PCA R&D Serial No. 3016a

Test Methods for Water-Soluble Sulfate in Soils (Updated)

by Xiuping Feng and Cyler Hayes

©Portland Cement Association 2010 All rights reserved

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ABSTRACT ACI 318, Building Code Requirements for Structural Concrete, contains requirements on constituent materials and mix designs for concrete structures in sulfate soils. The requirements set exposure classes and mitigation measures based on the level of soluble sulfates in the soil. However, the test method for determining the level of sulfates is not specified.* This same situation exists in other standards for concrete structures. The objective of this project was to provide data on water-soluble sulfates in soils measured using four commonly referenced test methods. These data were used to evaluate the potential assignment of exposure class based on the test method used. Ten soil samples were selected for evaluation to represent a range of sulfate levels. For a given soil, the range of results found by the four methods varied significantly relative to specified soluble sulfate limits, such that the same soil could be assigned a different exposure class based on the test method used. This confirms that specification of sulfate requirements should include reference to a standard test for soluble sulfates in the soil. It is recommended that ASTM C1580, Test Method for Water-Soluble Sulfate in Soil, be adopted as the reference test method. Based on the findings in this test program, suggested improvements to ASTM C1580 are outlined. KEYWORDS Chemical tests, codes, concrete durability, outdoor exposure, soil tests, specifications, sulfates, sulfate attack, sulfate exposure classification, sulfate soils, water-soluble sulfate. REFERENCE Feng, X. and Hayes, C. F., Test Methods for Water-Soluble Sulfate in Soils (Updated), SN3016a, Portland Cement Association, Skokie, Illinois, USA, 2010, 15 pages.

*Since this report was originally published, ACI 318 has been revised. Sulfate exposure requirements were unchanged although the format for designating exposure classes was revised.

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TABLE OF CONTENTS Page

Abstract ........................................................................................................................................... 2 Keywords ........................................................................................................................................ 2 Reference ........................................................................................................................................ 2 Introduction ..................................................................................................................................... 4 Objective and Scope ....................................................................................................................... 5 Test Program ................................................................................................................................... 6 

Sample Acquisition and Preparation ........................................................................................... 6 Comparison of Test Methods ...................................................................................................... 7 

Experimental Design ....................................................................................................................... 8 Test Results ..................................................................................................................................... 9 

Total and Acid-Soluble Sulfate Contents ................................................................................... 9 Water-Soluble Sulfate Contents ................................................................................................ 10 ASTM C1580 Test for Soils with High Sulfate Contents......................................................... 11 

Discussion ..................................................................................................................................... 12 Implications of Test Results...................................................................................................... 12 Observations on the Test Methods ............................................................................................ 13 

Recommendations ......................................................................................................................... 14 Acknowledgements ....................................................................................................................... 15 References ..................................................................................................................................... 15 

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Test Methods for Water-Soluble Sulfate in Soils (Updated)

by Xiuping Feng and Cyler F. Hayes*

INTRODUCTION American Concrete Institute (ACI) 318 Building Code Requirements for Structural Concrete contains requirements on constituent materials and mix designs for concrete structures in sulfate soils (Table 1). The requirements set exposure classes based on the level of soluble sulfates in the soil. However, the test method for determining the level of sulfates is not specified.† This same situation exists in other standards for concrete structures. Table 1. ACI 318-05 Table 4.3.1 Requirements for Concrete Exposed to Sulfate-Containing

Solutions†

Sulfate exposure

Water-soluble sulfate (SO4)

in soil, % by mass

Sulfate (SO4) in water,

ppm Cement type

Maximum w/cm

by mass

Minimum design

compressive strength, f'c,

MPa (psi)

Negligible < 0.10 < 150 No special type — —

Moderate 0.10 to 0.20 150 to 1500

II, IP(MS), IS(MS),

P(MS), I(PM)(MS), I(SM)(MS)

0.50 28 (4000)

Severe 0.20 to 2.00 1500 to 10,000

V 0.45 31 (4500)

Very severe > 2.00 >10,000 V + pozz 0.45 31 (4500)

The ACI 318 sulfate requirements apparently have their genesis in work of the U. S. Bureau of Reclamation (USBR). The USBR’s extensive testing for sulfate resistance of concrete resulted in requirements that have been published in their Concrete Manual for many years (Fig. 1). It is generally assumed that, in establishing their published table limits, the USBR determined soluble sulfates in soils using test procedures similar to their “Method of Test for Determining the

* Materials Scientist (XFeng@ctlgroup.com) and Senior Chemist (CHayes@ctlgroup.com), respectively, CTLGroup Inc., 5400 Old Orchard Road, Skokie, IL 60077-1030, U.S.A. Tel (847) 965-7500, www.ctlgroup.com. † The ACI 318 Building Code has been revised to ACI 318-08 since this report was first published. Sulfate exposure requirements were unchanged although the format for designating exposure classes was revised.

