Bond behavior of lightweight coconut shell concrete-filled circular steel tube column

Abstract

Coconut shell concrete is a lightweight concrete produced from waste coconut shells. In this paper, the bond strength between lightweight coconut shell concrete with silica fume and circular steel tube was experimentally investigated. Coconut shells were used as coarse aggregates and silica fume as the mineral admixture. Two concrete mixes with and without silica fume were tested for bond strength. The parameters of study were the D/t ratio, interface length, and the interface type (roughened steel surface and internal stiffeners). The steel tube thickness (2.5mm) was kept constant, and the external diameter (88mm, 114mm and 140mm), and the length of the tubes (300mm and 400mm) were varied. Silica fume significantly increased the bond strength and was evidenced through the micro-structural study of the interface with a scanning electron microscope. Higher bond strength was obtained in columns with a low D/t ratio, and increasing the interface length could not improve the bond strength. The combination of silica fume with internal stiffeners improved the bond strength by 5.33–27% more than the combination of roughened steel surface and silica fume. Test results were compared to EC4 and ANSI/AISC 360 recommendations. The test values exceeded code design bond strengths.