Pullout Behavior of Hook End Steel Fibers in Geopolymers

Abstract

This paper discusses the pullout load-displacement behavior of hook end steel fibers having double, triple, and quadruple bends in their ends in geopolymers and cement mortars. Two types of geopolymer are considered, heat cured fly ash geopolymer (HGP) and ambient air cured fly ash/slag blended geopolymer (AGP). All mortars were prepared using the same water/cement and alkali activator/binder ratios in the case of ordinary portland cement (OPC) mortar and both geopolymer mortars, respectively. The embedment length of all three types of hook end steel fibers in all three types of mortar was also the same. The OPC mortar is considered the benchmark of pullout load-displacement behavior of steel fibers in geopolymers. The flexural load-deflection behavior of the three types of hook end steel fiber–reinforced geopolymers and OPC mortars is also studied to evaluate the effect of multiple bends in hook ends on flexural load and deflection capacity. Results show that the maximum pullout load and pullout displacement increases with increases in the number of bends of hook ends of the steel fibers in all three mortars. A similar trend is also observed in the case of energy absorbed (toughness) during the pullout of hook end steel fibers in mortars. The maximum pullout load of all three types of hook end steel fiber was higher in the HGP mortar than in the AGP and OPC mortars. However, the pullout toughness of all three types of hook end steel fiber was higher in the AGP mortar than in the HGP and OPC mortars. The observed pullout load-displacement behavior of the hook end steel fibers correlated well with the flexural load-deflection behavior of the hook end steel fiber–reinforced mortars of the aforementioned three types with higher flexural load of hook end steel fiber–reinforced HGP mortar than that of the AGP and OPC mortars.