the language. For example, a tractor is something that pulls, and when a broken leg is put in traction, it's suspended to pull it apart and keep the muscles from pulling it together.

Tension, as you say, is indeed the term used in physics and engineering for the force on an object pulling it from either end.

[deepsun]

> exactly the opposite

No, steel is better in both ways, ten times over. It's just more expensive, concrete is a "filler" to cheap out construction.

If you think about it, all engineering is about cheaping out things. It's pretty easy to build awesome projects having unlimited budget.

[selcuka]

As one of my professors said back in time: "Steel is one of the best materials for a number of applications. We don't use it only because it's abundant. "Abundant" and "good" are not always mutually exclusive."

[aw1621107]

Just FYI, I think you're looking for "(in) tension" instead of "(on) traction".

[cma]

There's also stainless steel rebar

[mikepurvis]

Even without the rebar rusting, I think you can still have issues with the steel and concrete having difference thermal expansion properties, particularly for outdoor strucutures where a freeze/thaw cycle is in play.

Basically the rebar works itself loose over time and creates micro-fractures in the concrete that then get moisture in them and can cause expansion damage— all without the rebar itself ever rusting or "failing".

[cma]

Maybe so, OP mentioned they were very similar and that still seems to hold for stainless. How about the aggregates within? The composite makeup can result in different CoTE than the individual aggregates, I think that's one part of concrete sidewalks cracking though, sometimes near shaded/unshaded boundaries. Roman concrete supposedly had some self healing properties before the cracks grew, from the lime inclusions.

[21asdffdsa12]

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

[Izmaki]

> but that is more costly and and less efficient.

Maybe this is the clue as to why our concrete crumbles after 100 years: it's not economically efficient to make it last longer?

[rkangel]

A broader view of this point would be "the economic structures in some countries do not allow for investments with a long payback".

[PunchyHamster]

Or simpler: people don't exactly want a house layout that was popular 100 years ago. And definitely not the level of insulation it provided. Nor the fact putting any new wiring and piping thru concrete is PITA

Tastes change and so do other requirements.

but, if we actually built for longevity in use, we could build a very durable shell of a house and then use more perishable but easier to modify methods for inside. Build a nice durable brick and concrete shell then use wood and plasterboard for room walls and floors

[rkangel]

There are some downsides, but most people on the UK would prefer houses that were 100+ years old. In the village I live in the houses immediately around me are "only" 50 years old. Most of the ones on the main street are well over 100 years old.

Housing tastes don't really change that much. Yes over the years we've had to fit things like double glazing and better insulation but that's a whole lot cheaper (and better for the environment) than building a whole new building.

[Brendinooo]

Having been around enough houses (in the US) to have a balanced opinion - I personally prefer older houses but

- older houses tend to be a lot more inefficient in their use of square footage

- the rooms inside tend to be a lot less open, and one man's "fun/quirky layout" is another man's "why do I have to go down a step then immediately go up a step to cross a hallway"

- and, I begrudgingly admit (as I don't like how they wreck house aesthetics) people really like big, attached garages

My overall suspicion is that when a lot of people say they like old houses, what they really mean is that they like buildings that look beautiful on the outside and, to a lesser extent, have a sense of being rooted in some kind of context.

[jimnotgym]

Cupboards, nooks and crannies are one of the things people like in an old house. They are often a side-effect of chimney and fireplace construction. A new house in the UK has nowhere to put anything!

[PunchyHamster]

I think there might be some survivorship bias there - the house that survived 100 years in state where people still want it probably was built well, the 100 years old ones that didn't were scrapped/rebuilt

[freedomben]

> but most people on the UK would prefer houses that were 100+ years old.

Why do most people prefer older houses?

[rkangel]

I think two reasons:

Character and history - they tend to be more individual and different, and have more character than the cookie cutter modern mass builds.

Solidity - they tend to be more stone and brick, instead of the timber framed buildings that are more common in new builds.

[nly]

Primairly because old houses are on bigger plots and allow for extensions and conversions.

[rkangel]

In my area of the UK at least, the house layouts of houses built last year aren't appreciably different from those built 200 years ago. That's specifically comparing detached and semi-detached houses. Terraces are a bit different now.

> then use wood and plasterboard for room walls and floor

One of the things I LIKE about older houses is that the interior walls are more solid than plasterboard. There is zero plasterboard in my house and brick gives far better noise insulation than anything timber framed.

[jimnotgym]

Well, better than most timber frames. If you were to ask for a truly soundproof wall you are likely to get a timber frame in two layers with rockwool fill and double thickness plasterboard.

It was also common to build lathe and plaster covered interior partitions in the past. Way before plasterboard.

A modern one off house may well have concrete block downstairs walls to hold the floor up. Albeit, they may get covered with plasterboard 'dabbed on' anyway, to reduce drying time

[aYsY4dDQ2NrcNzA]

I’m passing my latrine down to our great grandchildren.

[Saline9515]

You don't really own a latrine, but just look for it for the next generation.