Most factors acting on concrete rheology work at an extremely small-scale level. Influencing factors in the millimeter or centimetre area are essentially restricted to sand and aggregates. The latter, however, make up 50 to 70% of the total volume of most concretes – a fact often ignored in research on controlling concrete processing properties. Whereas suitably chosen concrete admixtures and additives can influence rheology in a very targeted manner, sand and aggregates are less suitable for controlling rheology but nonetheless contribute to the rheology of the overall system. The actions of sand and aggregate can impose themselves upon the actions of admixtures and additives and, in unfavourable circumstances, even render them redundant [4, 5]. For this reason, any results concerning the processability of binding agent systems can only be transferred to concrete with great care. It is important to better understand the action of sand and aggregates in order to be able to harmonise them in such a way that they complement the action of superplasticisers positively, instead of working against them. Savings on costs can also be madeby this targeted fine-tuning.
Bundesanstalt für Materialforschung und -prüfung Berlin