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

Abstract

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. Geopolymer concrete offers several advantages over traditional portland cement-based concrete, such as a lower carbon footprint, excellent long-term durability, high compressive strength, early strength development, and the ability to utilize industrial byproducts like fly ash and slag. Additionally, geopolymer concrete production typically requires less water, contributing to conservation efforts in water-stressed regions. The addition of fibers to geopolymer concrete further enhances its mechanical properties, including flexural strength, crack control, toughness, and ductility. These properties are crucial but insufficient for determining the overall performance of geopolymer concrete in various structural applications. Ensuring the bond between concrete and reinforcement is crucial for the structural behavior and performance of reinforced concrete elements because it influences load transfer, crack control, and overall structural integrity. This experimental study investigates the bond behavior of fiber-reinforced eco-friendly fly ash–based geopolymer concrete with rebar. Beam samples are chosen for this study to simulate the bending behavior seen in real-structural applications, thereby providing findings that closely resemble field conditions. This approach aims to yield insights that are directly applicable to practical scenarios in construction and structural engineering.