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An article in The Economist makes the case for "wooden" skyscrapers:
New techniques mean that wood can now be used for much taller buildings. A handful are already going up in cities around the world. The 14-storey Treet block of flats in Bergen, Norway, is currently the tallest. But Brock Commons, an 18-storey wooden dormitory at the University of British Columbia in Canada, is due to be completed in 2017. That is when construction is expected to begin on the 21-storey Haut building in Amsterdam. Arup, a firm of engineering consultants working on the project, says it will be built using sustainable European pine. Some architects have even started designing wooden skyscrapers, like the proposed Tratoppen ("the treetop" illustrated above), a 40-floor residential tower on the drawing-board in Stockholm.
Wood has many attractions as a construction material, apart from its aesthetic qualities. A wooden building is about a quarter of the weight of an equivalent reinforced-concrete structure, which means foundations can be smaller. Timber is a sustainable material and a natural "sink" for CO2, as trees lock in carbon from the atmosphere. Tall steel-and-concrete buildings tend to have a large carbon footprint, in part because of the amount of material required to support them. Using wood could reduce their carbon footprint by 60-75%, according to some studies.
There are two main concerns about using wood to build high. The first is whether wood is strong enough. In recent years there have been big advances in "engineered" wood, such as cross-laminated timber (CLT) made from layers of timber sections glued together with their grains at right angles to one another. In much the same way that aligning carbon-fibre composites creates stronger racing cars, aircraft and golf clubs, CLT imparts greater rigidity and strength to wooden structures. A recent experiment by Skidmore, Owings & Merrill, a firm of architects, and Oregon State University, shows how strong engineered wood can be. The researchers used CLT in a hybrid form known as concrete-jointed timber. This featured an 11-metre wide CLT floor section with a thin layer of reinforced concrete spread across the surface. Thicker sections of concrete were added where the floor was supported by pillars. It was put into a giant test rig where a powerful hydraulic press pushed with increasing force onto the surface. The researchers wanted to see how the structure moved under load, but kept pressing in order to find its limits. The floor finally began to crack when the load reached a massive 82,000 pounds (37,200kg), around eight times what it was designed to support.
If you want to know what the second main concern is, you'll have to read the article. 😉
(Score: 3, Insightful) by Grishnakh on Wednesday September 21 2016, @03:36PM
In the forbidden zone on Cyprus, concrete buildings abandoned since 1974 are falling apart.
Yes, but as you pointed out earlier, modern concrete is made differently. You don't need to abandon concrete for it to fall apart; the Northeast is chock full of falling-apart concrete stuff that has been maintained. Sidewalks, in particular, are really bad; I used to live in NJ and they constantly replaced sidewalks in sections because they'd go bad from all the salt used in the winter.
One big advantage with the Roman concrete (aside from its different formulation) is that it isn't steel-reinforced, so it doesn't have the expansion problem you point out.
If we want to make really long-lived concrete structures (which we don't; we don't care about longevity as a society and aren't interested in spending extra money to achieve it), we'd figure out how to make concrete more like Roman concrete, then we'd reinforce it with heavily powder-coated steel I would think, to prevent corrosion.
(Score: 2) by deimtee on Wednesday September 21 2016, @07:42PM
We know how to make Roman concrete. Basically, replace most of the water with fly-ash. The Romans used volcanic ash (look up Pozzolanic cement).
The reason we don't make it today is that you have to tamp it down really hard, and continuously, as you add it to the form, and it takes a really long time to set.
If you cough while drinking cheap red wine it really cleans out your sinuses.
(Score: 2) by Grishnakh on Wednesday September 21 2016, @07:56PM
Well it'd be interesting if someone *did* start making things out of it then. Fly-ash is a readily-available byproduct of coal-fired power plants, and considered a hazardous waste, so it'd be nice if it was used for something productive. And Roman-style concrete should last far longer than the crap we use now. Of course, everyone wants everything in a hurry these days, so good luck getting anyone to adopt it, but if anyone did, it should be governments because they should have a vested interest in making things that last a really long time (infrastructural things like bridges for instance).
(Score: 2) by butthurt on Thursday September 22 2016, @12:19AM
you have to tamp it down really hard, and continuously, as you add it to the form
One of the pages to which I linked said that it was laid, not poured, because the aggregate used by the Romans was coarser than what we use today. The use of fly ash from the burning of coal, to approximate pozzolana, was advocated. I gather that fly ash is being used, but isn't the norm.
(Score: 3, Interesting) by deimtee on Thursday September 22 2016, @10:35AM
Regarding being laid, that was pretty much what I meant. You throw a layer in, then pound it down until there are no voids left, then do it again, ad nauseum. The mixture is barely damp so it doesn't settle like modern concrete. Fly ash does the same as pozzolana, it replaces water in the mix and fills the voids that the water in modern concrete leaves. The two main reasons for Roman concrete durability are the extra binding by the silica, and the lack of voids in the final structure. Making something porous is a good way to make it temporary.
If you cough while drinking cheap red wine it really cleans out your sinuses.