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Cold Weather Concreting on Frozen Surfaces

Cold Weather Concreting on Frozen Surfaces

(OP)
ACI and specs prohibit placing concrete on frozen subgrade, subbase, or footing surfaces, and concrete should not be placed around embedments which have temps below freezing. That said, what will be the actual effect (damage, risk, etc...) if concrete for an above-ground wall is placed inside unheated permanent insulating formwork (ICF) on top of a foundation wall which is below freezing with rebar at sub-freezing temp? Concrete will be mixed with hot water at plant and delivered at about 70 degrees F.

RE: Cold Weather Concreting on Frozen Surfaces

Only bad things will occur using frozen rebar, subgrade and forms.

RE: Cold Weather Concreting on Frozen Surfaces

ICF don't have the mass/conductivity to normally effect warm concrete and there should be no problem.  Frozen rebar if of sufficient size may cause an ice surface between the concrete and the reinforcing affecting bond.  It is likely that this will not occur with small bars normally encountered in ICF walls.

Civilperson is correct when he/she states that bad things can happen... Dik

RE: Cold Weather Concreting on Frozen Surfaces

70 degrees is really not that warm.

In addition to the rebar, the massive cold footing will very detrimental to the concrete in contact with it and above it for a distance proportional to the thickness of the concrete wall. - Permeability of the lower frozen concrete could be high and water penetration would definitely be a concern.

Even a lowly masonry basement contractor will protect the footings with insulation prior to wall construction. That is why they build a basement in the winter in 3-4 days from excavation to completion. - You do it quickly while it is still warm and can cure properly. Granted, they use 120-140 degree mortar and much warmer grout than your concrete.

RE: Cold Weather Concreting on Frozen Surfaces

ACI 306 "Cold Weather Concreting" is a very good reference for your conditions.  Regarding the reinforcing steel, ACI references a limited study that suggests metallic embedments with a cross sectional area greater than 1 in^2 should be no colder than 10 degrees F when immersed in concrete no less than 55 degrees F in order for freezing zone around the steel to be thawed and disrupted during placement and final vibration.  I agree with dik, this shouldn't be a problem with the typical #4 bars in ICF construction.

The concrete footing should be your greater concern and should at least be above freezing at the time of concrete placement (ACI recommends 35 degrees F mimimum).  It wouldn't take long for a ground-heat system line run along only one side of the wall to get this temp up.

Gregory A. Johnson, P.E.
www.midwesttestinglabs.com

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