Influence of Re-Dispersible Powders on Very Early Shrinkage in Functional Mortars

Abstract

Functional, high performance mortars such as Self-Leveling Underlayments (SLU), Tile Adhesives (TA) or Grouting Mortars (GM) are composed, besides complex binders, of mineral and organic fillers, and most importantly admixtures. Amongst the organic fillers, re-dispersible powders produced by spray drying from emulsions, are added to improve flexibility, adhesion and water resistance. These powders, however, also influence fresh properties such as workability and plastic shrinkage or sedimentation. Additionally they are prone to interfere with the hydration kinetics thus playing a role in the very early structuring process of a cement-based mortar.In this study, the influence of re-dispersible powders on sedimentation, plastic as well as chemical shrinkage in ternary binder composites has been investigated for the first 24 hours. The structuring process has been additionally characterized by the hydrate phase development. Ternary binders are defined in this study as compositions of Calcium Aluminate Cement (CAC), Ordinary Portland Cement (OPC) and Calcium Sulfate (CS̅).The addition of re-dispersible powders showed not only the well-known retardation in hydration kinetics, longer setting times and increased gel times but also changed dimensional stability. Dimensional changes occurring during the first 24 hours were monitored by different test devices in order to separate different shrinkage/expansion mechanisms. The measurements are compared to the in-situ measurement of phase development by XRD.