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Frequently Asked Questions
Cement & Concrete
Technology Home > FAQs > Test methods
for water-soluble sulfates
Q:The ACI Building Code (ACI 318) contains requirements
for concrete exposed to sulfate solutions; however, no guidance
is given on how to determine the level of sulfates. What test methods
are available to determine water-soluble sulfates in soil or water
that could be included in a project specification?
A: Four test methods are commonly
used in North America to assess sulfate exposure of concrete placed
in direct contact with soil:
- United States Bureau of Reclamation, “Method of Test
for Determining the Quantity of Water-Soluble Sulfate in Solid (Soil
and Rock) and Water Samples.”
- Canadian Standards Association (CSA) Test Method A23.2-3B,
“Determination of Total or Water-Soluble Sulphate Ion Content
of Soil.”
- California Department of Transportation (Caltrans) Test
Method 417, “Testing Soils and Waters for Sulfate Content.”
- ASTM International (ASTM) C1580, “Test Method for
Water-Soluble Sulfate in Soil.”
The methods differ in extraction ratio, extraction duration, and
sample preparation. Key characteristics of the four test methods
are summarized in Table 1.
| Table 1. Characteristics of Test Methods
for Water-Soluble Sulfate in Soils |
Test Method |
Sample Drying Method |
Measurement Technique |
Extraction Ratio Water:Soil (mL:g) |
Precision and Bias |
USBR
(May 1, 1973)
|
Air dry |
Electrical resistivity (total sulfate screen) andGravimetric
|
10:1 (or higher if gypsum is present) agitated for at least
6 hr. |
N/A |
| CSA A23.2-3B (2000) |
Air dry at room temperature and humidity |
Gravimetric (total SO4 screen and soluble sulfate) |
[9 x (%SO4 by acid-soluble method)]:1 agitated for 6 hr. |
N/A |
| Caltrans 417 (2006) |
Not stated in test method |
Ion chromatography
or Gravimetric (soluble SO4)
|
3:1 agitated for 15 min. |
N/A |
ASTM C1580
(April 2005)
|
18 to 24 h @ 110°C |
Turbidimetric or ASTM C 114 (soluble SO4) |
~8:1 and ~80:1 agitated for one hr. |
4.4% COV-S
21.2% COV-M
|
Hayes (2007)
compared the four methods and found that:
- The USBR test method is not well suited to
specifications for concrete structures. Critical provisions are
not defined in “specification language” that would
be enforceable in contracts or clear in dispute resolution cases.
Also, the method does not have a limit on the permitted extraction
ratio, nor does it require that the extraction ratio used is reported.
- The Caltrans method (California Test 417) is
an internal method developed by the California Department of Transportation.
The 3:1 extraction ratio is the lowest of the four methods and
consistently gave the lowest results for water-soluble SO4.
- The CSA method (A23.2-3B) is a consensus method
used in Canadian standards for concrete structures. It includes
a “built in” screening mechanism whereby total acid-soluble
sulfate is first measured. If the total sulfate value is 0.2%
or less, no further testing is required. This screening method
is efficient and useful. The extraction ratio is variable, defined
as a function of the total sulfate level.
- The ASTM method (C1580) is also a consensus
method. The method uses two extraction ratios with limiting ranges
for values determined at the different extraction and aliquot
levels based on sulfate solubility calculations. An advantage
of the ASTM method is that sample preparation, especially the
drying temperature, which can have a significant impact on the
sulfate content of a soil, is clearly defined. The ASTM method
gave consistently higher water-soluble SO4 results than the USBR
method. The method is written in mandatory language suitable for specifications and is the only method that contains a precision statement.
Refer to Hayes (2007)
for more information on the comparison of the four methods.
Reference:
Hayes, Cyler F., Test
Methods for Water-Soluble Sulfate in Soils, SN3016, Portland
Cement Association, Skokie, Illinois, USA, 2007, 13 pages.
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