Uni-axial behaviour of steel slag concrete-filled-steel-tube columns with external confinement

Using steel slag, a waste by-product in the steel industry to replace natural aggregates to produce concrete can offer a sustainable solution in mitigating the environmental problems due to huge depletion of natural aggregates and disposal of abundant slag. Extensive research studies revealed that steel slag concrete has superior strength and stiffness but may also cause unsoundness to concrete. To solve the problem, steel slag concrete-filled-steel-tube (SSCFST) column was proposed, in which the concrete's expansion would activate larger confining stress, and thereby enhancing the overall behaviour of the column. A total of 18 traditional concrete-filled-steel-tube (CFST) and SSCFST column specimens with and without external confinement were prepared and tested under uni-axial compression. The major testing parameters were the steel tube diameter to thickness ratio, steel slag coarse/fine aggregate replacement ratio and spacing of external confinement. Results revealed that by replacing 50% natural coarse aggregate with steel slag coarse aggregate or 50% natural fine aggregate with steel slag fine aggregate, the compressive strength of steel slag concrete increased but the flowability decreased. Besides, SSCFST columns showed superior mechanical behaviour than traditional CFST columns. With external confinement, the strength and stiffness were further improved. Lastly, a load-strain model developed previously by the authors was adopted to predict the mechanical behaviour of traditional CFST and SSCFST columns. Good agreement has been obtained between predicted and experimental results for traditional CFST column while for SSCFST columns, the model under-estimated the axial load and over-estimated the absolute hoop strain at a given axial strain attributed to the change in the packing structure and possible expansion of steel slag concrete.

Automated summary

Using steel slag as a substitute for natural aggregates in concrete production can address environmental issues caused by the depletion of natural aggregates and the disposal of slag. The use of steel slag-filled steel tubes enhances the strength and stiffness of the concrete. Experimental results showed that replacing 50% of natural coarse or fine aggregate with steel slag increased compressive strength but decreased flowability. Additionally, SSCFST columns exhibited superior mechanical behavior compared to traditional CFST columns, especially when externally confined.