Chemical attack to concrete by soil sulfate and chloride

[rhboe]

Trying to find out what levels of sulfate and chloride in soil would be considered a concern regarding chemical attack to foundation concrete. Any tables providing "degrees" of concern, e.g., "slight risk", "moderate risk", "high risk", etc.?

 

[dik]

You should use a blended flyash normal concrete specifically taylored for his type of exposure. Typically 25% flyash. High strength with lots of cementitious material.

Type 5, V, or 50 depending on where you are is contraindicated for chloride exposure.

Dik

 

[JedClampett]

In ACI 318-08, there is a table 4.2.1, which gives classifications of severity of exposure vs. chemical concentrations. Later on in the chapter, it recommends mixes to use for each exposure.

 

[Ron]

Don't cross post. I answered the same question in the Geotechnical forum.

 

[molerat2210]

The concern is mostly about the rebar in the concrete and not the concrete. Chlorides and sulfates are oxidizing agents that along with moisture and oxygen cause corrosion of the steel. FHWA performed a study related to corrosion of ferrous metal strips for MSE walls. It is available online and has tables with guidance on ranges of values. The typical parameters are pH, resistivity, sulfate content, chloride content and redox. The parameters in interelated and not independent of each other.

The corrosion of concrete footings is generally not a big concern since oxygen is limited below grade even when aggresive soils are present. Designers are more concerned about ferrous metal pipelines where galvanic and stray current corrosion is a problem. It can be a problem for concrete pipes and culverts where there is a nice combination of air, moisture and oxidizing agents. Resistance to corrosion of rebar in concrete can be improved by requiring low permeability concrete, epoxy-coated bars or increasing the depth of cover.

 

[dik]

The chloride attacks the rebar and the sulphate attacks the concrete... Use good dense concrete and adequate concrete cover to the rebar.

Dik

 

[worldofmud]

It may be worth getting hold of BRE Special Digest 'Concrete in Aggressive Ground'-UK paper but contains alot of info which you may find useful.