Micro and/or Nano-Silica modified moderate and high strength concrete: Rheology and synergistic effects on strength, elastic & inelastic behavior and microstructure

•The efficacy of micro and nano refinement remarkably increased as W/Cm decreased.•Compressive strength increment up to 37% was obtained with binary use of MS and NS.•Binary use of MS and NS extended the linear-elastic region of σ-ε diagrams.•When MS and NS are blended, MOE showed a more effective increase over time than.fc'•Combined use of MS and NS decreased the ft/fc' ratio drastically. Synergistic effects of micro-silica (MS) and nano-silica (NS) on moderate and high strength concrete properties were investigated. Efficacy of micro and nano refinement remarkably increased as the W/Cm ratio decreased, and up to 37% improvement in compressive strength was obtained. Moreover, the linear-elastic region of the stress vs. strain diagrams significantly extended. As a result of the synergistic effect, a very dense interfacial transition zone was formed. The time-dependent evolution of the elastic modulus was much more effective than the compressive strength development. However, the combined use of MS and NS significantly decreased ductility.