Development of Eco-Friendly Ultra-High-Performance Concrete Utilizing Waste OLED Powder as a Cement Substitute

This study investigated the use of waste organic light-emitting diode (OLED) powder as a partial cement replacement in ultra-high-performance concrete (UHPC) and its effect on the hydration and mechanical properties. TG-DTG analysis showed that the OLED powder promoted C-S-H formation and Ca(OH)<sub>2</sub> consumption, with the OL-30 mix (30% replacement) showing the most pronounced peak. OL-30 achieved the highest performance, with 204.10 MPa compressive strength, 19.87 MPa tensile strength, 0.70% strain, and 117.28 kJ/m<sup>3</sup> energy density. This improvement resulted from the secondary hydration and microstructural densification due to reactive SiO<sub>2</sub> and Al<sub>2</sub>O<sub>3</sub>. However, replacements above 40% caused a performance loss owing to inert particle accumulation. Overall, a 30% replacement was optimal, confirming that waste OLED powder is a sustainable, high-performance binder for next-generation ultra high-performance fiber-reinforced concrete (UHPFRC).