1、Standard Method of Test for Determining Water-Soluble Sulfate Ion Content in Soil AASHTO Designation: T 290-95 (2012) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-1a T 290-1 AASHTO Standard Method of Test for De
2、termining Water-Soluble Sulfate Ion Content in Soil AASHTO Designation: T 290-95 (2012) 1. SCOPE 1.1. This test method covers the determination of the water-soluble sulfate ion content in soil. This standard is divided into two parts. The first part specifies the procedure for sampling and preparing
3、 the sample to size for testing. The second part delineates two test procedures (Methods A or B) for the determination of the sulfate ion content in soils. The selection of the method is dependent on the concentration of sulfate ion and the accuracy desired. Two methods are given as follows: Section
4、 Method A: (Gravimetric Method) (1 to 7) and (8 to 16) Method B: (Turbidimetric Method) (1 to 7) and (17 to 26) 1.2. Method A is a primary measure of sulfate ion. Method B is less time-consuming, but often more liable to interference than Method A. It is particularly useful in the lower sulfate rang
5、e and can be used as a screening test. This method is directly applicable over the range of 10 to 100 mg/kg. 1.3. The values stated in SI units are to be regarded as the standard. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M 92, Wire-Cloth Sieves for Testing Purposes M 231, Weighing Devices Used
6、 in the Testing of Materials T 2, Sampling of Aggregates T 248, Reducing Samples of Aggregate to Testing Size 2.2. ASTM Standards: D859, Standard Test Method for Silica in Water D1129, Standard Terminology Relating to Water D1193, Standard Specification for Reagent Water E29, Standard Practice for U
7、sing Significant Digits in Test Data to Determine Conformance with Specifications E60, Standard Practice for Analysis of Metals, Ores, and Related Materials by Spectrophotometry E275, Standard Practice for Describing and Measuring Performance of Ultraviolet and Visible Spectrophotometers 2015 by the
8、 American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 290-2 AASHTO 3. TERMINOLOGY 3.1. For definitions of terms used in these methods, refer to ASTM D1129. PART IINITIAL PREPARATION OF TEST SAMPLES 4. SCOPE 4.1.
9、This method covers the dry preparation of soil and soil-aggregate samples, as received from the field, for use in determining the sulfate ion content in soils. 4.2. The following applies to all specified limits in this standard: For the purpose of determining conformance with these specifications, a
10、n observed value or calculated value shall be rounded off “to the nearest unit” in the last right-hand place of figures used in expressing the limiting value, in accordance with ASTM E29. 5. APPARATUS 5.1. The balance shall have sufficient capacity, be readable to 0.1 percent of the sample mass or b
11、etter, and conform to the requirements of M 231. 5.2. Drying ApparatusAny suitable device capable of drying samples at a temperature not exceeding 60C (140F). 5.3. SievesA series of sieves of the following sizes: 6.3 mm (1/4in.), 4.75 mm (No. 4), 2.00 mm (No. 10), and a pan. The sieve shall conform
12、to M 92, Wire-Cloth Sieves for Testing Purposes (Note 1). Note 1The sieve sizes that have an opening size of 6.3 mm (1/4in.) or larger shall conform to the requirements specified in M 92, excluding Column No. 7. This exclusion permits the use of heavier screens in nonstandard frames that are larger
13、than the 203.2-mm (8-in.) round frames. 5.4. Pulverizing ApparatusEither a mortar and rubber-covered pestle or any device suitable for breaking up the aggregations of soil particles without reducing the size of the individual grains (Note 2). Note 2Other types of apparatus are satisfactory if the ag
14、gregations of soil particles are broken up without reducing the size of the individual grains. 5.5. Sample SplitterA suitable riffle sampler or sample splitter for proportional splitting of the sample and capable of obtaining representative portions of the sample without appreciable loss of fines. T
15、he width of the container used to feed the riffle sampler splitter should be equal to the total combined width of the riffle chutes. Proportional splitting of the sample on a canvas cloth is also permitted. 2015 by the American Association of State Highway and Transportation Officials.All rights res
16、erved. Duplication is a violation of applicable law.TS-1a T 290-3 AASHTO 6. SAMPLE SIZE 6.1. The amount of soil material required to perform the individual test is as follows: Test Approx. Mass (g) Sieve Size Finer Than: Sulfates 250 2.00 mm (No. 10) 7. INITIAL PREPARATION OF TEST SAMPLES 7.1. The s
17、ample as received from the field may be dried in air or a drying apparatus not exceeding 60C (140F) prior to sample selection (Note 3). A representative test sample of the amount required to perform the tests shall then be obtained with the sampler, or by splitting or quartering. The aggregations of
