ASTM C563-16

3.1 The purpose of this guide is to estimate the SO_{3.2 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.}

3.3 This guide indicates optimum SO_{3.4 It should not be assumed that the optimum SO3.5 The guide is applicable to cements specified in Specifications C150, C595, and C1157.}

1.1 This guide 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 guide refers to the sulfur trioxide (SO_{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.