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Comment by gipp | Hacker News Reader

The last time I saw something about these highly porous pavement alternatives, it was pointed out they tend to be very vulnerable to freeze-thaw damage and that this damage also lowers the porosity dramatically. Basically making these kinds of materials unsuitable for urban use outside of tropical- or near-tropical areas. Has this changed?

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http://www.cement.org/cement-concrete-applications/paving/pe... "However, in climates prone to severe freeze-thaw cycles, some are hesitant to use pervious concrete pavements until it has been proven that pervious concrete can be made to resist freeze-thaw damage." Pittsburgh does go through freeze thaw cycle, so I assume there aren't much problems

https://www.unh.edu/unhsc/sites/unh.edu.unhsc/files/pubs_spe...

According to this, it also reduces the amount of salt needed 75% for deicing and the pavement doesn't seem to have been damaged from reading the abstract.

Well, if Pittsburgh is using it, it is terrible. We have so many potholes (and huge ones). It has become much worse over the last ~5 years. For several months we had a multi-foot hole blocked off by cones until the city could fix it. It essentially was in the middle of a two way road. It was terrible. I see more and more each winter.

That's not because of the cement but the geology of Pittsburgh itself. Limestone bedrock and the "underground river" contributes to potholes and other geologic anomalies. If anything, adding bioswales and having a way to put the water back into the ground would stop the potholes from happening in the first place.

Yes, but that still doesn't mitigate the rapid freeze/thaw effects on the concrete/asphalt that the City of Pittsburgh uses.

I think you are confusing sinkholes and potholes. The two aren't really related.

That sounds, from your description, more like a sink hole than a freeze-thaw induced crack? Hard to tell without seeing it.

The main problem I see with them is people's perception about what porous pavements do. Great, water goes through them... and then what? The ground underneath the pavement is not some unlimited sinkhole for water. The ground table can and does fill up. Then it doesn't matter how porous your pavement is.

Trees, grass, wetlands, etc, do better in part because they are preventing the water from leaving. They pool water in small puddles, they absorb water, leaves have water sit on them, etc.

Water flows through them, they don't really 'absorb' water. Of course there will be moments when it freezes when there's still water in them, but it's not equivalent to freezing a sponge. The parking lot on one of my buildings is paved with blocks like this (condition for getting the building permit), works great. Never slippery in winter, either. They weren't even more expensive than alternatives.

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