Air-entrainment of trowel-finished lightweight concrete per ACI 302.1

[MisterTone]

I'd like to gain some insight into why it MIGHT be okay to air-entrain hard-trowel finished concrete if it is lightweight instead of normal weight.

ACI 302.1R states:

8.11.4 Some lightweight aggregates can require further control of segregation, bleeding, or both. For this purpose, use no less than 4% entrained air in accordance with ACI 211.2.
Note: unlike its effect on normalweight concrete, the use of an air-entraining admixture in lightweight concrete that is to be hard-troweled does NOT lead to blistering. (emphasis added)

ACI 211.2 states:

2.4.1 ...the beneficial effects of air entrainment on concrete workability and cohesiveness are desirable and can be achieved at air contents of NOT LESS THAN 4.0%. (emphasis added)


Several questions arise:
1) Should 8.11.4 also be taken to mean that air entrainment would not lead to delamination also?
2) Why would lightweight be any different than normal weight, when the potential for trapping bleedwater below the surface would be the same? Is there some other mechanism at work here?
3) If the LW mix design uses normal weight coarse aggregate, but lightweight fine aggregate, should it be treated more like NW concrete in terms of air vs. troweling?
4) Given the above ACI guidelines, would it be "wrong" to still require the use of a no-air mix design for LW trowel-finished floor slab, just to be on the "safe" side to prevent possible delaminations?

Any thoughts or past experiences?

 

[TXStructural]

Most people attribute the delamination to trapping bleed water below a hard troweled surface, and air entrained concrete has this problem to a greater extent than normal. It seems that the bleed water migrates to the top more slowly in the presence of entrained air. Lightweight aggregates tend to hold the moisture, resulting in less bleeding. That's what I get from what I've read and heard.

 

[Ron]

I almost agree with TX, but the reason is not that the LW aggregate holds more water (well, it does), it is that the LW aggegate is not batched in a saturated surface dry condition as normal weight aggregate would be, causing what would be excess bleed water to be forced into the larger lightweight pore structure, thus resulting in less bleed water, thus less blistering.

Higher air entrainment is needed to counteract the potential for higher entrapped air in LW concrete.