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Plain Concrete Questions

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Regards,

I'd like to get some opinions on the following:

1. To what maximum slump would u recommend vibrating the concrete ?
Mindess & Young write that vibration is needed only for concretes with a
slump less than 50mm. Isn't this too low a value ? Do you think it's a
typo and should be 5" instead ?

2. How cold should it be to justify the use of air entrainment. I know
the definition of "cold weather concrete" from ACI 306 , but it applies
to the weather conditions during casting and until concrete reaches
500psi.
Can anyone quantify the terms "mild," "moderate" & "severe" exposure as
specified in PCA's "Design & Control of Concrete Mixtures?"

3. I am to cast a slab in a few weeks in an area where snow occurs for
about 4 months in a year with mild temperatures, maybe an average of 8°C
(46°F) and a max. low of -5°C (25°F) in the coldest month. This slab
will be exposed to one winter season only since next year, the
construction of several floors above that one is planned. Do u think I
should use air entraining admixtures in the slab ? Also, do u think I
should protect the steel dowels in waiting so as not to corrode, or do u
think the time span is too short to cause significant corrosion.

Thanks in advance,
Moni Serhal, MSCE