Research on the formation of M1-type alite doped with MgO and SO₃—A route to improve the quality of cement clinker with a high content of MgO

This paper discusses the effect of SO₃ dopants on the M₁ polymorph formation and mechanical properties of alite containing a high content of MgO. The structure of the M₁ alite is identified by XRD, high-temperature XRD and TEM analysis. A characteristic XRD pattern of M₁ alite doped with MgO and SO₃ is determined, and TEM results show that M₁ alite has an incommensurate modulated structure feature with 2.4 times the subcell dimension along [2¯ 1 0]_H ^∗ and could be expressed as ha^∗ + kb^∗ + lc^∗ + m/[2.4(−2a^∗ + b^∗)], where m = ±1. The First-Principles method is used to simulate the structure of M₁ alite, and the calculated Delta Cohesive Energy is approximately 11–12 eV between the M₁ and M₃ alite. Quantitative analysis is performed by the Rietveld method. The SO₃/MgO (mass ratio from SO₃ to MgO) and M₁% in alite [Formula presented]×100% are shown to have a strong linear relationship, which can be defined as [Formula presented]×100% = 24.73 + 108.11 * SO₃/MgO (%). Mechanical properties results show that appropriate SO₃ dopant can improve the compressive strength of alite containing high MgO while over dosed SO₃ will lead to a contrary effect because of the decomposition of alite. The relationship between M₁% in the alite and the compressive strengths at different ages is also given. The optimal M₁% in alite is approximately 68% and the best SO₃/MgO ratio is approximately 0.43 because the compressive strength could be maximized at each age.