3.1 The purpose of this guide is to estimate the SO₃ content for a hydraulic cement that gives maximum performance. The value obtained is one way to establish an appropriate level of sulfate in the manufacture of cements specified in Specifications C150, C595, and C1157.

3.2 The SO₃ content of a cement giving maximum performance is different at different ages, with different performance criteria and with different materials such supplementary cementitious materials and chemical admixtures. A manufacturer can choose the performance criteriato determine optimum SO₃ content. This optimum SO₃ content may be a compromise between different ages and different performance criteria.

Note 1: Typically, the optimum SO₃ content is higher the later the age.

3.3 This guide 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.

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

3.5 The guide is applicable to cements specified in Specifications C150, C595, and C1157.