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The role of sodium and sulfate sources on the rheology and hydration of C3A polymorphs

2021; Elsevier BV; Volume: 151; Linguagem: Inglês

10.1016/j.cemconres.2021.106639

1873-3948

José da Silva Andrade Neto, Paulo Ricardo de Matos, Ángeles G. De la Torre, Carlos Eduardo Maduro de Campos, Philippe Jean Paul Gleize, Paulo J.M. Monteiro, Ana Paula Kirchheim,

Mine drainage and remediation techniques

The higher reactivity of orthorhombic C3A (ort-C3A) in sulfate-containing solutions, compared with cubic C3A (cb-C3A), was previously related to the differences in crystal structure or the sodium in the ort-C3A pore solution. We analyzed the hydration of cb-C3A (in water and NaOH solution) and Na-doped ort-C3A in the presence of gypsum and hemihydrate. Calorimetry, in-situ XRD, TGA, and rheological tests were conducted. NaOH accelerated the hydration of cb-C3A, but ort-C3A still presented higher ettringite formation rate and earlier sulfate depletion. Ort-C3A pastes showed 10-20 times higher viscosities and yield stresses. Replacing gypsum by hemihydrate increased the ettringite precipitation rate and anticipated the sulfate depletion of ort-C3A but did not significantly influence cb-C3A hydration. The crystallization of hemihydrate into gypsum resulted in early (<10 min) stiffing of all C3A-hemihydrate pastes. Overall, the higher reactivity of ort-C3A is related to differences in crystal structure rather than the sodium in the pore solution.