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Quantity of Water-Soluble Sulfate in Solid (Soil and Rock) and Water Samples,” the current version of which is dated May 1, 1973. However this is not fully documented.

Figure 1. USBR Concrete Manual, 6th Edition, 1956. As other organizations such as ACI adopted requirements based on the USBR table, they have not consistently associated the table limits with the USBR test method for water-soluble sulfate in soils. Other test methods for water-soluble sulfates have been developed, but their relationship to the USBR method has not been established. OBJECTIVE AND SCOPE The objective of this project was to provide data on water-soluble sulfates in soils as measured using four commonly referenced test methods. These data were used to evaluate the potential assignment of exposure class based on the test method used. Initially, five soil samples were tested and evaluated (Hayes, 2007). This report is an extension of the earlier work. Five additional samples are included. The ten soil samples were selected for evaluation to represent a range of sulfate levels. The soil samples were evaluated for water-soluble sulfate content by the USBR method and by three other test methods commonly used to assess exposure for sulfate attack on concrete placed in direct contact with soil:

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United States Bureau of Reclamation, “Method of Test for Determining the Quantity of Water-Soluble Sulfate in Solid (Soil and Rock) and Water Samples,” 1973.

Canadian Standards Association (CSA) Test Method A23.2-3B, “Determination of Total or Water-Soluble Sulphate Ion Content of Soil,” 2000.

California Department of Transportation (Caltrans) Test Method 417-99, “Testing Soils and Waters for Sulfate Content.”

ASTM C1580-05, “Standard Test Method for Water-Soluble Sulfate in Soil.” TEST PROGRAM This study consisted of the following tasks:

Obtain representative samples of naturally occurring soils to represent a range of sulfate content levels.

Screen submitted soil samples for total sulfate content. Select ten soils that potentially represent the breadth of sulfate exposure categories as

listed in the ACI 318-05 table. Evaluate the selected soils by the four test methods. Report the findings.

Sample Acquisition and Preparation Requests for samples were sent to a number of contacts in areas around the country with emphasis on those areas reported to have high sulfate soils.‡ The requests included the following sampling procedures:

Remove and set aside soil and vegetation that represents the top foot of soil. Samples should be taken approximately one foot below ground level.

Take a sample of at least five kilograms. If possible remove large rocks, branches, etc. Double bag the soil in plastic and place in the plastic bucket provided. Label the container.

Although moist soil is acceptable, avoid areas that are excessively wet (greater than 20% water or very wet liquid mud). Do not dry the soil prior to shipment.

Do not add preservation materials such as methanol commonly used for VOC and other volatility studies.

Do not homogenize the entire sample as this is to be done in the laboratory. Ship the sample within two days of sampling.

Upon receipt, large rocks, vegetation, and foreign debris if visibly present were removed from submitted soil samples by hand. For each soil sample, a sub-sample was oven-dried at 45°C for 24 hours and the percent volatile loss was determined. A portion of this oven-dried sample was passed through a 50-mesh sieve. The sieved portion was then used to test total sulfate content by

‡ For protection against spread of invasive species and for pest management, the U.S. Department of Agriculture regulates the movement of soils from designated areas of the country. This placed some restrictions on available sites for high sulfate soils.

