Loading the lesson
Loading the lesson
Search AllRounder.ai
Search the courses, subjects, tracks, games and features, or jump straight to a page.
Search the courses, subjects, tracks, games and features, or jump straight to a page.
Learn it your way
A short class with Sarah and her students. The other ways are under More.
Sign up free to listen. Transcripts are free to read.
Today, we’ll discuss the carbonation of concrete. Can anyone tell me what carbonation is?
I think it’s when carbon dioxide reacts with concrete?
Exactly! Carbonation is the reaction between atmospheric CO₂ and calcium hydroxide in concrete. This reaction forms calcium carbonate.
What happens to the pH during this process?
Good question! The pH level decreases from about 12.5 to below 9, which is critical because it reduces the alkalinity that protects the reinforcement bars from corrosion.
Now that we understand carbonation, what do you think might happen to the concrete and its reinforcement?
Could it cause the steel to rust since the protective layer is gone?
Right! The reduction in pH exposes the reinforcement to corrosion, which can lead to cracking and spalling in the concrete.
What’s spalling?
Spalling is when pieces of concrete break away from the surface, often due to corrosion expansion.
How can we determine whether concrete has carbonated?
Is there a specific test for it?
Yes, one common method is using a phenolphthalein indicator. It turns pink in alkaline areas but remains colorless in carbonated zones.
So, we could use that to know if the concrete is still safe?
Exactly! This test helps us identify potentially vulnerable areas.
Lastly, what measures can we take to control carbonation?
Maybe using denser concrete?
Great idea! Dense, impermeable concrete helps prevent CO₂ ingress. Additionally, we can apply surface sealers to reduce exposure.
And what about the thickness of concrete cover over rebar?
Correct! Adequate cover thickness is crucial to protect the reinforcement from carbonated areas.
A chemical reaction between CO₂ and calcium hydroxide that lowers the pH of concrete.
Carbonation reduces the alkalinity, leading to increased risk of corrosion in steel reinforcement.
Phenolphthalein indicator test is used to identify carbonated areas in concrete.
Use of dense concrete, adequate cover thickness, and surface sealers to mitigate carbonation.
In a reinforced concrete structure, if carbonation reduces the pH effectively to less than 9, the surrounding steel reinforcement may start to corrode, leading to structural failure.
Applying a phenolphthalein test on a concrete sample can indicate which areas require more attention regarding waterproofing and protection against carbonization.
When CO₂ meets concrete strong, watch the pH drop, it won't be long!
Once upon a time, CO₂ frolicked in the atmosphere, eager to find concrete. It met calcium hydroxide and transformed it, causing havoc by lowering its defenses. The rebar, once protected, now faced a serious threat!
C.P.C. - Carbonation Protects Concrete (Think of keeping CO₂ out!)
C-RAP: Carbonation Reduces Alkalinity, leading to corrosion Problems!
Term
What is carbonation?
Click to flip
Term
What does a phenolphthalein indicator signify in concrete?
Click to flip
Term
What is the effect of carbonation on concrete pH?
Click to flip
Term
What happens to reinforcement due to carbonation?
Click to flip
A chemical process in which carbon dioxide reacts with calcium hydroxide in concrete.
An indicator that turns pink in alkaline conditions, used to test for carbonation.
A compound formed during carbonation that reduces the alkalinity of concrete.
The process where fragments of concrete surface break away, often due to corrosion.
Carbonation of concrete involves a chemical reaction between atmospheric CO₂ and calcium hydroxide in concrete, which reduces the protection of reinforcement steel from corrosion.
This section discusses the process of carbonation in concrete, detailing how it affects the material's alkalinity, leading to increased risks of reinforcement corrosion. It also covers methods for testing carbonation and effective control measures to mitigate its effects.
Carbonation of concrete is a chemical process where atmospheric carbon dioxide (CO₂) reacts with calcium hydroxide (Ca(OH)₂) present in the concrete mix. This reaction results in the formation of calcium carbonate (CaCO₃) and a significant reduction in the pH level of the concrete from approximately 12.5 to below 9. The lowered alkalinity diminishes the protective alkaline layer surrounding reinforcing steel, leading to an increased risk of corrosion.
Understanding the carbonation process is crucial for maintaining the structural integrity and longevity of concrete structures.