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Self levelling mortars - Raw materials, test methods and application properties

Pakusch, J. / Pietsch, I. / Denu, H.J. / Maier, S. / Blask, O.

Self levelling mortars for smoothing i.e. concrete surfaces are high-tech construction products. Formulations are highly complex containing a huge number of different raw materials. Among these, the polymeric cobinder and the (super)plasticizer play a key role in achieving the final properties. These are - beside the typical self-smoothing - a pot life of approximately 30 min and a setting time of 3 h to 6 h. After application the user needs a very rapid strength increase together with a high final compressive and/or flexural strength and excellent adhesion on different substrates. Although several European testing standards are actually under evaluation, there is only limited agreement about how to test certain properties of these products so far (i.e. strength increase). Therefore the contribution focuses on the application of new test methods for self levelling mortar's properties and their use in formulating self levelling mortars with acrylate based polymeric additives. Special attention is thereby payed on adjusting the open time and hardening time. To characterize both the self-smoothing properties and the open time, rheological methods are applied using a commercial rotating ball and a coaxial cylinder rheometer. The strength increase and the final strength could be monitored easily by ultrasonic speed measurements. The knowledge about the microstructure change of self levelling mortars with hydration and the described new methods for testing their workability properties were used to optimize the mortar's formulations based on acrylate polymer powders and powdered poly carboxylate ethers (PCE). As an example, the interaction between potassium carbonate and tartaric acid and their influence on the open time and the hydration rate in mixed cement systems was demonstrated. Rheology experiments exhibit differences in the self levelling properties of different plasticizer types.