How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues • Hacker News Board

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#221

Post by iknownothow » Fri, Jul 17, 2026, 9:08 PM UTC

cogman10 wrote: post #216

iknownothow wrote: post #74

For those not familiar, the secret ingredients are to do with the Lime Cycle [1]: 1) Quicklime/Slakedlime (Calcium Oxide, CaO) 2) Lime (Calcium Hydroxide, CaOH2) 3) Limestone (Calcium Carbonate, CaCO3) To keep it simple, typically you start with Quicklime (CaO) and after construction you end up with some mix of all three and after hundreds of years, the masonry transitions to mostly Limestone with microscopic traces…

> The only thing is, it requires maintainance, which is why Portland cement has taken over the world. What kind of maintenance and why did roman cement survive without it? Or are we simply looking at ancient survivorship bias where the surviving roman concrete structures survived through the lime cycle without maintenance until it was no longer required?

I mentioned elsewhere that time taken for setting is also a major factor for why Portland cement is preferred.

Maintenance is probably less of a factor but it also depends on the use case. Take what I have to say with a grain of salt. Lime is a living material that slowly converts lime to limestone. For some use cases, the lime needs to be replenished often through applying lime wash on the plaster of external walls or wet interior walls.

As for load bearing walls or regular interior plaster walls I'm not sure there is much maintenance you can do and they are fairly durable.

As far as I know Portland cement sets faster and is a stronger but has a life span of decades and does not lend itself to be repaired or replenished.

I'd like to also convey some vibes I have about this topic as follows. Imagine having a 2 storey family home made of concrete that you want passed on for many generations. In 50-75 years, repairs/upgrades would require a lot of demolition as concrete with rebar is very strong. Much of the old material is trashed and hard to recycle. A similar house made of lime based products and some stone and wood would lend itself more easily for similar repairs and seamless upgrades and can maintain the same aesthetic look for longer. It feels like lime based products are appropriately strong and suitable for the smaller scale. The old material can be treated like any old dirt or rubble and is less polluting.

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#222

Post by ln809 » Fri, Jul 17, 2026, 9:28 PM UTC

Fizzadar wrote: post #210

iknownothow wrote: post #74

For those not familiar, the secret ingredients are to do with the Lime Cycle [1]: 1) Quicklime/Slakedlime (Calcium Oxide, CaO) 2) Lime (Calcium Hydroxide, CaOH2) 3) Limestone (Calcium Carbonate, CaCO3) To keep it simple, typically you start with Quicklime (CaO) and after construction you end up with some mix of all three and after hundreds of years, the masonry transitions to mostly Limestone with microscopic traces…

Victorian brick houses are all lime based, pointing (mortar between bricks), render outside and internal plaster. (Ours is 140 years old ish). Lime is also more flexible (these houses have minimal to no foundation and constantly move), it’s breathable (no/less damp) and as such it also improves air quality indoors. It’s annoying to do because drying times are days/weeks not hours, but long run it’s a far superior mat…

Spain stone buildings too... common problem modern plaster on those stone walls, folk have forgotten the wall needs to breathe

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#223

Post by giardini » Fri, Jul 17, 2026, 9:30 PM UTC

Animats wrote: post #220

giardini wrote: post #204

Earlier quoted context omitted.

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 deter…

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

That's very nice but I doubt it will replace pipe clamps in ease of installation and cost in a real-world repair environment. Many leaks in say steel galvanized water pipes are the result of corrosion. Pinhole leaks form, then more and then enough water leaks to be noticed on either exterior or interior wall. Jose the Plumber will leave his radial welder in the shop (b/c power is out anyway in the affected area and he doesn't carry a generator on his truck) and reach for his box of pipe clamps. Problem solved and on to the next job.

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#224

Post by quickthrowman » Fri, Jul 17, 2026, 10:00 PM UTC

ErroneousBosh wrote: post #56

Animats wrote: post #54

Earlier quoted context omitted.

