Effect of concrete wet packing density on the uni-axial strength of manufactured sand CFST columns

River sand (RS) has been the most popular fine aggregate in concrete production. Recently, because of the continuing decline in supply of RS, alternative source of fine aggregates is needed. Manufactured sand (MS), which is produced by mechanical crushing of virgin rock or construction waste, is becoming more popular for replacing RS. Concrete containing MS has higher compressive strength but is more brittle. To promote the application of MS in concrete, concrete-filled-steel-tube (CFST) column is advocated to restore the ductility by composite action. It is believed that the improved strength and ductility of CFST column containing MS is due to the enhanced wet packing density (WPD) of concrete, which has been researched to affect significantly the mechanical performance of concrete. Nonetheless, there was very limited research carried out on the effect of WPD on the behavior of confined concrete and CFST column. Ergo, 15 CFST column specimens with MS replacing RS partially or totally were prepared and tested under uni-axial compression. It is evident that CFST specimens with concrete containing blended fine aggregates showed different axial load-strain behavior to those with RS concrete (especially the maximum strength and postelastic slope). More importantly, the normalized strength (maximum strength to squash load) of CFST specimens can be correlated positively to the WPD. This article thus provides a new insight into the interdependence between the uni-axial strength of CFST columns and the WPD of the in-filled concrete.