The Characteristics of Recycled Concrete Powder and Its Influences on the Properties of Cement-based Materials

To guarantee the efficient and high-value reutilization of waste concrete from construction waste,the waste concrete was mechanically ground,and three degrees of fineness recycled concrete powder （RCP） were obtained by different grinding time.By analyzing the particle characteristics of RCP with different fineness,the filling-densification effect of cement-RCP cementitious material system was quantitatively investigated based on Andreasen,Fuller,and Aim-Goff models.In addition,the macroscopic mechanical properties of cement paste mixed with RCP were studied,and the influencing mechanisms of RCP on the microstructure of cement paste was revealed.Macroscopic research results show that the particle fineness of RCP after grinding is smaller than that of cement.When the RCP replaces 0% to 20% cement,the packing density based on the Aim-Goff model increases with the increase of RCP content,whereas the macro-mechanical properties first improve and then degrade with the increase of RCP content.Microscopic results show that at 5% RCP content,beneficial hydration products such as C-S-H and beneficial pore increase in cement-RCP paste;while at >15% content,beneficial products decrease and harmful substances such as Ca（OH）2 and harmful pore increases.These research findings suggest that the incorporation of RCP can make the cementitious system denser,and the appropriate RCP content can improve the macro-and microscopic properties of cement-based materials.