Advanced Study of Columns Confined by Ultra-High-Performance Concrete and Ultra-High-Performance Fiber-Reinforced Concrete Confinements

Abstract

The need for concrete with ‘super’ strength and ‘super’ ductility for greater sustainability has been answered by the existence of ultra-high-performance concrete (UHPC) and ultra-high-performance fiber-reinforced concrete (UHPFRC). Over the last decades, UHPFRC has been implemented in actual concrete structures, as well as used to retrofit structural elements, including columns. However, the use of UHPC and UHPFRC confinement to strengthen normal concrete columns is still limited. Therefore, this research aims to investigate the advanced performance of columns using UHPC and UHPFRC confinement in the context of the strength and ductility of such columns, such as load capacity, stress–strain behavior, and the crack pattern in the failure mode. This research is an advanced study of several investigations previously carried out by other authors on the characteristics of UHPC and UHPFRC, as well as columns confined by UHPC and UHPFRC. The methods used in this research are experimental and analytical. The experimental results were compared to analytical calculations for validation. This research produced 12 short-column specimens confined by UHPC (CF0 series) and UHPFRC (CF1 and CF2 series) that contained 0%, 1%, and 2% fiber and were also tested for axial loading and various eccentricities as follows: e = 0, 35, and 70 mm. The results found that the normal strength concrete (NSC) columns confined by UHPC and UHPFRC could sustain a higher maximum load and stress, and also sustain greater vertical deformation and strain compared to the control specimens. It was noted that specimen CF2-35 had the highest load capacity, vertical deformation, maximum stress, and maximum vertical strain compared to specimen C-0 (control column with no confinement). The specimen CF2-35 (column confined by UHPC with a 2% fiber volume with an eccentricity of 35 mm) also exhibited a ductile failure mode and very minor cracks. It was also found that 75% of the specimens had 0–39% errors and 25% had 0–13% errors. The research proved that the addition of a volume of 2% fiber to the UHPFRC minimizes the crack of the failure mode and prevents confinement spalling of the column. This research has led to the conclusion that UHPC and UHPFRC confinements will increase the strength and ductility of columns.