18、 soil particles shall then be broken up in the pulverizing apparatus in such a way as to avoid reducing the natural size of the individual particles. Note 3Samples dried in an oven or other drying apparatus at a temperature not exceeding 60C (140F) are considered to be air dried. 7.2. The portion of
19、 the sample selected for sulfate testing shall be separated into fractions by one of the following methods: 7.2.1. Alternate Method Using 2.00-mm (No. 10) SieveThe dried sample shall be separated into two fractions using a 2.00-mm sieve. The fraction retained on the sieve shall be ground with the pu
20、lverizing apparatus until the aggregation of soil particles is separated into individual grains. The ground soil shall then be separated into two fractions using the 2.00-mm sieve. 7.2.2. Alternate Method Using 4.75-mm and 2.00-mm (No. 4 and No. 10) SievesThe dried sample shall first be separated in
21、to two fractions using a 4.75-mm sieve. The fraction retained on this sieve shall be ground with a pulverizing apparatus until the aggregations of soil particles are broken into separate grains and again separated on the 4.75-mm sieve. The fraction passing the 4.75-mm sieve shall be mixed thoroughly
22、 and, by the use of the sampler or by splitting and quartering, a representative portion adequate for testing shall be obtained. This split-off portion shall then be separated on the 2.00-mm sieve and processed as in Section 7.2.1. 7.2.3. Alternate Method Using 6.3-mm and 2.00-mm (1/4-in. and No. 10
23、) SievesThe dried sample shall first be separated into two fractions using a 6.3-mm sieve. The fraction retained on this sieve shall be ground with a pulverizing apparatus until the aggregations of soil particles are broken into separate grains and again separated on the 6.3-mm sieve. The fraction p
24、assing the 6.3-mm sieve shall be mixed thoroughly and, by the use of the sampler or by splitting and quartering, a representative portion adequate for testing shall be obtained. This split-off portion shall then be separated on the 2.00-mm sieve and processed as in Section 7.2.1. 2015 by the America
25、n Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 290-4 AASHTO PART IIDETERMINATION OF SULFATE CONTENT 8. METHOD AGRAVIMETRIC METHOD (SECTIONS 8 TO 16) 8.1. Scope: 8.2. This method is utilized to determine the amount
26、 of water-soluble sulfate ion in soil. It is directly applicable to samples containing approximately 20 to 100 mg/kg of sulfate ion. It can be extended to higher or lower ranges by adjusting the sample size. 8.3. This standard may involve hazardous materials, operations, and equipment. This standard
27、 does not purport to address all the safety concerns associated with its use. It is the responsibility of whoever uses this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 9. SUMMARY OF METHOD 9.1. Sulf
28、ate ion is precipitated and the mass determined as barium sulfate after removal of silica and other insoluble matter. 10. INTERFERENCES 10.1. Sulfites and sulfides may oxidize and precipitate with the sulfate. Turbidity caused by silica or other insoluble material would interfere if allowed to be pr
29、esent, but removal of such interference is provided in this method. 10.2. Other substances tend to be occluded or adsorbed on the barium sulfate, but these do not significantly affect the precision and accuracy of the method. 11. PURITY OF REAGENTS 11.1. Reagent grade chemicals shall be used in all
30、tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of
31、 sufficiently high purity to permit its use without lessening the accuracy of the determination. 11.2. Unless otherwise indicated, references to water shall be understood to mean Type II reagent water conforming to ASTM D1193. In addition, reagent water used for these methods shall be sulfate-free.
32、12. REAGENTS 12.1. Ammonium Hydroxide (sp gr 0.90)Concentrated ammonium hydroxide (NH4OH). 12.2. Barium Chloride Solution (100 g/L)Dissolve 100 g of barium chloride (BaCl22H2O) in water and dilute to 1 L. 2015 by the American Association of State Highway and Transportation Officials.All rights reser
33、ved. Duplication is a violation of applicable law.TS-1a T 290-5 AASHTO 12.3. Hydrochloric Acid (1+9)Mix one volume of hydrochloric acid (HCl, sp gr 1.19) with nine volumes of water. 12.4. Hydrofluoric Acid (48 to 51 percent)Concentrated hydrofluoric acid (HF). 12.5. Methyl Orange Indicator Solution
34、(0.5 g/L)Dissolve 0.05 g of methyl orange in water and dilute to 100 mL. 12.6. Nitric Acid (sp gr 1.42)Concentrated nitric acid (HNO3). 12.7. Picric Acid (saturated aqueous solution). 12.8. Silver Nitrate Solution (100 g/L)Dissolve 10 g of silver nitrate (AgNO3) in water and dilute to 100 mL. 12.9.
