Experimental and analytical studies on residual flexural behaviour of reinforced alkali-activated slag-based concrete beams after exposure to fire

Abstract

Understanding the flexural behaviour of reinforced alkali-activated slag-based concrete beams after exposure to a fire is imperative to ensure their safety use and develop adequate retrofitting measures. However, up to this point in time, no relevant investigations on this specific subject have been reported. This paper presents an experimental study comparing the flexural behaviour of alkali-activated slag-based concrete (AAC) and Portland cement concrete (PCC) beams exposed to the standard ISO 834 fire curve. The research considers concrete strength and heating duration as research parameters. The test results revealed that AAC beams displayed a lower temperature field and experienced less mid-span deflection increase compared to PCC beams during heating. Normal-strength AAC and PCC beams exhibited comparable losses in flexural capacity after being heated for 1 h or 1.5 h. However, PCC beam with a concrete strength over 80 MPa experienced more capacity loss due to severe spalling during heating. On the other hand, compared with PCC counterparts, AAC beams exhibited lower residual flexural stiffness and experienced greater stiffness loss, mainly due to the formation of more cracks induced by thermal shrinkage of AAC. The flexural capacity and stiffness loss of AAC beams increased with increasing concrete strength and heating duration after fire exposure. The residual flexural capacities of RC beams were predicted using a simplified analytical model that incorporates heat transfer analysis and the 500 ℃ isotherm method. The predictions demonstrated excellent agreement with the test results.