The effect of mechanical-thermal synergistic activation on the mechanical properties and microstructure of recycled powder geopolymer

To improve the activity and utilization of recycled powder (RP) obtained from scrap concrete, the effect of mechanical-thermal synergistic activation on the activity of recycled powder and the properties of recycled powder geopolymer (RPG) was investigated in this work. The compressive strength, scanning electron microscope(SEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and mercury intrusion pore measurement (MIP) were used to evaluate the mechanical property and microstructure of RPG, respectively. The optimal compressive strength was obtained when the activation temperature was 750 °C and the grinding time was 10 min. The 3-day, 7-day and 28-day compressive strength increased 77.91%, 109.88% and 108.18%, respectively, compared to the untreated recycled powder geopolymer samples. The microstructure analysis showed that the activation effect of single activation mode on the activity of recycled powder was not prominent; however, better properties and denser structure were obtained when the thermal-mechanical activation synergistically work. It is feasible to improve the utilization rate of recycled powder by synergistic activation and the effect is remarkable. •The recycled powder is used as the main primary material for preparing geopolymer.•A novel mechanical-thermal synergistic activation procedure of recycled powder is presented.•The strength of the synergistically activated recycled powder geopolymer is considerably greater than that of the untreated sample.•Synergistically activated recycled powder geopolymer pastes show better mechanical performance and denser morphology.