Experimental study on the slump-flow underwater for anti-washout concrete.

• A new test device and approach is proposed for the underwater flowability of UWC. • The effect of various mix proportion on underwater flowability of UWC are studied. • The test proves that the fluidity of concrete underwater is less than that in air. • A theoretical formula is deduced to interpret the underwater flowability loss. • An empirical formula for predicting underwater spread diameter of UWC is proposed. The workability of underwater anti-washout concrete (UWC), especially the flowability in particular application environments, was always a critical and controversial issue. In this paper, a new test device and approach have been proposed to study the behavior of underwater flowability of UWC and establish a relationship with laboratory slump-flow tests. Further, the effects of different mix proportions, such as aggregates, superplasticizer (SP), water-cement ratio (W/C), anti-washout agents (AWAs) type and dosage, beside yield stress and plastic viscosity of UWC were investigated. The differences (Δ d) between the spread diameter of the samples in air and underwater were compared. The results indicate that the flowability of concrete underwater is less than that in air, and it was proved that there is significant association between the yield stress and Δ d. Also, various factors that affect the spread diameter difference are prioritized to optimize the rheological properties and limit the underwater flowability loss as much as possible. Combined with the Roussel's flow model and stress equilibrium differential equations, the theoretical formula of interpreting UWC's underwater flowability loss by yield stress was deduced, which can certify that the buoyancy underwater counteracts part of the gravity that keeps the UWC flowing freely and reduces its maneuverability. Additionally, an empirical formula of underwater spread diameter of UWC was proposed according to the variation law that the spread diameter difference decreases due to the increase of yield stress. Finally, the outcomes provided basic theoretical reference to filling capacity of UWC when casting underwater. [ABSTRACT FROM AUTHOR]