Progress of hydration and the structural development of hemihydrate plaster

1 Crystal structure of a) calcium sulfate hemidydrate [12] and b) anhydrite III (right) [13]

(thanks to/mit freundlicher Unterstützung Dr Freyer, TU Bergakademie Freiberg)

2 Raman spectrum of the 6 h/160 °C sample

(thanks to/mit freundlicher Unterstützung Dr Freyer, TU Bergakademie Freiberg)

(thanks to/mit freundlicher Unterstützung Dr. Bräu, BASF/Trostberg)

3 Measured heats of hydration in relation to the phase composition

(thanks to/mit freundlicher Unterstützung Dr. Bräu, BASF/Trostberg)

4 Dihydrate content, determined by radiography, during the hard-
ening relative to material with a setting capability of 84 %
– 160 °C/6 h sample

5 Development of the structural strengths (determined as a complex shear modulus |G*|) of the hemihydrate plaster mixes, approximation by the Gompertz function

6 Influence of parameter a on the shape of the Gompertz function

7 Influence of parameter b on the shape of the Gompertz function

8 Influence of parameter c on the shape of the Gompertz function

9 Development of the structural parameters – storage modulus G’ and loss modulus G’’ – of the hemihydrate plaster mixes, semi-loga-rithmic representation

10 Scanning electron photomicrographs a) of the microstructure formed by the starting material, b) of the anhydrite III rich hemihydrate plaster and c) of the anhydrite III free hemihydrate plaster

Summary: The phase composition of a hemihydrate binder is crucial for its technological properties such as water demand, workability and rate of hydration. This work deals with the influence of different phase compositions in the binder on the hydration and the resulting solid body properties. This complex process can be reduced to a few characteristic parameters by approximation of this structure formation in a functional relationship.

1 Hydration and hardening of gypsum-based plasters

The hardening of gypsum building materials is based on the crystallization of calcium sulfate dihydrate from a solution that is supersaturated with respect to this phase. The intergrowth and interlocking of the resulting dihydrate crystals is mainly responsible for the formation of a solid body structure and is therefore the source of the strength and stability of gypsum products.

Calcium sulfate occurs in nature as dihydrate, known as gypsum rock, or as water-free anhydrite II. Both phases are used as natural raw materials for the building...

Issue 03/2009 Materials Science

Progress of hydration and the structural development of hemihydrate plaster

Related articles:

Acceleration of the setting of hemihydrate plaster with calcium sulfate dihydrate

Investigation of hydration mechanisms of alpha and beta hemihydrate

Quantification of structure formation in setting stuccoes influenced by additives

Influence of calcium sulfate and calcium hydroxide on the hydration of calcium sulfoaluminate clinker

Investigations of the hydration of calcium sulfate hemihydrate

ZKG 11/2010