Flexural and fracture properties of geopolymer concrete with delithiated β-spodumene

• First study on flexural and fracture behavior of DβS-based geopolymer concrete. • 25–50% DβS improves modulus of rupture, fracture toughness, and ductility. • Peak CMOD and post-cracking behavior enhanced, reducing brittleness. • Life cycle assessment shows 72% lower global warming potential vs cement concrete. • DβS valorizes lithium waste, enabling sustainable low-carbon construction. Geopolymer concretes offer substantial environmental benefits, along with notable durability and mechanical advantages, relative to traditional cement concrete. However, geopolymer concretes exhibit relatively brittle fracture behavior and limited flexural performance when cured at ambient temperature. For the first time, this research evaluates flexural properties of ambient-cured geopolymer concrete prepared with delithiated β -spodumene (D β S), a lithium refinery residue. Four unique mixes were formulated by partial or full substitution of fly ash (FA) with D β S at 0% (control), 25%, 50%, and 75% of the total binder. Mechanical properties, including compressive and splitting tensile strengths, and fracture-related parameters of load-bearing capacity, crack mouth opening displacement (CMOD), modulus of rupture, fracture energy, fracture toughness and ductility index, were systematically evaluated. Results indicate that a partial replacement of FA with D β S (25–50%) significantly enhances the mechanical performances. Although the best results are obtained at 25% replacement, at 50% D β S replacement, the 28-day compressive and splitting tensile strengths increase by 10% and 8%, respectively, relative to the control concrete. Load-bearing capacity and peak CMOD improve by about 4%, while modulus of rupture, fracture toughness, and fracture energy increase by 4%, 33%, and 2%, respectively. The ductility index increases substantially at full FA replacement, reaching up to 2.2 times that of the control concrete. A life cycle assessment further confirms that increasing D β S content in geopolymer concrete substantially reduces environmental impacts, with the greatest benefits observed at 50% substitution. Overall, the findings demonstrate that D β S not only improves the mechanical characteristics of geopolymer concrete but also significantly enhances its flexural behavior and fracture resistance. This improvement is critical for the construction sector, as flexural performance governs crack resistance and ensures structural integrity of elements under bending stresses.