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Re: Sulfates

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William,

1.  It is unlikely you will find any maps on sulfate content of soil.  It can vary from street to street and can come from many types of sources including water leaching, farming, contamination, and naturally occurring.  For a general idea you could call several geotechs and/or testing laboratories in the area.  If you have control over the geotechnical scope of work I would always include sulfate and chloride testing.  The reason for this works both ways.  Geotechnical reports will always recommend Type II cement just to cover their butts.  The last several reports I reviewed I was able to challenge them on this based on their own testing and got them to allow Type I.  Any good geotech should understand how to include sulfate testing in their report.

2.  Specifying Type II is almost a standard now for fear of being sued latter in life.  If you have the test data then it is pretty simple to look up the requirements in ACI 318 Table 4.3.1.

PCA performed a lot of testing back in the late 1980's and authored a report called "Durability of Concrete in Sulfate-Rich Soils".  I am not sure if it is still available.  They tested different w/c ratios, cement contend, cement types, mineral additives, etc.  The big conclusion was that with a w/c of 0.40 or less the cement type had no effect.  This was also true of w/c ratios above 0.55.  The mineral additives all improved sulfate resistance with silica fume being the best.

3.  ASTM is in the process of developing a new test for sulfates in soil but for now you can specify ASTM D516 and they should be able to get you what you want.

Thomas Hunt, S.E.
ABS Consulting



"Sherman, William" <ShermanWC(--nospam--at)cdm.com>

08/30/2002 06:46 AM
Please respond to seaint

       
        To:        "SeaInt Listserver (E-mail)" <seaint(--nospam--at)seaint.org>
        cc:        
        Subject:        Sulfates



1. Are there any references, such as maps, which show where sulfates in
soils or groundwater are of concern or more specifically where they are not
of concern? Is there any way to readily determine if sulfate testing of
soils is needed in a given area? According to one of my soil's textbooks
"Sulfate attack of concrete occurs throughout the world, especially in arid
areas, such as the southwestern United States....Typically the geotechnical
engineer obtains the representative soil or groundwater samples to be tested
for sulfate content". But often soil's reports to not report sulfate test
data and some geotechnical engineers don't seem very familiar with doing
routine testing for sulfates. So when do you require that sulfate testing be
done and when do you neglect it?

2. I generally specify Type II cement for concrete in contact with soils,
but recently some Contractors and cement suppliers are requesting the use of
Type I cement and say that they "aren't aware of any sulfate problems in the
area" but don't provide any specific documentation of that. Can "moderate
sulfate resistance" be obtained by controlling cement content and w/c ratio
while using Type I cement? Type F fly ash used with Type I cement is known
to improve sulfate resistance - but is there a way to know if a specific mix
with Type I cement and fly ash has adequate sulfate resistance without doing
a 6-month to 1-year sulfate test per ASTM C 1012?

3. What test method should be used to test for sulfates in soil and/or
groundwater? The standard test methods I've found don't seem to clearly
cover the sulfate ranges that are of concern for attack on concrete.

All in all, requirements for sulfate testing seem to be rather vague in
standard documents.


William C. Sherman, PE
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com