Behaviour of concrete-Filled steel tube having granulated blast furnace slag as fine aggregate in normal strength concrete after exposure to elevated temperature

The significant growth of steel production in India has led to a considerable increase in the production of granulated blast furnace slag (GBS). To resolve the environmental concerns associated with GBS production, it can be used as a substitute for natural fine aggregate in concrete within concrete-filled steel tube (CFST). However, literatures regarding the behaviour of GBS aggregate added concrete-filled steel tubular columns (GBSCFST) after exposure to fire is very limited. Hence the present research work aims to investigate fill the aforementioned research gap. A total 30 number of GBSCFST specimens having square, circular and rectangular shapes, including both intermediate and stub columns, are tested. GBS is used as fine aggregate for preparing infill concrete. All the specimens are heated to varying target temperatures of 200°C, 400°C, 600°C and 800°C with a temperature holding time of 2 h in a furnace. Afterwards, the specimens were left inside the furnace for cooling purposes. Axial compression load was applied to all the specimens by using a compression testing machine with a strain-controlled procedure. The reduction in the load carrying capacity ranged from 1.07% to 12.68% for stub specimens and 1.05% to 19.35% for intermediate specimens heated upto 600°C. However, the load carrying capacity experienced a significant reduction reaching a maximum percentage decrease of 24% and 34% when heated at 800°C. The primary failure shapes observed were local buckling and bulging in stub specimens and mid-height buckling in intermediate specimens.