Gradations of recycled coarse and fine aggregate (RCA and RFA) were modified, and then used to cast 288 recycled concrete (RC) cube specimens. The influence of gradation modification on cube compressive strength variability of RC and the related mechanism were studied. Results showed that the gradation curve of RCA and RFA was not fine enough according to the present codes,the gradation modification was a way to optimize the gradation curve of RCA and RFA, and the respective bulk density was increased and the crushing index was reduced.The cube compressive strength of RC decreased with the increase of the RCA replacement ratio in general, whereas the strength variability appeared when the RCA replacement ratio equaled 50%.The compressive strength showed normal distribution with the standard deviation ranged from 1.0 to 3.0 MPa.But the variability rose up with the standard deviation less than 3.0 MPa when the RCA replacement ratio was 50%.The standard deviation of RC compressive strength obviously decreased after the gradation modification,which meant that the scatter of the compressive strength was controlled.Besides,the variability of RC increased with the RFA replacement ratio increased from 0 to 30%.
