Air Content below Spec - Foundation Wall

[jfudo]

I typically specify 4%-6% air content in foundation walls, upstate NY so freezing is a problem. I just got some concrete test results that show some of the trucks have air contents as low as 1.5%.

Does anyone have any suggestions on how to fix this without having them remove all the bad walls? Can the surfaces be sealed to provide the same protection?

 

[Loui1]

It's not a question about sealing the concrete but keeping it from freezing. The air allows the concrete to be durable under freeze/thaw cycles. I dont know of any way to introduce this property once the concrete is poured. IMHO It will end up spalling if you allow it to remain and it is subjected to freeze/thaw.

 

[boo1]

Is the spaulding a result of the absorbed water expanding when to becomes ice?

 

[JAE]

If no water ever gets into the concrete, then freeze-thaw damage would not occur. You could try to seal off the concrete with heroic measures, but unfortunately I would think that some how, some way there would be water infiltration eventually and then potential F-T damage.

 

[civilperson]

If the basement space is heated (never freezes), then the walls could be insulated on the outside to insure against freeze/thaw of the wall from cold adjacent subgrade. Works in Albany.

 

[dougantholz]

First determine the level of damage that you can live with. If it is a retaining wall or footing, some loss of section may be acceptable structurally and visually.
Second determine if this is going to be subject to moisture as JAE and others have suggested. If it is not going to see a change in moisture (below the water table or well above it) then it may not be a problem.
Third this is most likely a maintenance issue for the owner. I would let the owner decide if they are willing to live with the risk of problems in the future versus cost of repairs now. It may not be the owners cost but the hassle of getting it fixed may not be worth it to them. Get it in writting if the owner is assuming some additional risk for not repairing.

 

[youngstructural]

I don't think that air entrainment below 6% in any winter exposure is ever a good idea. Also I strongly agree with JAE, there is no way to seal the concrete (for the life of the structure) which will prevent water from getting into the concrete. It will get in: Water always finds a way.

Civilperson's suggestion that you could neglect air entrainment if you heat the basement is a good idea, but can be problematic in practice. In Canada we will do this for slabs on grade which are heated, but never for walls heated or no. They absolutely require air entrainment. The problem is the thermal conduction path for heat loss is so short. If the power goes out/heater breaks down (even overnight, just once!), the concrete is likely to crack. That big empty space directly next to the wall (the basement) just doesn't have the capacity to retain heat, and geothermal heat will not aid you as it would in the case of a slab (where the heat is rising up through your concrete).

IMHO: I would insist that the wall be removed and repoured (unlikely, as it is difficult and prohibitively expensive) or excataved and insulated with an appropriate number of inches of bearing capacity (RATED structural foam), down to a sufficient depth to retain the heat in the basement/house in the event of a short period of heater loss. Both DOW and 3M make appropriate products (Styrofoam SM or Highload by DOW, alternatively Celfortec Inc.'s CELFORT, or acceptable alternative). Be certain to insist on a load bearing (RATED) foam, with an appropriate allowable capacity to resist the thrust of the backfill. Otherwise the backfill will just crush the foam and destroy the insulating value. Good/useful rule of thumb: 1" load-bearing foam = 1'-0" of soil cover. As civilperson signed off: Works in Ontario. Good luck!

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...