Sulfates in Hardened Concrete 1

[Busman]

I am assisting an industrial client reviewing cracking distress in an 8-inch thick elevated slab. Visual petrography suggests that there is evidence of external sulfate attack limited to crack surfaces, likely a result of the chemicals to which the slab is exposed. The slab is reinforced with epoxy coated rebar, and there are no current indications of corrosion of the rabar or structural distress. I plan to recommend (which we previously recommended) that the cracks (which appear to be shrinkage and temp related) are sealed with an appropriate sealant for use in such a severe environment in combination with an appropriate chemical resistant surface coating.

The client has asked us to also perform sulfate content testing on the cores which were obtained. It seems that they want to know if the sulfates are penetrating the concrete surface in addition to that which is detected within the cracks. I don't think that is it necessary, but I was going to try to oblige them with testing. I have a lab experienced with the typical chlorides, carbonation, and sulfate testing of soils, but they are not aware of a standard test for sulfates in hardened concrete. I can not find a standard for this or information for comparative purposes of the results if we were to find a test method.

Has anyone had experience testing for sulfates in hardened concrete? Any suggested laboratories or references for discussion based on the results of the tests? Any thoughts on the subject would be appreciated.

 

[Ron]

Xray diffraction or Xray fluorescence will detect sulfates. Though sulfates in soils are usually the attach mechanism in concretes, any source of sulfates can create attack. I would recommend that you test the cores as your client suggests. Gradient sulfate testing is not difficult. You can drill into the cores at different depths to determine depth of penetration.

I developed a procedure for gradient chlorides sampling that could be used for sulfate testing as well....it is attached.