1、Standard Method of Test for Electrical Resistivity of a Concrete Cylinder Tested in a Uniaxial Resistance Test AASHTO Designation: TP 119-151American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-3c TP 119-1 AASHTO Standa
2、rd Method of Test for Electrical Resistivity of a Concrete Cylinder Tested in a Uniaxial Resistance Test AASHTO Designation: TP 119-1511. SCOPE 1.1. This test method covers the determination of the electrical resistivity of concrete to provide a very rapid indication of its resistance to the penetra
3、tion of chloride ions. This test method is applicable to types of concrete where correlations have been established between this test procedure and long-term chloride ponding procedures such as those described in ASTM C1556. Examples of such correlations are discussed in the references (Sections 15.
4、2. and 15.3). 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 safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices
5、and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: R 39, Making and Curing Concrete Test Specimens in the Laboratory T 23, Making and Curing Concrete Test Specimens in the Field T 24M/T 24, Obtaining and Testing Drilled Cores and Sa
6、wed Beams of Concrete 2.2. ASTM Standards: C670, Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials C1202, Standard Test Method for Electrical Indication of Concretes Ability to Resist Chloride Ion Penetration C1556, Standard Test Method for Det
7、ermining the Apparent Chloride Diffusion Coefficient of Cementitious Mixtures by Bulk Diffusion 3. SUMMARY OF TEST METHOD 3.1. This test 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 cores or cy
8、linders through the longitudinal axis of the geometry. Alternative geometries can be used, with proper determination of the geometry factor. A set of stainless steel plates is used as the electrodes, between which the test sample is placed. An AC current is applied to the plates, and the correspondi
9、ng voltage is measured. From this, the resistance is determined and normalized by the ratio of cross-sectional area to the length, termed uniaxial resistivity. The resistivity is related to ion penetration resistance. 2015 by the American Association of State Highway and Transportation Officials.All
10、 rights reserved. Duplication is a violation of applicable law.TS-3c TP 119-2 AASHTO 3.2. This method highlights how uniaxial resistivity can be determined using a commercially available Wenner probe array. This equipment consists of a four pin array of electrodes used in the measurement of surface
11、resistivity. Current is passed between the outer probes, while potential is measured between the inside probes. The electronic display of these units most often directly calculates the apparent surface resistivity. In these cases, to compute uniaxial resistivity, an additional factor of 2a is needed
12、, where a represents the spacing of the probes. This is described in more detail in Section 11.1. 4. SIGNIFICANCE AND USE 4.1. This test method covers the laboratory evaluation of the uniaxial electrical resistivity of concrete samples to provide a very rapid indication of their resistance to chlori
13、de ion penetration. Research has shown a good correlation between resistivity and chloride exposure tests, such as ASTM C1556, on companion cylinders cast from the same concrete mixtures (Sections 15.2 and 15.3). Resistivity can be related to the diffusion coefficient of chloride ions by the Nernst-
14、Einstein equation (Section 15.4). 4.2. The electrical resistivity of concrete is a material property that depends on the resistivity of the solution within the pores, the pore structure, and the degree of saturation. 4.3. This test method is suitable for evaluation of materials and mixture proportio
15、ns for design purposes and research and development. 4.4. The numerical results (resistivity, in kohmcm) from this test method must be used with caution, especially in applications such as quality control and acceptance testing. The qualitative terms in the left-hand column of Table 1 can be used in
16、 most cases unless otherwise noted by the specifying agency. Values in the right column in Table 1 were developed using Ohms law from the classification provided by ASTM C1202 and show good agreement with relationships provided in literature (Section 15.7). Table 1Chloride Ion Penetrability Classifi
17、cation Chloride Ion Penetrability ClassificationaUniaxial Resistivity (kohmcm) High 207 aEstablished by ASTM C1202. 4.5. The details of the test method apply to 100-mm (4 in.) and 150-mm (6 in.) nominal diameter specimens. Other specimen diameters or geometries may be tested with appropriate changes
18、 in the geometry factor employed in the calculating equation. (See Reference 15.8.) 4.6. Sample age may have significant effects on the test results, depending on the type of concrete and the curing procedure. Most concretes, if properly cured, become progressively and significantly less permeable (
19、more resistive) with time. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c TP 119-3 AASHTO Figure 1Uniaxial Electrical Test Setup 5. INTERFERENCES 5.1. This test method can produce misleading resul
20、ts when calcium nitrite has been admixed into a concrete. The results from this test on some such concretes indicate lower resistivity values, that is, lower resistance to chloride ion penetration, than from tests on identical concrete mixtures (controls) without calcium nitrite. However, long-term
21、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 results of this test similarly. Long-term diffusion tests are recommended if an admixture effect is suspected. 5.2.
