Mechano-Chemically Activated Recycled Concrete Powder as Supplementary Cementitious Material: Sustainable Pathway for High-Performance Recycled Aggregate Concrete

This study systematically investigated the mechanisms of physical grinding, chemical exciters, and physical-chemical synergistic activation on the activity enhancement of recycled concrete powder (RCP) and evaluated the effect of activated RCP on the mechanical properties, permeability, and microstructure of recycled aggregate concrete (RAC). The activation mechanism was elucidated by means of the strength activity index (SAI), lime uptake, X-ray diffraction, and scanning electron microscope. The results showed that physical activation with an optimal milling time of 30 min enhanced the SAI of RCP to 75%, chemical activation with an optimized compounding ratio ( 5 % Na 2 SiO 3 + 3 % Na 2 SO 4 ) by response surface methodology increased the SAI to 85%, and physical-chemical coactivation further increased the SAI to 92%. The mechanical properties of RAC with 20% synergistically activated RCP were optimal, and its 56 days compressive strength, split tensile strength, and flexural strength reached 37.5, 3.8, and 7.7 MPa, respectively, which were significantly improved compared with those of the single activation group. Meanwhile, the primary water absorption, secondary water absorption and chloride ion permeation flux of the synergistically activated group were reduced by 16.1%, 53.4% and 27.1%, respectively, compared with the baseline group, which was found to be attributed to the optimization of the densified interfacial transition zone in combination with the microanalysis. This study confirms that the synergistic physical-chemical activation can efficiently release the potential gelling activity of RCP, which provides theoretical support and a technical path to enhance the performance of recycled concrete and the resourceful utilization of construction waste.