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1.1 These methods determine the water soluble sulfate content of cohesive soils used in construction by using the colorimetric technique. Two methods are presented in this standard. Method A is for use in the field and Method B is for use in the laboratory. The colorimetric technique involves measuring the scattering of a light beam through a solution that contains suspended particulate matter. Measurements of sulfate concentrations in construction soils can be used to guide professionals in the selection of appropriate stabilization methods and to assist in assessment of potential deterioration in concrete structures.

1.2 The field method, Method A, is used as a screening test for the presence of sulfates and their concentration. The laboratory method, Method B, provides better resolution than the field method.

1.3 Ion chromatography is also an acceptable alternative method that can be used to evaluate results, however, it is outside the scope of this standard.

1.4 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.5 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026, unless superseded by this test method.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

5.1 Where sulfates are suspected, subgrade soils should be tested as an integral part of a geotechnical evaluation because the possibility that sulfate induced heave may occur if calcium containing stabilizers are used to improve the soils and sulfate reactions may also cause deterioration in concrete structures. When planning to treat a soil used in construction with lime, testing the soil for water soluble sulfates prior to treatment becomes very important (Note 2).

5.2 When sulfate containing cohesive soils are treated with calcium-based stabilizers for foundation improvements, sulfates and free alumina in natural soils react with calcium and free hydroxide to form crystalline minerals, such as ettringite and thaumasite.4 Thaumasite forms when ettringite undergoes changes in the presence of carbonates at low temperatures.5 The sulfate minerals expand considerably when they are hydrated.