By 2050, the world will accumulate a substantial 43.4 million tons of waste wind turbine blades. Utilizing the powder from grinding these waste blades as a new supplementary cementitious material (SCM) presents an optimal recycling solution and resource utilization. The powder primarily consists of both organic (polymer resin) and inorganic (glass fiber) phases. It is essential to remove the polymer phase to achieve improved pozzolanic reactivity of the glass phase. This removal was achieved through thermal treatment in this study. Based on thermogravimetric (TG) analysis, polymer removal temperatures were set at 550 °C, 600 °C, 700 °C, and 800 °C. The optimal temperature was identified as 550 °C for the highest activity in the alkaline solution. The impact of polymer removal on pozzolanic reactivity was analyzed through various tests including paste flowability, exothermic heat flow, compressive and flexural strength, mercury intrusion porosimeter (MIP), TG, and scanning electron microscope (SEM). For paste sample with 30 % replacement ratio, the experimental results show that, the removal of polymer phase is beneficial in achieving a 0.46-h shorter hydration induction period, 9.4 % higher flowability, 10 % less pore volume at 90 days, and 20 % higher compressive strength. This study confirms that the pozzolanic reactivity of recycled powders from retired wind turbine blades can be improved by removing the polymer phase, making the recycled powder a potential SCM. This research is crucial for developing a new recycling route for waste wind turbine blades.