1、Standard Method of Test for Surface Resistivity Indication of Concretes Ability to Resist Chloride Ion Penetration AASHTO Designation: T 358-171 Technical Section: 3c, Hardened Concrete Release: Group 1 (April 2017) American Association of State Highway and Transportation Officials 444 North Capitol
2、 Street N.W., Suite 249 Washington, D.C. 20001 TS-3c T 358-1 AASHTO Standard Method of Test for Surface Resistivity Indication of Concretes Ability to Resist Chloride Ion Penetration AASHTO Designation: T 358-171Technical Section: 3c, Hardened Concrete Release: Group 1 (April 2017) 1. SCOPE 1.1. Thi
3、s test method covers the determination of the electrical resistivity of water-saturated concrete to provide a rapid indication of its resistance to the penetration of chloride ions. This test method is applicable to types of concrete where correlations have been established between this test procedu
4、re and long-term chloride diffusion procedures such as those described in ASTM C1556. Examples of such correlations are discussed in the reference shown in Section 15.2. 1.2. The values stated in SI units are to be regarded as the standard. 1.3. This standard does not purport to address all of the s
5、afety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: R 39, Making and Curing C
6、oncrete Test Specimens in the Laboratory T 23, Making and Curing Concrete Test Specimens in the Field T 277, Electrical Indication of Concretes Ability to Resist Chloride Ion Penetration 2.2. ASTM Standards: C670, Standard Practice for Preparing Precision and Bias Statements for Test Methods for Con
7、struction Materials C1202, Standard Test Method for Electrical Indication of Concretes Ability to Resist Chloride Ion Penetration C1556, Standard Test Method for Determining the Apparent Chloride Diffusion Coefficient of Cementitious Mixtures by Bulk Diffusion 3. SUMMARY OF TEST METHOD 3.1. This tes
8、t method consists of measuring the resistivity of 200-mm (8-in.) or 300-mm (12-in.) nominal length and 100-mm (4-in.) or 150-mm (6-in.) nominal diameter cylinders or cores by use of a 4-pin Wenner probe array. An alternating current (AC) potential difference is applied by the 2017 by the American As
9、sociation of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 358-2 AASHTO surface resistivity apparatus at the outer pins of the Wenner array generating current flow in the concrete. The resultant potential difference between the t
10、wo inner pins is measured. The current used and resultant potential along with the affected sample area are used to calculate the resistivity of the concrete. The resistivity, in kilohms-centimeters (k-cm), has been found to be related to the resistance of the specimen to chloride ion penetration. 4
11、. SIGNIFICANCE AND USE 4.1. This test method covers the laboratory evaluation of the electrical resistivity of concrete samples to provide a rapid indication of their resistance to chloride ion penetration. Wenner probe measurements have shown good correlations with other electrical indication tests
12、 such as the T 277 and the ASTM C1202 tests. In most cases, the electrical resistivity results have shown good correlation with chloride exposure tests, such as ASTM C1556, on companion cylinders cast from the same concrete mixtures (see references in Sections 15.2, 15.4, and 15.5). 4.2. This test m
13、ethod is suitable for evaluation of materials and material proportions for design purposes, as well as for research and development. 4.3. The qualitative terms in the left-hand column of Table 1 should be used in most cases unless otherwise noted by the specifying agency. The numerical results (resi
14、stivity, in k-cm) from this test method must be used with caution, especially in applications such as quality control and acceptance testing. Table 1Chloride Ion Penetration Chloride Ion Penetration Surface Resistivity Test 100-by-200-mm (4-by-8-in.) Cylinder (k-cm) a = 1.5 150-by-300-mm (6-by-12-in
15、.) Cylinder (k-cm) a = 1.5 High 254 199 a = Wenner probe tip spacing 4.4. The details of the test method apply to 100-mm (4-in.) and 150-mm (6-in.) nominal diameter specimens. Other specimen diameters may be tested with appropriate changes to the Wenner probe tip spacing and the correction factor in
16、 the calculating equation. (See reference in Section 15.3.) 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 358-3 AASHTO Figure 1Four-Point Wenner Array Probe Test Setup 5. INTERFERENCES 5.1. Thi
17、s test method can produce misleading results when calcium nitrite has been admixed into a concrete. The results from this test on concrete mixtures including calcium nitrite indicate lower resistivity values, that is, lower resistance to chloride ion penetration, when compared to tests on identical
