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/C150M, C595/C595M, and C1157/C1157M.

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, optionally in presence of supplementary cementitious materials and admixtures. Several alternate methods are allowed: compressive strength of concrete or mortar, heat of hydration of paste or mortar, and drying shrinkage of mortar.

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 in the field using the same materials. The optimum SO₃ is influenced by parameters such as ambient and fresh concrete temperature, admixtures, and supplementary cementitious materials.

3.5 The guide is applicable to cements specified in Specifications C150/C150M, C595/C595M, and C1157/C1157M.