Impact response of fibre reinforced geopolymer concrete beams with BFRP bars and stirrups

Abstract

Increased number of studies of the performances of geopolymer concrete (GPC) structures reinforced with fibre reinforced polymer (FRP) under static loadings have been reported recently, aiming at developing an alternative of the traditional constructions with ordinary Portland concrete (OPC) and steel reinforcement because GPC is a sustainable construction material and FRP is corrosion resistant. Study of the dynamic performance of GPC structures reinforced with FRP is, however, very limited. This study experimentally investigates the impact response of ambient cured GPC beams reinforced with different types of fibres and basalt fibre reinforced polymer (BFRP) bars. Four GPC beams reinforced with steel fibres or synthetic fibres and two control beams made of GPC and OPC without fibre reinforcement were cast and cured under ambient conditions. The volume fraction of fibres varied from 0 to 0.5% were used in concrete mix and BFRP bars and stirrups were used for longitudinal and transverse reinforcements respectively. All the beams were tested under drop-weight impact and after impact tests, the damaged beams were monotonically loaded under three-point bending tests to obtain the residual strength. The experimental results demonstrate that the presence of fibres reduced damages in the crushing zone and mitigated the concrete cover spalling at the bottom of the beams. Also, increasing the volume fraction of fibres shifted the crack patterns and failure modes of the beams from shear-flexure to flexural dominance. However, adding fibres had insignificant effects on the peak impact force, reaction forces, and mid-span displacement. The findings from the residual strength tests indicate that the beams with higher fibre dosage which failed in flexural dominance mode under impact loading have smaller residual strength, different from the expected performance observed in the fibre reinforced concrete beams under static load. Discussions are provided to explain these observations.