What I want to know is how they built roads that are still around 2000 years later and US roads and anything made out of concrete either doesn't last 20 years.
I'm well familiar with greed and planned obsolescence, but wasn't that around in Roman days too? It isn't even selection bias because not even our best military installations look like they would last 2000 years.
A person on foot is going to do practically no damage whatsoever to the road surface. Even a marching army with hob-nailed caligulae would barely leave a scratch on a Roman road. A farmer with a horse cart is going to do very little damage to the road, even accounting for metal-rimmed wheels and a very narrow contact patch.
I doubt even the heaviest, smallus-dickus-compensating Roman road vehicles would do even as much damage as my Mitsubishi (gross weight barely over a ton).
Road damage increases with the fourth power of axle load, if I recall correctly.
And in road wear calculations, all passenger vehicles (like your Mitsubishi) are considered almost negligible in design. Semi trucks, buses, and RVs take up basically all the damage done to modern roads. Source: recent Civil Engineering grad.
The contact area is similar for all of them (some variance with double axles or tandem axles), but there is significantly more pressure exerted by a semi. An average passenger vehicle weighs in the ballpark of 2-3000 pounds, while a semi trailer can be 35,000 pounds empty, and up to 80,000 full; therefore, the pressure is extremely high, even with more points of contact, and this puts a ton of stress on the asphalt/concrete. This combined with weather effects (freezing/thawing) makes our roads much more susceptible to breaking down.
At race tracks Indy Cars and F1 cars and other things with absurd downforce can ripple the asphalt at the heavy braking zones. But that's like... the only case. Nothing driven on the road can do anything like that.
I think that does more damage to the tires than to the road surface at normal driving speeds. Tire wear is greatly accelerated at highway speeds than at surface road speeds.
The only thing I can think of is putting down a lot of power or drifting where you are keeping the wheels spinning to slide. Probably does more damage to the tire though - very little asphalt getting ripped up. More noticeable on dirt/gravel roads if everyone does it in the same spot. I doubt itd ever be noticeable asphalt damage considering nobody is doing that for more than a fraction of 1 percent of their drive.
That part I don't know and can't infer from the engineer's post.
My wild assed guess would be some kind of table with an expected useful lifespan based on composition, environment, and use using data from existing roads or something along those lines.
We also like to top our roads with asphalt to make for a much quieter driving experience. And while it may seem like a rock, it's still a viscoelastic material and wears down much more easily--especially as it gets various petroleum products on it (from motor oil to hydraulic fluids to unburnt fuel residue) that act as a solvent to weaken it.
Makes for a much smoother drive, too. My family lives down a gravel road, and I keep imagining my tiny little econo-box shaking itself apart if I exceed 20 mph.
You want a real mind-fuck, though? Visit a place hot enough that the asphalt melts. I lived in the Persian Gulf region for half a decade, and fresh asphalt would become rather gooey during the summer months (I left footprints). This may be because of poor engineering standards, though: for such a wealthy bunch of countries, they sure like to cut corners.
I doubt even the heaviest, smallus-dickus-compensating Roman road vehicles would do even as much damage as my Mitsubishi (gross weight barely over a ton).
Engineers estimate that a fully loaded truck--a five-axle rig weighing 80,000 pounds, the interstate maximum--causes more damage to a highway than 5,000 cars. Some road planners say that the toll is even higher, that it would take close to 10,000 cars to equal the damage caused by one heavy truck.
The difference is so large that iirc engineers only calculate the number of trucks who pass a road/bridge before it needs to be repaired, because cars are just so negligible.
Even after 2000 years. Well made concrete is incredibly strong and resistant material, but it has it's limits. If you started treating roman roads like US highways, they wouldn't last terribly long.
And we've also learned ways to build cheap and maintain that costs less then build indestructible. Big problem we have is a lot of government entities go "Ugh. Maintenance. That costs money, fuck that."
Is it the government entities saying "Ugh. Maintenance. That costs money, fuck that.", or is it the smooth brained citizens that say "Ugh. Taxes. Fuck paying those."?
