Day 6 of Night Sky Observatory Build

Today Mike T. and I got a fairly early start, and everything was going to plan. We added the joist hangers around the perimeter and in the center section. Then we started placing the deck floorboards on the northern side of the frame with the plan to be able to pour the concrete into the 16" Sonotube from the deck top to make life a bit easier. Got the first few boards in and then placed the sonotube in the 20" hole and centered it. Off to mix the concrete and start pouring. So far, so good.

Now the 16" tube is quite large, as the specs called for a 14" which I couldn't find anywhere. But the 16" should work just fine. It wasn't until the concrete got to the top of the tube when near disaster struck!! The plan was to backfill the hole around the tube after the column was centered. But the weight of the concrete, coupled with us tamping the concrete down to eliminate any voids in the concrete caused the tube to rupture. The tube fell to one side! There was obviously no way we were going to right it and so we pulled the tube completely out and let all that concrete collapse into the hole. The concrete now settled into one huge footer!! 

Quick thinking ensued and we decided that in order to save the day we would need to add a new section of concrete (about 18" or so) to set up on top of the existing 'new' footer before the original concrete started to set. We quickly headed out for the only Home Depot (about 20 minutes away) that had 16" sonotubes to get another tube and some rebar.

Once back at the site we cut the tube to the required length, pushed it down into the footer about 6-8" and drove five, 48" long rebars into the still wet cement of the footer. We then poured another 3 bags of concrete into the new sonotube. It was pretty much level (just a fraction off) and so we decided to leave well enough alone. I then placed the j-bolts into the top of the concrete column for the pier attachment. Done!

The good news is that the huge footer and rebar reinforced 18" top section might actually be stronger than the planned 16" column - might even be considered overkill. So be it. 

Tomorrow, we place the remaining boards. Then I plan to allow the concrete to cure for 96 hours. By Sunday I should be able to mount the pier for a quick test.