huangyhg

deciphering air entrainment requirements
the summerized specs read:
for normal weight concrete air content =
•no entrained air for concrete placed in foundation
�% +- 1.5% entrained air uno
�% +- 1.0% entrained air for mixes with compressive strength greater than or equal to 5000 psi
�% +- 1.0% entrained air for mixes with compressive strength less than or equal to 5000 psi placed in aggressive
(aggressive environment = exterior)
so for slab-on-grade with interior exposure and placed with 4000 psi concrete the air requirement is ______?
by the specs given it's either 5+-1% or the member is considered part of the foundation and thus no a/e required.
for sog interior exposure, i'd spec 0-3% to accommodate entrapped air. no air entrainment necessary... air entrainment does, however, help with placing concrete.
i'd read your specs as having to conform to #1, 3.5 to 6.5. i think the spec writer has 1 and 3 confused. should have higher for exterior exposure if freeze-thaw is an issue.
dik
agree with dik. the spec asks for 5%+-1.5%. i would check with the engineer to verify this requirement, particularly if the slab has a mineral aggregate hardener or is trowel finished.
i understand the conclusion; however, is it possible that the eor considers s-o-g, retaining walls, and foundation walls as "foundation" and thus no a/e required?
on the general notes page of the structural drawings under the foundation section there are notes on footings, foundation walls, drilled piers, s-o-g, retaining walls, soil density, bearing capacity, etc.
he must be considering s-o-g as "foundation", right? that's the only way his a/e criteria make sense. also makes more sense considering the vast majority of interior slabs get trowel finish. 6 1/2% + trowel = delamination right?
what say you guys?
agree with dik...interior application, so air entrainment not necessary; however, there is ambiguity in the specification so it requires interpretation by the author or the engineer in responsible charge. submit an rfi.
i don't think of the slab-on-grade as part of the foundation. however, i don't know of an official definition that would rule it out. if your eor has slab notes under the foundation section, then he/she may consider it as such.
from what i've read, steel troweling of slabs with 5%+-1 1/2% air can contribute to blisters, finishing problems and weak concrete at the surface.
generally... for an ambiguity in the contract, the courts rule against the person who drafted the contract...fwiw
dik
boffintech, a few questions for you.
1. is this project a building?
2. is the project located in a a region where air-entrained concrete is typically specified for freeze-thaw resistance?
3. if the answer to the preceeding question is negative, do you know why air-entrained concrete was specified?
henri,
1, yes
2, yes
the given criteria do not cover all possible concrete
what method of concrete placement will you be using?
1. gunite (dry mix)
2. shotcrete (wet mix)
3. cast in place
if your using gunite, i don't think an air entraining admixture can even be added.
3. cast-in-place

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