Evaluation of Bonding Shear Performance of Ultra-High-Performance Concrete with Increase in Delay in Formation of Cold Joints

Abstract

This study set out to derive the optimal conditions for ensuring the monolithicity of ultra-high-performance concrete (UHPC). Direct shear tests were performed to examine the influence on the bonding shear performance. The experimental variables included tamping and delay, which were set to 0, 15, 30, and 60 min. SEM and XRD analyses of the microstructure and composition were performed. The direct shear tests showed that the bonding shear strength was enhanced by the addition of tamping. For the normal-strength concrete (NSC), it is thought that a monolithicity of around 95% can be attained with a cold joint formation delay up to 60 min. In contrast, while the normalized bonding shear strength reduction of UHPC with a delay of 15 min was the lowest at around 8%, a dramatic degradation in the bonding shear performance was observed after 15 min. XRD analyses of the middle and surface sections revealed the composition of the thin film formed at the surface of the UHPC and, as a result, the main component appeared to be SiO2, which is believed to be a result of the rising of the SiO2-based filler, used as an admixture in this study, towards the surface, due to its low specific gravity.

Microstructural Investigation of Heat-Treated Ultra-High Performance Concrete for Optimum Production

“…UHPC contains a large quantity of unreacted cement clinkers despite the HT [ 12 , 14 , 31 , 32 ]. This is primarily because there is an insufficient amount of water for the complete hydration of the cement [ 7 , 33 ].…”

Elephant skin formation on UHPC surface: Effects of climatic condition and blast furnace slag content

“…The uppermost layer apparently contains hydration products that cause early densification. Similarly, Lee et al [29] observed a smooth surface which can cause some cold-joint issues during the casting process of UHPC. They concluded that the film formed on the casting surface consists of SiO 2 crystalline structures and that this is the cause of the degradation of the bonding performance in terms of cold-joint formation.…”

Numerical Modelling of Concrete-to-UHPC Bond Strength

“…For different structural applications, such as repairing and strengthening old concrete structures or connecting full-depth deck panels using closure joints [53,54], casting UHPC next to concrete at different ages or even casting UHPC next to steel [55] highlights the challenge of bond strength between these two materials. A bi-surface shear test setup was selected to measure the bond strength for smooth and rough interface surfaces between the two materials to quantify the interfacial bond strength between UHPC and NSC [56,57].…”