Aspects of Gypsum-Free Portland Cement

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Title: Aspects of Gypsum-Free Portland Cement

Author(s): Harald Justnes

Publication: Special Publication

Volume: 288

Issue:

Appears on pages(s): 1-14

Keywords: calcium acetate; calcium formate; calcium nitrate; chemical admixture; gypsum; low energy cement; delayed ettringite formation; rheology.

Date: 9/14/2012

Abstract:
Calcium sulphate (e.g. gypsum) is the common set regulator in portland cement. It has been shown that ground calcium sulphate (e.g. gypsum) is the common set regulator in portland cement. It has been shown that ground clinker can be set regulated by other calcium salts than gypsum, in particular calcium acetate, formate, and nitrate. Rheology of paste is improved when gypsum is replaced by the other salts, probably due to less water binding and less needle shaped surface hydration products than ettringite. For in particular calcium nitrate the cumulative hydration temperature is reduced, which opens up for low-energy cement without changing clinker chemistry. Removing calcium sulphate all together may also allow heat curing or evolution of hydration heat in massive structures to exceed 70°C (158°F) without risking delayed ettringite formation (DEF). These aspects have been elucidated by experiments in the present paper.