r/science • u/mvea Professor | Medicine • Nov 03 '19

Chemistry Scientists replaced 40 percent of cement with rice husk cinder, limestone crushing waste, and silica sand, giving concrete a rubber-like quality, six to nine times more crack-resistant than regular concrete. It self-seals, replaces cement with plentiful waste products, and should be cheaper to use.

https://newatlas.com/materials/rubbery-crack-resistant-cement/
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u/leno95 Nov 03 '19

Concrete as a road surface shouldn't be used in areas where there are extreme differences in temperatures in the first place.

Given Sweden regularly has warm summers and cold winters, it could be argued in some parts there's a difference of 50°c between hot and cold periods, which will definitely ruin the concrete.

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u/[deleted] Nov 03 '19 edited Nov 04 '19

In Southern Canada we get tempretures that swing between -40c in the winter and +40c in the summer. Concrete on structures is constantly being touched up and any roads made of it are often in pretty rough shape. Most of them are asphalt.

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u/leno95 Nov 03 '19 edited Nov 03 '19

Asphalt, tarmac or even compressed hard core are far better surfaces than concrete in many countries.

Concrete is a wonder material until weather is a factor.

Edit: not everyone will know what hardcore means in this context; it's typically gravel/crushed concrete around 40mm in diameter used as a sub-base for roads, blinding in trenches and is the large aggregate used in concrete. In the UK it's typically called hardcore or MOT Type 1.

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u/McVoteFace Nov 03 '19

That’s not correct. Asphalt routinely gets ‘milled and filled’ and everyone is happy until it falls apart in 5 years. Continuously reinforced concrete pavement has a life span over 50 years

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u/leno95 Nov 03 '19

This is down to suitability and the requirements of the road. RC roads and pavements are better in some scenarios, and tarmac/asphalt are better in others.

RC roads will be far more expensive even when replacement and maintenance is considered, but that's a balance that is typically weighed up prior to building it.

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u/McVoteFace Nov 03 '19

Not when they go to the MEPDG design software and 22” of asphalt has the same service life as 11” of concrete.

In my state, maintenance costs for asphalt are more expensive than concrete. That gets into present value cost comparison and is subjective

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u/meganmcpain Nov 03 '19

It also depends a lot on the specific environment of the pavement. Design life of concrete might be 50 years, but in a cold weather climate you'll get about 30 before major rehab/repaving needs to be done. Properly paved asphalt should have 10-15 good years in it (design life 20-25), but this is also heavily dependent on how bad the winters are.

The thing no one in these comments mentions is there really isn't any good paving material for large temperature fluctuations, but concrete has more long term durability and thus cost effectiveness for communities. Asphalt may be more "flexible" but that also makes it a lot less strong, and when the weather is cold enough it won't be flexible anymore.

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u/lkraider Nov 03 '19

Granite rock make a good pavement material that can last millenia. Not the most confortable to drive over tho and needs maintenance on the base soil for differences in compaction/erosion.

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u/meganmcpain Nov 03 '19

The base is also something lay people don't consider, but it's so important for performance! I remember working on a concrete street that wasn't in good shape, but it wasn't very old. It turned out that back when it was last reconstructed they experimented with a clay base, which of course just trapped water under the pavement that then froze in the winter and made it heave and crack.

There are just so many variables involved in design and construction of pavement that affects its performance. Add in other issues like cost, logistics, and maintenance and there really is no blanket solution.

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u/thx0138 Nov 03 '19

One reason concrete gets used selectively in some areas it does well in is the cure time before the road is drivable. Asphalt is a matter of hours or less and immediately for small patches. Concrete is 24-48 hours at least. (I don't remember the exact times but this should be a decent ballpark)

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u/McVoteFace Nov 03 '19

We designed some 6hr cure time patches a couple of years ago. Patching is kind of a niche item though

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u/thx0138 Nov 03 '19

Interesting, that would definitely help with that aspect.

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u/iamnotaclown Nov 03 '19

The same asphalt is recycled into the new surface, though. Asphalt is the most recycled product in North America.

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u/McVoteFace Nov 03 '19

If I gave you a battery that could charge in a minute but you had to charge it every 4 hrs versus a battery that you never had to charge and would last you 8 years then you had to replace it. Which battery would you chose?

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u/iamnotaclown Nov 03 '19

Depends on the energy cost of production. Recycled asphalt is going to be cheaper since no clinker is required.

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u/McVoteFace Nov 03 '19

Offset by millions of idle cars sitting in construction