Mystery solved! Blue strings are pre-stressed concrete, which is an awesome thing to exist. http://t.co/TM81NUItR2 ghelleks ...from Twitter 2013-03-28 1 Minute Mystery solved! Blue strings are pre-stressed concrete, which is an awesome thing to exist. http://t.co/TM81NUItR2 — Gunnar Hellekson (@ghelleks) March 28, 2013 Share this:TwitterFacebookLike this:Like Loading... Published by ghelleks View all posts by ghelleks Published 2013-03-28