Effect of Glass and Basalt Fibers on the Bond–Slip Behavior of Steel Rebar in Eco-Friendly Fly Ash–Based Geopolymer Concrete: A Relative Comparison Using the Hinged Beam Approach

Geopolymers, a type of concrete extensively researched in recent years, demonstrate mechanical properties comparable to conventional concrete. It is widely acknowledged that the main aim of adding fibers to conventional or geopolymer concrete is to improve its flexural and tensile strength. However, there remains a notable gap in the literature regarding the impact of fibers on the bond between reinforcement bars and geopolymer concrete. This paper presents the findings of an experimental investigation of the effect of glass and basalt fibers on the bond stress behavior of eco-friendly fly ash–based geopolymer concrete. The study explores the bond performance of fiber-reinforced geopolymer concrete specimens, considering fiber type and amount as experimental variables. To this end, beam samples with different fiber types (basalt or glass), fiber amounts (2 kg/m3 or 4 kg/m3), and embedment lengths (5Ø or 20Ø) were produced. Hinged beam bending tests were conducted on the prepared specimens after heat curing at 100°C for 24 h. The experimental results reveal that both types of fibers positively influence the bond behavior of the geopolymer concrete. Additionally, the bond stress values of glass fiber-reinforced geopolymer concrete specimens were found to be slightly higher than those of basalt fiber-reinforced counterparts. Furthermore, it was observed that maximum bond stress values decrease with increasing fiber content and embedment length for both glass and basalt fiber specimens.