The Influence of Paste Thixotropy on the Formwork-Filling Properties of Concrete

摘要

Self compacting concretes for precast applications were scaled-down to concrete-equivalent grouts where only the surrounding paste around bigger particles was studied in a rheometer. Low shear rate steady-state flow curves feature a non-monotonous variation of shear stress versus shear rate, with a minimum stress obtained for a critical rate. The thixotropy description initially developed by Roussel, Le Roy and Coussot1 was successfully applied to the data in order to model this behaviour. Extending the study over different superplasticizers showed that their influence depends on the molecular architecture. Specific concrete tests were developed in order to assess workability and formwork-filling retention while applying as little energy as possible to the material. The trends observed at the rheometer scale were confirmed showing that structure build-up kinetics has a major influence on concrete placing and that superplasticizers may help control it up to some extent.