1、Standard Method of Test for Determining Minimum Laboratory Soil Resistivity AASHTO Designation: T 288-12 American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-1a T 288-1 AASHTO Standard Method of Test for Determining Min
2、imum Laboratory Soil Resistivity AASHTO Designation: T 288-12 1. SCOPE 1.1. This test method covers the laboratory determination for the minimum resistivity of a soil. 1.2. The principal use of this test method is to determine a soils corrosivity and thereby identify the conditions under which the c
3、orrosion of metals in soil may be sharply accentuated. This standard is divided into two parts. The first part involves obtaining and preparing the sample to size for testing, and the second part describes the test method for determining the minimum laboratory soil resistivity. Note 1When less than
4、5 percent of a material passes the No.10 sieve, this test method may not be indicative of the corrosion potential of the material. 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,
5、 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 Standard: E29, Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications PART IINITIAL PREPARATION OF TEST SAMP
6、LES 3. SCOPE 3.1. This method covers the dry preparation of soil and soil-aggregate samples, as received from the field, for soil resistivity determination. 3.2. The following applies to all specified limits in this standard: for the purpose of determining conformance with these specifications, an o
7、bserved 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. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is
8、a violation of applicable law.TS-1a T 288-2 AASHTO 4. APPARATUS 4.1. BalanceThe balance shall have sufficient capacity and be readable to 0.1 percent of the sample mass, or better, and conform to the requirements of M 231. 4.2. Drying ApparatusAny suitable device capable of drying samples at a tempe
9、rature not exceeding 60C (140F). 4.3. SievesA series of the following sizes: 6.3 mm (1/4in.), 4.75 mm (No. 4), 2.00 mm (No. 10), and pan as required for preparing the sample for the minimum soil resistivity test. The sieves shall conform to M 92, Wire-Cloth Sieves for Testing Purposes (see Note 2).
10、4.4. 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 of soil (see Note 3). 4.5. Sample SplitterA suitable riffle sampler or sample splitter for proportional spl
11、itting of the sample and capable of obtaining 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 canva
12、s cloth is also permitted. Note 2The 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 than the 203.2 mm (8 in.) round
13、 frames. Note 3Other types of apparatus are satisfactory if the aggregations of soil particles are broken up without reducing the size of the individual grains. 5. SAMPLE SIZE 5.1. The amount of soil material required to perform the minimum soil resistivity test is as follows: Test Approx Mass (g) S
14、ieve Size Finer Than: Resistivity 1500 2.00 mm (No. 10) 6. INITIAL PREPARATION OF TEST SAMPLES 6.1. The sample as received from the field shall be dried in air or a drying apparatus not exceeding 60C (140F). A representative test sample of the amount required to perform the minimum soil resistivity
15、test shall then be obtained with the sampler, or by splitting or quartering. The aggregations of soil particles shall then be broken up in the pulverizing apparatus until the aggregation of soil particles is separated into individual grains in such a way as to avoid reducing the natural size of the
16、individual particles (see Note 4). Note 4Samples dried in an oven or other drying apparatus at a temperature not exceeding 60C (140F) are considered to be air dried. 6.2. The portion of the dried sample selected for minimum soil resistivity testing shall be separated into fractions by one of the fol
17、lowing methods: 6.2.1. Alternate Method Using 2.0-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 a pulverizing apparatus until the aggregations of the soil particles are broken into separate grain
18、s. The ground soil shall then be separated into two fractions using the 2.00-mm sieve. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 288-3 AASHTO 6.2.2. Alternate Method Using 4.75-mm and 2.00-
19、mm (No. 4 and No. 10) SievesThe dried sample shall first be separated into 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
20、 sieve. The fraction passing the 4.75-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 6.