35、Sulfuric Acid (sp gr 1.84)Concentrated sulfuric acid (H2SO4). 13. TEST PROCEDURE 13.1. Weigh 100 g of the soil sample for testing. Put the test sample into a 500-mL Erlenmeyer flask. 13.2. Add 300 mL of distilled water. Stopper the flask and shake the mix. 13.3. Centrifuge the sample; if the sample
36、exhibits turbidity, filter the sample through a 0.45-m membrane filter. A drop of concentrated nitric acid may be added, if needed, to precipitate finely divided suspended matter (Note 4). 13.4. Pipet 30.0 mL, or measure a quantity of the clear sample containing sulfate ion equivalent to 20 to 50 mg
37、 of barium sulfate (BaSO4) into a 250-mL beaker. Adjust the volume by evaporation, or dilution with water, to approximately 200 mL. Adjust the acidity of the sample to the methyl orange end point and add 10 mL excess HCl (1+9). If a quantity other than 30 mL is used, substitute the volume of the ali
38、quot into the calculation in place of 30 mL. Note 4Silica may be removed before applying this method by dehydration with HCl or perchloric acid (HClO4) in accordance with the respective procedures in ASTM D859. In this case, the ignition described in Section 13.8 need not be done in a platinum cruci
39、ble. 13.5. Measure into the beaker a quantity of the clear sample containing sulfate ion equivalent to 20 to 50 mg of barium sulfate (BaSO4). Adjust the volume by evaporation or dilution with water to approximately 200 mL. Adjust the acidity of the sample to the methyl orange end point and add 10 mL
40、 excess of HCl (1+9). 13.6. Heat the acidified solution to boiling and slowly add to it 5 mL of hot BaCl2solution (Note 5). Keep the temperature just below boiling until the liquid has become clear and the precipitate has settled out completely. In no case shall this settling period be less than 2 h
41、. Note 5Faster precipitation and a coarser precipitate can be obtained by adding 10 mL of saturated picric acid solution and boiling the sample 5 min before adding BaCl2. 13.7. Filter the suspension of BaSO4on a fine, ashless filter paper and wash the precipitate with hot water until the washings ar
42、e substantially free of chlorides, as indicated by testing the last portion of the washings with AgNO3solution (Note 6). Avoid excessive washing. If any BaSO4passes through the filter, pour the filtrate through the paper a second time (Note 7). Note 6Do not attempt to obtain a completely negative te
43、st for chloride. Discontinue washing when no more than a faint opalescence is produced in the test. Using a small amount of ashless 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 290-6 AASHTO fi
44、lter paper pulp in the suspension will aid in filtration and reduce the tendency for BaSO4to pass through the filter. Note 7If the filtrate is poured through the paper a second time, AgNO3must not be present in the filtrate. 13.8. Place the filter paper and contents in a tared platinum crucible (Not
45、e 4), and char and consume the paper slowly without flaming. Ignite the residue at approximately 800C for 1 h, or until it is apparent that all carbon has been consumed. 13.9. Add a drop of H2SO4and a few drops of HF, and evaporate under a hood to expel silica as silicon tetrafluoride (SiF4). Reigni
46、te at about 800C, cool in a desiccator, and determine the mass of the BaSO4. 14. CALCULATION 14.1. Calculate the concentration of sulfate ion (SO4) in milligrams per kilogram, as follows: 411500sulfate, mg/kgWS= (1) where: W = grams of BaSO4, and S = grams of sample used, e.g., 100 g soil 300 mL wat
47、er30 mL aliquot10 gSS=Sulfate Ion Content in Soil: ( )( )( )sulfates mg/kg as determined above 100mg/kg moisture free 100 percent moisture= (2) 15. REPORT 15.1. Report the sulfate content as computed in Section 14.2 on a moisture-free basis in units of milligrams per kilogram (mg/kg). Report this va
48、lue to the nearest whole number in accordance with the rounding-off method in ASTM E29. 16. PRECISION AND BIAS 16.1. Data are not available at this time. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.T
49、S-1a T 290-7 AASHTO METHOD BTURBIDIMETRIC METHOD (SECTIONS 17 TO 26) 17. SCOPE 17.1. This method is intended for rapid routine or control tests for the water-soluble sulfate ion in soil where extreme accuracy and precision are not required. It is directly applicable over the range of 10 to 100 mg/kg of sulfate ion (SO4). 18. SUMMARY OF METHOD 18.1. Sulfate ion is converted to a barium sulfate suspension under controlled conditions. Glycerin solution and a sodium chloride solution are added to stabilize the suspension an
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