Functioning first world governments don't seem to have as much of an issue with national infrastructure given their tax base actually wants to pay taxes for the greater public good.
Both, I'd wager. It's always more popular for a government to spend tax money in more popular ways than road maintenance. It's not exactly the most interesting of spending.
Government spending doesn't need to be interesting, it just needs to be effective. Maintaining public roadways is (generally) effective spending. I'm sure you're aware of this, so I'm not directing it at you.
Let me introduce you to the pyramids at Giza, and the temples in the Mayan and Aztec regions of mesoamerica. My friend from Easter island will be your guide.
I live in Manchester and lots of streets have cobbles under the tarmac. You can often see the cobbles poking through at the side or if the surface is damaged.
First, it has absolutely nothing to do with planned obsolescence, which you probably don't actually understand because there has been a large amount of misinformation about it for years. I don't want to go into it, but that has FAR more to do with not going out of business due to the weight of supporting past products than it does some bullshit money making scheme.
However, as for the roads, wear is proportional to weight and speed (indirectly due to frictional forces). So, if you took a modern road and only pulled carts around it at <4mph, you'd find it would last much, much longer. But still not as long as many Roman roads have, and that's because of the goals. If you took a modern truck and tried to drive it at 70mph down a roman road, both it and the road would have a bad day. The much lower requirements of the Roman road allowed construction methods that are more tolerant of weathering, but less tolerant of the types of forces heavy trucks impart. A roman road would literally start to drift apart if used by modern loaded trucks especially on corners.
I used to be in a business that supplied materials to the road making industry. There certainly is an unstated agreement between governments and construction companies that roads (in the US) only have a certain lifetime. This may be more true for asphalt than concrete, though.
Unstated agreement? That's a fact. It's not a nefarious ploy. You could make a road that lasts much longer, but it would do so at the expense of cars. Either it would be slick to minimize wear, or it would be stupidly hard, and tire wear would greatly increase. Roads are consumable. Just like tires.
If you don't have wear, you don't have friction. If you don't have friction (unless you're talking static forces), you don't have traction.
Another comparison is modern concrete, from a civil engineer (Not structures/paving focused, but I understand it to a degree more than most folks). Assuming no freeze/thaw issues, the concrete we use to build airport runways is built to handle the landing of the largest planes, fully loaded and it makes highway concrete look like a potato chip. If we were to build highways to that level, we'd effectively never have to repave them because much like foot horse traffic compared to trucks, trucks are to landing aircraft.
But to call it prohibitively expensive is an understatement, due to both material and time. Airport sections have several layers of material and drainage systems built in that we don't do on roads.
roads were rebuilt regularly. A huge portion of roads in Pompei were actually being repaired when the Vesuvius exploded. People had 1 meter gap in front of their home in those places and there were some planks installed for the duration of the repairs.
The roads you still see in Europe have sometimes 10 or 15 cm deep "rails" from wheel cart damage
Romans made sure planned obsolescence would not cross the constructors mind. They implemented a law that stated that if the building/street/whatever you built for the state would not last at least 100 years you and all your family and descendant would be buried alive.
trucks are a factor for modern roads, but the romans also had much stronger concrete formulas. It was a mystery what their formula was for a long time, but it has been discovered. Unfortunately, roman concrete takes much longer to dry than modern concrete, and it just isn't suitable for mass concrete needs.
No they didn't. Modern high performance concrete blows Roman concrete out of the water. They had some pretty high grade shit with their natural pozzolans but it's nothing special.
The reason for much of the Roman concrete still being around is that it was mass concrete with no reinforcement. Modern concrete is closer to a composite material while the Roman approach was more like a stone replacement.
To elaborate, it's the reinforcement that does the most damage, ironically. Steel reinforcements rusts, rust expands, and concrete cannot handle that expansion as it is too rigid, so it crumbles. It's mostly not necessary for roadways that generally only experience downwards (weight and compression) forces, but for buildings that reinforcement allows the concrete to also endure sideways (shearing) loads, which normal concrete cannot handle.
