FYI this was recently posted on Clayart, it seems relevant to sculptures, not certain about pavers.
There's excellent information on claybodies for outdoor hard-freeze environments in Val Cushing's handbook. He gets pretty technical in terms of figuring how suitable a particular claybody might be, but the basics make sense. It did surprise me when I found out about this, because initially seemed counterintuitive. You don't want to use a highfire claybody unless it is 0% absorption, which is hard to achieve. The problem with most highfire bodies is that there is still some absorption, and over time the water absorbs, and then in a hard freeze it can't get out and the piece cracks or spalls. That's the same reason it's so dangerous to refire a piece that has been in regular daily use in contact with water. The moisture has impacted into the piece and can't escape in the firing, and the piece can explode with enough force to destroy everything else in the kiln and even the kiln itself. I have seen this happen.
Most of the architectural terracotta decorating the exterior of so many buildings in New England and across the Midwest was fired to low-midrange - around cone 2 or 3. The idea is to have enough porosity to allow the pressure of freezing water to escape, but enough mechanical strength to keep the pressure from fracturing the clay, and the right terracotta body fired to low-midrange does that. Regular lowfire bodies are of course very porous with inadequate mechanical strength, and we've all seen examples of lowfire pots, sculpture, or tiles left outdoors in hard-freeze climates, where the surface starts to spall off and eventually the piece just disintegrates.