Yes, it has been a long time in between posts. All the details that had to be worked out to do the partial perimeter pour paled in comparison to the back and forth to finalize the forms for this pour!
The final dimensions of the wine cellar walls needed to be checked and rechecked and checked again, and then misunderstandings about where the insulation was going to be, where and how the plumbing needed to be supported, and how high up it needed to be wrapped, and which parts of the slab were to be insulated from which set us back a couple of weeks. This was complicated by needing any modification to be approved by the structural engineers. It was finally a set of hand sketches of cross-sectional details initially drawn by Catherine then duplicated by our General Contractor Paul Delgros that were approved and we now all agreed what it was that we were trying to build.
The resulting forms for the wine cellar area were the most convoluted set of concrete forms imaginable. The wide footings for the straw bale library were in place with the embedded posts for the shear. So now the final plumbing was complete, the new forms were in place (the right place!), the insulated slab and the non-insulated slab were isolated at the correct parting lines, the structural engineer signed off, the city signed off, and we were ready to do the second pour to complete the non-insulated slab sections.
Five concrete trucks and a “cleanup” poured tons and tons and tons of concrete into our massive slab. The trucks were late, so the concrete crew was working into the early evening to finish floating the garage floor, which was lucky for us. On our way home, we stopped in at the house site and were able to put hand prints and our names into the still wet cement in one corner of the garage – now the house really is ours! Nat put her age in, so we had to follow suit…. someday 40 will seem young.
We used 25% fly ash in the concrete which is a waste byproduct of coal burning and is often used in concrete to improve it’s pouring characteristics and its strength. 25% fly ash means that 25% of the portland cement in the concrete was replaced with fly ash – what that means in terms of total percentage of the final concrete is fly ash, I’m not really sure, but since the portland cement is one of the largest CO2 producing components of the concrete, displacing much of it is good from that point of view. The Minnesota Center for Sustainable Building research estimates that if you use 25% fly ash instead of the standard 9%, you get an 11% reduction in CO2 emissions in your concrete manufacturing. It also improves the flow, and up to a certain point, the strength of the concrete (the maximum strength improvement comes around 25-35%).
One concern occasionally brought up about high fly ash use is heavy metals from the coal burning such as lead, arsenic and mercury are now encased in your concrete, but I guess I’d rather have them encased there than sitting out in a leach field somewhere getting washed into the ground water. Another concern sometimes brought up is that by providing a market for a byproduct of coal burning, you are supporting the coal industry… I find that argument a bit hard to believe – surely the US dependance on coal has very little to do with whether anyone can find a use for its waste products. So using this waste product that in turn offsets high carbon production manufacturing seems green enough for us!