Effective low-energy mixing procedure to develop high-fluidity cementitious pastes

Abstract

Preparing a high fluidity paste is a major step in ultra-high performance concrete (UHPC) development with
respect to its self-compacting ability as well as its ultra-high strength. In this regard, some experiments have
been carried out in order to study various superplasticizer (SP) addition methods and times. Among these
procedures, stepwise and delayed methods seem to be more efficient compared to direct addition of SP with
or immediately after water addition. However, few studies regarding water addition time and method have
been conducted since now. In this research work, the effects of water and SP addition methods on the fluidity
of paste were investigated. The results demonstrated that stepwise and delayed water beside delayed SP
addition remarkably reduce the flow time. This maximum fluidity was achieved after totally 15 minutes of
mixing including 3 minutes after 70% of water addition to powder, as first-part water, 6 minutes after SP
addition and finally an extra 6 minutes after second-part water which is 30% of the total water. Based on this
procedure, the opportunity for developing self-compacting and durable UHPC could be accessible.
Furthermore, using higher content of aggregates and supplementary cementitious materials would be possible
due to higher fluidity of the paste which finally results in an eco-efficient UHPC.