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carbon dioxide
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msquared48
Structural
This string's a gas.
Mike McCann
MMC Engineering
Mike McCann
MMC Engineering
racookpe1978
Nuclear
Be careful of the assumed differences between "science lab" definitions of gas motion, and the real world.
"Air" is a well-stirred mix of O2 (32 AW)and N2 (28 AW), with less than 390 ppm of CO2: 390/1,000,000 or 0.39 percent. CO2 is heavier than the average molecular weight of "air", and Brownian motion will tend to mix it up (even in very, very, very still air) but ... in the real world, the wind and ventilation MUST mix up ALL air in a parking garage to such an extent (meaning forced movement plus convection of hotter exhaust fumes) than the CO poisons are diluted enough to be safe.
CO2 release from curing concrete will be concentrated at the surfaces (top and bottom and walls) of the concrete, because it is going to come out of every surface. An enclosed underground room would build up CO2. But that CO2 rate is small compared to other gasses.
CO (12 + 16) molecular weight is lighter than CO2 (12 + 16 + 16) but it will be present in exhaust at rates 1000 to 5000 greater than CO2. Since CO (if not diluted) will kill quickly and with no odors, your first concern must be forced ventilation (or natural wind flow) to prevent CO deaths/exposure. That forced movement will combined with but completely overwhelm any Brownian motion (the molecule-to-molecule vibration by uneven numbers of collisions of a gas by nearby gas molecules) exchange of CO2 in air.
"Air" is a well-stirred mix of O2 (32 AW)and N2 (28 AW), with less than 390 ppm of CO2: 390/1,000,000 or 0.39 percent. CO2 is heavier than the average molecular weight of "air", and Brownian motion will tend to mix it up (even in very, very, very still air) but ... in the real world, the wind and ventilation MUST mix up ALL air in a parking garage to such an extent (meaning forced movement plus convection of hotter exhaust fumes) than the CO poisons are diluted enough to be safe.
CO2 release from curing concrete will be concentrated at the surfaces (top and bottom and walls) of the concrete, because it is going to come out of every surface. An enclosed underground room would build up CO2. But that CO2 rate is small compared to other gasses.
CO (12 + 16) molecular weight is lighter than CO2 (12 + 16 + 16) but it will be present in exhaust at rates 1000 to 5000 greater than CO2. Since CO (if not diluted) will kill quickly and with no odors, your first concern must be forced ventilation (or natural wind flow) to prevent CO deaths/exposure. That forced movement will combined with but completely overwhelm any Brownian motion (the molecule-to-molecule vibration by uneven numbers of collisions of a gas by nearby gas molecules) exchange of CO2 in air.
racookpe1978
Nuclear
No: CO is hazardous to people occupying the garage (later) when it is in use: Thus, the absolute need for ventilation (to remove the CO) in the garage during use is going to provide more than enough ventilation to remove the CO2 from the concrete during construction ...
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- #29
Sorry, I have been away from this site a few days. All very interesting and fascinating comments. Seems that there are many factors to condider. Thank you all. Thanks particularly "Skis and Bikes". Although some comments strayed from my original question, they were still of interest. My original question was related to carbon dioxide and carbonation to the underside of an insulated concrete slab which is the floor of a heated condo building above the garage. Perhaps I can rephrase my question as follows:
Given:
a) the insulation that will keep the slab soffit warm,
b) the Code required ventilation in a garage,
c) the CSA exposure Class C-1 concrete (w/cm = 0.40 maximum),
d) 25 mm clear concrete cover to the bottom bar
Question:
What is the likelihood of corrosion damage to the slab soffit due to carbonation in the 100 year design service life of the building? My opinion is that it is negligible. Anyone think it is significant?
Given:
a) the insulation that will keep the slab soffit warm,
b) the Code required ventilation in a garage,
c) the CSA exposure Class C-1 concrete (w/cm = 0.40 maximum),
d) 25 mm clear concrete cover to the bottom bar
Question:
What is the likelihood of corrosion damage to the slab soffit due to carbonation in the 100 year design service life of the building? My opinion is that it is negligible. Anyone think it is significant?
- Thread starter
- #31
SkiisAndBikes
Structural
100 years is a long time to project .... however, given your parameters, I would also not expect carbonation to lead to any widespread deterioration. I would not be surprised if during 100 years there were some small, localized soffit delaminations due to carbonation at crack locations. Likely insignificant. I would expect a waterpfoofed podium slab subjected to chlorides to deteriorate significantly more over 100 years.
Keep in mind that if the slab is indoors, heated and not subjected to chlorides or exterior exposure, it is unlikely a C-1 concrete will be used for the slab unless you specifically specify.
Keep in mind that if the slab is indoors, heated and not subjected to chlorides or exterior exposure, it is unlikely a C-1 concrete will be used for the slab unless you specifically specify.
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