I just finished reading "The Concrete Mixer" in the Illustrated Man. This is one story where I'm confused about the symbolism at the end...what is it supposed to mean???

Okay, I just reread it myself. I think the idea is that American Earth Society itself is the concrete mixer. It doesn't matter which way doom comes to the Martians--one way or another they will be mixed into one mass glob. I guess it symbolizes intelligent individual thought inevitably succumbing to dumbed-down collective thought. (I liked the bit about the evil chocolates.)