The pouring of the bond beam was the source of certain amount of concern, since it is is well-known that freezing before the concrete has set will significantly weaken the concrete. We discuss and dismiss any thought of actually heating the space around the concrete. I discover the Army Corps of Engineers' Cold Regions Research Engineering Laboratory (http://www.crrel.usace.army.mil/), which has a significant research program in "cold weather concreting". The lead researcher is very generous with his time and knowledge. He explains that our conditions aren't very extreme (we never thought the were that bad), and increases our comfort that the we shouldn't have too much trouble. Concrete cures via an exothermic reaction which gives off 1 watt per gram, and we were pouring a little less than 20 cubic meters. At 2242 kilograms per cubic meter, that's 45 megawatts of heat. The bond beam has a cross section of 16" x 24" (sorry for mixing units here), which means the volume to surface ratio is quite high. I placed a recording thermometer under the insulation blankets, a few inches above the concrete. Another thermometer was left outside to capture the ambient temperature. The graph below makes clear that any concern about the concrete was unnecessary. (Of course, we'll repeat the whole exercise about concern with the slab, which doesn't have the surface-to-volume ratio advantage that the bond beam does. )