18、concrete mixtures (controls) without calcium nitrite. However, long-term chloride diffusion tests indicate the concretes with calcium nitrite were at least as resistant to chloride ion penetration as the control mixtures. Note 1Other admixtures might affect res ults of this test similarly. Long-term
19、 diffusion tests are recommended if an admixture effect is suspected. 5.2. Sample curing condition is known to affect the resistivity of the solution in the pore structure (see Section 15.4). Lime-water curing on average reduces resistivity by 10 percent. 5.3. Because the test results are a function
20、 of the electrical resistance of the specimen, the presence of reinforcing steel or other embedded electrically conductive materials may have a significant effect. The test is not valid for samples containing reinforcing. 5.4. Sample age may have significant effects on the test results, depending on
21、 the type of concrete and the curing procedure. Most concretes, if properly cured, become progressively and significantly less permeable with time. 5.5. The degree of water saturation and concrete temperature may have a significant effect on the electrical resistivity of concrete. A standardized con
22、ditioning procedure has been developed to minimize this effect. a a a Equipotential Lines Current FlowLinesPotentialMeasured(V)(I)AC Current AppliedConcrete Surface to be Tested 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a viola
23、tion of applicable law.TS-3c T 358-4 AASHTO 5.6. Factors that are known to affect resistivity as well as chloride ion penetration include water/cement ratio, pozzolans, the presence of polymeric admixtures, air-void system, aggregate type, and degree of consolidation. 6. APPARATUS 6.1. Surface Resis
24、tivity ApparatusApparatus needs to be able to supply a flat-topped trapezoidal wave at a frequency of about 13 Hz and a pk-pk level with a nominal voltage limit of 25V pk-pk. Use a Wenner probe capable of an adjustment of the probe tip spacing to 38.1 mm (1.5 in.). Figure 2Surface Resistivity Appara
25、tus with 4-Pin Wenner Probe Array 6.2. Specimen holder to prevent specimen rotation while under test. (See Figure 3 for example.) Figure 3Specimen Holder 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.T
26、S-3c T 358-5 AASHTO 7. REAGENTS AND MATERIALS 7.1. None required. 8. TEST SAMPLES 8.1. A set is composed of a minimum of three samples. Sample preparation and selection depends on the purpose of the test. For evaluation of materials or their proportions, samples may be (a) cores from structures or f
27、rom larger diameter cast cylinders, (b) 100-mm- (4-in.) diameter cast cylinders, or (c) 150-mm- (6-in.) diameter cast cylinders. Cylinders cast in the laboratory shall be prepared following procedures in R 39. Unless specified otherwise, moist-cure test samples for 28 days prior to testing (Notes 2
28、and 3). Note 2Moist-cure in a 100 percent relative humidity moist room is the preferred curing method. Note 3Accelerated Moist-CuringProvide 7 days of moist-curing in accordance with R 39 for specimens prepared in the laboratory or in accordance with the standard curing procedure of T 23 for specime
29、ns prepared in the field. After 7 days of moist-curing, immerse the specimens for 21 days in lime-saturated water at 38.0 2.0C (100 3F). The accelerated moist-curing procedure has been found useful in providing an earlier indication of potential property development with slower hydrating supplementa
30、ry cementitious materials. Because the two different curing methods may not provide the same results, the specifier of the test may require a correlation between results for extended moist-cured and accelerated moist-cured specimens and establish appropriate acceptance criteria when the accelerated
31、moist-curing procedure is used or permitted. 8.2. Transport the cores or field-cured cylinders to the laboratory in a moist condition in a sealed watertight container. If samples must be shipped, they should be packed to be properly protected from freezing and damage in transit or storage. 8.3. Imme
32、diately after removing the sample from the mold, make four indelible marks on the top finished circular face marking the 0-, 90-, 180-, and 270-degree points of the circumference. Randomly assign one of the marks as 0 degrees, and then counterclockwise assign the next mark as 90 degrees, and so on.
33、Extend the marks onto the longitudinal sides of each sample. On the longitudinal sides of the sample, mark the center of the sample to use as a visual reference during testing. (See Figure 4 for example.) 2017 by the American Association of State Highway and Transportation Officials.All rights reser
34、ved. Duplication is a violation of applicable law.TS-3c T 358-6 AASHTO Figure 4Sample Marking 9. CONDITIONING 9.1. In order to saturate concrete cylinders with water, they must remain in a 100 percent relative humidity condition (moist room) from the moment of mold removal to the moment of the test.
