BAUHAUS-UNIVERSITÄT WEIMAR

Milieu-dependent effect of retardants on hydrating calcium sulphate binders

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1 Effects of different substances on the onset of setting of a hydrating alabaster gypsum (plaster of Paris) (according to Mallon [2])

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2 Change in the setting behaviour of a gypsum plaster paste retarded with tartaric acid (0.03 %) (Basis modelling plaster 2, l/s = 0.6) as a function of the amount of NaOH added

3 Characterization of the setting behaviour of gypsum plaster paste retarded with tartaric acid (0.03 %) (basis modelling plaster 2, l/s = 0.6) based on the ultrasonic runtime as a function of the amount of NaOH added

4 Characterization of the hydration progress of gypsum plaster paste retarded with tartaric acid (0.03 %) (basis modelling plaster 2, l/s = 0.6) based on temperature measurement as a function of the amount of NaOH added

5 Change in the setting behaviour of a gypsum plaster paste (basis modelling plaster 2, l/s = 0.6) retarded with Retardan-200 P (0.0016 %) as a function of the amount of NaOH added

6 Characterization of the setting behaviour of gypsum plaster paste (basis modelling plaster 2, l/s = 0.6) retarded with Retardan-200 P (0.0016 %) based on ultrasonic runtime measurement as a function of the amount of NaOH added

7 Characterization of the hydration progress of the gypsum plaster paste (basis modelling plaster 2, l/s = 0.6) on the basis of temperature measurement as a function of the amount of NaOH added

8 Effects of different substances on the start of setting of a hydrating modelling plaster (plaster of Paris) with adjustment of the pH value using NaOH:(the amounts of additives used are relative to the calcium sulphate binder)

To meet technical and economic requirements, calcium sulphate binders must exhibit varying properties. Especially in respect of the open processing time and the setting time, the binders must be adjustable in a time period from a few minutes to several hours. To meet these requirements, the use of additives to regulate setting is necessary [1]. Objective of this work was to characterize the effect of selected retardants on a plaster of Paris paste as a function of the pH value (adjusted with NaOH).

1 Introduction

Mallon [2] has defined the retardation factor as the quotient of the start of setting of gypsum plaster paste containing a retardant to the start of setting of a gypsum plaster paste without a retardant. The corresponding pH value was adjusted with an alkali or acid. The milieu-dependent effect is illustrated in Figure 1.

Reul [3] established in his investigations that selected retardants (application concentrations 0.03… 0.1 % relative to the binder mass) have a different effect with different calcium sulphate binders. For instance, DL malic acid, citric acid and mesotartaric...

TEXT Dr.-Ing. Hans-Bertram Fischer¹, Dr. Markus Müller², Olga Mandrikova, I. Khripacheva
¹Bauhaus-Universität Weimar, F.A. Finger Institute for Building Material Engineering, Weimar/Germany
²Sika Services AG, Zurich/Switzerland