Mixing technology for better concrete

Abstract

Concrete standards require that concrete must be mixed until the mix appears to be homogeneous. Scientific studies reveal the reasons why: When using conventional mixers, the mixing result deteriorates over a prolonged mixing time. Mixing times must therefore be short. For simple concretes, this is sufficient. Problems frequently arise, however, with fine-grained concretes (such as fair-faced concrete, concrete for roof tiles) and "modern concretes" like self-compacting concrete (SCC), high performance concrete (HPC) and ultra-high performance concrete (UHPC). For these applications, intensive shear mixers have proved to be advantageous. The paper shows, in which ways these advanced version of the simple mixers can be used beneficially. The mixer types described in this paper are based on a history that looks back on experiences with first ring trough mixer in 1903, and planetary mixers since 1906. The basic foundation for the today’s successfully implemented mixing system of intensive shear mixers was laid in 1924. Thanks to a rotating mixing pan design, the material is conveyed to the mixing tools. This implies numerous unique advantages unique and has fostered their use in more than 300 industries – also in the field of concrete. Today the mixers - in sizes from 1 litre up to 3000 litres - are equipped with just one rotating mixing tool; machine sizes up to 12000 liters are available. These mixers produce superior mixing qualities which evidently cannot be achieved in any other mixing system. Based on a number of studies about mixing quality, the paper points out the properties of different mixing systems. This allows the reader to determine when he will benefit from which mixing system.