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the CSA test method. This was done for screening purposes to ensure a range of sulfate levels would be evaluated. If selected for continued study, the remaining oven-dried sample was split into appropriate portions for each test method. Samples were prepared for USBR and Caltrans test methods by passing through a No. 10 (2-mm) sieve. Samples were prepared for the ASTM C1580 test method by continued oven drying at 110°C for another 24 hours prior to passing the sample through a No. 30 (0.6-mm) sieve. The percent volatile loss for drying at 110°C was also determined. A total of eighteen soil samples were received from various locations throughout the United States. After the prepared samples were screened for total sulfate content, ten were selected for full evaluation. Comparison of Test Methods Key characteristics of the four test methods are given in Table 2. A primary factor is the extraction ratio, and this is a point of debate in selecting and evaluating test methods for sulfate in soils (Rebel, et. al., 2005). The USBR method is often quoted as having a water-to-soil extraction ratio of 10:1 (mL/g). However, the method also states “Soil samples containing gypsum may require a higher than 10:1 water-to-soil ratio to ensure complete solution of all gypsum present. If all gypsum is not in solution, the sulfate content of the extract will not reflect the true percentage of sulfate in the soil.” There is no maximum limit on the extraction ratio permitted, but guidance in the method indicates it is a function of total sulfate as estimated by electrical resistivity testing. The CSA method also bases the extraction ratio on total sulfate, specifically nine times the determined acid-soluble SO4 to one part soil. The Caltrans method uses a 3:1 ratio. The ASTM method uses two extraction ratios (~ 8:1 and ~ 80:1) and the percentage of SO4 is determined based on a combination of results for both solutions. The duration of extraction also differs by test method and temperature during extraction is not clearly defined in the methods except that it is reasonable to assume standard laboratory environments are intended as the default condition. The methods also differ regarding sample preparation prior to testing, specifically soil drying conditions. For this program all samples were initially dried at 45°C for 24 hours. This was done to provide a consistent basis for comparison. The ASTM C1580 has a specific drying requirement which was followed prior to testing by that method. Only the ASTM method contains a precision statement.§ The single operator coefficient of variation of 4.4% indicates the results of two tests by the same operator on the same material should not differ by more than 12.4% of their average. The multilaboratory coefficient of variation of 21.2% indicates that results of two different laboratories on identical samples of a material should not differ by more than 60% of their average. While it can be argued that this is a rather imprecise method, the precision of the other methods is not documented.

§ It is assumed that the turbidimetric method was used for determination of the precision statement, but this is not stated in the method.

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Table 2. 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) and Gravimetric

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 (March 1999)

Not stated in test method

Turbidimetric* or gravimetric (soluble

SO4)

3:1 agitated for 15 min.

N/A

ASTM C1580-05 18 to 24 h @

110°C

Turbidimetric or ASTM C 114 (soluble SO4)

~8:1 and ~80:1 agitated for 1

hr.

4.4% COV-S 21.2% COV-M

* A new edition of Caltrans 417 issued Nov. 2006 replaces the turbidimetric method with ion chromatography.

EXPERIMENTAL DESIGN A total of eighteen soil samples were received from various locations throughout the United States. After being screened for total sulfate content by CSA Test Method A23.2-3B §5.1 (2000) and by chemical analysis ASTM C114-06, “Standard Test Methods for Chemical Analysis of Hydraulic Cement,” ten soil samples were selected for further investigation based on their total sulfate content. Testing of water-soluble sulfate in soil samples was conducted in accordance with each test method. Table 3 shows the procedures for each sample. It should be noted that ASTM C1580 includes the turbidimetric method as the default method, and the gravimetric method as an option. Samples 1733006, 1733005, 1733002, 1733001, and 1825101 were tested in triplicate for each of the four test methods; sample 1982002 was tested in triplicate by the CSA and ASTM methods, but in single runs by the other two methods. The other four samples were tested in single runs by the four methods.

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Table 3. Experimental Procedures

CTL ID USBR ASTM Caltrans CSA

w/s Method w/s Method w/s Method w/s Method

1733006 10 G 8, 80 T 3 T N/A G

1733005 10 G 8, 80 T 3 T N/A G

1733002 10 G 8, 80 T 3 T 2 G

1733001 10 G 8, 80 T 3 T 2 G

1825101 10 G 8, 80 T 3 T 31 G

1982002 10 G 8, 80 T, G 3 T 18 G

2048601 10 G 8, 80 T, G 3 T 187 G

2048603 10 G 8, 80 T, G 3 T 218 G

2048604 10 G 8, 80 T, G 3 T 158 G

2048605 10 G 8, 80 T, G 3 T 194 G Key: G – gravimetric, T – turbidimetric, w/s – water-to-solids.

TEST RESULTS Total and Acid-Soluble Sulfate Contents Total sulfate contents and acid soluble sulfate contents for the ten selected soil samples were determined by chemical analysis and by the CSA method, respectively. Results are given in Table 4. The standard deviation calculated from triplicate tests is included when applicable. Results indicate that the first four soils contain lower amounts of total and acid soluble sulfates and the other six soils contain higher amounts of total and acid soluble sulfates. It should be noted that the CSA method permits total acid-soluble SO4 to be reported for water-soluble SO4 when the acid-soluble value is 0.2% or less. For the last four soils in Table 4, with highest sulfate levels, the acid soluble sulfates detected by CSA method are substantially lower than the calculated sulfates determined by chemical analysis. This may indicate a deficiency in the amount of BaCl2 that is added in the CSA test to precipitate sulfates in solution.

