[b112]

It also seems crazy in certain areas, such as where the ground freezes in winter. All those little pores will freeze and break, turning the entire concrete mass to powder.

People hate unneeded work, so in the old days, if there were large boulders of granite in fields to clear, they'd hand drill holes in the top. Then, over a few winters, the freezing water would break the granite.

[Retric]

It's less of a problem than you would think as water that's liquid will drain through it and snow etc doesn't expand. You generally get pot holes because water pools in an a layer and then expands and contracts, but if it's draining that's not a problem.

Also, air entrainment has long been (~1930's) used as a means of freeze thaw resistance because it allows some deformation without cracking. Porous concrete has similar flexibility.

[hedora]

There are technologies that have different advantages and weaknesses vs. porous concrete. For instance, TruGrid holds fine gravel in place using tiles made of recycled water bottles. It's ADA approved for wheelchairs, and certified compatible with stiletto heels (by someone that must have an absolutely bizarre certification facility).