22、 Since the test results are a function 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 specimens containing reinforcement or steel fibers. 5.3. The curing cond
23、ition is known to have a large impact on measured resistivity values. Lime water curing can significantly influence the resistivity of the solution inside the pores of the concrete. As such, it is suggested the volume of solution surrounding the test specimens during curing be minimized and not to e
24、xceed a volumetric ratio of 3.0 (solution to specimen). 5.4. The degree of saturation of the pores inside the test specimen is known to greatly influence the measured resistivity. As such, care should be exercised when conducting measurements on samples with unknown moisture contents or histories. F
25、or these types of samples, it is suggested that they be vacuum saturated using the procedure described in ASTM C1202. Further, the storage of samples under water in lime water curing does not guarantee that they remain saturated. Care should be exercised in the interpretation of results on samples o
26、f low-permeability concretes. 5.5. The temperature of the test specimen significantly influences measurements of uniaxial resistivity. As the temperature of the specimen increases, the resistivity decreases; decreases in temperature produce an increase in resistivity. For a proper comparison, the sa
27、mple should always be tested and conditioned at standard temperatures, i.e., 23 2C (73 4F). 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c TP 119-4 AASHTO 6. APPARATUS 6.1. Resistivity ApparatusAn
28、 alternating current resistivity meter shall be used. Common types are those used in the measurement of surface resistivity. (Examples are shown in Figure 2.) (a) (b) (c) (d) Figure 2Examples of Resistivity Meters 6.2. Conductive MediumGood electrical contact must be provided between the test specim
29、en and the electrodes. This can be accomplished through the use of a conductive medium, such as a saturated paper towel, conductive gel, or a set of sponges, with a maximum thickness of 6 mm. The last of these has been quite successful in practice. The medium must, at minimum, be the size of the cro
30、ss section of the test specimens. These steps might introduce additional errors into the measurements but can be corrected as described in Section 10.3. 6.3. Stainless Steel PlatesThe stainless steel plates should be at least the size of the cross section of the test samples. Thickness should be app
31、roximately 6 mm. The electrodes should be allowed to be connected to the resistivity test meter. Some effective types of connections are depicted in Figure 3. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable
32、law.TS-3c TP 119-5 AASHTO (a) (b) (c) Figure 3Example of Connections to Stainless Steel Plates 6.4. CableCables should be used to connect the stainless steel plates to the resistivity meter. Good results have been seen with 18 AWG stranded copper wire with two conductors. The cable should be fixed o
33、n one end with the connections to the plates and on the other end with connections to the resistivity meter. 7. REAGENTS AND MATERIALS 7.1. None. 8. TEST SPECIMENS 8.1. A set is composed of a minimum of three specimens. Sample preparation and selection depends on the purpose of the test (Note 2). 8.
