structural drawings / general notes / concrete non-carbonated 1

[boffintech]

I'm looking at a set of structural drawings that has a general note in the reinforced concrete section which reads:

--- Concrete shall be non-carbonated in areas exposed to weather.

I've never seen this requirement called out like this so before I ask him what his intent was I wanted to bounce it off you guys.

I understand the basics of carbonation, that it is the result of the dissolution of CO2 in the concrete pore fluid, blah, blah, blah.....

I assume it is engineer’s intent that the contractor place dense concrete of low permeability made with a low water/cement ratio that is less susceptible to carbonation. Since porous and permeable concrete made using a high water/cement ratio is more susceptible to carbonation it should not be used.

However, is it possible to place totally "non-carbonated" concrete? Or is his phraseology just awry?

 

[CELinOttawa]

I may be in line to learn something here, but as far as I know carbonation is as you state: A process that occurs as the concrete reacts with the atmosphere.

Perhaps the designer meant C-XL class, without explaining this sufficiently to the craftsman? Weird for sure... Ask for clarification.

 

[Ron]

Carbonation occurs with time unless the concrete is exposed to flame-type heaters during curing. Specifying "non-carbonated" concrete at the beginning means the specifier doesn't know much about concrete!

Essentially all concrete is non-carbonated at time of placement and curing.

 

[JedClampett]

Maybe they meant the drinks were to be non carbonated?

 

[CELinOttawa]

Draftsman! I hate this autocorrect...

 

[Ron]

JC....all specifications should say that flat beer is not allowed on jobsite.

 

[concretemasonry]

Almost all concrete is subjected to the carbonation since the chemistry of "wet/newer" concrete is imperfect (only about 70%) and there is always free lime (CaO) that will react over a long time (with some small amount of moisture that is always available.when there is moisture to tie up the excess.

There are some factory processes for concrete products that can partially or totally complete the process since they are small enough for equipment to make them or create an ideal environment. Some products are subjected to carbon dioxide and warm temperatures (140F) for 24 hours or to high pressures in saturated steam at 360F that requires about 6 hours including transporting and cooling down (reducing the pressure). The latter is referred to as "autoclaving" that essentially ties up all the free lime immediately.

Autoclaving is better than "autocorrect" because it is managed and controlled. That is why surgical implements in hospitals are "autoclaved" between uses.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.