How do I know what sulphate exposure class to assign to my concrete?

[Mike Mike]

I'm designing a handful of exterior concrete piers to support fence posts. There is no geotech report and no sulphate testing. Do I have to use S3 per ACI 318-19 19.3.1? Is there a map that indicates where sulphate issues are common? In the link below, Ron suggested USDA may have some info, but I wasn't able to find anything on the googler.
Link

 

[dik]

You need to find out the soluble sulphates in the soil. This would likely be provided by the geotechnical consultant.

Sulphate Resisting Cement is recommended for following type of constructions:
[ul]
[li]Foundations.[/li]
[li]Piling works.[/li]
[li]Construction in contact with soils or ground water having more than 0.2% or 0.3 % g/l sulphate salts respectively.[/li]
[li]Concrete surfaces subjected to alternate wetting and drying such as bridge piers, concrete surface in tidal zone, apron etc.[/li]
[li]Effluent treatment plans.[/li]
[li]Chimney, cooling towers.[/li]
[li]Coastal protective works such as sea walls, break waters, tetrapods etc.[/li]
[li]Building near seacoast.[/li]
[li]Chemical industries, water storage, sumps, drainage works.[/li]
[li]Suitable for underground works where Sulphate is present in the Soil and water.[/li]
[/ul]

https://theconstructor.org/concrete/sulphate-resistant-cement/23428/

and from the Canadian Code... see attached.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1692572306/tips/Sulphate_Resistant_susezo.pdf[/url]

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Mike Mike]

Thanks dik, I'm designing a handful of exterior concrete piers to support fence posts. There is no geotech report and no sulphate testing. Do I have to use S3 per ACI 318-19 19.3.1? Is there a map that indicates where sulphate issues are common?

 

[dik]

I don't know... you should be able to find out what is common practice in the area, either from engineers, contractors, geotekkies, building officials or ready-mix outfits... good luck.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Mike Mike]

okay well thanks anyways dik, I work all over the US and the world, and would rather not have to check with locals on every job

 

[RWW0002]

I work all over the US and the world, and would rather not have to check with locals on every job

Pretty much everything that governs foundation design and soil properties is going to be very site specific and "checking with the locals" of some sort (officially via geotechnical expertise or unofficial via common local practice) will likely be necessity. Common construction practices, soil properties, soil strength, depth of bedrock, water table concerns and much more.. all will vary significantly across the country (and even more so across the world..) Sulfate resistance will likely be the among the least of your worries.

Even with this only being support of fence posts, I find it a bit odd that you would worry so much about sulfate and not the other properties that will likely have much more of an impact on your foundation design..

 

[dik]

Else spec everything for S3 to make sure it works? You need to know this stuff. Sulphate attack can be serious.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Mike Mike]

RWW, wouldn't it be simpler and more economical to specify S3 than to conduct a soil investigation? How small and inconsequential does a project have to be for you to waive your "necessity"? I have frost depth, water table, and presumptive load bearing values per IBC chapter 18. What other properties do you use in your design?

 

[RWW0002]

Depending on the extents and cost of the foundation and the load demand, a conservative approach like you mention above may be appropriate (especially if you are designing something that is not a "building" and without significant risk to human life). One approach may be to simply make some reasonable and conservative assumptions, and put these assumptions on the design documents for other's to decide whether to adjust the design to their specific site.