35、 10. PROCEDURE 10.1. During the test, the air temperature around the specimens shall be maintained in the range of 20 to 25C (68 to 77F). 10.2. Remove the first sample from the moist room or water tank and transfer the sample to the sample holder with the 0-degree mark on top. The concrete sample sh
36、all be tested within 5 min of being removed from the moist room or water tank. Immediately clean the surface with a saturated sponge or towel. The surface should be saturated surface wet before and during testing. (Note 4). Note 4One recommendation is to place th e sample into a pan with about an in
37、ch of water and rotate the sample during testing in order to prevent the sample from drying. If the sample begins to dry, the resistivity readings drift higher, increase variability in the readings, and give erroneous results. Frequently changing the water is also recommended (approximately every fi
38、ve samples). Keeping the sample surface wet during testing reduces testing variability. 10.3. Place the Wenner array probe on the longitudinal side of the sample, making sure the longitudinal center mark is equidistant between the two inner probe pins. (See Figure 5.) Top (Finished Face)090 270180Ci
39、rcumferential MarksLongitudinalCenter Marks 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 358-7 AASHTO Figure 5Wenner Array Placement 10.4. Record the measurement from the display unit after th
40、e reading becomes stable. (See Table 2 in Section 11.) 10.5. Rotate the sample from the 0- to the 90-degree mark, and repeat the steps in Sections 10.2 through 10.4. 10.6. Rotate the sample from the 90- to the 180-degree mark, and repeat the steps in Sections 10.2 through 10.4. 10.7. Rotate the samp
41、le from the 90- to the 270-degree mark, and repeat the steps in Sections 10.2 through 10.4. 10.8. Rotate the sample to the 0-degree mark and repeat the steps in Sections 10.3 through 10.7 for the sample in order to obtain a second set of readings at each degree mark. These will be used to obtain an
42、average of two readings at each location. 10.9. Repeat the steps in Sections 10.1 to 10.8 for the other samples in the set. 11. CALCULATION AND INTERPRETATION OF RESULTS Table 2Sample Table for Recording the Surface Resistivity Readings Surface Resistivity (SR) Readings, k-cm Sample 0 90 180 270 0 9
43、0 180 270 Average A B C Set average Curing condition correction ( 1.1 lime tank or 1.0 for moist room) Penetrability based on test 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 358-8 AASHTO 11.
44、1. Calculate the average resistivity and the percent relative standard deviation (%RSD) for each sample in the set. If the %RSD is above 7.5 percent, immerse the sample in a water bath (20 to 25C (68 to 77F) for 2 h, and then repeat the test. If the %RSD on the second set is below 7.5 percent, use t
45、he last set of readings to compute the average. If the %RSD is greater than 7.5 percent, then average all 16 readings. 11.2. Calculate the average resistivity of the set. 11.3. If the samples were cured in a lime-water tank, multiply the set average by 1.1. If the samples were cured in a 100 percent
46、 relative humidity moist room, multiply the set average by 1.0. 11.4. Use Table 1, with the appropriate cylinder size, to evaluate the chloride penetration resistance based on the resistivity. These values were developed from data on various types of concretes. 12. REPORT 12.1. Report the following,
47、 if known: 12.1.1. Source of core or cylinder, in terms of the particular location the core or cylinder represents; 12.1.2. Identification number of core or cylinder; 12.1.3. Type of concrete, including binder type, water/cement ratio, and other relevant data supplied with samples; 12.1.4. Descripti
48、on of specimen, including presence and location of reinforcing steel; 12.1.5. Curing history of specimen; 12.1.6. Test results, reported as the surface resistivity measured; and 12.1.7. The qualitative chloride ion penetrability equivalent to the surface resistivity measured (from Table 1). 13. PREC
49、ISION AND BIAS213.1. Precision: 13.1.1. Single-Operator PrecisionThe single-operator coefficient of variation of a single test result has been found to be 6.3 percent (Note 5). Therefore, the results of two properly conducted tests by the same operator on concrete samples from the same batch and of the same diameter should not differ by more than 21 percent (Note 5). 13.1.2. Multilaboratory PrecisionThe multilaboratory coefficient of variation of a single test result has been found to be 12.5 percent (Note 5
