A comprehensive experimental investigation on tire char replacement in geopolymer concrete: Mechanical and fracture features

In alignment with the carbon-neutral objective, environmentally friendly construction materials, such as geopolymers, have garnered significant interest due to their by-product constituents and reduced carbon emissions throughout the manufacturing process compared to conventional cementitious concretes. Notwithstanding the current fascination with green concretes, the impact of tire char on the mechanical and fracture characteristics of geopolymer concrete has been overlooked. This study examines the reclamation of tire char as a by-product of pyrolysis in the geopolymer mix. Both fine and coarse aggregates were systematically substituted with tire char from 0 % to 12 % in 2 % increments. A total of 21 bending prisms, measuring 100 × 100 × 400 mm, were cast using 7 unique geopolymer blends. The specimens were subjected to deflection-controlled loading via a three-point bending test following the creation of a central edge notch on the test specimens. The 2D digital image correlation (DIC) was employed to get the deflection and strain map under successively rising deflection loadings. After the bending test, axial compressive forces were exerted on the fractured segments of the bending prisms. The experimental results were analyzed from several perspectives, including (i) axial compressive strength, (ii) flexural strength, (iii) fracture energy, and (iv) unstable fracture toughness. Compressive strength increased by 39.9 % as a result of substituting tire char at a ratio of 12 %. Substituting 4 % tire char into the mixture improved the mean flexural strength by about 40.8 %. Similarly, the mean fracture energy also showed an increasing trend beyond the 4 % tire char replacement.