AASHTO T 291-1994 Standard Method of Test for Determining Water-Soluble Chloride Ion Content in Soil《水溶性氯离子含量测定的标准测试方法》.pdf

1、Standard Method of Test for Determining Water-Soluble Chloride Ion Content in Soil AASHTO Designation: T 291-94 (2013) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-1a T 291-1 AASHTO Standard Method of Test for D

2、etermining Water-Soluble Chloride Ion Content in Soil AASHTO Designation: T 291-94 (2013) 1. SCOPE 1.1. This test method describes the procedures for sampling and testing a soil for chloride ion content. This standard is divided into two parts. The first part specifies the procedure for sampling and

3、 preparing the sample to size for testing. The second part delineates two test procedures (Methods A or B) for the determination of the water-soluble chloride ion content in soil. Two methods are given as follows: Section Method A: (Mohr Titration Method) (1 to 7) and (8 to 16) Method B: (pH/mV Mete

4、r Method) (1 to 7) and (17 to 28) 1.2. Method A is based upon the Mohr procedure for determining chloride ion with silver nitrate. Method B utilizes a pH/mV meter. By comparing the mV readings to the calibration curve, determine the chloride ion content. 1.3. The values stated in SI units are to be

5、regarded as the standard. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M 92, Wire-Cloth Sieves for Testing Purposes M 231, Weighing Devices Used in the Testing of Materials T 2, Sampling of Aggregates T 248, Reducing Samples of Aggregate to Testing Size 2.2. ASTM Standards: D1129, Standard Termino

6、logy Relating to Water D1193, Standard Specification for Reagent Water D2777, Standard Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water D3370, Standard Practices for Sampling Water from Closed Conduits E29, Standard Practice for Using Significant

7、Digits in Test Data to Determine Conformance with Specifications 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 291-2 AASHTO 3. TERMINOLOGY 3.1. For definitions of terms used in this test method

8、, refer to ASTM D1129. PART IINITIAL PREPARATION OF TEST SAMPLES 4. SCOPE 4.1. This method covers the dry preparation of soil and soil-aggregate samples, as received from the field, for use in determining the chloride content. 4.2. The following applies to all specified limits in this standard: For

9、the purpose of determining conformance with these specifications, an 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. BalanceThe balance shall ha

10、ve sufficient capacity, be readable to 0.1 percent of the sample mass, or better, 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 (1/4-

11、in.), 4.75-mm (No. 4), 2.00-mm (No. 10) sieve, and a pan. The sieve shall conform 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 e

12、xclusion permits the use of heavier screens in nonstandard frames that are larger 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 ind

13、ividual grains (Note 2). Note 2Other types of apparatus are satisfactory if the aggregations 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 ob

14、taining representative portions of the sample without appreciable loss of fines. The 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

15、 American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 291-3 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 Tha

16、n: Chlorides 250 2.00 mm (No. 10) 7. INITIAL PREPARATION OF TEST SAMPLES 7.1. The sample 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 th

17、en be obtained with the sampler, or by splitting or quartering. The aggregations of 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 tempe

18、rature not exceeding 60C (140F) are considered to be air dried. 7.2. The portion of the sample selected for chloride 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 u

19、sing a 2.00-mm sieve. The fraction retained on this sieve shall be ground with the pulverizing 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

20、-mm and 2.00-mm (No. 4 and No. 10) SievesThe dried sample shall be separated into two fractions using a 4.75-mm sieve. The fraction retained on this sieve shall be ground with the pulverizing apparatus until the aggregation of soil particles is separated into individual grains and again separated on

21、 the 4.75-mm sieve. The fraction passing the 4.7-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

22、Section 7.2.1. 7.2.3. Alternate Method Using 6.3-mm and 2.00-mm (1/4-in. and No. 10) SievesThe dried sample shall be separated into two fractions using a 6.3-mm sieve. The fraction retained on this sieve shall be ground with the pulverizing apparatus until the aggregations of soil particles are sepa

