Simple tools for achieving self-compacting ability of concrete according to the nature of the limestone filler
Résumé
This paper reports the assessment of self-compacting ability at the scale of concrete whatever the nature of the limestone filler (LF). In practice, differences in chemical and physical properties of LF are rarely taken into account during the design process, yet they are most often considered as the causes of segregation during and after placing, and of poor external aspects. The actual cause of the design defect can be resolved by developing tools capable of uniting the properties and the interactions among all components in order to achieve self-compacting flow. Basically, a two-phase approach was exploited by using existing test methods. At the scale of paste (cement + LF + High Range Water Reducer Admixture (HRWRA or superplasticizer) + water), the arrangement of particles in suspension was determined through the wet packing measurement. Starting from the maximum packing density as the reference state related to the water volume needed just to fill the voids between the solid particles, the rheological properties of pastes designed with different cements (OPC, slag cement) and different LF were measured and analyzed according to the excess water to solid surface area ratio. The water absorbed and adsorbed by the aggregates was also determined for the gravel/sand mass ratio, which was optimized from the packing measurement. Irrespective of the nature of the cement/filler combination, and provided that the HRWRA content was sufficient to lower the yield stress of the paste (the yield stress was then no longer affected by excess water variation), the association of the two phases (paste + wet aggregates) enabled a unique viscosity criterion to be evidenced at the paste scale for the design of easy flowing, stable self-compacting concretes. The viscosity criterion was validated by using another skeleton of aggregates and different natures of cement, LF and HRWRA.