Hi
I would like to ask about the carbonation in concrete. What is minimum concentration of carbon dioxide in concrete that it leads to form calicuim carbonate and occur the carbonation?or the minimum concentration of Ca(OH)2 to do the same result.?
Not sure what the minimum concentrations are, but carbonization of concrete is a natural process-the reverse of the process whereby CO2 is driven off at high temperatures to form Ca(OH)2, when exposed to CO2 (mostly in air)
Normally caarbonization is a result of poor curing and/or a high water cement ratio concrete, or other compromising of the EXPOSED surfaces of the concrete via exposure of the concrete surface to CO2 in the air. Good curing/sound dense concrete surfaces or other means of prtecting the surface of the concrete would markedly reduce the risk of "carbonization"
Dear Abbas
The concentration of carbon dioxide is dictated by the relative humidity. If the concrete is too dry (relative humidity RH 90%) CO2 cannot enter the concrete and the concrete will not carbonate. Optimal conditions for carbonation occur at a RH of 50% (range 40-90%).
I hope this helps.
Good luck
Dear Abbas
carbonation of concrete can takes place at very low concentration of CO2 as low as 0.03 percent. carbonation of concrete takes place in presence of moisture only because gaseous CO2 is not reactive with hydrated cement.
concentration of Ca(OH)2 is also very important because CO2 most readily react with it and form CaCO3. When all Ca(OH)2 has become carbonated pH value reduce to 8.3.
for more detail please refer Properties of concrete by AM Neville
Dear Abbas,
Even the 0.03%-0.04% concentration of CO2 in atmosphere (which is relatively low) can cause carbonation in a long exposure periods with a slow rate (say 1-2 mm/year). Typically a high concentration of CO2 will just accelerate the carbonation process and that's why we need to increase the CO2 concentration in accelerated test environments (3% to 5% CO2 concentration) to increase the rate of diffusion and enhance the carbonation rate. In addition, about 60% RH and slightly high temperature (around 35-40 deg. Celsius) will be optimal for maximizing the carbonation depth.
Regarding the CH content, there is no real limit. Actually, the higher CH content corresponds to reduced rate of carbonation and decrease in carbonation depth, and vice versa. That's why using pozzolans and converting CH to C-S-H may lead to increase in carbonation depth (note that modifications in pore structure due to use of pozzolans may affect the reults as well).
Feel free to send me message if you had further questions. You can also find some relevant information in my papers available at my profile.
Good luck.
I thank your attention . I viewed your contribution in research gate , I think you interesting in durability of concrete.
Now, I am PhD student in UK and I am working on the effect of climate change on durability of concrete in term carbonation, chloride and corrosion in UK and Iraq.
I would like to continue with you if you do not have a mind about that .
with regard
Abbas AL-Ameeri
What should be carbonation rate in UHPC and OPC? Plz explain also give me reference if u have any i am working on it.
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