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Table 4. Sulfate Content by Chemical Analysis and CSA Method

Sample

Volatile loss after oven

drying at 45°C, % by mass

Total SO3 % by mass

(ASTM C114)

Calculated as SO4,

% by mass (ASTM C114)

Acid soluble SO4,

% by mass (CSA)

Standard deviation

1733006 8.8 N/A N/A 0.01 0.01

1733005 18.5 N/A N/A 0.02 0.02

1733002 3.0 N/A N/A 0.19 0.03

1733001 28.3 N/A N/A 0.25 0.02

1825101 19.1 N/A N/A 3.49 0.24

1982002 22.5 1.82 2.18 1.95 0.02

2048601 1.7 34.97 41.96 20.83 N/A

2048603 1.2 40.04 48.05 24.22 N/A

2048604 4.1 29.81 35.77 17.55 N/A

2048605 1.4 36.68 44.02 21.56 N/A

Water-Soluble Sulfate Contents Table 5 shows the test results for water-soluble sulfates in the ten soil samples by each of the four methods. The ASTM data reported for the first six soils were obtained by turbidimetric method; no ASTM data are reported for the other four samples because the high levels of soluble sulfates exceeded the range of the turbidimetric method. Because of the problem with the turbidimetric method at high soluble-sulfate levels, the ASTM C1580 tests were repeated using the gravimetric method as discussed below. Table 5. Water-Soluble Sulfate Results for Selected Soils

Sample

Total volatile loss, % by mass

Water-soluble sulfate content, % SO4 by mass of soil

ASTM USBR CSA Caltrans

Mean Standard deviation

MeanStandard deviation

MeanStandard deviation

Mean Standard deviation

1733006 10.3 0.02 0.00 0.01 0.00 N/A N/A 0.01 0.00

1733005 20.8 0.02 0.00 0.00 0.00 N/A N/A 0.00 0.00

1733002 4.1 0.18 0.00 0.14 0.01 0.11 0.01 0.11 0.00

1733001 30.3 0.02 0.00 0.01 0.00 0.00 0.00 0.00 0.00

1825101 N/A 1.71 0.19 1.32 0.01 2.06 0.16 0.43 0.01

1982002 22.5 1.73 0.08 1.61 0.00 1.99 0.03 0.87 N/A

2048601 1.7 OR N/A 1.39 N/A 27.11 N/A 0.40 N/A

2048603 1.2 OR N/A 1.46 N/A 33.04 N/A 0.47 N/A

2048604 4.1 OR N/A 1.57 N/A 25.74 N/A 0.55 N/A

2048605 1.4 OR N/A 1.41 N/A 29.04 N/A 0.38 N/A Key: OR – outside range.

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ASTM C1580 Test for Soils with High Sulfate Contents As shown in Tables 2 and 3, both Caltrans and default ASTM test methods use turbidimetric methods. However, the test results showed (Table 5) that the turbidimetric method could not be applied to soil samples with high sulfate contents. In ASTM C1580-05, a nonmandatory Note 3 states:“These values were derived from the limits on the sulfate test of 5 to 40 mg/L, and a solubility of sulfate of 1.6 g/L at pH 7 when calcium sulfate is present. The method is not applicable for soils outside this range. For those samples, see the Annex.” The Annex to ASTM C1580-05, although mandatory, is not explicit. It states: “If a sample falls above 3.33% sulfate, then different sample masses and/or dilutions can be used. If this procedure is followed, then the mg SO4 from the turbidimeter reading shall be maintained within 5 to 40 mg/L.” In addition, during testing, it was found that the turbidimeter readings kept drifting from the actual value with time. This required the test results to be periodically corrected with standards (turbidity blanks). Because of the problem of using the turbidimetric method in the ASTM C1580 test method for soils with high sulfate contents, testing by the gravimetric method was performed on five soil samples with higher sulfate levels. The gravimetric method is a permitted option in ASTM C1580. In accordance with ASTM C1580-05, two extraction ratios with two aliquots for each extraction ratio were evaluated for each soil sample. Test results are shown in Table 6. These results represent the average of two aliquots for each extraction ratio, designated as ASTM 8:1 and ASTM 80:1.

