Once the piles were in the excavator came out to dig trenches for the foundation’s grade beams, which were drawn as 2’6″ wide by 2′ high, with the bottom of the beams at an elevation of 3′, which was 4’8″ below finished grade. The structural engineer indicated that the bottom of the grade beams should be at least 3’6″ below grade to avoid any frost problems.
Next the concrete subcontractor’s team assembled the forms for the grade beams and cut the piles off such that the pile tops would be embedded into the grade beams by 6″. I had asked the pile driving contractor about treatment of piles where cut but they either did not know what to do, or didn’t want to have to do anything. The plans called for cut end treatment per AWPA M4-84, I figured out that meant a product called tenino copper naphthenate 2%, so I ordered a gallon of that from poles.com and treated the cut ends of the piles myself. No cap was required, the grade beams just get poured on top of/around the pile tops.
I had gone back and forth with the structural engineer on #6 (3/4″) vs #5 (5/8″) rebar for the grade beams, the concrete sub said that #6 was unusual for residential construction, but if we dropped from 6 to 5 the engineer wanted to add bars. So we decided to use the #6, but have the rebar supplier, Harris Rebar, pre-cut and pre-bend for us, including a bunch of #3 stirrups. The structural engineer also called for galvanized, after discussing we backed off on that and went with plain black bar, as this stuff was going to be encased in concrete and below grade, as well as probably over engineered. The engineer also wanted placement/shop drawings for the rebar, when I figure out what that meant I did the drawings myself.
We were in to December now, which is not an ideal time to pour concrete. The structural plans called for 5000 psi cement, I managed to get that dialed back to 3500 psi to save a little money, and I think we ended up using 4000 psi. When we were ready to pour daytime temps were in the 40s and overnight temps in 20s and one night in the teens. So O&G used hot water, a non-chloride accelerator, and a mid range plasticizer. It took 7 truckloads of cement, I think about 63 cubic yards.
I pushed the cement sub to put blankets on the grade beams for some thermal protection, and also pushed back against pulling the forms off too quickly.
For this first pour I had a lab come out to catch and test samples of the concrete. Two cylinders tested at 3980 and 4120 psi at 7 days, and six cylinders from two samplings averaged about 4500 and 4900 psi at 28 days. So despite the cold the concrete strength was good.
