Spent 10 minutes on the Googles with a variety of search terms and couldn't find anything. There's a bunch of NK apartment collapses (but nothing specifically about concrete / balconies) and one in SK[0] which sounds plausible but obviously they weren't left in the concrete and chainsawed when dead.

[0] https://en.yna.co.kr/view/AEN20221023001300315

I recall it was reported in the Sunday Observer in the early 1990s but I have struggled to find any references