Effect of viscosity and shear regime on stability of the air-void system in self-consolidating concrete using Taguchi method

Abstract

Achieving suitable air-void characteristics in self-consolidating concrete (SCC) can be a difficult task due to the various influencing factors, including rheology and shear history. The effect of viscosity and shear regime on air-void system (AVS) of different SCC mixtures was evaluated using Taguchi method. The investigated SCC mixtures were proportioned with various high-range water-reducer (HRWR) and viscosity modifying admixture (VMA) combinations. Three different shear regimes, corresponding to static, semi-static, and dynamic were evaluated. These regimes simulate the concrete at rest, transportation, and casting processes, respectively. The characteristics of AVS were investigated immediately after mixing and up to 60 min after the first contact between water and binder using the ASTM C231 and air-void analyzer (AVA) test methods. Test results showed that the viscosity and shear rate regime are key factors affecting the AVS in SCC. High viscosity SCC mixtures exhibited better stability of air bubbles and spacing factor, regardless of the shear regime. On the other hand, the maximum size of aggregate showed the lowest contribution. Based on the statistical analysis, the optimum levels of control factors to minimize the variation in air volume (up to 60 min) and spacing factor are quantified. This consists, by order of importance, of the static shear regime and high viscosity of the mixture. Under these conditions, a high effective air fraction can be secured. Indeed, greater effective fraction of air bubbles is observed in high viscosity SCC compared to that of low viscosity mixtures.