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Title: Effect of Thixotropic UHPC on Interfacial Properties as an Overlay

Author(s): Du

Publication: Web Session



Appears on pages(s):



Date: 10/17/2021

Thixotropy is a time-dependent shear thinning property of the non-Newtonian fluid that behaves as the solid under the static condition and changes to the fluid by agitating or vibrating. This study evaluates the effect of Nanoclay (NC) and ambient temperatures on thixotropy of ultra-high-performance concrete (UHPC) made with 0.23 water-to-binder ratio. A new type of liquid well-dispersed attapulgite Nanoclay was first used in this study. The paste mixtures were proportioned with a fixed high-range water reducer (HRWR) content and varying NC content between 0 and 0.20%, by mass of binders. Besides, the ambient temperatures were varied to mimic the typical environmental temperature in practice (i.e., 10?, 25?, and 35?). Test results show that the thixotropy of UHPC pastes with various NC content between 0 and 0.20% were in the range of 0.091~3.147 Pa/min (10?), 3.327~72.604 Pa/min (25?), and 54.945~681.183 Pa/min (35?), respectively. On the other hands, higher thixotropy decreased the bonding strength between UHPC overlay and substrate concrete. This was related to the increased entrapped air and porosity on the interface. The use of vibration is demonstrated to effectively improve the bonding properties of thixotropic UHPC overlay. Higher vibration amplitude reduce the vibration time to achieve the optimal interfacial properties. Results show that, for NC-0.20% at 25?, the bonding strength was increased from 1.22 MPa to 1.63 MPa by 33.6% when 45s vibration under 1.59 mm amplitude or 60s vibration under 0.79 mm amplitude are applied, respectively.