Rheological analysis and molecular dynamics modeling of Ultra-High Performance Concrete for wet-mix spraying

Abstract

The Sprayed Ultra-High Performance Concrete (SUHPC) is one of the most promising methods for the rapid construction and stabilization of concrete structures. In this work, viscosity-modified agents (VMA) are used to adjust the rheological parameter of Ultra-High Performance Concrete (UHPC) slurry for wet-mix. The obtained results show that 0.5‰ hydroxypropyl methylcellulose (HPMC) doped SUHPC exhibits the most suitable plastic viscosity and static yield stress without significant reduction in mechanical properties. Subsequently, the spraying technique is employed to produce SUHPC blocks, and about 16% improvement in mechanical properties can be observed in this study compared to the conventional casting UHPC. The X-ray CT results show that the fiber in SUHPC blocks tends to be parallel to the sprayed surface and exhibits a lower porosity, which is beneficial for withstanding radial tensile stress. Additionally, to further understand the effect of moisture on the viscosity regulation mechanism of HPMC in this study, the molecular dynamics method is employed, which demonstrates that the formation of water clusters and intermolecular hydrogen bonds between HPMC molecular chains can slightly increase the yield stress of HPMC at low moisture content.