Experimental study on strength and ductility of steel tubular stub columns filled with geopolymeric recycled concrete

Geopolymeric recycled concrete (GRC) is a new construction material which takes environmental
sustainability into account, by using alkali solution and fly ash to completely substitute Portland cement
as well as by replacing natural coarse aggregate with recycled coarse aggregate. GRC could be used together
with steel hollow sections to form composite section. There is very limited study on such GRC filled
tubular sections. This paper presents an experimental study on GRC filled tubular stub columns. A total of 12
specimens were tested. The main parameters varied in the tests are: (1) two section sizes of square hollow sections
(B × t) with 200mm×6mm and 150mm×5mm; (2) different concrete types: GRC and recycled aggregate
concrete (RAC); (3) different recycled aggregate (RA) replacement ratios of 0%, 50% and 100%. The relationship
of load versus axial strain was recorded and analysed to compare the ultimate strength and failure
mechanism. Meanwhile, the ductility of the columns was investigated by a ductility index (DI). The results
show that the ultimate strength decreased with increasing RA contents for both GRC and RAC filled columns.
The influence of RA content on the strength was greater in GRC than that in RAC. The effect of RA content
on the ductility of the columns was further investigated. Simulation method for predicting load versus strain
relationship is discussed for RAC and GRC filled steel tubular columns with different RA replacement ratios.