Exposed Structural Concrete

[canstruct]

Hi Guys,

We have designed a one storied concrete flat slab structure for underground parking garage, the deck of which serves as a parking on top. It is in construction and contractor want to expose the slab in winter, as he can't finish in one month time. He is of opninon that protective membrane shall be applied not below -10 deg C for good bonding. I am wondering that even hair line cracks would cause the ingress of deicing agenets like salts and that is the start of deterioration of concrete, as in Toronto temp can reach below -40 deg C. Can somebody suggest, is it ok to expose the concrete uptil required temperature or is there any other method to apply protection below -20 deg C. This is a flat slab structure and cover to slab is as per code for normal exposure.

Thanks and appreciate for a practical advice.

 

[shin25]

I am not quite clear! Are you saying that the contractor will be pouring the slab in sub freezing temp. or will be curing in sub freezing temp?

 

[civilperson]

Use air entrained concrete, (5-7%), and cover with poly sheets after initial set for cure and for protection from weather. The cure should be at 20 degree C and above, (use insulated blankets and heaters), until F'c is achieved. The full strength concrete will be fine in the coldest weather.

 

[shin25]

Try the following links,

http://www.cement.org/tech/faq_cold-weather.asp

http://www.nrmca.org/aboutconcrete/cips/27p.pdf

 

[canstruct]

Yes contractor will finish before freezing temperature or you can say finish concreting, but cannot apply asphalt topping in freezing layer.
It is difficult to change the tendered items. It is safe to expose concrete for three or four months of exposure to hardened concrete as normally exposed to slab on grades etc.

 

[hokie66]

Is your concern that the deck will be used for parking over the winter and deicing chemicals used? I would be concerned about that as well if the concrete, cover, curing, etc did not anticipate that case. And the deck will require thorough cleaning before the membrane can be applied once the weather is warmer. All the water and cleaning agents required to do that may be a problem for the level below.

The joy of living in a cold climate. Oh well, apparently global warming is on the way.

 

[miecz]

Consider a Liquid Membrane Curing/Sealing Compound that meets AASHTO M148.

 

[shin25]

If deicing salt is a concern, then you probably can apply penetrating sealer (like ATS-100) on the surface for protection during this time.