Why C40 concrete is used for underground pit?

[tmgczb]

In our project， structural concrete is of C30 but the grade of concrete for underground pit is C40.
When I was asked this question at site，my answer was anti-corrosion.
Some colleagues consider C40 is used for pit because of anti-permeability.
What is the actual reason？
We just follow company standard，so it is difficult to answer such questions.

 

[dik]

Any chance for salt water intrusion? If something is spec'd at C40 and you get the OK to change it to C30, then you have 'bought the design' in the event there are any problems. I've done lots of pits at 25MPa, but if there are salt issues or corrosion issues, then 35MPa is my goto minimum.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[JLNJ]

Some codes require minimum concrete strengths due to environmental conditions, exposure, etc.

 

[tmgczb]

Indeed，ACI 350 is one of them.