Bonding behaviour of BFRP bars & punching behaviour of BFRP-reinforced geopolymer concrete slabs subjected to monotonic-cyclic loadings and elevated temperatures

In the first stage of this study the bond performance of basalt fibre reinforced polymer (BFRP) bars and geopolymer concrete (GC) was investigated, as it is an essential factor that affects strength and durability of reinforced concrete structures. The outcomes obtained from the direct pullout test showed that the ribbed BFRP bars have adequate bond to GC through the ribbed around its surface, which provides the required friction forces and mechanical interlock. The bond between BFRP bars and GC has comparable bond performance to steel-reinforced GC and BFRP-reinforced ordinary concrete (OC) and performed better than BFRP bars and OC. The results also indicated that as the BFRP bar diameter and the embedment length increases, the average bond stress between the BFRP bars and GC decreases, and it increases with an increase in the compressive strength and the cover thickness. In the second stage the punching shear behaviour of 16 GC two-way slabs reinforced by BFRP bars under monotonic-cyclic loadings was investigated. The tested specimens indicated that the crack patterns and failure modes were almost similar regardless of the type of reinforcement or their ratio. In addition, upon increasing the concrete strength and reinforcement ratio, a higher punching shear capacity and lower deflections were obtained under cyclic and monotonic loading. The punching shear performance of BFRP reinforced GC slabs was found to be superior than that of OC. On the other hand, the ultimate load capacity of the slabs tested under cyclic loading was lower than the capacity of the slabs tested under monotonic loading. Furthermore, the slabs reinforced by FRP had a better fatigue performance compared with slabs reinforced by steel bars with respect to cyclic loading. In the Third stage, behaviour of 24 GC two-way slabs reinforced by BFRP bars after exposure to different level of elevated temperatures was investigated. The parametric study results indicated that slabs reinforced with BFRP bars have a higher elevated temperature resistance than slabs reinforced with glass fibre reinforced polymer (GFRP) bars. Moreover, upon increasing the reinforcement ratio, a higher punching shear capacity and lower deflections were obtained at both ambient and elevated temperatures. Additionally, the high-temperature resistance of GC slabs was better than the high temperature resistance of OC slabs. The slabs with a higher cover thickness exhibited better performance after elevated temperatures.