What's with the name? Did I miss where cement played a part in the doujin?
This work refers to Episode 2 of Season 2 when Natsuki just wore a shirt with the words "Cement Addiction" on it. She was called out by the others because it was one of those, often nonsensical, shirts with cool-sounding English words on it you'd often find in Japan.
The author of this work translated Cement Addiction into Japanese and used the word 中毒 (chuudoku) meaning "addiction", the latter kanji being the word 毒 for "poison". Whether or not there is a real addiction to cement is anyone's guess. But there seems to be actual "Cement Addiction" shirts that came out after the anime aired.