Abstract

This presentation contributes to a better understanding how sample preparation influences technological parameters. Over the last ten years research in the field of rheology, setting and curing behavior and strength evolution clearly shows that the obtainable results are strongly dependent on the sample preparation conditions. Firstly the flow properties of refractory castable are not only affected by the water addition but also by the mixing conditions. Imprecise adjustments of the power input significantly change the flow properties and in consequence the densification of the material. On the one hand for material development in the laboratory this requires mixing devices where the mixing energy input can be monitored and adjusted precisely at least for the set of samples prepared for a single material development. On the other hand mixing conditions on site should be checked carefully for the reason that it is common knowledge that often the mixing devices available in the users industry do not cover the requirements for a proper mixing of highly dispersed refractory castables therefore castables will behave different.

In principle it is not necessary to mention that curing time and ambient curing conditions impact the technological properties measured thereafter. However it is worth to mention that even small deviations of the curing conditions show a strong impact on the results. Special care has to be taken with regard towards the relative ambient humidity. Even if the relative humidity is adjusted to 95 % as recommended by ISO 1927 a significant loss of pore water is recordable. Less pore water leads to a significant increase of the green strength. It is highly recommended to adjust not only the curing temperature but also the prevailing relative humidity because it affects the dry-out behavior over the curing time. At this point it is important to reflect the mixing conditions again, because at this early stage of preparation this high-energy input changes the temperature of the admixture and already leads to a significant loss of mixing water.

In the presentation we will demonstrate and conclude that reliable and reproducible results can only be obtained if all preparation parameters are adjusted to constant conditions and also point out that only proper documentation will lead to transparent results. This is necessary for a stringent material development in a laboratory and should also be part of every publication in the refractory castable research.