DEMANDS OF ACCURACY OF MOISTURE MEASUREME NT SYSTEMS FOR CONCRETE PRODUCTION

Moisture content is an important characteristic of quality during the concrete production. By introduction of standards ISO 9000 quality mea surement methods gain importance during the certification of industria l processes. Commercially available microwave sensors were tested in t he laboratory for aggregate influences of bulk density variations, gra in size and salt content. The microwave drying was applied as a quick reference method. It was necessary to find out suitable locations in t he technological process with small density variations, because no den sity independent sensor was available. Moisture measurements were carr y out in the aggregate bin but also within the mixer. By using the var iance analysis for estimation of interferences, disturbing measurement s a catalogue of demands for the further development of microwave mois ture sensors have been worked out.