Self-compacting concrete paste constituents: Hierarchical classification of their influence on flow properties of the paste

This paper aims to clarify the influence of the constituent nature and dosages on the rheological properties of cement paste within the framework of self-compacting concrete design. The paste mixes were made with ordinary Portland cement, limestone filler, a superplasticizer (polycarboxylate type) and a viscosity agent (nanosilica). Their flow properties were characterized through spreading diameter, static yield stress and apparent viscosity. In order to take implicit variations of constituent proportioning induced by relational constraints into account, a mixture experiment technique was adopted. A matrix of experiments was build up allowing a polynomial model to express each rheological response according to the dosages of the constituents and some trends about the effect of the various mix constituents and their interactions to be found. A descriptive analysis of the data base only showed that the rheological responses fell into three distinct consistency groups. Consequently, statistical tools (variance analysis, binary tree method coupled with the bootstrap technique) were used to establish a hierarchical classification of the constituents. Results showed that the superplasticizer and the viscosity agent are dominant in yield stress. The apparent viscosity is controlled by cement and superplasticizer at small velocity gradient while it is controlled by powder (cement + filler) and water at higher velocity gradient. The viscosity agent acts at rest rather than during the flow.