AASHTO T 358:2021 Standard Method of Test for Surface Resistivity Indication of Concrete’s Ability to Resist Chloride Ion Penetration.
This test method consists of measuring the resistivity of 200-mm (8-in.) or 300-mm (12-in.) nominal length and 1 00-mm (4-in.) or 1 50-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 surface resistivity apparatus at the outer pins of the Wenner array generating current flow in the concrete. The resultant potential difference between the two inner pins is measured. The current used and resultant potential along with the affected sample area arc used to calculate the resistivity of the concrete. The resistivity, in kilohms-centimetcrs (ku-cm), has been found to be related to the resistance of the specimen to chloride ion penetration.
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 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 method is suitable for evaluation of materials and material proportions for design purposes, quality control and acceptance, 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 from this test method must be used with caution, especially in applications such as quality control and acceptance testing.
5.1 This 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 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 1—Other admixtures might affect results of this test similarly. Long-term 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.AASHTO T 358 pdf download.