21、2.1. 6.2.3. Alternate Method Using 6.3-mm and 2.00-mm (1/4in.- and No. 10) 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 int
22、o separate 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 separated on
23、 the 2.00-mm sieve, and processed as in Section 6.2.1. PART IIMINIMUM SOIL RESISTIVITY DETERMINATION 7. SCOPE 7.1. This method covers the laboratory procedure for determining the minimum resistivity of soil samples. The values obtained from this method are relatable to the corrosion potential that a
24、 soil may exhibit. 8. APPARATUS AND MATERIALS 8.1. Resistivity MeterAn alternating current (AC) meter or a 12-V direct current (DC) meter utilizing a Wien Bridge (AC bridge) with a phase sensitive detector and a square wave inverter that produces a nominal alternating signal at 97 Hz (see Note 5). 8
25、.2. 100-, 200-, 500-, and 900-ohm resistors with a 1 percent tolerance. 8.3. Soil BoxSee Figures 1 and 2. 8.4. 2.00-mm (No. 10) sieve conforming to the requirements of M 92. 8.5. Mixing Pans (noncorrosive; e.g., stainless steel, plastic). 8.6. Graduated cylinder, 100-mL capacity. 8.7. Distilled wate
26、r or deionized water that has a resistivity greater than 20 000 (ohm) (cm). 8.8. Straightedge, 305 mm (12 in.) length. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 288-4 AASHTO Note: All dimen
27、sions are shown in millimeters. Figure 1Soil Box for Laboratory Resistivity Determination (not to scale) 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 288-5 AASHTO Note: All dimensions are show
28、n in millimeters. Figure 2Soil Box for Laboratory Resistivity Determination (not to scale) 9. CALIBRATION OF RESISTIVITY METER 9.1. Calibrate resistivity meter (follow manufacturers instructions): 9.1.1. Zero the resistivity meter by clamping the two leads together, and adjusting the meter (if neces
29、sary). 9.1.2. Connect the leads of the resistivity meter to the 100-ohm resistor and read the meter. Repeat this process with the 200-, 500-, and 900-ohm resistors. 9.1.3. If the readings are within 10 percent of the resistance of the resistor, the meter is functioning satisfactorily. 2015 by the Am
30、erican Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 288-6 AASHTO 10. SOIL RESISTIVITY DETERMINATION 10.1. Select the material for testing in accordance with T 248 and separate on a 2.00-mm (No. 10) sieve. Approxim
31、ately 1500 grams of the material passing the 2.00-mm (No. 10) sieve will be required for testing. 10.2. Add 150 mL of distilled water to the prepared soil. Mix the sample thoroughly and cover the test sample with a damp cloth and allow the sample to stabilize until equilibrium has been reached, or a
32、llow to cure a minimum of 12 h. 10.3. Zero the meter as per manufacturers instructions. 10.4. Clean the soil box thoroughly with distilled water. 10.5. Thoroughly mix and place the sample in the soil box in layers and compact (moderate compaction with the fingers is sufficient). Trim off the excess
33、material with the straightedge. 10.6. Measure the resistance and calculate the resistivity of the soil in accordance with the instructions furnished with the meter and record the test value. 10.7. Remove and retain the soil from the box, add 100 mL of distilled water to the sample, and mix thoroughl
34、y. Clean the soil box with distilled water prior to performing the next test. 10.8. Repeat the process of placing, compacting the soil in the box, then measure the resistance and calculate the soil resistivity (see Note 6). 10.9. Repeat the steps in Sections 10.4 to 10.8 until a minimum value can be
35、 determined. 10.10. The minimum value is used for computing the minimum soil resistivity and reporting (see Note 7). 11. REPORT 11.1. The minimum soil resistivity value determined above should be reported in units of (ohm) (cm). 11.2. The minimum soil resistivity utilizing the typical soil box is: (
36、 ) minimum soil resistivity minimum reading ohms 6.67 cm= (1) (See Note 8.) Note 5Most resistance meters without an inverting circuit allow the sample under test to polarize during measurement causing the reading to vary (i.e., drift). Note 6In some soils, the minimum soil resistivity occurs when th
37、e specimen is in a slurry condition. When this occurs, it is necessary to thoroughly mix the soil slurry and then pour the slurry water into the soil box until full. If the soil box doesnt reach its capacity with the addition of the slurry water, add just enough of the mixed soil into the box until
38、the soil box is filled; then take the reading. Note 7The minimum soil resistivity can occur at any moisture content. Note 8Multiplying constant for each soil box is derived by: ( )( )22surface area of one electrode cmcmmeasured average distance between electrodes cm cmcm= =(2) 2015 by the American A
39、ssociation of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 288-7 AASHTO Typical soil box:15.24 cm 4.445 cm6.67 cm10.16 cm=(3) The soil box may be constructed of either 6.4- or 12.7-mm (1/4-or 1/2-in.) acrylic plastic. If other s
40、ize soil boxes are used, it will be necessary to determine the correct multiplier. It should also be noted that it may be necessary to prepare extra soil for testing to fill the soil box. 12. PRECISION AND BIAS 12.1. Data 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.