Table 6. Water-Soluble Sulfate Results for Selected Soil Samples by ASTM Gravimetric Method

Sample ID Water-to-soil extraction ratio

ASTM 8:1 ASTM 80:1

1982002* 1.80 1.82

2048601 1.29 35.52

2048603 1.26 14.24

2048604 1.39 16.85

2048605 1.20 15.69 * Average of six results from triplicate tests.

Based on the results shown in Tables 5 and 6, the exposure class for a concrete placed in direct contact with these soils was determined by the ACI 318 table limits and is shown in Table 7. Because ASTM C1580-05 provides no requirement, the gravimetric results were arbitrarily averaged for the two extraction ratios.

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Table 7. Sulfate Exposure Based on Test Method

Average water-soluble sulfate content,

%SO4 by mass of soil (ACI Exposure Class)

Sample ID ASTM USBR CSA Caltrans

1733006 0.02

(Negligible) 0.01

(Negligible) 0.01*

(Negligible) 0.01

(Negligible)

1733005 0.02

(Negligible) 0.00

(Negligible) 0.02*

(Negligible) 0.00

(Negligible)

1733002 0.18

(Moderate) 0.14

(Moderate) 0.11

(Moderate) 0.11

(Moderate)

1733001 0.02

(Negligible) 0.01

(Negligible) 0.00

(Negligible) 0.00

(Negligible)

1825101 1.71

(Severe) 1.32

(Severe) 2.06

(Very Severe) 0.43

(Severe)

1982002 1.73

(Severe) 1.61

(Severe) 1.99

(Severe) 0.87

(Severe)

2048601 18.40**

(Very Severe)1.39

(Severe) 27.11

(Very Severe) 0.40

(Severe)

2048603 7.75**

(Very Severe)1.46

(Severe) 33.04

(Very Severe) 0.47

(Severe)

2048604 9.12**

(Very Severe)1.57

(Severe) 25.74

(Very Severe) 0.55

(Severe)

2048605 8.44**

(Very Severe)1.41

(Severe) 29.04

(Very Severe) 0.38

(Severe) * Total acid-soluble sulfate per CSA method. ** Average of test results for gravimetric method at the two extraction ratios.

DISCUSSION Implications of Test Results Several observations can be made regarding these results. The ASTM method gave consistently higher water-soluble SO4 results than the USBR method, although the differences were not significant enough to impact selection of exposure class according to ACI 318-05 for the samples tested at lower sulfate levels (1733006, 1733005, 1733002, 1733001, 1825101, and 1982002). The Caltrans method gave consistently lower results, again with no impact on the selection of exposure class at lower sulfate levels. Results were considerably different at higher sulfate levels (2048601, 2048603, 2048604, and 2048605), where the ASTM and CSA methods gave measurably higher results because of their higher dilution rates (based on arbitrarily averaging results of the two extraction ratios for ASTM C1580).

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Table 7 indicates the exposure class designation for all lower sulfate samples was relatively consistent based on the different test methods even though the range of water-soluble SO4 values for a given soil sample could be significant. With the exception of Sample 1825101 and the four high sulfate soils, there were no differences in exposure class based on test method. This reflects the relatively large range of water-soluble SO4 values specified for each exposure class as much as it does any close correlation between methods. It also was somewhat fortuitous in that, except for Sample 1825101, results for the samples tested fell within classification brackets, and were not “borderline.” Even considering the above discussion, it is quite possible that results based on the different methods for low sulfate soils could have resulted assignment of a different exposure class for the samples tested. Consider sample 1733002 for example. Within the precision of the ASTM test method, it is conceivable that the sample could have tested at a 0.20% SO4, which would have moved it to the “Severe” classification, just as a variation of 0.02% could have moved it to the “Negligible” classification based on the Caltrans method. And it is very likely that samples “on the border” of classification ranges would be impacted by the test method, particularly if one laboratory used ASTM C1580 while another laboratory used Caltrans 417. This issue becomes more significant at higher sulfate levels with differences between the “Severe” and “Very Severe” classification. As would be expected, differences in extraction ratio become more significant for soils with higher sulfate levels. Clearly a test method should be specified when sulfate requirements such as those in ACI 318 are invoked. One of the questions that instigated this test program was whether the test methods being used are consistent with the USBR method that served as the basis for the exposure classifications in ACI 318 and other standards. None of the methods used in this project gave identical results to the USBR method primarily due to differences in extraction ratios. However, as noted earlier, the USBR method is somewhat ambiguous regarding extraction ratios for higher sulfate soils. Given that it is a consensus method that can be readily updated, the ASTM method appears to be promising as a reference test for sulfate exposure requirements. The ASTM test results, although somewhat higher, were reasonably consistent with the USBR method test results over the range of soils tested when taking differences in extraction ratio into account. Within the practical application of such tests, it would be reasonable to use the ASTM method in conjunction with the ACI 318 sulfate requirements without change to the table limits. Observations on the Test Methods The legacy USBR test method was developed for internal use at the Bureau and is not well suited to current general 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 permits extraction at higher water-to-soil ratios than the 10:1 standard extraction ratio. While this is not “wrong,” the method does not have a limit on the ratio, nor does it require reporting the value used.