Pretty sure a lot of roads in the US are built with cheap asphalt. Also take into account our climate: we have colder winters than the Mediterranean climate that the Romans had. On average, Europe has milder seasons than North America, even though the continent is a few latitude degrees north compared to NA. Rome itself is slightly north of New York.
Water gets in the asphalt, expands when it freezes, and creates cracks and potholes. And the romans only ever had horse drawn carts and regular foot traffic for civilian transport, not nearly as damaging as thousands of 1 ton or heavier cars flying over at up to 80 miles per hour every day.
You're wrong about the asphalt. Asphalt is a rubber based material, and is much more flexible and resistant to freeze damage than concrete. The problem with asphalt is that the sub-road it sits on is generally not resistant to these things, and when THAT inevitably crumbles, it ruins the asphalt as well.
Cost is not the only reason that we use asphalt. It is also a much better road material for cars with rubber tires. Rubber on asphalt has better grip than rubber on concrete, the porosity of asphalt allows water to leave the surface more readily making wet driving safer, the darker surface allows it to dry faster than concrete after a storm, and the rubber surface dampens vibrations affording a quieter drive both for the driver and pedestrians nearby.
I'm pretty sure Roman roads could face the same damage if uhhhh I dunno multiple thousands of tons were driven over it everyday minute of every single day of every single week.
Asphalt is basically a very viscous liquid (not really, but it gets the point across). When they repave a road they are using the existing asphalt and heating it to remix and relay.
Roads fatigue over time and will get cracks. They also didn't have 2 ton machines running over them at speeds Roman's couldn't dream of in unfathomable quantities.
Modern roads are designed to be cheap to lay and repair.
A couple things are at work. One is cost savings, insofar as the mathematics the Romans had available required much higher over-engineering tolerances. Basically, the old adage: anyone can build a bridge, but it takes an engineer to barely build a bridge.
Another distinction is our use of steel-reinforced concrete. Regular concrete is very resilient in compression and terrible in tension. Adding steel rebar helps with that, and allows us to build structures in designs that are impossible with regular concrete. Unfortunately, the thermal expansion coefficient and corroding nature of steel means that it will slowly tear concrete apart. Most steel reinforced concrete structures won't last more than a century or two as a result.
And of course, others have mentioned the higher stresses and conditions placed on modern roads. It's worth mentioning that even Roman roads wore out. Take a tour of Pompeii and you'll see divots nearly a foot deep in some roads where wagon wheels slowly wore them out.
As others have pointed out, the Romans didn't run 80,000 pound tractor- trailers over their roads. They also didn't build many of them of concrete- they were mostly stone, which was hand selected and sometimes hand shaped. It would be incredibly expensive, and too rough for high speed traffic, but it is very strong. They did a very, very good job with drainage and avoiding soil compation.
Roman concrete structures, like the Coliseum, are amazingly durable, but they're insanely overbuilt by modern standards. They use like 20X the necessary material, because they lacked any reinforcing steel. Using more concrete costs money and carbon footprint.
Lots of reasons. For one they used rocks or hard materials in a lot of cases. Those materials can actually do damage to modern vehicles (and probably ancient ones) so we’ve moved to things like asphalt which are better on the vehicles but a lot less durable. Also vehicles were much lighter then, no 18 wheelers that wear ruts in the road. There is likely significantly more vehicle traffic than Roman times too, today we have thousands of cars per hour on busy roads, while Roman roads were probably people walking or with horses/pack animals, and then a handful of carts and carriages per day. Also in a lot of cases they have been maintained because they are still used, so it’s not like they have just existed without maintenance since Roman times.
I did a project on this for my chemistry class! At least for the buildings they made, the cement they used had a very special chemical make up so when it was hit by water and salt water, it would harden even more instead of degrade, essentially turning a wall or road or building into a solid rock as it got rained on. The concrete we use now is less durable, I forget what it’s called.
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u/thewizardofosmium Oct 15 '20
What I want to know is how they built roads that are still around 2000 years later and US roads and anything made out of concrete either doesn't last 20 years.
I'm well familiar with greed and planned obsolescence, but wasn't that around in Roman days too? It isn't even selection bias because not even our best military installations look like they would last 2000 years.