6 ms·
Roman architectural revolution
- littlestymaar 4y agoThe saddest thing with modern concrete constructions compared to Roman ones is that although Portland cement is much better than the Roman one, the use of rebar makes reinforced concrete construction ephemeral: as soon as the rebar start rusting, the concrete fractures, giving way to more water to further oxidize the metal leading to the inevitable decay of the building.
- readthenotes1 4y agoWell, they used rebar in the coliseum in Rome... It got stolen if I recall correctly
- bsder 4y agoAyup. The whole reason why the Coliseum held together in a seismically active zone was the fact that the Romans used iron clamps and lead rebar. One of the reasons why you see "drill holes" in the Coliseum is that was how people were extracting the valuable metals. Of course, once the clamps and rebar were extracted, the Coliseum was now quite vulnerable to earthquakes.
- jutrewag 4y agoThat’s interesting. Wouldn’t lead rebar solve the problems we’re having with rust and corrosion (radioactivity/toxicity question aside). Does it even have the structural strength to be useful?
- bsder 4y agoLead wouldn't solve our modern uses of rebar. Rebar in modern concrete is mostly to provide stength in tension as opposed to "compression" (which concrete is quite strong in). Modern building then relies on this strength. The lead rebar in the Colisseum was mostly to keep blocks that were laid in compression the ability to stay locked and aligned even if they got shifted a bit.
- jaclaz 4y agoLead has nearly no tensile strength. It was used to fix the clamps/braces to keep stones together in the stone masonry, the clamps themselves were steel alright. https://artofmaking.ac.uk/explore/tools/18/Metal-clamp/pin https://artofmaking.ac.uk/explore/tools/18/Metal-clamp/pin
- KineticLensman 4y agoIIRC correctly from a visit to a Roman site in Jordan, the Romans used thin lead sheets between the segments of tall columns (in temples etc). This allowed the columns to flex slightly. The guide demonstrated this by inserting a coin between two segments, and you could see the coin moving very slightly up and down as the apparently immobile column moved.
- regularfry 4y agoWhere can I read more about this? I've not come across lead rebar before and Google is being spectacularly unhelpful.
- Etrnl_President 4y agoYou can use basalt rebar, saves on concrete too.
- CuriousCosmic 4y agoI can hope that as basalt rebar becomes cheaper and closer to a steel analogue, it'll supersede traditional steel rebar.
- jutrewag 4y agoIt’s going to be a while. Steel is $0.30 per linear foot while basalt rebar is around $2.25 per linear foot. That’s almost an order of magnitude difference.
- jaclaz 4y agoSteel is priced on its weight, a linear foot tells nothing unless you specify the diameter of the rebar (or its weight per unit of length).
- wolfram74 4y agoHow much variation is there in rebar diameter? I thought it was pretty standardized. If so length to length comparison would make sense. Though I am curious about price fraction, is the rebar half the cost of a chunk of reinforced concrete? a quarter? a tenth? I suppose it varies with how much reinforcement there is.
- jaclaz 4y agoLots of variation. Typically used diameters in buildings (Italy, Europe) are from 10 to 24 mm, but 6 and 8 smaller diameters (mostly used in electrowelded nets or in smaller pre-cast manufacts) and larger diameters 26 28 30 32 mm (only used in large structures like bridges) do exist. https://www.oppo.it/tabelle/tondi_sezionexnumero.htm https://www.oppo.it/tabelle/tondi_sezionexnumero.htm So, a range from 0.2 to 6.3. kg per meter. Cost is (aproximation) between 1.5 and 2 €/kg, it depends on a number of factors and is a fluctuating one, though it is usually the same in a same country, without much difference on the specific area. Typically a foundation will have between 60 and 90 kg of steel per cubic meter, pillars and walls between 80 and 120, and slabs/beams between 100 and 150. Cost of concrete is even more varied and it is heavily (even in the same country) affected by the cost of the local aggregates (sand, gravel, etc.) so it is hard to make a ratio valid everywhere, but surely it is much higher than what you hypothized. If we assume that price of concrete (not reinforced) is 100-120 €/m3, this ratio to rebar cost is at least 1:1, but could go up to as much as 1:3.
- mitthrowaway2 4y agoIn what ways is Portland cement better than Roman cement?
- littlestymaar 4y agoIt has much better mechanical properties.
- jaclaz 4y agoIt is not necessarily "better", it is "different": https://news.ycombinator.com/item?id=31834833 https://news.ycombinator.com/item?id=31834833 https://news.ycombinator.com/item?id=29377799 https://news.ycombinator.com/item?id=29377799 Currently the trend in cement is to add pozzolanic components to portland based cement in larger quantities to combine the best of the two (fast setting and high resistance of Portland with resistance to water and cracks of Pozzolanic).
- brutusborn 4y agoSome places regulate the use of coated rebar to reduce corrosion risk. We could also use stainless rebar. The real problem is that there is not many incentives to construct things to last, the implicit assumption is that we will want something different in <100 years, so why build it to last? You could do lots of things to increase building life, but fundamentally people want things built cheaper and faster with the latest stuff, and don't care about long term implications. Although I wish people would care about these things, the truth is that it is the minority who do.
- littlestymaar 4y ago> Although I wish people would care about these things, the truth is that it is the minority who do. Actually, most layman do care about it, but short-term KPI-driven management (in the private and public sector alike) don't, because as you say they don't have the proper incentives.
- brutusborn 4y agoMaybe we just know different people. In my experience laymen may care about it in the sense of “I wish my apartment building wasn’t falling apart” but not in the sense of “I want to build a house that my great grandkids can live in” because that’s hard and costs lots more money (upfront). Part of the problem is information, in that it’s hard to know how long things will last. But I think this is secondary to most people being short term focused. I’d love to see a building company offering special materials for an extra long design life, but I doubt many people would be interested.
- loxs 4y agoMost laymen would not and do not pay for lasting buildings.
- throw_pm23 4y agoThey would not pay because they would not trust that the contractors actually did the thing which made the building last more. There is an information asymmetry which creates a market of lemons. If I would build with my own hands I would use the best that money can buy.
- trabant00 4y agoModerd concrete buildings have a higher that useful life. And for the few exceptions we can always consolidate.