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The Caltrans method (California Test 417) is an internal method developed by the California Department of Transportation. As such it is consistent with California DOT specification requirements. The 3:1 extraction ratio is the lowest of all the methods. It has been reported that this method has worked well in classifying soils for use with sulfate limits such as those in ACI 318-05. As would be expected given the extraction ratio, in the tests conducted in this program the method consistently gave the lowest results for water-soluble SO4 relative to the USBR, CSA, and ASTM methods. 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 0.20% or less, no further testing is required. This screening method is efficient and useful, although such screening can be included in a specification or practice, and is not essential to a test method. The extraction ratio is variable, defined as a function of the total sulfate level. The ASTM method (ASTM C1580) is also a consensus method, and was developed relatively recently with the first edition published in 2005. As such, it is consistent with use in current specifications. The method uses two extraction ratios with limiting ranges for values determined at the different extraction and aliquot levels based on sulfate solubility calculations. Given that sample preparation, especially the drying temperature, can have a significant impact on the sulfate content of a soil, this method clearly defines sample preparation and drying procedures. ASTM C1580 allows both turbidimetric and gravimetric measurement techniques to be used. However, because turbidimetric measurements can “drift” from the actual value over time the results must be corrected with standards (turbidity blanks) periodically. The ASTM method does not require periodic correction checks, which makes it susceptible to drift. The gravimetric method is not susceptible to drift because it measures the weight of barium sulfate formed. RECOMMENDATIONS Based on the test results from this project, the following recommendations are made:

ASTM C1580 should be proposed as the standard test method for determination of water-soluble sulfate levels in soil for assignment of sulfate exposure limits in ACI 318 or similar standards.**

ASTM C1580-05 should be revised to:

o Discontinue the use of the turbidimetric measurement technique as the default

method and require gravimetric measurements (or qualified ASTM C114 methods) as the default and reference method.

o Update procedure in Paragraph 8.3 to reflect use of gravimetric method. o If the turbidimetric method is maintained as an alternate, update Note 3 and

Annex to clarify provisions for high sulfate soils. ** Since this work was conducted, ACI Committee 318 has adopted ASTM C1580-05 for inclusion in ACI 318-11.

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o Clear provisions should be added to require correction of readings to account for

drift of the instrument if the turbidimetric technique is used as an alternate method.

o Update the precision and bias statement based on revisions to the measurement

techniques.

o Add a note to recommend that total acid-soluble sulfate values be used for screening.

o Add provisions to clarify the evaluation of gravimetric results based on extraction

ratio. ACKNOWLEDGEMENTS The research reported in this paper (PCA R&D Serial No. 3016a) was conducted by the CTLGroup with the sponsorship of the Portland Cement Association (PCA Project Index No. 05-10 and 05-10a). The contents of this report reflect the views of the authors, who are responsible for the facts and accuracy of the data presented. The contents do not necessarily reflect the views of the Portland Cement Association. Special thanks to Dr. Kevin Folliard at Texas University at Austin, Mr. Orville Werner at CTL/Thompson, staffs of California Portland Cement Co., Holcim (US) and TXI who were instrumental in providing soil samples for this project. The authors would also like to thank Raja Naamane, Cecylia Wedzicha, and Rick Stevenson of CTLGroup for their contributions to this project. REFERENCES Hayes, Cyler F., Test Methods for Water-Soluble Sulfate in Soils, SN3016, Portland Cement Association, Skokie, Illinois, USA, 2007, 13 pages. Rebel, B., Detwiler, R., Gebler, S., and Hooton, R., “The Right Sulfate Test Makes a Difference,” Concrete International, February 2005, pages 49 to 52.