Concrete exposed to both chlorides and sulphates

[CanuckPE]

I was asked to prepare a concrete mix design for concrete exposed to both chlorides and sulphates. The application is a shallow pump foundation resting on sulphate rich soils. The top of the pump is exposed to chlorides. Appropriate specs for chloride exposure is C-1 (A23.3), and sulphate exposure is S-2. Wonder what exposure class one should go for in this case.

 

[canwesteng]

C-1/S-2, some requirements are additive (such as testing for sulphate resistance), others you pick the most severe requirement (concrete strength)

 

[dik]

Unless you have a lot of slab, I'd err on the conservative side. I'd go for and HS or HSb mix with a 30 or 35 MPa strength. Check with the geotekkie...

 

[EngDM]

C-1/S-2, some requirements are additive (such as testing for sulphate resistance), others you pick the most severe requirement (concrete strength)

Are you saying that you'd write it out as C-1/S-2 in your concrete notes? I've never seen drawings with a dual-type called up like that; I've always just picked the one with more severe constraints.

 

[canwesteng]

I put both in the notes - since for sulphate and chlorides you won't necessarily have one be critical. I guess you could just write out the requirements otherwise

 

[EngDM]

I put both in the notes - since for sulphate and chlorides you won't necessarily have one be critical. I guess you could just write out the requirements otherwise

Interesting, and I guess it makes sense since they are different adatives.

 

[dik]

Interesting, and I guess it makes sense since they are different adatives.

They are two different processes... The sulphate cause the formation on Etringite or gypsum which is expansive and causes the deterioration of the concrete.

 

[canwesteng]

I'd like to hear from others. Haven't got any push back from contractors, clients or concrete plants doing this but I'll confess I just invented putting multiple classes on the drawing on my own, in lieu of some verbose requirements copy pasted from A23.1