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 hav…

> 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…

> 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 ;)

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#225

Post by carabiner » Fri, Jul 17, 2026, 10:48 PM UTC

flippyhead wrote: post #169

I heard once that if the Roman civilization had continued, the state of current technology would be something like 500 years more advanced. I don't know if I ever believed it, but sometimes I do.

can we not do this

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#226

Post by baybal2 » Fri, Jul 17, 2026, 11:50 PM UTC

throw0101d wrote: post #139

Animats wrote: post #54

Earlier quoted context omitted.

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 hav…

> 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.

[dead]

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#227

Post by baybal2 » Fri, Jul 17, 2026, 11:58 PM UTC

metalman wrote: post #80

corrosion of rebar is so significant that there are specs for the acidity of rock used for agregate in the concrete. Older rock that has been "washed" by billions of years of water permiating it , is then used, fetching a premium. Look into it and there are periability numbers for everything, which is how water has gained it's reputation as the universal solven, and granite, hard as it is, is also a bit of a sponge.…

[dead]

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#228

Post by quickthrowman » Sat, Jul 18, 2026, 12:07 AM UTC

Animats wrote: post #220

giardini wrote: post #204

Earlier quoted context omitted.

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 deter…

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

Propress compression fittings which use a hydraulic press are effective enough for domestic water pipes, along with traditional solder joints.

Electrical compression fittings are excellent too, but some engineers still specify exothermic welds (cadwelding) for grounding conductors in particular.

I did a project a couple years back with a mechanical contractor that used a similar machine to the one in the video you shared, except theirs was a bit larger ;) They were welding 18” HPDE pipes together for a geothermal district energy project, we were laying some puny 2” schedule 80 conduit that was glued together with primer and cement for future fiber cables that will connect to the meters of the customers of the district energy system.

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#229

Post by giardini » Sat, Jul 18, 2026, 4:49 AM UTC

quickthrowman wrote: post #228

Animats wrote: post #220

Earlier quoted context omitted.

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

Propress compression fittings which use a hydraulic press are effective enough for domestic water pipes, along with traditional solder joints. Electrical compression fittings are excellent too, but some engineers still specify exothermic welds (cadwelding) for grounding conductors in particular. I did a project a couple years back with a mechanical contractor that used a similar machine to the one in the video you sh…

ProPress are a (high-quality) solution but IIRC for copper piping.

PEX water piping expands and fails less(than galvanized) in freezing temperatures. This is the current accepted replacement for galvanized water piping.

PVC piping is also used but doesn't develop the pinhole leaks that galvanized steel pipe does. However it can fatigue and develop leaks.

AFAIK all can be patched with, ta-da, pipe clamps!

But most water leaks, especially in winter freezing, arise in old rusting galvanized steel piping. I'm not a plumber but I was a condominium association officer and president and so got to choose, watch and pay for repairs.

We had only copper, PVC and galvanized water lines. The copper was well underground and so failed only once in 20 years due to age and a nearby tree shifting the pipes. The PVC never failed but we had almost none. The galvanized pipe was a guaranteed failure every winter unless we took serious precautions when temperatures dropped.

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#230

Post by dev_l1x_be » Sat, Jul 18, 2026, 7:09 AM UTC

otherme123 wrote: post #37

dev_l1x_be wrote: post #34

Earlier quoted context omitted.

This is exactly what we did with houses, buildings. We had perfectly functional 100+ years old fully functional, gorgeous buildings and we replaced those with brutalist concrete/glass barely functional garbage.

In Europe we have plenty of old buildings. The good ones (i.e. made by very wealthy people) tend to be decent, with a skew towards huge living rooms but tiny rooms. The cheaper ones are a mess to mantain: cold in winter, hot in summer, expensive to renovate (it could be more expensive to renovate than to build a new one), bad to no isolation, in my region terribly humid, usually too dark with minuscule windows for mo…

The insulation is the easiest to add to old buildings.

Red bricks offer better thermal insulation than dense standard concrete. Because of their porous clay structure, red bricks absorb heat slowly during the day and release it at night.

Solid concrete blocks, conversely, are highly conductive and absorb/transfer heat much faster, usually requiring added insulation.

We could just fix the insulation where it is bad instead of tear down the entire housing unit and rebuild it with concrete / glass / metal.