23、rated into individual grains and again separated on the 6.3-mm sieve. The fraction passing 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 s

24、eparated on the 2.00-mm sieve and processed as in Section 7.2.1. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 291-4 AASHTO PART IIDETERMINATION OF WATER-SOLUBLE CHLORIDE ION CONTENT BY MOHR TI

25、TRATION METHOD (METHOD A) 8. SCOPE 8.1. This method covers the test procedure for the determination of water-soluble chloride content of soils. 8.2. Samples containing from 10 to 150 mg/kg of chloride can be analyzed by this test method. These levels are achieved by dilution as described in the test

26、 method. 8.3. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of whoever uses this standard to consult and establish appropriate safety and health practice

27、s and determine the applicability of regulatory limitations prior to use. 9. SUMMARY OF METHOD 9.1. This test method is based upon the Mohr procedure for determining chloride ion with silver nitrate. The chloride reacts with the silver ion before any silver chromate forms, due to the lower solubilit

28、y of silver chloride. The potassium chromate indicator reacts with excess silver ion to form a red silver chromate precipitate. The end point is the appearance of the first permanent orange color. 9.2. This test method is suitable for analyzing solutions with a pH between 6.0 and 8.5. 10. INTERFEREN

29、CES 10.1. Sulfide, bromide, iodide, thiocyanate, cyanide, phosphate, sulfite, carbonate, hydroxide, and iron interfere in this test method. Sulfide, sulfite, and thiosulfate can be removed with a peroxide treatment, but usually no attempt is made to remove bromide and iodide because they are usually

30、 present in insignificant quantities compared to chloride. If necessary, the pH can be raised and the hydroxides of several metals, including iron, can be filtered off. Iron, barium, lead, and bismuth precipitate with the chromate indicator. 11. APPARATUS 11.1. Buret, 25-mL capacity. 11.2. Hot plate

31、. 11.3. Magnetic stirrer and TFE-fluorocarbon-coated stirring bars. 11.4. Buret, 50-mL capacity, 0.1-mL gradations. 11.5. Pipets, 1, 5, 10, 25, 30, and 50 mL. 11.6. Beaker, 250 mL. 11.7. Erlenmeyer flask, 500 mL. 2015 by the American Association of State Highway and Transportation Officials.All righ

32、ts reserved. Duplication is a violation of applicable law.TS-1a T 291-5 AASHTO 11.8. Centrifuge with tubes capable of holding at least 50 mL. 11.9. Phydrion papers covering pH 1 through 11 in 1-pH units. A pH meter is preferable, if available. 11.10. BalanceThe balance shall have sufficient capacity

33、, be readable to 0.1 percent of the sample mass, or better, and conform to the requirements of M 231. 12. REAGENTS 12.1. Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specification of the Commit

34、tee 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 sufficiently high purity to permit its use without lessening the accuracy of the determination. 12.2. Nitric Acid So

35、lution (1+19)Add one volume of HNO3(sp. gr. 1.42) to 19 volumes of water. 12.3. Purity of WaterUnless otherwise indicated, references to water shall be understood to mean reagent water conforming to ASTM D1193, Type III. 12.4. Silver Nitrate Solutions: 12.4.1. Silver nitrate solution (1 mL of soluti

36、on is equivalent to 1 mg of chloride). Dissolve 4.79 g of AgNO3in distilled water. Dilute to 1 L. Add one drop concentrated nitric acid (HNO3) and dilute to 1 L in a volumetric flask. The HNO3will eliminate any precipitation of silver hydroxide that would change the concentration. Standardize agains

37、t sodium chloride (NaCl). Store in an amber-brown bottle to protect the solution from light. 12.4.2. Silver Nitrate Solution, Standard (equivalent to 2 mg Cl/mL)For chloride concentrations slightly higher than specified in Section 12.4.1, this is a more concentrated standard. Dissolve 9.5834 g of Ag