34、1.1. For evaluation of materials or their proportions, samples may be one of the following: 8.1.1.1. cores from test slabs or from large diameter cylinders; 8.1.1.2. 100-mm (4-in.) diameter cast cylinders; or 8.1.1.3. 150-mm (6-in.) diameter cast cylinders. 8.1.2. For evaluation of structures, sampl
35、es may be one of the following: 8.1.2.1. 100-mm (4-in.) diameter cylinders cast and cured at the field site, or 8.1.2.2. 150-mm (6-in.) diameter cylinders cast and cured at the field site. 8.1.3. Cylinders cast in the laboratory shall be prepared following procedures in R 39. Unless specified otherw
36、ise, moist cure test specimens for 28 days prior to the start of specimen preparation (Note 3). 8.1.4. When cylinders are cast in the field to evaluate a structure, care must be taken that the cylinders receive the same treatment as the structure, for example, similar degree of consolidation, curing
37、, and temperature history during curing. Note 2The maximum allowable aggregate size has not been established for this test. Users have indicated that test repeatability is satisfactory on specimens from the same concrete batch for aggregates up to 37.0-mm (1.5-in.) nominal maximum size. 2015 by the
38、American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c TP 119-6 AASHTO Note 3This test method has been used with various curing durations and curing regimens to meet agency guidelines or specifications. Care should b
39、e exercised when comparing results obtained from specimens subjected to differing curing conditions. 8.2. Transport the cores or field-cured cylinders to the laboratory in moist condition in sealed (tied) plastic bags. If specimens must be shipped, they should be packed with insulation to be properl
40、y protected from freezing and damage in transit or storage. 8.3. Special processing is necessary for core samples where the surface has been modified, for example, by texturing or by applying curing compounds, sealers, or other surface treatments, and where the intent of the test is not to include t
41、he effect of the modifications. In those cases, the modified portion of the core shall be removed. 9. CONDITIONING 9.1. Specimens should be conditioned in an effort to keep them saturated. This is accomplished by conditioning them in solutions of saturated lime water. The volume of solution surround
42、ing the samples should range from two up to three times the volume of the sample. Convenient implementations of this would be three 100-mm 200-mm specimens with sufficient solution to cover the specimens by 38mm or one 150-mm 300-mm specimen in a single 5-gal bucket. 9.2. The curing temperature is i
43、mportant, as increased temperatures accelerate the hydration reactions. During condition, the specimen temperature should be maintained at 23 2C (73 4F). 9.3. Alternatives sample curing regimes are allowed as approved by the sponsoring agency. Care should be taken when comparing samples subjected to
44、 different curing regimes. More information is available in Section 15.7. 10. PROCEDURE 10.1. During testing the specimen temperature should be maintained at 23 2C (73 4F). 10.2. The testing should be conducted on a non-conductive surface. This might include a rubber or plastic base or mat. 10.3. Th
45、e use of surface resistivity equipment to measure uniaxial resistivity requires the plates be attached to the probe tips. The left two probe tips should be connected to one plate and the right two to the opposite plate. Good electrical contact must be ensured, and an example is depicted in Figure 4.
46、 Figure 4Connections of Plates to Probe Tips on a Wenner Surface Resistivity Meter 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c TP 119-7 AASHTO 10.4. Resistance of the Conductive Medium: 10.4.1.
47、 The conductive medium used to ensure contact between the test cylinder and the electrodes should be measured. This standard suggests the use of thin sponges saturated with the same saturated lime water solution used as storage for the tests specimens. 10.4.2. The resistance of each of the top and b
48、ottom mediums should be measured, as shown in Figure 5. The resistance of each individual sponge is largely dependent on its moisture content. The moisture content of the sponge is dependent on the weight placed on top it (e.g., large weights push more water from the sponge). To ensure that the mois
49、ture contents remain the same, the weight it carries during the test should be used. For the top sponge, Figure 5(a), only the top plate should be placed as a weight. For the bottom sponge, Figure 5(b), the top plate and the cylinder should be used to provide the weight. The cylinder should be placed above the top plate, so that its resistance is not measured. The goal of this is to provide a correction for sponge resistance, as discussed in Section 11.1. Many sponges show a constant resistance, so these can be measured periodicall
