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Why was Roman concrete so durable?

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Re: Why was Roman concrete so durable?

#81

Post by ogogmad »

For people who don't know the difference between cement, mortar and concrete:

Cement is a substance used for producing mortar and concrete. It's never used on its own. It is a "binding agent". Note that the term "cement" is often not used correctly in everyday speech, with people talking about gluing bricks together with cement, when bricks are actually glued together with mortar.

Mortar is the glue between bricks. You can see it between the bricks in any brick wall. It is produced by mixing cement with sand. This results in a paste which hardens after being applied to a brick.

Concrete is a substance that can be put into any shape, and then hardens. The bricks in a brick wall can be made from it. (More examples?) It is produced by mixing cement with sand and gravel (which are larger rocks).

There is also reinforced concrete, which the Romans didn't have. While concrete by itself can in principle be moulded into any shape, this can sometimes fall apart after hardening. Reinforcement refers to putting the concrete around metal wiring, which allows for more versatile shapes while maintaining stability.

Feel free to provide corrections.

Re: Why was Roman concrete so durable?

#82

Post by nemo44x »

elzbardico wrote: post #75
nemo44x wrote: post #63

Earlier quoted context omitted.

Then multiple that by 20 (the lifetime of the road surface) and factor in that the resurfacing is significantly cheaper than the initial build and you quickly find roads are easily subsidized by property taxes.

They are not subsidized, they are an infrastructure common good that is financed with taxes.

It depends. Where I live the roads in our neighborhoods are paid for by the town (property taxes) and many roads that run through the town are paid for by the county (income taxes) and then the highways are paid for by the state in part via tolls and other ones by the Federal Government via taxes.

Re: Why was Roman concrete so durable?

#83

Post by insane_dreamer »

jcadam wrote: post #10
insane_dreamer wrote: post #4

Earlier quoted context omitted.

cobblestones for the roads

That is... not a smooth ride.

it's not so bad; where I grew up in France many streets were cobblestone and it was fine. It's pretty rare in the US though except I've noticed it in streets where they have trams running--presumably to reduce the need for maintenance on those streets.

Re: Why was Roman concrete so durable?

#84

Post by avidiax »

nemo44x wrote: post #63
magicpin wrote: post #36

Earlier quoted context omitted.

A fun exercise is to calcualte the cost of some road in a neighboorhood, and compare that to the total collected property tax of all the homes along that road.

Then multiple that by 20 (the lifetime of the road surface) and factor in that the resurfacing is significantly cheaper than the initial build and you quickly find roads are easily subsidized by property taxes.

There are two sides to this coin. The roads need repair continually and resurfacing eventually, yes. What happens when property values and the local economy begin to deteriorate instead of prosper? All those utilities and public rights of way still need those repairs, but there's no appetite to raise property taxes, and the tax base is dwindling, and there's little reason to keep paying the mortgage on a depreciating house, especially once 2/3rds of your street is gone.

How sustainable is a system that requires perpetual good times?

Calling it a ponzi scheme is a stretch, but this guy seems to be the only one talking about this: https://www.strongtowns.org/journal/2020/8/28/the-growth-pon...

Re: Why was Roman concrete so durable?

#85

Post by insane_dreamer »

naikrovek wrote: post #8

the article talks about evidence which has always been present in evaluations of Roman concrete which was "disregarded as merely evidence of sloppy mixing practices, or poor-quality raw materials," and this kind of thing REALLY infuriates me, as a layman. if you don't know how to make Roman concrete, don't assume anything about what you see in Roman concrete while you're trying to figure out how it was made. The mode…

> modern-day belief that we are superior to humans thousands of years ago is just an absolutely insane idea, to me

totally agree that kneejerk response when we see something that doesn't match our current methods is "those people didn't know what they were doing" is both potentially incorrect and certainly unhelpful to the advancement of science

Re: Why was Roman concrete so durable?

#86

Post by ggm »

ogogmad wrote: post #81

For people who don't know the difference between cement, mortar and concrete: Cement is a substance used for producing mortar and concrete. It's never used on its own. It is a "binding agent". Note that the term "cement" is often not used correctly in everyday speech, with people talking about gluing bricks together with cement, when bricks are actually glued together with mortar. Mortar is the glue between bricks. Y…

Reinforced concrete in part is designed to provide structural strength under tension forces. Concrete is stable in compression but has weak resistance to tension. Pretensioned reinforced concrete permits longer unsupported spans but even vertical concrete can benefit from reinforced bars, to prevent spalling. (I believe). Not all reinforcing steel has to be tensioned to be useful, that's a technique for long spans.

Reinforced steel bars hence rebar.

Re: Why was Roman concrete so durable?

#87

Post by [deleted] »

newsclues wrote: post #72
betaby wrote: post #62

Earlier quoted context omitted.

I live in Montreal too, and while all what you say is true ... the same is not true for the xUSSR cold cities I lived before immigration. So quality makes difference. Also planing and designing for less maintenance. Concrete structures from the same era across xUSSR are in way better shape.

Montreal has infrastructure problems because of systemic corruption with the local Mafia. To think that the USSR had better infrastructure (less corruption) than modern day corrupt places like Montreal is a brutal shock.

[deleted]

Re: Why was Roman concrete so durable?

#89

Post by eole666 »

twelve40 wrote: post #64

> following all of the detailed recipes that had been optimized over the course of many centuries i wonder how all those detailed recipes were passed around for many centuries and now all is gone. Was it all passed down verbally?

In the 6th century, big volcanic eruptions, low temperatures and plagues bringed a dark age in Europe and other parts of the world. A large part of the population died. Maybe those recipes were lost during this period.

Re: Why was Roman concrete so durable?

#90

Post by adolph »

adrian_b wrote: post #12

The research paper: https://www.science.org/doi/10.1126/sciadv.add1602

One method to reduce cement’s carbon footprint (which accounts for up to 8% of total global greenhouse gas emissions), is to improve the longevity of concrete through the incorporation of self-healing functionalities. The resulting extended use life, combined with a reduction in the need for extensive repair, could thus reduce the environmental impact and improve the economic life cycle of modern cementitious constructs.

I wonder:

How much of an environmental impact this would make given the number of structures that are not useful before the concrete requires repair?

How much of Roman concrete's reputation for durability comes from survivorship bias--the structures that lasted were just lucky?

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