BAUHAUS-UNIVERSITÄT WEIMAR

Milieu-dependent effect of retardants on hydrating calcium sulphate binders

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...

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