ASTM C563-07

The purpose of this test method is to estimate the SO₃ content for a hydraulic cement that gives maximum compressive strength in mortar made and cured at 23 °C. The value obtained is used to establish an appropriate level of sulfate in the manufacture of cements specified in Specifications C 150, C 595 and C 1157. In Specifications C 150 and C 595 it is used to justify exceeding the prescriptive limits for SO₃.

The SO₃ content of a cement giving maximum compressive strength is different at different ages of mortar; typically this SO₃ content is higher at 3 days than the 24-h, and often higher for 7 days than that for 3 days. A manufacturer can choose the age of 24-h, 3 days or 7 days for specimens at which to determine optimum SO₃ content.

This test method indicates optimum SO₃ content for cement in mortar made and cured at a standard temperature of 23.0 ± 2.0 °C (73.5 ± 3.5 °F). The optimum SO₃ increases with increasing temperature and may increase when water-reducing admixtures are used.

It should not be assumed that the optimum SO ₃ estimated in this test method is the same SO₃ content for optimum performance of a concrete prepared from the cement.

The test method is applicable to cements specified in Specifications C 150, C 595, and C 1157.

1.1 This test method describes the determination of approximate optimum SO₃ for maximum compressive strength at 24 h, 3 days, or 7 days by measuring the change in strength produced in hydraulic cement mortar as a result of substituting calcium sulfate for a portion of the cement.

1.2 This test method refers to the sulfur trioxide (SO₃) content of the cement only. Slag cements and occasionally other hydraulic cements can contain sulfide or other forms of sulfur. The determination of SO₃ content by rapid methods may include these other forms, and may therefore produce a significant error. If a significant error occurs, analyze the cement for SO₃ content using the reference test method of Test Methods C 114 for sulfur trioxide.

1.3 Values stated as SI units are to be regarded as standard.

1.4 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 and health practices and determine the applicability of regulatory limitations prior to use.