Superplasticizers in the calcium sulfate system – plasticizing action and influence on hydration

1 Structural composition of the superplasticizers (left: polycondensate, centre: polycarboxylate, right: polymer with phosphate groups) from [3]
1 Structural composition of the superplasticizers (left: polycondensate, centre: polycarboxylate, right: polymer with phosphate groups) from [3]
2 Slump flow using different superplasticizer concentrations (ß-HH, l/s = 0.7)
2 Slump flow using different superplasticizer concentrations (ß-HH, l/s = 0.7)
3 Curve of heat flow rate relative to the superplasticizer (25 °C, ß-HH, l/s = 0.7)
3 Curve of heat flow rate relative to the superplasticizer (25 °C, ß-HH, l/s = 0.7)
4 Curve of conductivity relative to the superplasticizer concentration (l/s = 200, 25 °C, laboratory-grade HH)
4 Curve of conductivity relative to the superplasticizer concentration (l/s = 200, 25 °C, laboratory-grade HH)
5 Curve of conductivity relative to the superplasticizer concentration (l/s = 20, ß-HH, 25 °C)
5 Curve of conductivity relative to the superplasticizer concentration (l/s = 20, ß-HH, 25 °C)
6 Relative diagrammatic comparison of the region in which the accelerated advance of hydration starts (turn-off area) relative to the concentration of the particular superplasticizer
6 Relative diagrammatic comparison of the region in which the accelerated advance of hydration starts (turn-off area) relative to the concentration of the particular superplasticizer
7 Light-optical photo­micrographs of the dihydrate relative to the superplasticizer concentration (ß-HH, l/s = 20, 25 °C)
7 Light-optical photo­micrographs of the dihydrate relative to the superplasticizer concentration (ß-HH, l/s = 20, 25 °C)
Dihydrate crystals crystallized from suspension (starting ­material – hemihydrate plaster)
Dihydrate crystals crystallized from suspension (starting ­material – hemihydrate plaster)

How do superplasticizers influence the hydration of calcium sulfate? Systematic investigations were used to compare the action of polycondensate and polycarboxylate superplasticizers with that of the latest dispersion technology from BASF – a comb polymer with phosphate groups. The addition of the superplasticizers was shown to obstruct not only the nucleation but also the crystal growth.

1 Introduction

The use of superplasticizers to optimize the consistency and the amount of water required is now indispensable for numerous practical applications in the field of calcium sulfate binders. This development started with sulfonated polycondensate products based on lignin, melamine and naphthalene. After polycondensates had proved successful in numerous binder systems there followed a new generation of superplasticizers, the polycarboxylate ethers (PCEs). These are characterized by significantly greater effectiveness and long-lasting flowability. PCEs can also be adapted specifically...
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ZKG 02/2013

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ZKG 02/2013

Ressort:  Materials
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TEXT Dipl.-Ing. Manuela Marschetzky, Dr.-Ing. Hans-Bertram Fischer, Prof. Dr.-Ing. Horst-Michael Ludwig
Bauhaus University Weimar, Department of Building Materials, Weimar/Germany

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