And smoke it!

On the map clean cut, at the start look up, there should be a cement tube hanging from a crane. Simply chuck a grenade through the tube like cement thing. Just look up and around and you should see it hanging. Once you spot it, try to aim your grenade at the inside of it not right through it. Aim it inside and try to bounce it off the inside and get it right through. make sure it doesnt go under. Once it goes through the achievement will pop up

This is a secret achievement.