Rheological characteristics of Ultra-High performance concrete (UHPC) incorporating bentonite

This study aims to optimize the rheological properties of Ultra-high performance concrete (UHPC) based on the rheology pre-control strategy. To be specific, bentonite is employed as a rheology controller, and the UHPC skeleton is developed by the Modified Andreasen and Andersen (MAA) model. Then, the rheological properties, mechanical properties, and microstructure of the developed UHPC are evaluated carefully. The obtained results reveal that the addition of bentonite can effectively regulate the rheological properties of UHPC. More exactly, When the bentonite content rises from 0 wt% to 15.0 wt%, the flowability of the UHPC slurry decreases by 55.71%, while the static yield stress, dynamic yield stress, plastic viscosity and thixotropy increase by about 17.05 times more, about 5.57 times more, about 1.16 times more and about 0.04 times more, respectively. Due to the improvement of the rheological properties of the developed UHPC matrix, the orientation and distribution of the utilized steel fibres can be significantly improved, which could bring a maximum increase of about 60% for the UHPC flexural strength. Additionally, based on the microstructure analysis results, there is optimal bentonite content, which is beneficial for obtaining a much denser structure of UHPC composite.