38、NO3in approximately 700 mL of water. Add one drop concentrated nitric acid (HNO3) and dilute to 1 L in a volumetric flask. Standardize against sodium chloride (NaCl). Store in an amber-brown bottle to protect the solution from light. 12.4.3. Silver Nitrate Solution, Standard (equivalent to 5 mg Cl/m

39、L)For chloride concentrations higher than specified in Section 12.4.2, dissolve 23.9582 g of AgNO3in approximately 700 mL of water. Add one drop concentrated nitric acid (HNO3) and dilute to 1 L in a volumetric flask. The HNO3will eliminate any precipitation of silver hydroxide, which would change t

40、he concentration. Standardize against sodium chloride (NaCl) by procedure described below. Store in an amber-brown bottle to protect the solution from light. 12.5. Sodium Chloride Solution: 12.5.1. Dry 2 to 6 g of high-purity (minimum 99.5 percent) sodium chloride crystals at 110 5C for 1 h and cool

41、 in a desiccator to room temperature. 12.5.2. Weigh 1.6484 g of the NaCl crystals. Transfer the crystals into a 1-L volumetric flask, dissolve, dilute, and mix well. A quantity of 1 mL of this solution provides 1 mg of Cl. 12.5.3. A 0.2 mL blank can be utilized or determine the indicator blank by su

42、bstituting 100 mL of reagent grade water for the sample and perform the following: 12.5.3.1. Check the pH with a meter, if available, or with phydrion paper. If the pH is in the range of six through eight, proceed immediately to the step in Section 12.5.3.2. If the pH is below six, add 2015 by the A

43、merican Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 291-6 AASHTO sodium bicarbonate to adjust to the above range; if the pH is above eight, add nitric acid to adjust to the above range. 12.5.3.2. Add two drops of

44、 potassium chromate solution. 12.5.3.3. Titrate with silver nitrate solution until the indicator begins to turn from yellow to red. 12.5.3.4. Indicator blank is the volume of AgNO3required to the end point. Record this value as the blank. 12.5.4. The titre (T) of the silver nitrate solution is given

45、 in the following equation: 3mg CL usedTmL AgNO required blank= (1) 12.5.5. If the titre (T) of the solutions are not exactly 1.0, 2.0, or 5.0 mg of Cl per mL AgNO3, it may be desirable to dilute the solutions if they are too concentrated or add more silver nitrate if they are too weak. In either ca

46、se, restandardize the resulting solution. 12.6. Potassium or Sodium Chromate, Indicator SolutionPrepare a 5 percent solution (5 g/100 mL) and adjust the pH to 7.0 with HNO3(1+19) or NaHCO3powder described in Sections 12.2 and 12.7. 12.7. Sodium Bicarbonate (NaHCO3)Powder to adjust the sample pH to 8

47、.3. 12.8. Standardization of Silver Nitrate Solutions: 12.8.1. Pipet 25 mL aliquots of NaCl solution to standardize the AgNO3solution (1 mg Cl/mL) and dilute to 100 mL with water. For the higher concentrations use 50 mL aliquots of the NaCl solution to standardize the AgNO3solution (2 mg Cl/mL) and

48、dilute to 100 mL with water. Use 100 mL of the NaCl solution to standardize the more concentrated AgNO3solution (5 mg of Cl/mL). 12.8.2. Add 1 mL of 5 percent indicator solution (see Section 12.6), 1 g of sodium bicarbonate powder, and titrate to the appearance of a permanent orange color preceding

49、a red precipitate. The analyst must practice this titration to become familiar with this color. 13. TEST PROCEDURE 13.1. Weigh 100 g of soil into a 500-mL Erlenmeyer flask. Add 300 mL of distilled water. Stopper and shake vigorously for 20 s. After 1 h, repeat shaking. Centrifuge the sample. If the sample exhibits turbidity, then filter the sample through a 0.45-m membrane filter. 13.2. Check the pH and titrate a 30-mL aliquot for chlorides as follows: 13.2.1. Check the pH with a meter, if available, or with phydrion paper. If the pH