Air Content in Dry Cast/PreCast Box Culverts

I have recently speced out pre cast box culverts. The box culverts that are being used are cast by the "dry cast" method. The concrete mix designs were submitted with "zero" slump concrete and air content of 2%. My question is, "Is there any literature to support 2% air is adequate for freeze thaw conditions?" The precaster said that the air cannot be increased in this method of casting. Any help would be greatly appriciated.

 

[ishvaaag]

Maybe this reference can serve you

"Air-entrainment shall conform to ASTM C-231 (AASHTO T-152)"

 

[Ron]

Two percent is marginal to prevent freeze thaw problems. Chances are you'll get a bit more from entrapped plus entrained air, but only the entrained air is greatly effective against freeze-thaw deterioration. The reason they are limiting the air content by specification is that they use a lot of vibration to consolidate the "no slump" concrete. The vibration reduces the air content, so they don't want to be in a position of "guaranteeing" more than a couple of percent air.

Functionally, you should be able to specify more air (and get it) but they have to choose between "no slump" and reasonable air content. As the air content increases, so does the "flowability" of the concrete, so technically the more air they add, the less likely they will get true "no slump" concrete. They should, however, be able to control their mix to achieve both appropriate air content values and achieve the consolidation and placement control they desire.

 

Thanks to both of you for your help!