Concrete pouring in sub-zero weather?

[Xelebes]

I was walking downtown on Saturday (I wasn't alone!) and I saw the construction site of the YMCA building. I found it odd that they were pumping cement in very non-ideal weather for cement-pouring. It was -10 C and there was snow forecasted later in the evening.

I work in the cement industry on the manufacturing of cement products (more specifically grouts and floor hardeners). I know that pouring concrete in subzero weather has many risks such as the concrete freezing, longer curing (hardening) times and threats of expansion-contraction cracking. So I was definitely concerned about the lack of heating units used to warm the concrete as it cured. I didn't see any.

Anyone care to comment on this?